CNC PM-728V-T

[rwm]

Definitely ask PM about that one before you modify anything. (I assume you have a PM conversion kit?)
Robert

 

[Toolmaker335xi]

That looks slick! I have a 728 that will eventually be CNC so I am watching with interest. Those limit switches look pretty large and beefy? Is that just overkill? I see you went with double ended steppers and kept the handles. I was advised not to do this. How do the handles turn when using it manually? Does it require a lot of force or could you use it manually? Those are funky sleeves you made to fit the handles. Integrated key? Any info on how you made those? What size stepper do you plan for the Z? Sorry but I have more questions than advice!
Robert

Thanks, sorry for the late replies. I work 3rd shift and sleep during the days...

The limits are probably overkill but the price was cheap so I decided to use them. The hand wheels aren’t really hard to crank at all. The only draw back I have is that it’s a little jerky and wants to rest at increments of a few thousands but they make it nice to back it off if a limit or if I want to just face something off real quick with out firing up the computer. They slip right in and off no problem. I wire EDM’d the adapters. Just a solid piece of aluminum.

I have ( I think, need to double check) 565oz nema 34’s.

 

[Toolmaker335xi]

Well, I went ahead with the PM728 CNC conversion installation. All the parts were in the package, and they fit the kit. I've assembled the X and Y axes, at least have the ball screws and end plates in place. Nice kit.

However, I found the assembly drawing (all the direction that came with the kit) shows M6-1x16 cap screws (part #911) holding the Y front plate to the machine. These screws came with the kit and the counter sinks in the Y plate fit these M6 cap screws. Now the kicker. The original screws, and thus threads in the base casting, are M8! Has anyone else run into a similar problem?

I suppose I'll re-drill/bore the kit's Y plate for the original M8 cap screws. May be a trick to align to the existing holes as the mill doesn't have a functional Y lead screw. Would have been easy if I'd known before taking the mill apart.

Thanks. Stay safe.

Hugh

I did not have this issue. It may be possible they altered your machine with bigger threads to fix a damaged thread? Just a guess. Mine were M6 and so far required no modifications.

 

[Toolmaker335xi]

You should be using shaft couplers made for CNC. These would be the "Lovejoy" style jaw couplers with an elastomer spider (must be the zero backlash kind). Even better would be a disc or bellows type coupling. The helical spring coupling are garbage for this application.

Eliminate the play in the screw mounting, then any remaining backlash must be in the ballnut. If you have double nuts, shimming between them is exactly how you should reduce backlash, although I'd be talking with the screw manufacturer or kit seller to explain why it is so bad. I bet you spent good money for the kit and they should make it right.



Yep, that is allowed and most people do just that. Assign them the same setting in ports and pins.



I highly recommend Mach 4. I'm a big user of it and happy to help you out if you need. I also highly recommend a motion controller like the Ethernet Smoothstepper (ESS) for Mach 4. You can use the parallel port with a paid plug-in, but it is like towing your new Ferrari behind some horses.

I’m using the couplers with the elastomer spider that came with the kit. I’ve considered the disc type, but I’ll be waiting till I get new motors. Right now just have 40$ steppers. I was just reusing the G540 I already had to get it up and functional.

I did get the home switches to function as limits too, thank you. Probably going to go ahead with getting mach4. This is just the first phase of this conversion, I will be upgrading to a centroid controller but haven’t decided yet if I want to spend the extra on the Oak or just get the acorn and have more of a budget for better motors and other upgrades.

I’ll be contacting PM to see what they have to say about the backlash in Y... I did notice the x ballnuts had a +8 etched onto it and I have .0008-.0009 back lash on x but didn’t notice anything in the y. But also wasn’t looking for it either... I just went and checked the z since it’s not installed and it has a +4 may be a 42 hard to tell if it’s just a squiggly line or a 2.

Thanks for the info

 

[Toolmaker335xi]

Hello new guy here.
I thought the couplers might be contributing to the backlash too, I tried a few haha. Mine also had alot of wobble on the x&y axis. I ended up going with the disk type and it fixed the wobble and cleared up about .0005 backlash. It must be in the nuts/screws. My Z is pretty bad...
View attachment 352156View attachment 352157View attachment 352158View attachment 352159

Thanks for sharing. The two I installed were tight. I couldn’t feel any noticeable wobble in them.

