PM-940m CNC - VS Motion Controller Conversion to Centroid Acorn

I was looking at a bigger motor last night. In a NEMA 34 the biggest Leadshine has is a 1699, I think. I didn't see if it would work with the drive we have though. I need to dig into that. Something else is happening that I didn't mention. Every once in a while the breaker for the drives trips, so I 'm suspecting either a broken terminal or the breaker is undersized. I wanted to enjoy the victory before I jump into that. This thing is probably going to add another 18 to 20 lbs to the head. I'm trying to build most of it out of aluminum. I just picked up some at the supply house. Now I have to start designing the layout. I'll keep you guys posted.
Regards,
Doug
 
Glad to hear that it's running pburgh! Hopefully you can make some chips this weekend! Seems weird that the breaker keeps popping... Do you know what the breaker is rated for? I'll look at mine when I get then we can compare.

Jake, are you sure you have a 1200 oz-in motor on the Z? Mine came with 900 oz-in on the Z and 600 oz-in on the X and Y. I've been toying with the idea of getting a bigger stepper for now, but you're right, the true fix is a servo. Even the little DMM DYN2's would be a huge improvement just because they are constant torque though out their RPM range.

So I have been machining a bunch of UHMW for testing, and I am very comfortable with the machine/control so I don't need to stick around except to blow chips out (need to install my mist coolant). However i'd be lucky to hit ±0.020", it's really bad. Even with Mach 3 and minimal tuning, i was ±0.005". How are you doing in the accuracy department Jake?

PZ
 
The original "spec / quote " I got says 1200 OZ stepper on the Z axis but it might have shipped with less, which would be a bummer. I'll check what the model number is on the actual Z stepper and reply later.
Screen Shot 2018-01-26 at 11.02.02 AM.jpg

As far as accuracy, I am going to be putting in the new AC bearings in the X, Y and Z axis, then I'll fine tune the steps to get correct steps per inch.
Basically, I haven't tested it for accuracy, sorry. However, how many IPM are you pushing it ? I only ask because you might be missing steps due to pushing those "little" steppers too fast ?
Also, I would really suggest looking into those end bearing blocks as I have and freeing up the other end ( lose the hand wheels and anything pinching the screw end ). Only then will you know if you are getting true ball screw backlash compared to binding due to the two ends pulling against the ball screws themselves. If that is occurring, I believe you could prematurely wear out your ball screw. Just something to think about. It really doesn't take long to dig into the X axis to inspect if the AC bearings inner races are hitting each other. However you'll need a press to put a washer in between the outer race to really fix it, if needed....
 
I just dug up my quote, and it says the same thing... dumb dumb...o_O

I 'm pushing it at 125ipm, and I really don't think I'm missing any steps. When I return to zero at the end of a part it's right were it started.

Also, if you miss steps at higher speed, i'm pretty sure it's all over but the crying. A missed step means that the motor output was actually stopped for a fraction of a second, but the drive keeps driving like it never stopped, so the motor now has to accelerate to that speed instantly. Every time I have missed a step, it's been very clear, and which ever axis misses the steps gets shifted for the rest of the run... makes for a very funny looking part.

That being said, I'm sure that it's possible to miss a step here and there and not notice, but I bet it's pretty rare. One of the DMM servos with a out put that can tell the acorn when it's off position is the way to go! Marty is doing a build on a router like that currently, I'm patiently watching that to see how it turns out.

PZ
 
86HS85 Z stepper is indeed what is on my mill. It’s 1200oz.
This weekend i’ll mill some circles and squares at various ipm ( with proper speed/feed rates) to check accuracy...
 
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I've been watching your thread daily and am enjoying the progress you are making. Thanks for the education.

For info you can get a NEMA 42 4200 oz in stepper for your Z axis. It's what I'm running on my PM-932 and it moves the head up and down like it's not even there. I also haven't had any issue with the Z axis creeping down when it's powered down.

I have 1600 oz in steppers on the X and Y. I can't remember a job where I missed steps. But I can say I've snapped off a few end mills and the mill didn't grunt a bit.

Good luck with your projects.
 
Guys, just a note about the stepper shaft size if you haven't noticed already. At least on my mill, and presumably yours, the nema 34 stepper motors have 14mm shafts. ( note the model number for the Z : 86HS85-14 ). So if we ever replace the existing with a bigger one, or servos, etc, we'll probably need to get new couplers ( lovejoy or other ). Not sure if 14mm is very standard at this point ?

p.s. I changed out my bearings in the Y axis last night and added a shim between them. I still have .0014 of backlash in the Y but my X has only .0004 which is nice. Someday I might get a new Y ballscrew or maybe have this one repacked with bigger balls.

oh, and thanks Tom !

Jake
 
Thanks Tom! I actually remember reading your build when I was toying with the idea of getting a manual machine and doing the conversion myself... In the end the lack of time won out, and I purchased this mill. Anyway your mill is pretty much my end goal...

I ran my first aluminum part with the Acorn yesterday. I made no changes to my motor tuning before I ran it and it came out ±0.0005"! This is according to measuring with my very nice Mitutoyo calipers... so I can only really claim ±0.001" but I'll take it! The ONLY thing I did different is I setup a new tool, so I'm wondering if I have a offset set wrong on the other tools... Again it was just a dinky little test part that was purely for testing accuracy and S&F for finish... it came out BEAUTIFUL! Only issue I have now is tram, looks like I'm going to have to shim my column a bit. Not looking forward to that.

Now that Jake got his new AC bearings installed, I think I'm going to tear open mine and see what it looks like as well. I'm a little worried that I am pre-maturely wearing the lead-screw after his comments.

Anyone have any good info on how to adjust the gibs?

PZ
 
phazertwo said:
Now that Jake got his new AC bearings installed, I think I'm going to tear open mine and see what it looks like as well. I'm a little worried that I am pre-maturely wearing the lead-screw after his comments.

Anyone have any good info on how to adjust the gibs?

PZ
Click to expand...

Just make sure you have the shims on hand before you tear it down unless you don't mind doing it twice. You can probably reuse the existing bearings though, instead of buying new.

Thats awesome to hear. You had me worried before regarding the lack of tolerance. How fast were you cutting ? IPM ?
Late last night I made a circle and square and came out .001 shy of my goal so its likely I need to measure the end mill. so far so good.
Sorry, nothing helpful to say about gib adjustment. I fear its something that requires feel ( experience ). Hopefully someone can chime in with something !

Jake
 
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Regarding Gib adjustment, I ran across NyCNC’s youtube from yesterday. He mentions they are doing a maintenance tear down of their Tormac 1100 and will be posting a video that will include gib adjustment . :-). Good timing !


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