Thermoplastics are a class of polymers that can be softened and melted by the application of heat, and can be processed either in the heat-softened state (e.g. by thermoforming) or in the liquid state (e.g. by extrusion and injection molding).
Table 3.10 displays the expected consumption of the major thermoplastics in 2014 for the three main geographic areas. These identified thermoplastics represent roughly 76% of the overall global consumption of plastics. Data are of uncertain order of magnitude and other figures may be found elsewhere.
The three classes of matrix materials are polymers, metals, and ceramics (Fig. 1.52). The properties of these types differ substantially and have profound effects on the properties of the composites using them.
Polymeric matrix. Polymer matrices generally are relatively weak, low-stiffness, viscoelastic materials; in fact, mechanical strength and stiffness come primarily from the reinforcing fibers or particles. There are two major classes of polymers used as matrix materials: thermosets and thermoplastics. At this time, for industrial applications, thermosets are the most widely used matrix resins for structural applications, although thermosets are making steady gains. Thermosets tend to be more resistant to solvents and corrosive environments than thermoplastics. Thermoplastics and elastomers have been deeply investigated for biomedical applications and will be further detailed later (see Chapter 4, Section 4.5).
Thermosetting resins. The key types of thermosetting resins used in composites are epoxies, thermosetting polyimides, cyanate esters, thermosetting polyesters, unsaturated polyesters, vinyl esters, silicones, and phenolics; it should be noted that this list is continually expanding. Epoxies are used to produce composites with excellent structural properties, for example, airframe structures and other aerospace applications. Epoxies tend to be rather brittle materials, but toughened formulations with greatly improved impact resistance are available; they cost more than other thermosetting polymeric matrices, but their advantages make them a primary choice for carbon- and aramid-fiber composites. Polyester resins are the most-used resins in commercial applications, because they are relatively inexpensive, easy to process, and corrosion-resistant. Unsaturated polyesters are widely used as matrices for fiber-reinforced composites, in boat hulls, building panels, and structural panels for automotive and aerospace applications.
Thermoplastic resins. Among thermoplastics, both amorphous and semicrystalline polymers are usable as matrices in composites. In particular, amorphous thermoplastics tend to have poor solvent resistance, whereas crystalline materials tend to be better in this respect. Relatively inexpensive thermoplastics like nylon are extensively used with chopped E-glass fiber10 reinforcements in countless injection-molded parts. There is an increasing number of applications using continuous fiber-reinforced thermoplastics.
Metallic matrix. Metals initially used as matrix materials were traditional alloys. Now, innovative metallic materials are tailored for use in composites. Main metallic matrix materials are alloys of aluminum, titanium, and iron; other metals used as matrix include magnesium, cobalt, silver, and superalloys. There was a significant amount of research on composites using intermetallic compound matrix materials, such as titanium aluminides, but these were largely unsuccessful.
Ceramic matrix. The key ceramics used as matrices are silicon carbide, alumina, silicon nitride, mullite, and various cements. Ceramics are very flaw-sensitive, resulting in a decrease in strength with increasing material volume. As a result, there is no single value that describes the tensile strength of ceramics. In fact, because of the very brittle nature of ceramics, it is difficult to measure tensile strength, and flexural strength is often reported. For that reason, monolithic ceramics are rarely used in applications where they are subjected to significant tensile stresses.
Carbon is an incredible ceramic material and includes materials ranging from lubricants to diamonds to structural fibers. The forms of carbon matrices resulting from the various carbon-carbon manufacturing processes tend to be rather weak, brittle materials. Thermal conductivities range from very low to high, depending on precursor materials and processes.
Thermoplastics are synthesized from plants in large amounts and transformed through chemical processing. Some of the most important thermoplastics are polyethylene [low density polyethylene (LDPE) and high density polyethylene (HDPE)], polypropylene (PP), poly(vinyl chloride) (PVC) and polystyrene . These polymers can be used in many possible applications structural purposes such as wire and light duty utilities. Thermoplastic polymers are also being used as a matrix for natural and synthetic fibers . Thermoplastic polymers can melt at specific temperatures and can be shaped and reshaped (through reheating) according to the mold. Reprocessing thermoplastic polymers can lose its physical properties due to a breakage of polymeric chains; it is best to not recycle thermoplastics.
Thermoplastic starch (TPS), in contrast to dry starch, is capable of flow. When thermoplastic starch is mixed with other synthetic polymers, these blends behave in a manner similar to conventional polymer blends. A one-step combined twin-screw/single-screw extrusion setup is suitable for the melt-melt mixing of LDPE and thermoplastic starch.
Glycerol is used as a plasticizer for starch in the content range of 29 to 40%. It is possible to manufacture a continuous TPS (highly interconnected) and co-continuous polymer/TPS blend extruded ribbon. This ribbon has excellent mechanical properties in the absence of any interfacial modifier and despite the high levels of immiscibility in the polarnonpolar TPS-PE system. A high degree of transparency is maintained over the entire concentration range due to the similar refractive indices of PE and TPS and the virtual absence of interfacial microvoiding.
Thermoplastic polyurethane elastomers (TPUs) (see Chapter 9 for a detailed description) are multiblock copolymers consisting of sequences of amorphous or low melting soft segments and rigid, hard segments, which have a crystalline melting point above room temperature. Many TPUs are compatible with PVC, and their blends exhibit only one major glass transition whose position on the temperature scale is raised with increasing levels of PVC .
