[thedave]

I have a PM-45-M Mill and am looking to power the Z axis just so I don't have to crank the handle. I don't have torque wrench but it took about 12 lbs hung off of the 8" crank to move it up easily.

I saw someone had a 240 oz-inch servo, who calculated he had 740 oz-inches at the crank shaft and it worked well.

I found this gear motor:

https://www.surpluscenter.com/item.a...tname=electric

Reversible AC Gear motor 177 RPM, 40 inch-lbs rating

Based on my math it should work on a 2:1 reduction.

My goal is something that just uses a simple switch and is reasonably cheap

1. On the above info, does that sound correct.
2. Does anyone know if driving the screw instead of the crank, would require more or less torque?
3. Would a v belt work? or a chain drive? the timing belt pulleys are expensive, looking for a cheaper solution, no CNC.
4. Anyone think a direct drive will this motor would work?

[vidio1]

I used this gearmotor on a Bridgeport clone trying to keep costs down:
https://www.surpluscenter.com/item.a...tname=electric
It worked, but was slower and a whole lot more trouble than a proper feed like one of these:Type 140 Power Feed I was using a 30 amp power supply, so that might have had something to do with it.
I'm not sure how well a gearmotor rated less than 1/3 that of a proper feed will work for you. The knee is just hard area to mount something to........

[LUCKY13]

A little something that might get you by until you figure a way. I took a 3/8 to 1/2 socket adaptor. Then I put it on a short 1/2 drive extention (which fit my crank shaft for the handle (removed the handle).


Well then I just chucked my 1/2 drill on the adaptor (3/8 side) and I use my drill to run the Z up and down. The Z just blows and I could not crank it the way I needed so I come up with this one night.


As far as the motor you linked I do think it would drive your Z. If a portable 1/2 batter operated drill will then that should.


You might also take the plate loose that holds the Z axis lower mount and gear assy. Mine was binding and there is a bit of slack in the mounting screws for that plate which allowed me to move it around to help the align the gears in the column better. I also loosened the plate that holds the handle crankshaft when I did this. I cant remember but I might of even put a shim under that crankshaft plate.


After working with the gear alignment it is crankable by hand without as much trouble as before. As long as I am just moving enough for a tool change I dont worry with the drill. But when needed I hit it with the drill and it goes up pretty quick.

IDK if yuo noticed but that motor you listed is rated in in-lbs, not in-oz's, so its probably stronger than your thinking. I believe thats around 640 in-oz when converted. It should work without any real strian. The RPM is the only real kicker on it. This will be a little slow, but not real bad. I used my drill in low gear before and its not two bad which is about 400 rpm. So you should be good with it.


The only thing IDK is if the rating is at the motor shaft, or after gearing it down. Either way it get you by.


BTW, I would just try it direct drive first. I think it will push it if you work on your Z gears in the column and get it all working smooth.


Jess

[LUCKY13]

BTW, by direct drive I mean to drive the crankshaft, not direct on the screw. Yea it will take more to drive the screw direct I believe because you have some ratio through the crank gears.



Now if you was going to take the screw out, and polish it, add bearings on the ends for support, and align the screw with the nut perfectly, then driving the screw from its end might be a different story. But most of the time with these machines that whole assembly does not set in there very good/alignment . Plus this is a pretty heavy head assembly to be lifting from just a screw.



One thing I have thought of doing was find a guy that has installed ballscrews in his Bridgeport. Talk him out of one of his old screws and using it in the Z axis with the nut that goes with it. Most times the screws in them machines are pretty good, much better than came in the RF-45's ( most of the 45's anyway). It would need cutting to fit and the nut would have ot be modified to fit but I felt this was one cheap way of getting a better screw setup for our machine.


If you was to add a belt/gear- chain/gear setup then that would be a different story also. But the screw doesnt set up high enough to get a gear/belt assembly on it, I dont think. If you was to get a old BP screw setup then you could cut it so there was room to attach to the end of it.


Putting a gear/belt drive on the handles crankshaft I dont feel is needed. Work on the alignment with the gears in the bottom of the column and try a hand drill on it like I discribed and see what you get. You will know more about what it takes to drive it then.


Jess