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

[pburgh]

Hey PZ, I was able to get a successful cut. I had to tac the spindle so I could get a true speed. That was the issue.
I also switched the motors to 2000 steps. I'm having trouble getting the z axis to tune and get consistent travel. I remember you and Jake saying you removed the manual gear to raise and lower the z axis with the handle. I haven't removed that yet, but I'm not getting consistent travel of the axis. I have to do some more testing to see if I can figure out where the issue lies. I hope it's not in the axis itself.

Regards,
Doug

 

[phazertwo]

Yes, we did both remove it, and it made a serious difference in how smooth the the Z moved, and how fast I could move it.

Were you having inconsistent issues before you changed to 2k steps, or did it start when you switched?

PZ

 

[pburgh]

I think I was having trouble beforehand. When I tuned the motor to 1" of travel it was right on. but I think the axis moving at longer runs would start to become inconsistent. I was trying to cut out a part that was a 1/4 thick and it ended up only going about half deep of that. Once I saw that happening I wanted to change to 2000 and tune it again. Then I discovered that if I set it to travel 3" I would get about 1/32 over 3. So you can image moving around the z axis up and down for homing and such I don't think I was getting accurate movement. At 2000 the adjustment is more touchy. I think i'm going to remove the gear on the z. I hope it's not too involved. I don't need any complicated issues at this point. I also hope it's not anything to do with the ball screw or any of the axis motion parts. I'm not too crazy about all of these mods. My back issue is seriously hindering me from doing too much. And i'm just talking about sitting.

On another note I was looking at your thread. You've been pretty busy. How do you like the the new bearings? I think i'm going to have to do something similar. The current motor is getting on my nerves. I was looking into using a 1.8 DMM servo for the spindle motor. what' are your thoughts on that? There's a little bit about using DMM servos on the Acorn forum.
Regards,
Doug

 

[phazertwo]

The servo for spindle motor has some awesome advantages. However at the end of the day it will limit your rpm to 3k... Which for me isn't enough.

PZ

 

[pburgh]

You should be able to at least double the speed with a 2 to 1 or better ratio. No?
Doug

 

[pburgh]

Hey one other question. I started to take that gear and shaft out of the z column. Please tell me you didn't have to remove the control panel to get that out of there. I'll be really bummed if I have to do that. Thanks,

 

[phazertwo]

You should be able to at least double the speed with a 2 to 1 or better ratio. No?
Doug

Correct. You can actually gear it to what ever speed you would like, however the largest (in my opinion) advantage to a servo spindle is the encoder. Everything I have read says that an spindle encoder needs to be 1:1 with the spindle, which makes perfect sense when it comes to things like ridged taping. I suppose, it might be possible with the right servo/drive that you could fool it at 2:1... but I'm not willing to guinea pig that one.

Though keep in mind I don't really care about ridged tapping. I know Jake has it all figured out and it sounded like he was doing it relatively frequently. I don't make many parts that use smaller threads, and I would rather thread mill, since it's a safer way to tap larger threads on smaller machines like these.

I did take the electrical enclosure off to get the the manual Z... then I realized I didn't need too. Unfortunately I don't remember quite how to do it. I feel like I pulled the way cover off the Z and was able to get it from there, I just needed to be creative. I'll try to go look at the parts and see if it jogs my memory. Sorry I don't have more info, I had a friends help for a few hours and just knocked it out and didn't think to take pics like normal.

PZ

 

[pburgh]

Hey thanks for the quick reply. I saw that on the Acorn forum about the 1:1 ratio. I was hoping that it would work because of the weight of a bigger 3 phase motor.
On the gear, it looks like there is an allen cap screw holding it on. I'm hoping to remove that and work the gear off. From there I was hoping to remove the shaft from the outside. I don't know how tight those bearings are packed in there. This is disappointing that this crank doesn't work like it should. Did you find that your headstock wants to lower itself once you take the power away from the stepper?

Doug

 

[cut2cut]

Hey guys, lots has kept me away from milling for quite some time but I hope to get back on the horse, Will try to remember what was needed to remove the Z manual crank. I vaguely remember documenting it somewhere, I hope!

Jake

 

[phazertwo]

Hey thanks for the quick reply. I saw that on the Acorn forum about the 1:1 ratio. I was hoping that it would work because of the weight of a bigger 3 phase motor.
On the gear, it looks like there is an allen cap screw holding it on. I'm hoping to remove that and work the gear off. From there I was hoping to remove the shaft from the outside. I don't know how tight those bearings are packed in there. This is disappointing that this crank doesn't work like it should. Did you find that your headstock wants to lower itself once you take the power away from the stepper?

Doug

It's not about torque, though torque is important too. It's about rotation positional accuracy. If the encoder is 1:1 with the spindle it knows EXACTLY what speed the spindle is moving and the index mark on the encoder will be in the same spot each rotation. Either way, the more I think about it, I think the best bang for your buck is just upgrading your motor and getting an encoder like Jake did. His setup seems to work, and it would be very easy to change over to a belt drive and just add an encoder. But again, unless you are going to ridged tap it's not necessary.

Also, just to be clear, my manual Z always worked correctly. Any gear set will add friction and therefore eat up power, this gear set is no exception. There is nothing technically wrong with the manual Z, it's just not needed, so getting rid of it gets you a little more chooch in the Z.

Anyway, I got out to the garage and looked at the gear. There is a socket head screw on the end, it takes a 6mm Allan. After I got the screw off I used a chisel between the bearing and the gear to drive the gear back. I think I had to use a pry bar to get it all the way off, rotating the shaft ~180° between each push. Then I did the same for the bearing (I think). Honestly if that doesn't work, you're better off sticking a sawzall in there and cutting the shaft...

Hey guys, lots has kept me away from milling for quite some time but I hope to get back on the horse, Will try to remember what was needed to remove the Z manual crank. I vaguely remember documenting it somewhere, I hope!

Jake

I was actually about to send you a message and see how it was going. I'd love to see some video of probing and ridged tapping!

PZ