The melt compounding and subsequent processing of the PVC/TPU blends are very similar to those of the PVC/COPE blends discussed in the previous section. Because of the heat sensitivity of PVC, only the softest TPU grades (i.e., those with hardness values of Shore A of 80) can be melt mixed with it safely. The PVC/TPU blends are also sensitive to moisture during processing, so it is necessary to dry them to less than 0.03% moisture content to maintain optimum properties .
For protection of the PVC/TPU compounds against UV radiation during outdoor exposure, either benzotriazole UV absorber for neutral or color compounds at amounts up to 2% loading or carbon black up to 5% loading for black formulations is recommended. Antioxidants, such as hindered phenols or organosulfur types, will extend the life of the products in outdoor exposures .
Blends of PVC with TPUs combine the toughness of the TPU with the stiffness and high modulus of the PVC. It is possible to obtain a wide range of hardness values by blending PVC with different hardness grades of TPU and added varied amounts of plasticizers to the PVC resin. The blend of PVC/TPU in the ratio of 70:30 by weight is equivalent to a commercial plasticized PVC compound in all respects yet displays a higher abrasion resistance and low-temperature flexibility.
The oil resistance of PVC/TPU blends is also improved over the plasticized PVC compounds. The immersion of such material in ASTM No. 3 Oil for 7days at ambient temperature has a negligible effect on the volume swell and causes no decrease in tear strength. The flexural performance improves with the increasing content of TPU: a compound containing 30% of TPU is markedly better than a commercial plasticized PVC material of the same hardness in both flex life and the cut growth resistance after oil immersion, and the trend continues with increasing proportion of TPU . There appears to be an optimum TPU content of 40% for oil resistance and an optimum of 50% for the other properties .
Thermoplastic matrix composites have been around for many years, with studies for aerospace applications being performed in the 1970s (Hoggatt, 1975; Maximovich, 1977). However, those early studies focused on amorphous thermoplastics which were susceptible to solvent attack. It was the introduction of semicrystalline polyetheretherketone (PEEK), in prepreg form, in the early 1980s which allowed thermoplastic composites to be considered for aircraft applications and this resulted in many detailed test programs in the 1990s. The aim here is not to give a history of high-performance thermoplastic composites, the reader can find this elsewhere (Cogswell, 1992a; Carlsson, 1991; Kausch, 1993), but rather to focus on the specific advantages of thermoplastic composites for marine applications.
First, an overview of available material options will be provided, followed by a discussion of manufacturing possibilities. Then the influence of the marine environment on the behavior of some thermoplastic composites will be described. A key area for future developments is underwater structures, and offshore applications will be discussed. Results showing how these materials behave under hydrostatic pressure loading will be given. The chapter will conclude with discussion of two related aspects, repair and recycling. These are specific to thermoplastics and could provide significant benefits for marine structures in the future.
The conventional fused filament fabrication (FFF) uses a thermoplastic ceramic feedstock that is liquefied by heating and pressed through a fine nozzle. For example, functional ceramic materials  and alumina  were processed using FFF. However, the efforts for the preparation of the thermoplastic ceramic feedstock in the form of spooled filaments constrain the FFF application for ceramics. Moreover, attainable resolution is relatively low, whereas the surface roughness is quite high by using this AM method.
The robocasting process, which is a computer-controlled deposition of colloidal pastes or slurries, is similar to FFF. In contrast to original FFF and other generative extrusion processes, the carrier fluid is a volatile solvent (water or organic liquid). In robocasting highly dispersed ceramic suspensions are used for AM of complex ceramic structures .
In  three types of so-called inkjet methods are described among them the Thermal Phase Change Inkjet. The jetting heads continue to lay the material droplets, and layers are formed. In comparison to the ink jetting technique used for deposition of tiny droplets of ink onto paper, in this process the ink is replaced with thermoplastic and wax materials. The droplets begin to cool and harden immediately after leaving the jetting head. Afterwards, a milling head passes over the previously created layer to produce a uniform thickness when one layer is complete. The material particles created from this step are removed by a vacuum as the milling process is taking place.
Moreover,  describes a three-dimensional printing technique which can be divided into direct printing and indirect printing techniques. The first-mentioned directly deposits a well-dispersed ceramic suspension via the injection nozzle . In a non-continuous approach, the nozzle position in a drop-on-demand-printer controls the destination of the droplets, which are generated only when required . The ceramic inks are typically prepared using two methods: using wax-based inks, which are deposited in hot-melt state and solidify on a cold substrate [83,109,110] or using ceramic suspensions, which dry through evaporation of the liquid. Reis et al.  claimed that loaded wax containing up to 45vol.% of particles can be successfully ink-jet printed.
Thermoplastic 3D-printing (T3DP) combines the advantages of FFF, robocasting and inkjet printing and resembles the three-dimensional printing technique described above. T3DP takes advantage of a dropwise deposition of a low viscous thermoplastic feedstock for building up a ceramic component. The method uses molten, thermoplastic feedstocks that are handled in a dispensing unit with xyz-positioning. The feedstocks are based on compositions that are known from low-pressure Ceramic Injection Molding (LP-CIM) [112, 113]. In contrast to the inkjet methods, the solid content of ceramic powders in the thermoplastic binder for T3DP is much higher. The melting temperature of the thermoplastic binder is relatively low (approx. 100C) and the viscosity is also relatively low as compared to typical thermoplastic feedstocks for high-pressure injection molding or for FFF. Thus the liquid feedstock can not only be simply dispensed via a thin nozzle as nearly endless filament which is similar to FFF and robocasting, but also be discontinuous as droplets by micro-dispensing technology, which allows the realization of very fine structures with smaller tolerances . The heated suspension is printed droplet by droplet (see Fig.4.27). The suspension immediately solidifies due to cooling because of the fast heat transfer from the printed suspension to the underlying layer or to the surrounding atmosphere. This T3DP concept has several outstanding advantages:
There are no restrictions concerning the applied powder material, because the consolidation of the droplets occurs by increasing the viscosity during cooling. Basically, it is possible to process all materials that can be dispersed in the molten feedstock.
