Drill Press Accuracy Questions

um, "deflect". Do you mean it wanders and the hole doesn't start where you think it should start? This is a function of the geometry of the end of your drill bit and also how "whippy" the drill bit is. A really rigid drill bit like a center drill shouldn't wander much if the surface is flat. If the surface is curved, then you can get much better results by cutting a small flat and starting the drill on the flat. For wood, this flat can be done with a small chisel or something (I'm no wood guy) and for metal, it can be filed.

You're correct, changing the table height loses your setup. This is a small inexpensive drill press, not a mill. Even if your rack were welded to the column you'd still lose some accuracy. Learn to locate your workpieces under the spindle axis. For many parts this can be done just by holding the workpiece on the table and letting it move a little as the drill bit picks up the indent. For many other parts this is too dangerous as the drill can catch at breakthrough and spin the workpiece, perhaps tearing a hole in your stomach. One approach I used to use is to use an X-Y drill vise mounted instead of the table. I got a whole lot of use out of that one. Beware that the quality varies hugely on those. I hand-picked mine from a bunch up at the Grizzly showroom 10-12 years ago, and it's real nice. I got a slightly bigger one from J&L a few years later and it was awful. None of them work perfectly. They all work better than a hand drill.

Really, my current best advice is to find a motivated seller of a mill-drill and get one of those. Those are lousy mills but real good drill presses.

Grant Erwin erstwhile author of

I have seen people use a hose clamp to firm up the rack. That age Delta is more than likely an import.

Well said, Grant.

Harold

English really is my first language, even if it doesn't show sometimes.

The point of the bit makes 1 move, in one direction - it doesn't move in a circle or make random motions. I could be convinced that it is the chuck that is moving, rather than the bit flexing, too. I don't see any sort of nut or screw or drawbar or ??? holding the chuck to the machine, so I'm not sure how I would tighten it if this is indeed the case.

I think your suggestion about the mill-drill is probably the right solution.

Chris

OK. Don't be so disparaging, not everyone is a skilled technical writer. Do you mean that if you chuck up a drill bit, power off, grab the outside of the chuck and wiggle that there is tangible side play in one or more directions? That would be terrible if so. Or do you mean that if you put a workpiece on the table, chuck up a drill bit, start the motor, and as you lower the drill bit into the workpiece as it touches it "skitters" around a little? These are two very different issues and I'm still not clear on which you've got going on.

Grant

Chris wrote:

It will help -- but what may help more is to get split point drill bits. Normal drill bits have what is known as a "chisel point" -- a bar across the center which really does not cut, and which on any irregular surface (or even on a smooth surface if you are coming in at an angle) will sort of "walk" on the ends of the chisel point until the bit deflects enough so the added force needed is sufficient to allow it to start to bite in.

A split-point has a more complex tip geometry, which terminates in a relatively sharp point which will not walk. That would help you get these bits started where you want them.

Good Luck, DoN.

of the chuck and wiggle that there is tangible side play in one or more directions? That would be terrible if so. Or do you mean that if you put a workpiece on the table, chuck up a drill bit, start the motor, and as you lower the drill bit into the workpiece as it touches it "skitters" around a little? These are two very different issues and I'm still not clear on which you've got going on.

For this to mean anything you have to define "slightly". Does it move 1/2 the drill bit diameter, 1/4, 1/8 ?? Does it skitter around a little as Grant asked and then drill to center? Does it skitter around and then drill to a circumference of the skitter pattern ?

Bob Sw> >>Do you mean that if you chuck up a drill bit, power off, grab the > outside

OK, now I've got it. This can happen on any drilling or milling machine. You simply need a more rigid setup. Use a shorter drill bit, or a center drill, just to get things going. I once bought about 5 6" long center drills. I use those when I'm going to drill with a bigger drill, like a 1/2" drill bit. Those are longer, and so I need more headroom above the table. I can still get down to the workpiece if I use a long center drill. Once you have the hole started, then use a skinny drill bit to go through. If the material is at all tough then pay strict attention to your speeds. 75 surface feet per minute is pretty good for HSS drills cutting steel. Take 300 and divide it by the diameter in inches to get a rough RPM. For instance, a 1" drill you'd run at 300 rpm. Or a 1/8" drill you'd run at 2400 rpm. Point is, don't run a small drill bit slowly. Bad things happen. I bought a whole box of 1/8" drills, top quality, best I could buy, because I so often drill my first hole with that size. Once you've got a through hole, on your little drill press I would step up slowly to your desired size, because that will minimize the forces deflecting your table.

A long skinny bit will almost always skitter on a new surface. You can sometimes get away with a short skinny bit i.e. a screw machine drill. Or you can center punch your holes and follow up your accurate centerpunch with a big whopping centerpunch you drive in with a 2 pound hammer. I know a good machinist who does that and his drills don't wander because his centerpunches catch the bit.

Grant

Chris wrote:

Somehow I often do things almost exactly the opposite of Grant. I usually use a slender drill that is long and has a lot of flex. I do centerpunch with a automatic center punch so that with a small drill the center punch dent holds the drill from slipping. With the part is a vise, but the table able to be moved, I move the part so the drill is no longer flexed to one side. That is the drill is exactly over where I want to drill. Then clamp the table from moving. Then I apply some pressure and after the drill has the drilled the hole out to the drill diameter I apply more pressure and drill through the part with the slender drill. Then I go to the full size drill for the hole that I want.

I am sure the way Grant said will work well, it just is not what I do.

Dan

Grant Erwin wrote in message

Dan sez: " I am sure the way Grant said will work well, it just is not what I do."

Your choice, of course. But with your "system" you would do nearly as well with a hand held drill. Grant's advice was for machinists.

Bob Swinney

Straight holes with the chuck aligned with the hole so it can be used to guide a tap. What more would a machinist want? I could do it with a wiggler instead of a flexible drill, but it would take longer. Try it when drilling a hole in a piece of round stock before deciding that it won't work well.

Dan