Countersinking with a too-fast drill press

In June 2005, I was having problems because my little 12" Delta
variable-speed drill press has a minimum speed of 500 rpm, which was a
real problem, especially when countersinking.
I had found an interim solution for larger holes: Put the countersink
in the hole and turn power on, releasing the downward pressure before
the press gets up to speed.
This did not work with small holes, and the 1/4-inch severance
countersink, working in 6061 aluminum, flooded with a water-based
coolant. I would have thought that a small countersink would be OK at
500 rpm, but the holes became ragged and misshapen.
Countersinking with a hand drill did work, making pretty holes, but
yielded inaccurate countersinks because it's so hard to drill straight
by hand.
I was busily tearing metal and hair when it occurred to me that tapping
is an extreme kind of machining, and yet one can get clean threads, with
the right lubricant. So I tried LPS Labs' "Tap-All". It worked, even
at 500 rpm.
Haven't tried it in steel and/or for large holes yet.
Joe Gwinn
Reply to
Joseph Gwinn
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If I had to bet money, I'd say you're not feeding fast enough (pushing hard enough). You should be able to countersink a 1/2" hole in steel at 500 RPM with some practice.
You have to feed *hard* into the material (you'll need a good chuck as most countersinks have pretty hard shanks) and retract quickly when you're at the desired depth - no dilly-dallying at the bottom or throughout the cut.
Your idea about the lube is good. Countersinks are easy to burn and hard to sharpen.
HTH.
Regards,
Robin
Reply to
Robin S.
I used to do this at work. Basically you are using the start windings and the mechanical inertia of the spindle and motor to keep things down to a slow enough speed that the c'sink doesn't chatter.
It also helps to use a single flute countersink.
Eventually I went with a VFD so now I can run those things slower than I would want to - if I wanted to, if you catch my drift.
Jim
Reply to
jim rozen
How do you keep from boring too deep? I guess one chews one hole up finding the right depth to set the depth limit stop to.
Not that I trust the depth stop to really prevent motion when pushed hard enough to avoid chatter.
This approach probably works better for large holes than for small ones.
Haven't burned one yet - probably too chicken to push it that hard.
Was in a used tool place last week. Saw a 3/8 mill with irregular heat colors, signs of heavy use in aluminum, and a bit of solidified aluminum "soldered" to one flute. My guess is that it was on a CNC mill happily hogging aluminum when the coolant flow failed.
Joe Gwinn
Reply to
Joseph Gwinn
--Plan B: go to the swapmeet and pick up a brace and bit; these work OK for this sort of thing and they're *great* for tapping..
Reply to
steamer
If you are able to vary the voltage to your DP, you will at least have more controllable torque at the motor, and can likely keep the speed constant at a given pressure. Proly not the greatest thing for the motor over prolonged periods, but for a duty cycle of, say, 20%, it should be OK. A variac would do, or a big-assed dropping resistor. Or, perhaps just two motors in series--a spare motor in series w/ your DP motor! ---------------------------- Mr. P.V.'d formerly Droll Troll
Reply to
Proctologically Violated©®
Yes, it is. As others sayd: More feed. Most people fear to feed countersinks and think the have to go sloooow. Noooo. :-) The first few 1/10mm feed fast, and then you can go back with feed. This helps.
If you have chatter, I guess your DP's table is not clamped (and so swinging a tad left/right). Fix that. Also, clamp your part to countersink in a (heavy) vice, and I bet your problem is gone.
Nick
Reply to
Nick Müller
A brace and bit! Actually, I have one that I bought new in the late 1960s. Used it mostly for installing locks - it's the best way to cut a clean 1-1/8 inch hole in a wood door without power tools. The trick was to bore until the lead screw just poked through the back side, back out, and complete the cut by boring from the back.
I hadn't thought of using it for tapping. It ought to work, at least for larger sizes. If I can keep the tap properly aligned by hand. What I've been using is a piloted tap wrench in the drill press.
Joe Gwinn
Reply to
Joseph Gwinn
The larger the tap, the greater the torque requirement (large at work is M36). Could be difficult.
You should try a spiral-point tap, in the drill chuck. Ideally your drill press reverses to pull the tap out. Probably still faster than hand tapping if you can only run the tap under power forwards.
Regards,
Robin
Reply to
Robin S.
So far, I have not needed to go beyond 3/8-16 and M8-1.25, but I have a few 1/2-13 taps ready to go.