Due to the relatively high solid content of the thermoplastic feedstock and the well-dispersed particles, a high packing density can be attained in the green component. Thus completely dense ceramic parts can be produced by T3DP.
The combination of precise deposition of small droplets with the fast deposition of filaments is one of the main advantages of T3DP. The small droplets enable a high resolution in critical volumes and the deposition of filaments guarantees a high production speed for volumes where no change in material occurs.
As an example, alumina suspensions were prepared by using alumina powder MR52 (Martinswerk, Germany) with d50=1.35m and a purity of 99.8wt% Al2O3. The powder content in the suspensions was varied between 86wt.% (58vol%) and 90wt.% (67vol%). As binder system, a mixture of paraffin and beeswax was used. The binder system and a dispersing agent were heated up to 100C in a heatable ball mill. Then the alumina powder was added and the suspension was homogenized by stirring for 72h at 100C. The rheological behavior of the suspension is a quality deciding criteria in T3DP. The properties of the suspensions determine essentially the formation of droplets (diameter, roundness, satellite droplets), which is important for resolution and accuracy of the manufactured components. An ideal suspension for the TD3P process should have a pseudoplastic behavior at a relatively low viscosity level. This means that the suspension has a shear thinning behavior, which results in low viscosity at high shear rates.
The heatable micro dispensing system MDV 3200A-HS (Vermes, Germany), a system for single droplet deposition, was used to deposit the different ceramic suspensions. This system consists of a piezo actor, which is actuated by a control unit, a needle inside a small chamber, which opens and closes a nozzle, and a lever system connecting the piezo actor with the needle.
For the suspension with a solid content of 62.5vol.% droplets with a diameter of about 300m and a roundness of 0.955 have been deposited. The investigated technology allows the deposition of droplets with nearly round shapes and the process of droplet formation showed a very high reproducibility with relative standard variations about 2% for droplet diameter and roundness. If the velocity of the xyz-positioning is very low and the frequency of the droplet formation is very high, an overlapping of the droplets happened and a dense structure can be manufactured out of single droplets. Fig.4.29 shows an alumina structure manufactured by T3DP and consisting of ten layers of single droplets which were deposited with a frequency of about 60Hz in about 5minutes.
Most TPUs are very compatible with PVC and such blends exhibit only one major glass transition, whose position on the temperature scale is raised with increasing levels of PVC . As it is the case with PVCCOPE blends, the most widely used blends are those where PVC is added to TPU to maintain the desirable properties of TPUs while reducing cost .
The main applications of blends of PVCTPU are in shoe soles and heels. Their main attributes are good wear resistance, good flexibility, good compression set, oil resistance, and reasonable cost. Essentially, the materials have better performance than pure PVC but lower cost than pure TPUs.
TPUs have higher mechanical damping than most elastomeric materials . The mechanical loss factor, tan, the ratio of loss modulus and storage modulus (G/G), and its dependence on temperature are shown in Fig.9.8 for two TPUs with different hardnesses. It is lower in the softer grades at room temperature. The temperature rise is also lower at equivalent deformation. Fig.9.8 also depicts the temperature dependence of the storage (shear) modulus (G).
Because TPU is a poor thermal conductor, the heat resulting from dynamic loading is dissipated slowly. The heat buildup is a function of both frequency and force applied. Therefore, parts, such as solid wheels or rollers made from TPU should not run at high speeds or overloaded. The choice of a suitable TPU for dynamic application depends on modulus. The higher is the stiffness, the lower is the deformation under comparable load.
Thermoplastics are a class of polymers that can be softened and melted by the application of heat and can be processed either in the heat-softened state (e.g., by thermoforming) or in the liquid state (e.g., by extrusion and injection molding). This is in contrast to the thermosets, the other class of polymers, which cannot be melted by the application of heat. Thermoplastic polymers can be processed repeatedly by the application of heat and can be recycled directly into making new products; however, it should be noted that repeated processing may cause deterioration in some of their properties. The common manufacturing processes used for making thermoplastic parts are injection molding, blow molding, and thermoforming.
In addition to the advantage of recycling, thermoplastics have several other advantages over thermosets. In general, they have higher ductility and impact resistance than thermosets. They can also be joined together by a variety of welding techniques, such as resistance welding, vibration welding, and ultrasonic welding. In general, the processing time for thermoplastic parts is significantly lower than that for thermoset parts. This is because processing of thermoset parts involves a chemical reaction (a curing or cross-linking reaction) in the mold, which, depending on the mold temperature and part thickness, can take several minutes to several hours. Processing of thermoplastic parts does not involve any chemical reaction in the mold. If injection molding is used for making thermoplastic parts, heating required for melting the thermoplastic polymer takes place outside the mold; only cooling of the parts takes place in the mold, which is usually accomplished in less than a minute.
Primary consideration is how fast the flutes of the cutter move against the material. A secondary consideration is the direction of rotation of the cutting tool (typically clockwise) and the interplay between the movement of the spindle and material, Climb vs. Conventional Milling.
The values below may be used in configuring milling operations when using a CAM program to generate G-code to make a cut, but unless your machine is essentially identical to the machine which they were used on, can be considered as only very general guidelines. All values should be verified and tested on a scrap of material first, then one should adjust to match desired chip size and surface finish and time required for completion.