I noticed etching on the ballnuts. Did you? The x had a +8 I didn’t pay attention to any before I put y in. Z is marked +4 or 42 hard to tell... I’m really hoping I don’t end up with .0042 in z.

 

[GB21]

Thanks for sharing. The two I installed were tight. I couldn’t feel any noticeable wobble in them.

I noticed etching on the ballnuts. Did you? The x had a +8 I didn’t pay attention to any before I put y in. Z is marked +4 or 42 hard to tell... I’m really hoping I don’t end up with .0042 in z.

I did notice the etching but I thought they might be production numbers or something. I was going to take a picture now I wish I would have....
If my memory serves me right 2 of them had 2 digit numbers and one had a 3 digit number like 127

 

[macardoso]

I did get the home switches to function as limits too, thank you. Probably going to go ahead with getting mach4. This is just the first phase of this conversion, I will be upgrading to a centroid controller but haven’t decided yet if I want to spend the extra on the Oak or just get the acorn and have more of a budget for better motors and other upgrades.

AFAIK, the centroid Oak and Acorn require use of their CNC12 software and are not compatible with Mach 4.

The Oak serves a different customer base than the Acorn. Make sure you need the features it has rather than getting it because it is a "better" board. The Oak is meant for you to use their drives with AC or DC servos. It is not appropriate for steppers, Clearpath servos, or servos with standalone drives.

 

[currinh]

I did not have this issue. It may be possible they altered your machine with bigger threads to fix a damaged thread? Just a guess. Mine were M6 and so far required no modifications.

I contacted PM Saturday PM expecting to hear back maybe Monday. They responded (by the time stamps) in 4 minutes saying one other customer had the same thread size problem. Their suggestion was to just drill out the casting for an M8 cap screw (and offered to if I wasn't comfortable). I did it today and the plate fits well now. I suspect it was a change in the PM728 manufacturing, it was too well done to be an error. I received the machine last spring so it was an early one.

My plan is to install home switches but no limit switches. With LinuxCNC you can set soft (software) limits which stop motion outside given offsets from home. Works well for a personal machine but a little sketchy if made for sale?

Thanks. Stay safe.

Hugh

 

[macardoso]

I contacted PM Saturday PM expecting to hear back maybe Monday. They responded (by the time stamps) in 4 minutes saying one other customer had the same thread size problem. Their suggestion was to just drill out the casting for an M8 cap screw (and offered to if I wasn't comfortable). I did it today and the plate fits well now. I suspect it was a change in the PM728 manufacturing, it was too well done to be an error. I received the machine last spring so it was an early one.

My plan is to install home switches but no limit switches. With LinuxCNC you can set soft (software) limits which stop motion outside given offsets from home. Works well for a personal machine but a little sketchy if made for sale?

Thanks. Stay safe.

Hugh

Most people double one limit switch as home on each axis. I’d recommend adding the second switch on each axis and doing both hard and soft limits.

Machines can mess up and the hard limits have saved me a few times. Also soft limits don’t work if jogging around prior to homing. I have soft limits set up and I’ve still hit the hard limits a few times.

If you just have steppers, they’d probably stall out, but I have servos that would definitely bend a screw or crack a casting before they faulted out.

it isn’t difficult or expensive to add them.

 

[Toolmaker335xi]

I contacted PM Saturday PM expecting to hear back maybe Monday. They responded (by the time stamps) in 4 minutes saying one other customer had the same thread size problem. Their suggestion was to just drill out the casting for an M8 cap screw (and offered to if I wasn't comfortable). I did it today and the plate fits well now. I suspect it was a change in the PM728 manufacturing, it was too well done to be an error. I received the machine last spring so it was an early one.

My plan is to install home switches but no limit switches. With LinuxCNC you can set soft (software) limits which stop motion outside given offsets from home. Works well for a personal machine but a little sketchy if made for sale?

Thanks. Stay safe.

Hugh

I purchased mine back in March and it had m6 threads... I wasn’t suggesting it was an error, but an alteration or rework. Some of the m6 threads in my machine are a little loose/sloppy.