Using a Z axis power feed for drilling/boring

grover

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I am looking at a PM940 (the one I have ordered doesn't even have an ETA yet) and one of the features I am wanting is the PDF which I assume is done with gears in the head unit. Pretty strong transfer of power I would think. I was wondering if you had a DC gear motor hooked up to a speed controller could you lock the spindle in the up position and feed the head down for drilling and using a boring head with the speed control turned way down? In other words what the PDF feature is used for. I have a new/old stock Leeson 90V 2 amp 1/4 hp 100 inch lb 125 rpm gear motor. Also have a new/old stock Dart speed controller with forward/brake/ reverse. With the shaft clamped in a vise grip you cannot stop it when it first starts to move with the speed turned down to lowest setting. I have heard the 90v DC motors have similar torque through out the speed settings as they are used to run conveyors and need the same power at whatever speed they are set at.

I was wondering if that would be too much pressure on the lead screw and nut assembly? I am thinking you do the same thing on the X axis but I know some times the downward pressure when drilling,say a 1" hole in steel, can be much greater. If it was a CNC ball screw it would probably handle it much better.

I was watching Pragmatic Lee on you tube and he has a Z feed coming in from the crank handle that turns at 67 rpm with no speed controller and he says it is to slow so this 125 rpm with a speed controller would be perfect I am thinking. Also assuming 125 rpm coming in from the crank handle shaft would be in the ball park what rpm would a motor used to turn the lead screw directly from the top have to be. How would I convert that numbers wise? I don't have a mill to look at otherwise I could open it up and use a tachometer on it. I was just wondering as I have a few other 90v DC motors that I could use to mount on top if I knew what rpm would be appropriate. Also how would you couple the motor on the lead screw at the top. I am thinking it can be done as that's where they put their Z axis power feed units.

Looking at a screenshot from Lee it looks like equal size gears so same speed? I could mount it on the top or side?

Now that I think of it boring probably wouldn't be as accurate as using the spindle bearings vs riding on the ways.

Also this from PM Lead Screw Type: Inch Pitch Acme Threads – 10TPI on X and Y Axis. Not Z I am guessing.
 

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Eddyde

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I have a similar mill.
It certainly could work and would be great for gross adjustments to the Z axis but a proper power down feed on the quill/spindle is much better for drilling etc. One of the advantages of a PDF is you can set it and walk away while it drills as it will stop moving down and retract the drill once it hits the depth stop. You could of course make your own depth stop with limit switches, etc.
 

MrWhoopee

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I'm not familiar with the PM940, but the power quill feed on a BP is not robust enough for drilling operations of any size. It is intended for boring.
I note that the description for the PM940 says the same.
"Available With Power Down Feed on Spindle (PDF Model Only) For Boring Operations"
 

benmychree

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I had an Induma 1-S, similar to a BP only a bit heavier, same thing as above, boring only with the spindle, any drilling overpowers the feed safety overload clutch.
 

Eddyde

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I have a BP clone head on my mill and have drilled with the PDF many times. I guess Ignorance was my friend.
 

grover

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Power downfeed, Figure 3-10, can be used to reduce
workload in many routine operations including drilling,
reaming, honing, and hole boring with single point tools
From the PM940 manual.


As I look at the manual this option is something I want. Drills the hole, when it hits the set limit disengages the PDF and pops the spindle up under spring pressure. Plus consistent feed for precision boring.

I saw that power feed z axis you tube video and I have the perfect components to implement it and my "I can do that thing" kicked in!
The trouble is to get the PDF option you have to buy the Z axis head power feed and the X axis power feed. I can understand Mat has to limit the options due to market constraints .

I was thinking I could get the Basic with hardened ways (which is due in June) as opposed to the one I have ordered which supposedly is due in fall. Someone here mentioned fall is a long ways off and I said no problem. But one starts thinking.......fall is a long ways off. In this new world who knows what will happen between now and fall. Bird in the hand vs bird in the bush vs bird flue plandemic 2.0?
 

Eddyde

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IMHO, it would not be possible to create the same effectively as a mechanical PDF simply with motors and a speed control. Also it would be a lot of work, at that point you might as well go the CNC route.
 

aliva

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I have BP clone tried drilling with auto feed but the clutch kept tripping, so I do it by hand
 

Eddyde

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There may be an adjustment for the clutch? My PDF will drill up to around ⅝" before the clutch starts to slip, and if it slips it re engages, drills a bit more, slips again and will cycle like that till it gets through the workpiece, kind of like an auto peck drill. I thought it was designed to work like that, but now I am unsure?
 
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