Using PM-728VT as a Manual Mill After CNC Conversion: Experiences Needed

[jdsantiagojr]

Hello everyone,

I've recently sold my old milling machine and am preparing to purchase the PM-728VT. I'm also considering adding the CNC conversion kit to it. However, I have a question for those who might have gone through this process: Can the PM-728VT still be used as a manual mill after installing the CNC conversion kit? If so, how does it perform, and are there any major compromises? I would appreciate hearing about any experiences or insights you might have on using it manually post-conversion.

Thank you in advance!

 

[Reddinr]

The mill looks a bit like my RF-45 type mill that I CNC'd a long time ago. I tried the mill manually a few times before I converted it and have been using it cnc and "manual-cnc" since then. I would say that one down-side is that you don't get the "feel" of the cutter action fed back onto the crank but I tend to just listen to the cutting noise for feedback and use known feeds and speeds. This machine has always had Mach 3 on an ancient XT computer running it using printer parallel ports. It works fine. If it ever breaks I'll move to Mach 4.

What is the controller for the VT?

I have a hand-held pendant that can be used for X, Y or Z travel at set speeds or by steps. You select a direction and then spin the MPG wheel. Also there are on-screen jog buttons that do the same. Quite handy for manual milling is entering simple g-code commands such as "g0 x1.5 y2.3435" to go a specific distance or to a specific point. I've done many jobs where I need to just drill say 6 holes equidistant. Quick and accurate.

Do you have a CAD-CAM software you plan to use? I'm using Bobcad still, an older version that still works well. There are other good options too.
What sort of work do you plan to do?

 

[jdsantiagojr]

The mill looks a bit like my RF-45 type mill that I CNC'd a long time ago. I tried the mill manually a few times before I converted it and have been using it cnc and "manual-cnc" since then. I would say that one down-side is that you don't get the "feel" of the cutter action fed back onto the crank but I tend to just listen to the cutting noise for feedback and use known feeds and speeds. This machine has always had Mach 3 on an ancient XT computer running it using printer parallel ports. It works fine. If it ever breaks I'll move to Mach 4.

What is the controller for the VT?

I have a hand-held pendant that can be used for X, Y or Z travel at set speeds or by steps. You select a direction and then spin the MPG wheel. Also there are on-screen jog buttons that do the same. Quite handy for manual milling is entering simple g-code commands such as "g0 x1.5 y2.3435" to go a specific distance or to a specific point. I've done many jobs where I need to just drill say 6 holes equidistant. Quick and accurate.

Do you have a CAD-CAM software you plan to use? I'm using Bobcad still, an older version that still works well. There are other good options too.
What sort of work do you plan to do?

Thanks for sharing your experience with your RF-45 type mill. It sounds like you've found a good balance between CNC and manual control, especially with the use of auditory feedback from the cutting process. I agree that losing the tactile feedback from the crank can be a downside, but your approach with the hand-held pendant and on-screen jog buttons seems quite effective for manual-like operations.

For the PM-728VT, I'm planning to use Linux CNC as the controller, inspired by a setup I saw from Dr. D-Flow on YouTube. I’m still undecided about the CAD-CAM software. I’ve been learning FreeCAD and have some experience with Fusion 360. Your use of Bobcad sounds interesting; I might look into that and other similar options.

Given your experience, do you have any recommendations on the electronics setup? I'm particularly interested in any advice on choosing stepper or servo motors, and any specific controllers or components that work well with Mach 3 or Linux CNC.

Thanks again for your insights. They’re very helpful as I consider this conversion.

 

[Reddinr]

My experience is only with Mach 3 and 4. I don't mind paying for good controller SW. I have purchased an ethernet smooth stepper so I can upgrade the computer to something more modern with Mach 4 (and stop using printer ports for control). I have not gotten around to it now for about 5 years. My servos are driven by Gecko servo drives.

Linux CNC on a cheap-old computer with well designed parallel ports (some are kind of weak signaled) and break-out boards wired to Gecko stepper drives and steppers is a low cost of entry.

I looked at linux CNC originally. From memory, Linux CNC had just a few specific choices as far as electronics. That may have developed more since I last looked.

As far as steppers vs. servos, I would personally go with servos. It depends on your budget though. Don't laugh but the biggest driver for me is to avoid the whine of the steppers. It really bothers me for some reason. Of course, I'm crazy because the screaming of the gear-box I'm fine with... Servos have other benefits too.

If I were starting from scratch: Mach 4, Ethernet smooth stepper, clearpath servos (with built-in drivers). Not a low cost direction though.
Others should chime in with their favorite electronics. There are quite a few options now that weren't around just a few years ago.

What are your priorities? Low cost, high performance, other?

For Linux CNC, I think you are limited to these (some are just general IO, some are servo drivers)

 

[jdsantiagojr]

My experience is only with Mach 3 and 4. I don't mind paying for good controller SW. I have purchased an ethernet smooth stepper so I can upgrade the computer to something more modern with Mach 4 (and stop using printer ports for control). I have not gotten around to it now for about 5 years. My servos are driven by Gecko servo drives.

Linux CNC on a cheap-old computer with well designed parallel ports (some are kind of weak signaled) and break-out boards wired to Gecko stepper drives and steppers is a low cost of entry.

