Z Axis Power Feed for Precision Matthews PM-728VT Mill

@rwm I was actually looking for your thread on this topic to post the priest conversion. You seem pretty set on the steeper route, can't say I blame you. I have been talking about doing something about my 727m's Z axis for a long while now. Might have to sit down and plan it out. Some good info came of this thread, I'll have to do some advanced head scratching now.
 
Hi All, and happy Holidays!

Having a Weis VM25-D, I lurk about this forum often as the two mills are (except for a few details) virtually identical particularly for this discussion. I too, wish to add a Z-Axis motor, but I would also like to add plunge milling to eliminate Quill deflection. So, I am writing to this sub-forum for thoughts and ideas. In fact, I hope it might be a Project with members' input.

With all gearmotors, the problem becomes the hand wheel is useless as you are fighting the gear reduction whose added effort to spin the hand wheel is proportional to the ratio of motor shaft RPM/gearset output RPM. Not entirely impossible to use the handwheel (unless the gear reduction is worm and wheel), but sure is way too much effort, especially fighting head weight when moving up.

In my humble view and with no ill will to Priest Tools, their Power Lift kit seems cheesy. The control plate looks like something I made as a kid, PWM would have been a nice addition, but I get it - it is a "Power Lift" only device, no need for speed control. The gear motor appears to be a run-of-the-mill unit available anywhere: https://rex-engineering.com/wp-content/uploads/2018/05/EX-BLDC.pdf. In fact, if you want to roll your own, my guess any surplus outlet like surpluscenter.com will have a comparable replacement. In any event from several reviews, the Priest gearmotor seems to be running on fumes just for its sole purpose: quick Up/Down. If my first link is correct as to the motor, it has 240 in/lbs (or lbs/in for the scientifically minded). Perhaps Priest can correct or confirm that torque spec? In any event it seems from reviews and videos of their product, it is running on the hairy edge. More motor or higher motor speed and more gear reduction is needed just to go up and down.

I would like to add this feature. But I also want to plunge mill into mild steel. Since this is homebrew and limited by experience and funds, motor/gearhead will not be the limiting case here, rather the rigidity and integrity of the mill. Will the column flex, leadscrew break, etc... I think that will be empirically found - you know when you are driving your mill too hard. So, now it gets down to the motor/gearbox...
  1. As stated previously, I personally would like to use the hand wheel as well as the power feed. Now we are talking either a BIG motor and small ratio gearbox ($$$), still with a difficult hand wheel turn.
  2. A moderate, higher speed motor with more gearing. Perhaps the hand wheel will need two men and a boy to turn.
  3. A high torque motor with a worm/wheel combination. In this event, there is no turning the hand wheel.
Of all the options, I like #3 with a clutch for engagement and disengagement. Gives me the force which I need to penetrate my work and allows me to use my handwheel. Of course, the clutch is the hard part :rolleyes:. I think dog clutches are entirely too complicated and I invite those who have made such clutches to toss in their thoughts for maybe I am completely wrong.

To me, a homebrew, cam-actuated is perhaps the easiest. But you need to dead-nuts on the lobe of the cam (for disengagement and release) and the Neutral detent has to be in command of Neutral, but not so stiff that it takes much effort to move the lever. Tolerances are important here. It could be a catastrophe for the lever to engage accidentally or in a panic, the operator cannot find neutral. Has anyone experience with lever-operated eccentrics/cams with detents?

I was thinking a bevel gear on the leadscrew and one on the shaft of the gearmotor. The gearmotor could either be pivoted or laterally slid for disengagement, though I expect lateral is best from perspective of positive engagement. The movement of the gear, if by cam could be engaged by spring action and disengaged by cam (not fail-safe) or engaged by solenoid and disengaged by spring (safer but bulkier).

Thoughts from this forum are very much welcome.

John
 
I
slow-poke said:
I added power lift for $13 on my Round column mill using a wiper motor from a Saturn Vue, might work for you.

Action video...... https://www.dropbox.com/s/26wb19hzack3i44/VerticalLift Movie-short.wmv?dl=0
Click to expand...
I like how quiet that is - you did a nice job. If it has enough torque you could add PWM and plunge or touch off...

I don't want to give up my handwheel and a gearmotor would require a clutch to take it in and out.