I do use spiral-point taps, and gun taps, but only by hand so far. Isn't 500 rpm a bit fast for a tap? How do you stop in time?
I have also been using a thread-forming 10-32 tap for some very deep blind holes in aluminum. I had been using various kinds of cutting taps, but it was touch-and-go, and I did break a few taps until switching to thread-forming taps for this job. None of the broken taps were Asian. Some were Greenfield, and some were Sossner (sp?).
Joe Gwinn
Reply to
Joseph Gwinn
OK. What seemed to be happening was that the countersink flutes became clogged with chips, reducing one to drilling aluminum with an aluminum tool. Not a good combination.
Everything was clamped, but the misshapen hole was in a 3" disk made of 0.060" sheet, which is hard to really clamp.
I'll have to do some experiments on waste stock. Thanks,
Joe Gwinn
Reply to
Joseph Gwinn
I have much better results in all materials, especially aluminum, using this type of countersink: look at Series 67
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Reply to
DanG
OK, this is nearly impossible with the 3 flutes countersinks. You need one with one flute of the type with one diagonal hole. They are good for deburring, but in a material so thin, you are deburring.
Nick
Reply to
Nick Müller
: I do use spiral-point taps, and gun taps, but only by hand so far. : Isn't 500 rpm a bit fast for a tap? How do you stop in time? --Well if this is a money making proposition and you plan to make bunches you might want to invest in a Tapmatic. Once you use one of these beauties you'll wonder how you got along without one for so long. OTOH they ain't cheap..
Reply to
steamer
I'd bet that the drill press would probably stall with the necessary amount of pressure being applied.
Reply to
Joe AutoDrill
I bet you are right, given my cute little drill press. Not that I've managed to stall it yet. Usually, the drill bit slips in the chuck.
Joe Gwinn
Reply to
Joseph Gwinn
Are there countersink tools available with three flats on the shank?
Reply to
Joe AutoDrill
I imagine that there are, but I haven't seen them. I imagine that the better grade of countersinks do not have the flats, the expectation being that one will use a better grade of chuck to match. My solution was to upgrade the chuck. I'd love to get a ball-bearing Jacobs chuck, but have not seen it offered with a J33 taper, only J3 and the like. My next drill press will not have J33 taper - too limiting.
Joe Gwinn
Reply to
Joseph Gwinn
According to Joseph Gwinn :
Doesn't your drill press have a Morse taper spindle? And how about your next one? If so, you can adapt it for almost *any* Jacobs taper.
Good Luck, DoN.
Reply to
DoN. Nichols
No. None of the current Delta drill presses do, even the large ones. One of the reasons I often refer to it as "cute"; it's not a compliment. So much for Delta. My next drill press *will* have a morse taper spindle. (Or will be a mill-drill with R8 spindle.)
I recently looked at an old variable-speed three-phase 20" Clausing drill press that was in very good condition and cost $650, but is a bit large for my little shop. This Clausing is a dollar a pound, and stands about 70" tall. I would have bought it were it a bit smaller.
That set me to thinking that a mill-drill of similar size and weight might be the ticket, given my limited space. (No way can I fit a 2000 pound Bridgeport. Nor do I really need anything that capable. But it would be nice.)
Anyway, my current list of requirements for a drill press follow:
1. Morse taper spindle.
2. T-slot table, with coolant drain. (Oddly, the little Delta has this.)
3. Minimum speed of about 100 rpm. Max speed not critical, but better than 2000 rpm is good. (The 500-rpm min speed of the little Delta is a big problem.)
4. Quill travel of at least 4 or 5 inches, with a depth stop that really works, but need not be quick to adjust. (The 3" travel on the cute little 12" Delta just isn't enough, and I am forced to unclamp the table far too often.)
5. Quill lock.
6. Variable speed. This can be mechanical, with single-phase motor, or it can be a VFD-driven three phase motor with step pulleys. I will provide and install the VFD if needed. (My background is electronics.) In a used machine (like that Clausing drill press), one may end up with mechanical variable-speed drive plus a VFD. I could make a rotary phase converter, but don't know where I would put it.
7. Motor voltage of 110 or 220 vac; 440 vac only won't do, because I don't want to need a big transformer. I have 110/220 vac 60 Hz single phase in my shop.
Comments?
Joe Gwinn
Reply to
Joseph Gwinn

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