Advice for DIY Z Axis Power Drive

Timely topic, I was thinking of doing something similar. Anyone know approx what torque numbers would be adequate? If I have to ballpark it from remembering the effort involved with the crank handle I'd say 20-30ft-lbs? not sure what that translates to but I was considering a car's window motor.

I just finished converting my RF30 to CNC (documented here) so that freed up the X axis power feed motor/brackets. I suppose I could take that apart and try to make that work but it'd be cheaper and simpler to just buy another motor.
 
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Does anybody have a method for measuring how much torque per is needed? It sounds like people are interested in doing this for different mills. I'm going back and forth between driving the rod directly, vs driving the hand crank shaft (which is geared I believe). I suspect the size motor is going to vary depending on which method is used.
 
Actually, now that I think about it I might just use a hand drill...I believe I saw it done on YT a while back. I have three or four of those lying around collecting dust.
 
stioc said:
Actually, now that I think about it I might just use a hand drill...I believe I saw it done on YT a while back. I have three or four of those lying around collecting dust.
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A hand drill is actually a good idea, it has a gear box and clutch mechanism in case you crash the head. You could probably gut the drivetrain and make a custom enclosure as well and run it from a DC power supply.
 
sfsteel said:
A hand drill is actually a good idea, it has a gear box and clutch mechanism in case you crash the head. You could probably gut the drivetrain and make a custom enclosure as well and run it from a DC power supply.
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The couple of issues that I can think of with using a drill motor is that the gears that I've seen are plastic. As long as the head moves up and down smoothly with no binding, that probably wouldn't come into play. The second thing would be speed and over-run.

The auto window motors would probably be plenty, and the motors for a lift gate would be even better.... as far as torque specs go. Very few of the motors that I have looked at have much for actual specifications like torque and full load current draw. That being said..... just about any attempt to re-purpose a motor intended for a different application will end up being a crap shoot to see if it works reliably or not. At least with several of us working toward the same goal, we can share notes and hopefully prevent duplicating disasters!! lol

I don't have my machine set up yet so not a lot that I can do other than research.
 
This hasn't been addressed, may not be germane to the discussion. My PM25 head moves .008 - .010 when the clamps are applied. I wouldn't want to be boring a round bore with the head bouncing around. I have fabricated a sprung button in the quill clamp to keep it in position (it flops around .0025 or so without) when I bore by hand, cranking the quill down with a boring head installed.
 
talvare said:
I built a knee drive for my BP mill a few years ago using a small Bodine gearhead motor I bought on e-Bay. I fabricated a mount and machined components for a manual clutch mechanism. The clutch acts as a safety device to adjust torque and allows me to dis-engage the drive so I can still crank the knee by hand. Here's a couple of photos:
View attachment 260942View attachment 260943

..........and yes, I did fabricate and install a chain guard.


Ted
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I like the open chain drive!
 
T Bredehoft said:
This hasn't been addressed, may not be germane to the discussion. My PM25 head moves .008 - .010 when the clamps are applied. I wouldn't want to be boring a round bore with the head bouncing around. I have fabricated a sprung button in the quill clamp to keep it in position (it flops around .0025 or so without) when I bore by hand, cranking the quill down with a boring head installed.
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Thanks for chiming in Tom.

I am new to my PM25 and have only limited shop experience over the years. Right now I'm not able to get out to the shop to finish setting up my machine, so anything I can learn ahead of time is greatly appreciated.

I am having a hard time picturing in my mind the movement that you describe and your fix. When you talk about the head moving .008 - .010...... are you talking about lateral movement of the head after the two clamps are tightened down..... or movement of the quill within the head? Maybe a couple of pictures would help me clear the fog??
 
When I tighten the two clamps on the left side of the head, the head moves about .008 left to right and .002 fore and aft. Its no big deal, unless i'm looking for precision and I forget to clamp it.
The quill is similar. it moves about .002, to .0025 to the right when I clamp it. I removed the clamp screw, drilled a hole in it to fit a small spring I had, cut a piece of brass to compress the spring and reassembled it. I can lock the quill with the clamp screw, or by not going quite so far, push it over to the right so it is usable. I suspect if I were boring a heavy cut the quill wold move against the spring.
The PM25 is a good mill for the price, I just accommodate it's foibles to my needs.
 
Okay.... I ordered a new 12 Volt motor that I hope will work out without any major complications.

https://vod.ebay.com/vod/FetchOrderDetails?itemid=372095953216&transid=1006962105024&ul_noapp=true

As listed above, there are several different options for the type of motor to use and prices run anywhere from $30 to several hundred dollars. The right angle style geared motors have a better overall appearance for me and this will be my first choice.

I plan to use a transformer switching power supply with at least 30 Amp capability to allow for future additions. My motor is rated at 6 Amps at full load so this size power supply should be beefy enough to handle just about anything.

In addition to the basic up down control switching, I will be mounting upper and lower limit switches for protection, as well a sheer type coupling between the motor and the hand crank shaft. One thing that I hope is that I will be able to avoid making any modifications that result in permanent changes to the basic machine.

Since there are several of us that want to do this mod, I hope that we can collectively put together all the information including sources, dimensions, and specifications to simplify the process for future owners. I will be starting a new thread and I invite everyone to follow and contribute thoughts, ideas, and recommendations on the new thread.

https://www.hobby-machinist.com/threads/pm25-mv-z-axis-power-feed.67657/

Hope to see you there!!
 
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