In addition, one needs to decide upon a cutting depth advancement, and the amount of stepover (how much each toolpath overlaps, see the Glossary). Using a smaller cutting depth advancement is one suggested strategy for coping w/ the design's lack of rigidity. See also References, Feeds and Speeds below.
The S1 and S2 both give good finish passes at around 1 pound cutting force per FSWizard. Roughing passes, maybe up to 10 pounds depending on how aggressive you want to be. Edward (Ford, the machine's designer) has posted an aluminum milling video with the S3 with good finish and parameters that FSWizard spits out about 4 pounds for. 
The feed rate (speed at which the machine head moves in XYZ space) and the speed rate (number of revolutions per minute the cutting tool revolves around its axis) need to be proportional to each other, so as to have the machine cut out suitably sized chips. If a calculator suggests one be greater or lesser than allowed by your machine, reduce or increases the other proportionally (w/in the limits of your machines frame and linear motion setup) so as to bring the other into range.
Chip load is a physical thing. It's the thickness of the thickest part of the chip that the cutter generates. If your cutting feeds are set up right (i.e. actually generating chips), you should be able to straighten out a chip (carefully! they can be sharp) and measure the thickness. That would be your chip load. I like to keep chip load constant, since the thickness of the chip has a huge amount to do with where heat goes, where cutting forces go, and ultimately the cleanliness of your cut and the life of the tool. I'll always start with the chip load to get a feed rate. Here's how that works:
You'll notice that cutter diameter doesn't come into play there. If you add it to your formula, you're going to come out with really weird numbers. Basically, I say I want each tooth of my cutter to take off a certain amount of material, say 0.004". Now let's say my cutter has two flutes, so every time it rotates I have two chips being removed. In order to remove 0.004" per flute, I have to move the cutter by 0.004*2, or 0.008" per revolution. Now I can multiply that out by my spindle RPM (12000, because why not) to get 0.008*12000 or 96 inches/min. You'll notice units cancel out to a sane unit of IPM for feed. "But Jeremy," you say, "If I'm trying to run my poor little 1/16 cutter through acrylic at 96 IPM it won't last two seconds! That's just too fast!" Well, I hear you. The thing is, it's not too fast. It's actually the appropriate speed to get a good cut. (I'm not vouching for 0.004" necessarily being an appropriate chip load for acrylic. I'd actually suggest something more along the lines of 0.002" to 0.003", but that's a discussion for another time.) The thing at this point in time that will break your cutter is excessive cutting forces, which come from the last variable in our cutting equation: depth of cut.
Many places will have fundamental rules of thumb for how deep you should cut with your CNC router. They'll say "cut at 1/2 your cutter diameter," or something along those lines. Ignore that for these models. I don't trust something that simple, as its bound to be overlooking something. In this case, proper chip and cutter loading. There are a lot of ways to use a lot of math to calculate how deep you should cut, but at the end of the day you're still using a shapeoko machine, which is quite flexible. What I'm saying is, every machine will be different and hard to predict. Start shallow (won't hurt anything) and work down deeper and deeper until it sounds like your cutter is really loading down, then back off a shade and remember that value. I usually suggest starting with 0.012" depth per pass for harder plastics (acrylics) and 0.024" for woods. Those will be very light cuts, and you can play with increasing them more and more until you're happy with how the cut goes. 
One thing to understand is that depth (axial depth, along the cutter) vs width (radial width, or stepover) is very different in traditional machining as opposed to cnc routing. In traditional machining, you tend to start out with a block of material slightly oversize of the actual part. You then whittle it away to reveal the part hidden inside, which usually involves very deep axial cuts with a very shallow radial cut. This is the opposite of routing, in which we're cutting parts out of sheets, so most of the time we have no choice but to have 100% radial engagement (full width of the cutter is cutting). This is less than optimal, and means that we have to cut shallower to compensate. Most "rules of thumb" for cut depth don't quite grasp the fact that you are more or less locked in to 100% width of cut. You can't choose an optimal depth and adjust the width to compensate as normal. You can implement various strategies to do that when cutting parts out of a sheet or panel, but it really doesn't make any sense in that context because it's much less efficient from a cycle time perspective.
The whole thing needs to be really stiff to cut steel. If the deflection at the tip of the cutter (cutter plus whatever it is attached to) is more than the thickness of the chip, (feed per tooth) then it is guaranteed to chatter, and not cut well. This is why milling machines are HEAVY.
Work hardening occurs when the chip of material being removed is thinner than that zone of material which the impact of the cutting forces affects. It is why steel and to a lesser degree certain non-ferrous alloys are so difficult to cut. Excellent discussion from: https://community.carbide3d.com/t/high-speed-chatter-video/26749/32
Many steels work-harden, especially austenitic stainless (e.g. AISI 304, 316 etc). Every cut involves large plastic shear deformation in a thin zone near the surface, and as a result, the freshly cut surface can be harder than the original material. Now, if you take a big-enough chip, the next cutting edge is biting into the material below the hardened zone, but with a very small feed/chip thickness, you will plough precisely through that thin sliver of the surface that the previous cut just hardened. Not optimal.
Increasing cutting speed will increase temperature in the shear zone. In one way, that is beneficial because the strength of the material usually drops with temperature. But: The hardness of the tool drops with temperature as well - edges will blunt quickly (effect: rake down, edge radius up), tool life goes down more than productivity increases. This is much less pronounced in aluminium alloys, because they loose much of their strength at 300C which isnt very challenging for Carbide. In alloyed steel, you can easily reach 700C at high cutting speeds. You may get away with that with very good heat management (high-pressure internal coolant, very small AE or AP), but without, the tool will be blunt after a few inches and start to throw white sparks (meaning > 1000C).
