jlawren6
07-25-2005, 10:18 AM
After following these forums for many years, I finally took the plunge and bought a lightly used (approx 30 hours) 2002 PRT96. At this point, its all setup, the vacuum table is in place, and I have maybe 3 to 4 hours of cutting time on it myself from surfacing the table, cutting the vacuum grid, and just playing around. My first real job for it involves cutting a lot of dados and rabbets in 3/4" Birch ply. Before cutting the actual pieces, I decided to cut some test dados to dial in my feed speeds, RPM, and cut direction in the material I will be using (the sheet I have acutally measures 0.7"). This is where the problem arose. All of the 0.7" wide by 4" long test dados that I cut were too narrow when the 0.7" dimension was along Y, but not when along X. Depending the the cut direction, they ranged from around 0.65 to 0.68. The more undersized cuts occurred when using the conventional cutting direction. Some basics on how I was making these cuts:
Bit - 3/8" two flute downcut carbide spiral
RPM - 10,000 setting on the PC router
Feed Speeds - Ranged from 1.5 in/sec to 2.5 in/sec, but the majority of them were run at 2 in/sec after my first trials.
Depth of cut - Normally two passes at 0.175" depth.
Method - Have used one of three methods with the same results; CR command in SB3, Part Wizard area clear (inside out) generated SBP file, and manually programed M3 moves. I've use the CR command the most though.
Holddown - Vacuum table (8 Zone, one active, powered by Fein) with one clamp on the edge for good measure.
As far as troublshooting, I'm about 98% sure at this point that it is a mechanical issue. Per the display, the tool is going where it is told and I have not found that I'm losing any steps. The dust collector is also out of the picture for these cuts so there should be no electrical interference there. Everything is also grounded well (Router to Z slide, Z slide to Y carriage, Y carriage to X carriage, X carriage to frame, frame to control box). All the bolts and pinions are tight. I've readjusted the X and Y motors and I believe they are set correctly. I've also gone through the Z axis and adjusted it to minimize any backlash and eliminate lateral movment. The bearings are tight and my slide has an additional set of bearings near the bottom of the slide similar to some early Alpha photos I saw and, I believe, what Gerald has setup on his machine.
When adjusting the X and Y motors, I noticed that the Y motor has some noticable backlash. Turning the pinion by hand a small amount, I can hear a light click when it stops in both directions (motor off and free from rack). The shaft is moving with the pinion. I get the same thing with the X1 motor, but to a lesser degree and the X2 motor is solid. Given this, I did a very crude experiment to quantify the Y axis free play. I plunged the bit about 0.3" into the material, retracted it, and verified that the hole was 0.375". I then plunged again and pushed/pulled on the Y axis with light to moderate force (I'm guessing around 10 - 20 lbs). While doing this, I can see the axis move a small amount including it's bearings and the pinion/shaft. I can also hear the bit cut more material. After retracting the bit and measuring again, my 0.375" had expanded to 0.4225" in the Y direction. Doing the same procedure in X resulted in a 0.3825" hole. The amount of freeplay in Y corresponds to what I saw with the undersize dados and seems excessive to me. As far as I can tell, the only thing that gives the Y carriage rigidity in that direction is the Y motor and the pinion to rack engagement.
Do these number see high to anyone else with more experience and am I missing any other adjustments that might influence what I'm seeing?
I plan to run some more controlled cuts tonight and document things a little better. Anys suggestions on what I might try would be appreciated. I also want to determine if I can come up with a workaround for this one job so that I can get it out the door and spend some more time tuning. I'm hoping that a lighter second pass with bring me to the right size.
Thanks,
Jon
Bit - 3/8" two flute downcut carbide spiral
RPM - 10,000 setting on the PC router
Feed Speeds - Ranged from 1.5 in/sec to 2.5 in/sec, but the majority of them were run at 2 in/sec after my first trials.
Depth of cut - Normally two passes at 0.175" depth.
Method - Have used one of three methods with the same results; CR command in SB3, Part Wizard area clear (inside out) generated SBP file, and manually programed M3 moves. I've use the CR command the most though.
Holddown - Vacuum table (8 Zone, one active, powered by Fein) with one clamp on the edge for good measure.
As far as troublshooting, I'm about 98% sure at this point that it is a mechanical issue. Per the display, the tool is going where it is told and I have not found that I'm losing any steps. The dust collector is also out of the picture for these cuts so there should be no electrical interference there. Everything is also grounded well (Router to Z slide, Z slide to Y carriage, Y carriage to X carriage, X carriage to frame, frame to control box). All the bolts and pinions are tight. I've readjusted the X and Y motors and I believe they are set correctly. I've also gone through the Z axis and adjusted it to minimize any backlash and eliminate lateral movment. The bearings are tight and my slide has an additional set of bearings near the bottom of the slide similar to some early Alpha photos I saw and, I believe, what Gerald has setup on his machine.
When adjusting the X and Y motors, I noticed that the Y motor has some noticable backlash. Turning the pinion by hand a small amount, I can hear a light click when it stops in both directions (motor off and free from rack). The shaft is moving with the pinion. I get the same thing with the X1 motor, but to a lesser degree and the X2 motor is solid. Given this, I did a very crude experiment to quantify the Y axis free play. I plunged the bit about 0.3" into the material, retracted it, and verified that the hole was 0.375". I then plunged again and pushed/pulled on the Y axis with light to moderate force (I'm guessing around 10 - 20 lbs). While doing this, I can see the axis move a small amount including it's bearings and the pinion/shaft. I can also hear the bit cut more material. After retracting the bit and measuring again, my 0.375" had expanded to 0.4225" in the Y direction. Doing the same procedure in X resulted in a 0.3825" hole. The amount of freeplay in Y corresponds to what I saw with the undersize dados and seems excessive to me. As far as I can tell, the only thing that gives the Y carriage rigidity in that direction is the Y motor and the pinion to rack engagement.
Do these number see high to anyone else with more experience and am I missing any other adjustments that might influence what I'm seeing?
I plan to run some more controlled cuts tonight and document things a little better. Anys suggestions on what I might try would be appreciated. I also want to determine if I can come up with a workaround for this one job so that I can get it out the door and spend some more time tuning. I'm hoping that a lighter second pass with bring me to the right size.
Thanks,
Jon