Taking the CNC Plunge

[TomS]

I'm not sure Marks setting for C001, C002 & C003 apply to the PMDX-107

Try these settings:

A001 - 01 Control Terminal
C001 to 00:FW
C002 to 01:REV

I believe Aref is only used with a POT.

Works perfect! The spindle responds to M3, M4 and S commands. I knew it had to be something in the 107 or VFD configuration but with so many VFD parameters it was a bit confusing as to which one's did what, at least to me.

Ran the calibration routine and set max RPM with no problems. Had to readjust deceleration values because it was taking about a minute to coast down from top speed. All is good now.

Thanks again for your help.

FWIW - posted on the PMDX forum same time I posted here. Still no response from them. Another reason, and there are many, why I like this forum.

Tom S.

 

[jbolt]

Awesome!

 

[TomS]

Awesome!

Today was a good day. Spent some time cleaning up wiring and motor tuning. I'm ready to make parts!

I really like the way the PMDX-126 runs the motors. They seem to be operating smoother and the X and Y backlash I was chasing a few months ago is much less. Not sure why the backlash is better but it was about .007" and measuring it today it's about .0015". Maybe it's the way the board processes pulses. Homing is much improved as well. My old BoB would reverse the drive as soon as it hit the home switch. With this BoB it hits the switch, pauses for a moment, then reverses. Much more sophisticated.

Tom S.

 

[TomS]

I ran my first job with the new electronics a couple of days ago. The job ran OK but the finish sucks. See the picture below and focus on the slot chamfer. The same roughness is also present on the slot sidewall. Digging deeper I ran some tests today to see if I could isolate the source.

I have adequate spindle bearing preload because I get about 15 to 20 deg F metal temperature rise in the areas around the bearings after running at 8600 rpm for thirty minutes. I ran a couple of more detailed tests at different preloads before reaching this conclusion. I've also read that some people have experienced poor surface finish when converting to AC bearings b ut haven't been able to find out if going back to tapered rollers solved the problem.

My tool changer draw bar has about 6" of stick out above the spindle. Thinking the drawbar may be whipping at high rpm I removed my tool changer and tried a R8 collett and standard draw bar. I took a cut on a test piece of aluminum at 8600 rpm using a 3/8" 4 flute carbide end mill and there was no difference in surface finish. Slowed the speed down to 4000 rpm, still no difference. Then down again to 2200 rpm and no difference. Also played with feed rates but still no change in surface finish.

Next I removed the belt and ran the motor. It was smooth and quiet through it's rpm range.

The other two sources, that I can think of, are the spindle pulley bearings and the spindle drive sleeve to spindle spline interface. Spinning the spindle pulley by hand the bearings seem smooth. Moving on to the drive sleeve/spindle spline interface there is some clearance that is evident when running. There is a noticeable rattle that becomes more pronounced as speed goes up. If I could eliminate the sleeve and install the pulley directly on the spindle I would. Problem is I need about 1/2" of spindle quill travel for my tool changer to work.

I'm looking into some sort of sleeve, possibly Delrin, that has an interference fit between the spindle splines and the drive sleeve. Not sure this will take care of the rattle though.

I'm looking forward to feedback from the forum on correcting the surface finish issue.

TIA

Tom S.

Picture of my surface finish. Notice the roughness of the slot chamfer.

 

[Davd Flowers]

Coolant?? Yes? No?
My first thought is not to go chasing your tail, but need more information. What are you using to evacuate the chips and are you using any sort of coolant?
My chamfers looked similar if I dont use any sort of coolant. Just a couple shots of wd40 worked wonders.

 

[TomS]

Coolant?? Yes? No?
My first thought is not to go chasing your tail, but need more information. What are you using to evacuate the chips and are you using any sort of coolant?
My chamfers looked similar if I dont use any sort of coolant. Just a couple shots of wd40 worked wonders.

I'm using Rustlick 5050 and flooding the cutting area with two nozzles. Don't know the exact pressure but it's somewhere around 50 psi. Chips aren't a problem.

Here's a picture of the parts. You can't see the surface roughness but the periphery and slot side walls are as rough as the chamfer. Not what I consider acceptable.

Tom S.

 

[Davd Flowers]

Have you checked the run out with a test indicator?

 

[TomS]

Have you checked the run out with a test indicator?

Good point! Not since I changed out the bearings. Before the bearing changeout runout was nearly zero, maybe .0001". I heading out of town this morning and can't get to it until tomorrow evening.

Tom S.

 

[Davd Flowers]

One other thing I can think of. What alloy are you cutting on? I ran into some that was annealed (I think anyway) and it was gummy and didn't finish well at all.

 

[jbolt]

A couple of thoughts;

Do you lock the quill when running?

On the spline, mine rattled a lot when I first did the CNC conversion. I solved that by pumping the space between the splines full of high pressure grease.