Most of us have experienced this exact problem: Run a HSS drill at too high RPM in steel, and it will blunt before you make more than a little dent. Happens quickly because the heat cant get away in this case, and the blunt tool only makes things worse (higher forces, more friction, more heat)
Note that different materials will respond to cutting in different ways, and will ultimately be cut with differing levels of accuracy. Discussion in: Re: Accuracy: Not sure if this is a MakerCAM issue.
Carbide Create has two notable sets of feeds and speeds for the Shapeoko --- build 433 uses a chipload-based calculation, while 440 and later use a set of pre-calculated feeds and speeds which are intended to be quite conservative, so as to minimize problems.
I made a test piece with 30, 6mm holes, using 2d pocket, bore and circular tool paths. All three strategies was tested with and without finish passes. With climb and conventional. And any combination. And I also tested boring conventional with 0.3mm stock to leave and then a contour/profile path at full depth to finish off the hole. I haven't gone through the numbers thoroughly yet. But so far a few things I've noticed.
It seems Gadgetman was on to something with single-cut operations vs choosing a roughing and finishing two part strategy. All my best holes (size, roundness and finish) were made by single operations that did the full diameter at once!
Secondly using conventional milling produced the best results. Some with climb milling was ok as well, but the general result was that anything concerning climb milling (be it complete single cut operations or used as finis passes) gave a little worse result.
The best two were simply 2D pockets (normal pockets) and bore cut as a single conventional milling operation. Those two produced the best looking holes and finish and was closest to spec. Of the two I think I prefer bore, since it's quicker to set up and quicker to cut.
...Use a simple 3 x 3 matrix method to judge DOC and speed. Make 9 small square (pocket)s in a piece of the wood, and vary the speed and feed across the 9 (also) varying the DOC and feed. When a DOC and feed looks good, check to make sure the chips are little C shapes instead of dust or burnt dust. 
It is always a good idea to test and prove out a G-code path, esp. the first time one uses it. One can of course do an air cut, one anxious user piled up flour and had the endmill drag through that, or one can use a less expensive material (poplar rather than walnut, aluminum rather than brass).
For aluminum: The most important thing is to make sure chipload is at least 0.001 (0.0008 for 1/16) minimum. If cutting under 50% diameter you need to use a chip thinning calculator to see actual chip size.
Ideally when milling metals one would use an upcut bit, so as to clear chips --- however, given the narrower bits which a Shapeoko is likely to be using, plunge depth is typically limited to 0.25mm (0.01") which ameliorates the difficulty of clearing chips. Even so, some users have found it helpful to increase the width of cuts to aid in chip clearance as noted in Re: ORD Bot Hadron. Note that downcut bits are intended for woodworking and may present a combustion hazard in some metals, and will certainly be quickly dulled from re-cutting chips if used w/ metals.
The typical (ideal?) technique would be to find the Surface Feet Per Minute (SFM) (available in references such as: http://niagaracutter.com/techinfo/millhandbook/speedfeed/sfm.gif ) for the metal in question, then calculate:
When milling aluminium, you have to know which alloy you're milling. Aluminium is like wood: milling oak, pine or balsa wood is not the same. For instance in aluminium you have series (1000 to 8000), each of which is alloyed with different elements (specified in parentheses below) to achieve differing mechanical properties.
Depending on the aluminium alloy you're milling, the material can melt and stick to your endmill. If this happens, try to change the cut parameters: fewer flutes, lower RPM, faster feedrate, also try coolant while milling (WD40, water or aluminium specific coolant fluid). This is less likely to happen with harder alloys such as 2017.
If aluminum galls on an endmill, a bathroom drain clearing product (such as Draino) may be used to remove the material (please check the chemistry of this first against the composition of your end mill and its coating).
I cut a "grill" into the "protection plate" that covers the electronics of the shapeoko 3 to mount an 80mm fan, i did it no problem without lubricant. My settings: 2 flute 8mm carbide bit 1000mmpm Stepown 1 mm Overlap 3 mm Dewalt set on 5
0.015 DOC at 15 IPM, then start increasing it by 0.005 and another 5 IPM, until it starts to make too much chatter/noise. Every machine/set up is a little differentfind YOUR sweet spot.... 10k to 15k rpm 
Termed architectural aluminum, it may be identified by the profile having square edges (usually other grades have slightly rounded edges similar to steel angle). Inexpensive and easily extruded.
3 flute, 45deg flute, carbide, 4mm diameter ... 21k RPM, dry, climb cutting ... Spiral downcut along a 1mm radius, .4mm per revolution (leading to a 6mm hole) ... feedrate of 500mm/min with a forward step of 0.5mm (12% tool engagement)
cut on my SO2, with a feed rate of 300mm/min and a 0.1mm depth of cut... Dremel. I used a speed of around 15000 rpm and plenty of WD40 as lubricant. The thing that made the biggest difference to the finish was blasting all the chips out with air at regular intervals. ... On the down side, it blasts small chips of aluminium and WD40 all over the place, so there is plenty of cleanup required afterwards...
1/8" single flute spiral end mill from Inventables. Step down was .2mm per pass, feed rate of 400mm/min. Makita's speed was set to about 3-1/3 on the dial, which goes up to 6. I used some silicone spray initially, but I ran out and cut most of the job dry, periodically vacuuming chips out of the cut.