I have a NEMA 34 stepper motor, driver, and controller I hadn't used so I tossed them on the electronics bench to check them out. I think I dialed the frequency in right, but it is no load and might need some tweaking once doing work. Today I purchased a 14mm keyed LoveJoy coupler for the motor, a 1/2 to get drilled and tapped to M16 x 1.5 for the Z-Axis leadscrew, and a heavy-duty spider. I have a chunk of 1 1/2" x 6" x 6" aluminum for the spacer/adapter between the motor and the top of the column. It will drive the leadscrew directly.

Once I machine-out the aluminum, it is strictly a bolt-on affair. The only resistance to using the hand wheel will be the pole magnets of the stepper, which won't be hard to overcome but might give it a clunky feel as you rotate it. A variable reluctance stepper would prevent the pole magnet problem but would provide less torque than the PM version. In any event, it was the highest torque I had at 12 Nm. It will certainly power raise and lower. I am curious what it might do in a plunge situation.

In any event, I still have to mill the spacer/adapter plate; hopefully I can get to it this weekend. I need to put a 1 1/2" hole in its center. Either I use a hole saw then a boring bar or I pop for an annular cutter. Once I have it together, I toss some photos and thoughts.

Thanks,
John
 
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This^ is exactly what I want to do. Please keep us updated on your progress with pics! I hope the NEMA 34 is big enough. I had the same idea to thread one side of the coupler and use a screw to clamp it to the shaft. Not bearing on the shaft, but closing down the threaded collar. I would like to see your driver setup.
 
Have the plans and most material. Much work should be done on a lathe, but I don't have one - only a rotary table. And I'm a Newb. And I want perfection. Three things already at odds. But I have time and am moving forward. Once I have the adapter plates and body machined it is all cake. Yes, I will take pics along the way and post.

I would appreciate thoughts on control logic and application, regarding speed (assuming it can plunge). Logic meaning; if plunged, an UP command would start slowly until it clears the work. Without a prior plunge, an UP command would just go as fast as reasonable until stopped by limit switch or operator. Application means how to implement the logic - a single SPDT momentary toggle switch and a separate speed control? That set-up for plunging and a button for fast UP/DN? A two-sided potentiometer with a center OFF detent (this would make the controlling logic simple, but I am not sure the center detent is safe - that is, it is positive enough to quickly find Detent and stay there)? Also, where to put the controls? I don't like the left-handed panel (sorry South-Paws) hanging off the main control panel. As I am plunging I want to have my eyes and controls near the work (or DRO or both). There is that area on the head that angles from the front face to the top... Sure wish there were more base area under the table. Anyway, plenty of time for thinking, for once again, I am learning my milling skills as I go.

Thanks for the interest.

John
 
Hi All,

It has been a while since I last checked-in on this thread. I promised I would carry it through, and I am on my way to fulfilling that promise. My aim was:
  • Make this solution work for both my Weiss and the PM-24 machines
  • Allow use of Z handwheel without complicated clutch
  • Use COTS parts as much as possible
  • Minimal effort
  • Least cost vs quality/features
  • Professional look
  • Ergonomic placement of controls

I have the mechanical end buttoned up. I started machining a 3-part adapter/riser that would raise the motor high enough to clear the Z leadscrew coupler and provide mechanical attachment of the motor to the column top. As I was surfing one day, I came across a 1-piece solution from Asia that does all I was doing but much more rigid, elegant, cheaper, and a lot less work. I ordered it and though it forever to arrive, it is now in my possession and I can continue. The quality is amazing and will give a good look to the finished product. I do need to open-up a hole on the column end to clear the coupler. I do not yet have a lathe (though one is coming!) but do have a RoTab so I can use an end mill and get a nice hole that is concentric with the leadscrew/drive axis. My work is crazy now and we have out-of-town family coming, so I am busy and maybe the lathe will arrive before I can return to the project. Please be patient with me. I am not retired and am wasted at the end of the day (sometimes in more than one way :rolleyes:), so I cannot pop this out like bread from a toaster.

Staying with the COTS idea, I have a NEMA 34 motor, driver, controller, and power supply, LoveJoy coupler - total cost ~200. They play nicely together. The controller is a good match for the driver with quick rise-time and rather symmetrical pulses when viewed on an O-scope. My only complaint is when switched-on, the Stepper is barely turning, BUT it is turning. I need to decide if this slow RPM is OK because once the Enable is sent to the driver it turns. A larger potentiometer would probably slow it down, but it will always have some pulse frequency and will affect the high end as well as duty cycle. My gut is that it is fine, but it is a test that must be made. I also purchased a loadcell I can put into the vise and quantify the Plunge force - good data.

