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Do you experience problems drilling accurately, even when you have nicely center punched the correct location for a hole? My drill press was letting the bit dance around a bit (quite a bit) when starting a hole, so the hole frequently ended up just off the position where it needed to be. While you might get away with this on some types of wood work (but not on precision jobs of course), it can develop into a major problem for your metal projects.
First of all, lets make sure we are talking about the same things. In a drill press, the quill is the hollow shaft that surrounds the spindle. The spindle is the rotating shaft that the chuck is mounted on. The spindle turns with respect to the drill press housing, while the quill does not turn with respect to the drill press housing. Instead, the quill can be lowered along with the enclosed spindle (and chuck!), so that a drill bit mounted in the chuck can contact the workpiece. A rack and pinion mechanism allows the quill to be lowered. The rack is usually cut into the quill itself, the pinion is rotated by the operator with a handle. This is how you make the drill press drill a hole.
Radial quill play is unwanted lateral movement of the quill. You can test your drill press for radial quill play by lowering the quill, say to half its maximum extension, fix it in place, and pushing with your thumb on the quill side. If you can feel the quill move in the housing, you have too much play in your quill. Try this again with the quill fully extended to find out what the worst-case scenario may be.
If you have a dial indicator you can easily measure radial quill play by reading on the dial indicator how much the quill gives, or better moves radially, when you apply pressure with your thumb. Measure this in different places around the quill circumference, and that will give you an overall idea. I am sure I do not need to state this, but your machine is not turned on during this operation.
How much quill play is too much? Hard to say in general, as it depends among other factors on the precision of the machine construction so maybe a better question is how much quill play can you afford, and if your holes turn up consistently in some unwanted place, then you know you have too much of the goody.
A different kind of quill play problem is axial play, which is unwanted movement of the quill in the vertical direction, i.e. with respect to the spindle. Axial play manifests itself under drilling pressure and often causes vibration in the whole machine. Causes of axial play may include worn, improperly adjusted, or low quality spindle bearings, but that is another story and another fix (new spindle bearings installation is described here).
Most likely, because you bought a cheap drill press machined to low standards, most likely from over the pond. No criticism implied here, I did as well, and I would not exactly call mine cheap. Maybe made cheaply, for sure not sold cheaply, as it is a rebranded Taiwanese mid-size drill press that sells for about 600$! Not exactly a 99$ deal, and here I am telling the story.
So why does quill play develop? In most presses, the quill is supported by and travels in a bore in the cast iron machine housing. In cheaper drill presses, the bore is often not machined precisely enough. These drill presses often come with a good amount of quill play straight out of the box, and for free. In better drill presses, the steel quill travelling in the cast iron bore wears the bore out with time, and this is normal. Actually, the fix I did on my cheap machine is a standard adjustment on many American and European quality drill presses, especially vintage machines! If you wonder why today so many presses do not have this adjustment anymore as a standard feature, other than for saving a few bucks in the production process, I do as well.
If you have a professional drill press, you most likely will not be reading this anyway, as your quill will be precision-grounded, bearing a hard chrome finishing, and travelling in bronze bushes mounted in the cast iron bore. It will last a lifetime when properly cared for. Such a machine however is usually out of reach for the shallow pockets of most hobbyists.
Before moving on, as cast iron is prone to cracking, and you may wonder if there is a danger of cracking the housing when you apply pressure to the slit via the adjustment bolt. This obviously depends on the solidity of the housing of your particular machine, so it s hard to give a definitive answer. I dont see a problem if you are doing this to fix a small play in the quill and if you never apply pressure to the slit when the quill is not mounted in the bore. On the other hand, if you are trying to fix a play, and crank down on the adjustment bolt on an empty bore, you may be asking for trouble. By the way, I dont see how you could fix that amount of play anyway.
The slit will be about 2-3 long, the exact length depending on your machines physical dimensions. The key point here is that it needs to cut through both bore quill support surfaces. The bore usually has two surfaces contacting the quill, and if your slit is cut too short and only goes through one of them, it will not be able to exert the compressing action. The slit needs to extend a bit (something like three quarter to an inch, depending on how thick the housing is) beyond the second bore quill support surface to be able to exert closing pressure. The slit should be quite narrow, a practical dimension is around 40-50 thousands, I cut mine to 30 thousands (0,8mm).
I recommend cutting the slit on a milling machine using (surprise, surprise) a slitting saw. This gives a nice, clean cut. Now, recommending is easy, but I am sure you wonder, what if I do not have access to a milling machine? You can still do this using a keyhole saw, of course it will be hard work to get an accurate result, but it can result in a proper job if you have good manual skills.
No need to worry about cutting oil, as cast iron is best cut dry, but no matter how you make the cut, you will end up with cast iron chips inside the housing. Unless you have completely stripped down your machine before you did the cut, like I had to do to mount the housing securely on the milling machine table, protect bearings left in the housing (typically pulley bearings) to prevent contamination. Clean the housing well to remove chips. You may want to use a vacuum cleaner for cast irons chips, as they are very fine, almost powdery.
The key point here is to check the available space between the inner housing surface and the quill to select a bolt size that will clear the moving quill. The adjustment bolt should not contact the quill, as it would be in the way of its vertical travel.
Often there is not much clearance between the quill and the inner housing surface, and you will have to measure and experiment to select the right size bolt (I actually used threaded rod). As this determines the size of the holes you need to drill, do this before you drill the wrong size holes!
Also, it helps to drill as near as you can to the inner housing surface. The whole thing is a bit tricky if you do not have much space, as the inner housing surface can be quite rough from casting and have protrusions that are in the way. It is even trickier if you do not have a second drill press to drill the holes like me. Luckily I could drill the holes on the milling machine after cutting the slit.
I got away with a 3/16 (5mm) bolt, but had to grind the central section a bit to clear the quill. I also had to use a Dremel tool to grind away casting irregularities protruding from the inner housing surface to be able to get the adjustment bolt near enough to the inner housing surface to clear the quill.
Once you put it all back together, you use the adjustment bolt to eliminate the quill play. I used a nylock nut on one side of the threaded rod section that conveniently doubled up as adjustment bolt, and two regular nuts on the other side, the first one contacting the housing to apply and maintain pressure, the second one to lock the first one in place once the adjustment was done.
Be aware that the adjustment you need to make is quite small, in my case less than a half turn of the nut to go from contact with the housing to completely kill the play in the bore. Do not tighten the nut excessively or you will lock the quill in place. As it happens with adjustments, experiment a bit by playing with the adjustment nut while you lower the quill and apply lateral pressure, and you will hit the sweet spot. By the way, three hands come handy to do this.
With that Albrecht- like chuck, any appreciable runout from it is very unlikely, but with the standard keyed drill chuck that comes with most inexpensive drill presses, there is usually one optimum hole for tightening with the key that will consistently give the best (lowest) runout, all one has to do is chuck up a new bit or one that is known to be true, and lightly touch down on a small, thin piece of metal and observe the movement, mark the keyhole position that produces the least amount of oscillation and that's as good as it gets.
Nice tip. I'll definitively try it out. By the way, the chuck is exactly an Albrecht look-alike, not the real thing, but it is of better quality of other drill press components, and did run true. The real issue in my case was the play in the bore. In general, the chuck certainly is another good candidate for causing trouble.