Superglue. I use a thick (>4mm) piece of aluminium larger than what I need to cut, clamp that to the wasteboard and then dab a few drops of standard cyanoacrylate superglue on the thin sheet and slap it to the larger, thicker piece. Then I break out my 1.2mm 1-flute endmill (http://www.ebay.com/itm/1-20mm-0472-sin ... 58a7df7885) and run it at a feed rate of400mm/min, plunge 100mm/min and a pass depth of 0.2mm. The spindle... runs at full tilt. When I'm done all I have to do is give the thin sheet a good whack sideways and it pops right off the larger sheet. 
Speaking of pushing my machine hard, by pure accident I've actually been able to cut 22 gauge weld steel in a single pass at 7 IPM. It was smoking quite a bit but the machine was marching along without missing steps or jerking. I'll never do that again though, but it was cool to see the machine pushed to its limits. The intention was to make a 0.005" pass.
One user, danielfarley was successful using an 800W spindle w/ settings of: carbide tool - two flutes, 2mm wide, 100--140 mm / min, used some WD-40 as lubricant... although some tooling works better with no lubricant. Unfortunately, this has a potentially high cost in tooling, w/ endmills only lasting for cutting of a single (small) part in this instance.
More successful was forum user dottore in An afternoon with stainless, making a "turner's cube" on a much upgraded Shapeoko 2 (Makita RT-0701, aluminum bed, belt drive Z-axis w/ Acme screw, cooling system, &c.).
Brass is available in a wide variety of alloys each w/ markedly different characteristics, Engraving Brass (CZ120 / CW608N) which has 2% lead added to it, or Free Machining Brass (CW614N / CZ121) which has 3% lead content are lovely to machine.
Discussion of machining brass tags: http://www.shapeoko.com/forum/viewtopic.php?f=7&t=6477&p=50695 Finished results in Engravering Brass (CZ120) http://www.shapeoko.com/forum/viewtopic.php?f=30&t=8371
For smaller details, I use a 20 degree tapered end mill, with a .004 tip. MeshCam thrives when I'm running these small details. Tool settings: .127mm DPP, .020mm Step, 200mm feed, 100mm plunge, .050 OAD.
Note that lead will bio-accumulate, and dust must be handled with that in consideration. Any cutting or fabrication involving fumes or the potential for fumes must use suitable exhaust hoods and filtration.
Whether or not the metal is annealed is an important consideration. Metal hardness varies WILDLY in the jewelry world, and some alloys just don't machine well, no way around it. You really need to know both the alloy and temper of what youre machining to have any success.
There is a heat issue with all plastics, the idea is to remove as much material in one rotation of the spindle as possible then move on. If you dwell in one place too long your bit will heat up and the material will heat up, leading to distortion, bad smells, and dull bits. Single flute bits will help.
Info: When milling plastics you want "chips" to come off the bit. If you find that you are instead getting "threads" of material you need to either increase your speed or increase your depth (preferably not both). You will notice a difference depending on the direction your mill is going. If you get a lot of "chatter" (bit seems to hop) while milling uphill (where bit is turning into the material) you'll want to slow your job down slightly.
Delrin is the DuPont brand name for Acetal (Polyoxymethylene (POM)). Moderately expensive plastic which machines extremely well. Suited for use in bearings and wear applications (it was originally developed as a replacement to the plectrums in harpsichords). Can be machined to tight tolerances, and will wear for long periods without lubrication. Suggestion is twice the DOC and feedrate as 6061 aluminum. Other machinists note it works much like soft brass.
According to some machinists, Delrin must be allowed to rest for about 24 hours after initial machining, and then the last finish cut (0.001") to precise dimension can be taken. Very sharp tools, lots of coolant, and temperature limits are recommended.
Plastic that can easily be found in your local supermarket as a white cutting board (but also available in other colors). Only limitation is they are typically quite thin, usually not greater than 1/4"(6mm) thickness. Thicker material is available (9mm or so is sold as "half-inch" cutting boards), while larger boards in half-inch or even 3/4" thickness are available from specialty suppliers or online. Much larger and thicker panels are available from specialty plastics shops, sign shops and possibly local hardware stores.
Note that boards which are molded (as opposed to cut) may be swollen or otherwise out of dimension along the edges, or somewhat shrunken towards the center, depending on how they are cooled coming from the mold.
.25" end mill 4 flute (I run 2 flute at 150 ipm (up to 180 ipm can be done but chatters along Y-axis) - .130" doc - .1 stepover - 160ipm - 16k rpm [https://www.facebook.com/groups/unofficialshapeoko/permalink/32 83/?comment_id=32 46&comment_tracking=%7B%22tn%22%3A%22R3%22%7D)
One datapoint, Improbable Construct notes "2 flute 1/8" endmill, 40% step over, 1/16" cut depth, 27000 RPM, at a feed speed of 1200 mm with good results. Of course that was with dual Y motors and the double X mod."
"... around 1 or 2 on the DWP611 speed and I feed about 750mm/min with a two-flute carbide end mill. I find I can do about a 4mm maximum depth cut before I start having rigidity issues, but for roughing a full plunge slot at this speed I get significant chatter in the Y direction, where my SO3 is least rigid." 
"The 34 mm/sec with a 1/4" flat cutter at 3.17 mm step was way too fast. Router speed makita at 3. Had a perfect cut at 12 mm/sec, 3.17 step and router at 4 makita with 1/4 " flat carbide3d cutter. 1/2" hdpe in 4 passes." 