I prefer not to write the functional requirements in a vacuum as y'all have ideas I might not think of. The basic functions are:
  • Fast UP
  • Fast DN
  • Adjustable plunge speed
Considerations should be:
  • Limit switches for absolute travel stops or current-sensing stops (or both)
    • While the upper stop never changes, a limit switch at the bottom does not account for the work and we don't want the head to crash into that, so current stops make sense, no?
      • Should the current stops be adjustable? A current stop for steel will likely take out plastic or aluminum work.
  • What about the speed at which the head travels after a plunge to clear the work when moving UP? Is the consensus of the Group that after a plunge, the head may move up at full speed? If it should be withdrawn slowly, is the original Plunge speed a good speed for withdrawal? If not, this is a bigger than "at first glance" problem for it really is more of a CNC thing as we must know where the work begins in the Z-Axis. If it is decide that the original Plunge speed is the way to go, it should be noted that once clear of the work either the user will have to increase speed via the speed control or UP button OR we go down the path of the CNC thing (which takes the simple out of the goals).
  • The need to check where the Plunge speed is set before beginning a plunge operation. I think a lock-out can be created using a voltage reference and a comparator, though repeatability will have to be thoroughly tested.
  • What control switches are required? ON/OFF, UP/DN, Plunge (and speed control).
    • Is ON/OFF sufficient or do we need an Oh **** switch?
    • Should UP/DN be adjustable too and for what reasons?
    • Discreet push button, toggle, or an all-in-one lever control? The latter will add design complexity, require additional space on an already crowded platform, and the detent could prove to be challenging. It must be strong enough to be safe, but there cannot be over-shoot when moving the lever out of detent.
  • Assuming discreet switches, where is the best place to mount the panel/box on the mill? To me, Priest Tool's solution is Sophomoric and I am right-handed anyway. That is a discussion in itself.
As this project proceeds, I will take photos, create a complete BOM and supplier list, a schematic, and detailed instructions (though it is really straight forward).

I look forward to feedback from those who are interested. Like I said, I do not want to do this in a vacuum - others' ideas always produce a better product.

Thanks,
John
 
YouTuber Joseph Higgins implemented a Stepper Motor solution and covers it (high level) in his review of the PM-728VT. He put the controls in a separate box that attaches magnetically to either the side of the mill control box or to the side of his vise, a clever and simple approach.


Great info on this thread so far.
 
The Vevor X-axis power feed units are around $125, and I have adapted two of them to drive the table and the head unit on a Rockwell EFI drill press. Really, if there's a shaft you want to rotate, I feel that there is a way to make a power feed work. There is a big brass bevel gear, with a hole and keyway for your shaft. A nut on the end of the shaft keeps the bevel gear in place. Probably making a new shaft is necessary because it needs to extend out a bit more than original. Make a relatively simple adapter block from your equipment to the power feed attach point and you're close to a solution. The units have limit switches that are pretty flexible to install...they come apart and can be mounted in different ways as needed. You can do all this without hacking up your equipment or the power feed units, given a little thought.
 
Appreciate the feedback. I actually have the parts and the electronics done but life has gotten in the way so it sits on the electronics bench collecting dust right now.

I elected to use a LoveJoy coupler to account for misalignment and threaded one of the halves to replace the lock nut on the Z leadscrew. The coupler required a riser which I was going to fab but found exactly what I was going to make on Ali-Express for peanuts.

Still open to suggestions are operating control ergonomics and features others might like. I'm right handed so a left mounted box may not be so practical for me. Plunging something with precision while my arm is across my field of vision is not appealing and I dont trust my left arm in an "Oh sh*t" moment. I also want an auto 'Fast-Up' and variable speed Down in addition to the ability to dial in plunge rate. I have all that working but am not sure where to mount controls (once again - ergonomics). I've been looking at the 45 degree blank area at the top of the mill's head, but I think I want to pass a 1/2" quill stop through there. In the end I was thinking of a small console mounted on the table or pedestal.

I appreciate the posts. Hope to hear more ideas. You guys are great. When I finally get a hole in my hectic work life, I'll post the photos, BOM, and electrical schematic for all that I have done.

For those who want a reliable and not chintzy Z assist, this does that wonderfully. I have a strain gauge so I can quantify the actual force it is capable in plunge mode and will do so once it is mounted and characterized.

Love this Group.

Cheers,
John
 
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