I looked at linux CNC originally. From memory, Linux CNC had just a few specific choices as far as electronics. That may have developed more since I last looked.

As far as steppers vs. servos, I would personally go with servos. It depends on your budget though. Don't laugh but the biggest driver for me is to avoid the whine of the steppers. It really bothers me for some reason. Of course, I'm crazy because the screaming of the gear-box I'm fine with... Servos have other benefits too.

If I were starting from scratch: Mach 4, Ethernet smooth stepper, clearpath servos (with built-in drivers). Not a low cost direction though.
Others should chime in with their favorite electronics. There are quite a few options now that weren't around just a few years ago.

What are your priorities? Low cost, high performance, other?

For Linux CNC, I think you are limited to these (some are just general IO, some are servo drivers)
View attachment 493208

I'm also leaning towards servos over stepper motors. I've initially budgeted just for the machine and conversion kit and will pick up other parts gradually, including the servos.

Considering your insights, do you think it’s worthwhile to add a DRO for the periods I might run the machine manually? I’m evaluating the redundancy and fallback benefits of a DRO, especially in case of system failures. Would you say this investment is justified, or is the computer feedback sufficient for manual operations?

 

[Reddinr]

I would not add a DRO. Just be sure the encoders on the servos are of good quality and that your wiring is done well with good practices and shielded signal cables etc. I'm sure I must have missed some steps on my machine over the years but none that I recall having any noticeable effect on a part. (Excluding crashes and the day I tuned it.) I don't do things with NASA tolerances though.

 

[Huub Buis]

I have 2 lathes converted to CNC and can still turn the hand wheels by hand for manual turning, something I do quite often. When I turn the hand wheel, I also turn the stepper motor but I can feel the force I apply to the lathe as good as before the CNC conversion.
There is a drawback. When I turn the hand wheel, I also turn the stepper motor. As soon as I take my hand of the hand wheel, the stepper motor wants to return to its natural step positions because it is a permanent magnet motor and accuracy is influenced by half a full step size. So for turning tight tolerances I need to do it by CNC.
I am going to CNC a manual mill the same way.

 

[jdsantiagojr]

I have 2 lathes converted to CNC and can still turn the hand wheels by hand for manual turning, something I do quit often. When I turn the hand wheel, I also turn the stepper motor but I can feel the force I apply to the lathe as good as before the CNC conversion.
There is a drawback. When I turn the hand wheel, I also turn the stepper motor. As soon as I take my hand of the hand wheel, the stepper motor wants to return to its natural step positions because it is a permanent magnet motor and accuracy is influenced by half a full step size. So for turning tight tolerances I need to do it by CNC.
I am going to CNC a manual mill the same way.

Thanks for sharing your experience! It sounds like you've found a clever solution for maintaining manual functionality alongside CNC capabilities. I'd love to see how you've set everything up. Would you be willing to share some images of your setup?

 

[jdsantiagojr]

My experience is only with Mach 3 and 4. I don't mind paying for good controller SW. I have purchased an ethernet smooth stepper so I can upgrade the computer to something more modern with Mach 4 (and stop using printer ports for control). I have not gotten around to it now for about 5 years. My servos are driven by Gecko servo drives.

Linux CNC on a cheap-old computer with well designed parallel ports (some are kind of weak signaled) and break-out boards wired to Gecko stepper drives and steppers is a low cost of entry.

I looked at linux CNC originally. From memory, Linux CNC had just a few specific choices as far as electronics. That may have developed more since I last looked.

As far as steppers vs. servos, I would personally go with servos. It depends on your budget though. Don't laugh but the biggest driver for me is to avoid the whine of the steppers. It really bothers me for some reason. Of course, I'm crazy because the screaming of the gear-box I'm fine with... Servos have other benefits too.

If I were starting from scratch: Mach 4, Ethernet smooth stepper, clearpath servos (with built-in drivers). Not a low cost direction though.
Others should chime in with their favorite electronics. There are quite a few options now that weren't around just a few years ago.

What are your priorities? Low cost, high performance, other?

For Linux CNC, I think you are limited to these (some are just general IO, some are servo drivers)
View attachment 493208

I've done a bit more digging into this, and it seems like I might have to begin with stepper motors to kick things off. Servos are turning out to be pricier than I initially anticipated

 

[Huub Buis]

Thanks for sharing your experience! It sounds like you've found a clever solution for maintaining manual functionality alongside CNC capabilities. I'd love to see how you've set everything up. Would you be willing to share some images of your setup?

I have mounted the stepper for the Z-axis in the lathe gearbox and the stepper for the X-axis at the back of the X-axis. I have done this also for my mini lathe. Here you find pictures and drawings for the mini lathe setup.

For the mill, I will mount the stepper for the X-axis on the left side of the table. The X-axis will be mounted on the front using a belt to keep the stepper away from the hand wheel. I have a hand wheel on top of my Z-axis and I will also mount the stepper using a belt so the hand wheel is free to use.
Beware that the "spinning hand wheel" can hurt if you get to close of it. I only use small (1.2 Nm lathe, 2 Nm mill) steppers so the impact is not severe. If you use a high power stepper/servo and run at high feeds, you could be insured.