But if it helps, I was using the .125" endmills that came with the nomad (so, 2 flute). 7500 rpm spindle speed 68.3 in/min cutting feed rate (feed per tooth .0046") 17.075 in/min plunge feedrate .03" stepdown All climbmilling
spindle speed constant at 10000rpm. For 0.1mm flat end mill, I plucked in the feed rate as 76.5mm/min and the plunge rate as 2mm/min and for 0.2mm flat end mill, I used the feed rate and plunge rate as 186mm/min and 7mm/min respectively. 
Note that what is sold as 0.25" thick acrylic is typically manufactured to metric 6mm (0.236"). Thickness tolerance for typical manufacture is 0.02", engineering plastics are available w/ tighter tolerances (0.005" from McMaster-Carr).
Trochoidal milling: 3mm endmill feed - 1750mm/min DOC - 10mm plunge - 650mm/min trocoidal stepover - 12.5% trochoidal width - 50% http://community.carbide3d.com/t/trochoidal-milling-is-amazing/6063/7
Extruded acrylic tends to "store" energy and may randomly crack if one presses in a part as a friction fit. This happened when I.C. tried pressing in the magnets on his DWP611 shoe and broke a couple. A further issue is that it will have two separate optimal feed/speeds for cutting, one along the extrusion axis, the other at 90 degrees to it.
Moderate tensile strength with good abrasion resistance, but low impact resistance (tends to split or crack under shearing forces). Handle carefully due to its brittle nature. Easily shaped with application of heat (150--250 degrees F).
Commonly Available Colors: Clear, Opaque (White, Grey, Black, Red, Yellow, Blue, Green), Solid Tints (White, Grey, Bronze, Red, Blue, Green, Yellow, Amber), Fluorescent/UV Tints (Amber, Red, Green, and Blue)
2. Go thick. I dont mean buy a foot thick slab and try to mill it down to what you need. I needed to cut a lens that will likely be sanded on both sides to increase the opacity. So I got some extruded acrylic from the big blue box store that was double what I needed and have accounted for that change in my overall design
3. O flute up cut and somewhere between 1 and 3 for dial setting on the Makita. It was doing an amazing job until the retract height thing got me and snapped it clean off. There was a bit of build up, but itd get to a thickness then fling off. After this broke, I switched to a straight cut but it didnt do nearly as nice a job and really failed to eject the chips.
1/8" cutter single flute, 1800 rpm, feed rate of 50"/minute (1200mm/min) and plunge rate 24"/minute (600mm/min) with depth of cut 1mm. Possible to increase the depth of cut if your endmill is suitable. Notes from IC for cutting his dust shoe:
Note that there are safety implications for heating / burning PVC, esp. w/ a laser, due to its chlorine content and exposure to its dust (may cause asthma or other respiratory problems). See http://toxtown.nlm.nih.gov/text_version/chemicals.php?id=84
With these settings Nylon 6 cuts very well with no heat problems. Most of the swarf was small flakes and there was very little 'fluff' left on the work piece. With a plunge rate limited to 150mm/minute and at the lowest speed on the Kress spindle drilling is a disaster and melts the plastic. A faster plunge rate may help.
Carbon fiber can be cut, but requires dust collection (the dust is hazardous and electrically conductive) and is tough on bits, requiring more frequent replacement. Carbon Fiber Plates and Aluminum Bearing Blocks
Nick Offerman has an excellent guideline --- if working with any sort of rare/expensive wood the project should be expected to last at least as long as it took the tree to grow --- it's reprehensible to my mind to make some trivial, ephemeral thing out of a tropical hardwood.
Forum user cchristianson posted the following numbers in Re: First real project! dimensional letter shop sign: 24 in (609.6mm)/min for feed with 5 in (127)/m plunge @ 1/16" passes (1/8" 4 flute end mill). The same values were used for a very hard mahogany as well.
Theoretical: 1/4 inch carbide bit try 12-18000 rpm and 762--2,286mm/min (30--90 ipm). 1/8 inch depth per pass. Leave about .01 inches for a full depth finish pass at the lower ipm range. Depending on the machine you may need faster or slower. You might also need a different step down.
MDF (medium-density fibreboard) is a relatively easy material to cut. It's soft and evenly composed, so the bit should have no trouble working through it at a consistent pace. The main concern when cutting MDF is that cutting will yield a lot of airborne sawdust (which, due to how MDF is made, can be harmful to to inhale). Wearing a dust mask is certainly not a bad idea, and is recommended.
Another concern is that the waste will expand somewhat when it is cut, filling a slot, which may become an issue if one needs to cut more than a pass or two. Rather than slotting, cut pockets which are at least half again the bit diameter.
You should also be aware of burning issues while cutting MDF. If your cuts are making the wood darker and/or producing a smell, try using a faster feed rate or a better bit (a 2-flute carbide endmill works very well, 2 flute end mills with TiAN coating are suggested). Faster feed rates prevent the bit from staying in one place for too long, which is a factor in overheating.
Geometry Diameter: 1.000 in Flute Length: 0.125 in Included Angle: 2.0 Num Flutes: 3 2D Cutting Parameters Feed Rate: 80.0 in/min Cut Depth: 0.010 in RPM: 16000 3D Cutting Parameters Feed Rate: 80.0 in/min Stepover: 20.0% RPM: 16000 Finish Allowance: 1.000 in 
Compression bit from Toolstoday Router Bits and Saw Blades: "1/8 compression at 40ipm at full depth cutting 1/4 plywood all day, dewalt speed 3. you can go faster, but it wont be as smooth a cut."
This is the protocol I use for walnut stool seats, about 18 x 16 ovals (I have to orient them 45 degrees to get an 18 wide oval). The wood is 12/4 walnut sawn from the log and then air dried for 4+ years. The CAM is from Fusion 360.
Janka Hardness is the standard technique for measuring the hardness of wood. See Guesstimating Feed Rates for a technique for using these numbers to derive a first approximation for cutting a softer or harder wood which one has numbers for.
I cut this as a test first cut before moving onto heavier materials. I used a conical shape cutter that came with my rotary tool. It's coated with some sort of rough particles. The edges of the cuts are rather messy, which would be tricky to clean up (e.g. with sandpaper), especially in areas where little "islands" have been cut (inside the "a" and "e") as there's not much left below to hold them in place.
High density polyurethane foams are often used in sign-making, as well as for props. Density ranges from 10--30 pounds per cubic foot. Creates a gritty dust which is hard to clean up. See Tooling Board below.
One brand name is Plastazote. Use dual-colour for tool drawers, top: 5mm (less than 1/4"), then for the color below, adjust to match drawer thickness (leave a reasonable amount of space above). mill fast speed with low rotation speed.
Polyurethane tooling board machines very well, and lacking grain, holds excellent surface detail. Density ranges from 20--50 pounds per cubic foot. Popular for pattern-making, product mockups and toolpath testing (hence the name).
A horizontal roughing cut was done at 80IPM with a 0.25in, 0.060 corner radius end mill from lakeshore carbide (where I buy all my tools). The DNP611 was set to 3.5 on the speed controller. Stepover was 50% with a 0.055" step down, and stock remaining set to 0.02". Finishing was done at 120IPM with a 0.125in ball nose mill, 15% stepover. A leading edge curve following cleanup path was run with the same 1/8" ball mill and an 8% stepover.
I have a small endmill 1/32 that I use. I lay down a layer of masking tape on the spoil board, then a layer of tape on the back side of the leather and use spray adhesive to stick the backs of the tape together. It does a pretty good job, but you will have to do some sanding and burnishing on the edges of the leather to smooth it out since the endmill leaves a rough edge on the leather
Discussion here: http://www.sawmillcreek.org/showthread.php?213915-CNC-router-for-Plaster-Moulds&p=2227973#post2227973 and here: http://www.camheads.org/showthread.php?t=3377 and discussion about various materials here: http://www.cnczone.com/forums/haas-mills/63483-anybody-ever-milled-hard-plaster.html
Ceramic matrix composites (CMCs) have been developed to overcome the intrinsic brittleness and lack of reliability of monolithic ceramics. The main objective was to introduce ceramics in structural parts used in severe environments, such as in rocket engines and heat shields for space vehicles. Replacing heavy super alloys with CMCs in advanced engines will allow an increase of the temperature at which the engine can be operated and will yield significant weight saving.
The present chapter deals with the state of the art on the material design, processing, properties control and applications of fiber reinforced Ceramic Matrix Composites during the last few years. The chapter starts with a discussion on the current state-of-the-art reinforcement materials used for the fabrication of continuous fiber reinforced ceramic matrix composites. The discussion also focuses on the different types of fiber architectures currently being used/developed. The fiber/matrix interfacial domain is a decisive constituent of continuous fiber reinforced SiC based Ceramic Matrix Composites. Here the fiber/matrix interfacial characteristics are examined with respect to crack deflection and composite mechanical behavior. An account of the processing routes of CMCs, focusing PIP processing using various preceramic polymers is provided. An appreciation on the ability of this route in controlling the microstructure and elemental composition and its effect in controlling the final thermo-mechanical properties of the matrix is included. Final section of the chapter deals with the oxidation behavior of Ceramic Matrix Composites, need for oxidation protection coatings, requirements for a good coating material, various research activities carried out on oxidation protection coatings, different methods of applying the coating and finally future scope of developing coatings for ultra-high temperature environments.
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Ceramic ball mill is also called (Intermittent ball mill/Batch ball mill). Ceramic ball mill can be used to grind feldspar, quartz, clay, silica and other hard brittle materials. It is widely applied in industrial production of high fine grinding materials.Ceramic ball mill grinding has dry and wet ways, of which the dry grinding can produce ultra-fine powder with the fineness of1000-16000 mesh.
The material goes to the first hopper after the spiraling by the quill shaft from the feeding equipment. The hopper has ladder sheathing or corrugated sheathing with steel balls inside, which will fall under the effect of centrifugal force by barrel turning to ram hard and grind material.
After the kibbling in the first hopper, by monolayer partition panel, the material will enter the second hopper, which has plane scale board with steel ball inside to grind material. The powder material will be discharged from the grid plate to finish the grinding.
In ceramics, ball mills are used to grind down materials into very fine particles. Materials such as clay and glaze components can be broken down in a ball mill by getting placed into rotating or rolling jars with porcelain balls inside them. During milling, the porcelain balls pulverized the materials into an incredibly fine powder. Ball mills can be used to further break down or refine a single material, or you can place multiple materials into a ball mill jar to mix as you pulverize -- this is a very common industrial solution for mixing glazes that require the smallest of mesh sizes. Ball mills basically function like a mortar and pestle, but on a much larger scale.
Here at The Ceramic Shop, we carry ball mills and accessories produced by strong and reliable Shimpo. Shimpo's line of heavy duty ball mills allow for very precise grinding and mixing of both dry and wet materials. The porcelain jars are available in a variety of sizes, ranging from one liter to ten liters in capacity, so you can really customize your ball mill outfit to suit your needs. If you are a potter working out of your home or a shared studio, and dont have the space or budget for a full-scale ball mill setup, consider Shimpos ball mill wheel attachment -- this ingenious setup allows you to turn any standard potters wheel into a makeshift ball mill!