Problem with error or missed steps or something?

[rustyolddo]

Just put the finishing touches on my converted mini-mill. Using a Hobbycnc 4AUPC board and TCNC 4.01. Mill is set up with 5TPI ball screws, controller is 1/8 step.

I've got a simple stick font engraving file that I'm using to test. It engraves a single line of text .100' high. When I run the file the, the text doesn't end up being on a straight line it kinda rides a wave. Some letters like G, O & S are compressed or smaller than the other letters like L, F, I, etc. At first, I thought it was the backlash comp. I went and set that up on all 3 axis using a DTI to tweak it in on all 3 axiz. It didn't make a difference.

I'm running 4.01 on a Pentium laptop, booting from a DOS floppy. I disabled all the power management in BIOS. Made sure the 'Precision' was set to 0 to eliminate rounding. Reverse axis delay is 100ms, ARC factor is 1.

I'm at a loss as to what the problem is. I know the code is good as I've used the exact same code to do the work on a Bridgeport. I'm not running anywhere near the limits on accel, start & max vel and at these small movements, I doubt the max speeds would come into play.

Any suggestions?

[abasir]

Tried with a desktop PC? We have several similar threads in the past... the voltage from the parallel port may be too low.

[rustyolddo]

Originally Posted by abasir Tried with a desktop PC? We have several similar threads in the past... the voltage from the parallel port may be too low.

Thanks. I checked it tonite, port voltage is 3.3V on a H, too low for a valid HI state. I recall seeing some kind of adapter or port board mentioned somewhere that would correct the problem. Hopefully I can find that reference again.

[rustyolddo]

Tried a desktop PC tonite. It made no difference. Going to go witha new copy of Turbocnc and try reposting the code. Maybe a rounding error??

[ger21]

Did you check the voltage on the desktop port? Sound like lost steps. What size motors? any noticeable binding?

[rustyolddo]

Originally Posted by ger21 Did you check the voltage on the desktop port? Sound like lost steps. What size motors? any noticeable binding?

I did check the voltage on the port, with the laptop it was 3.3V so I went with a desktop computer. Same results. I've got Vexta PH296 NEMA 34 motors. I checked the gibs, Im using 5/8" ball screws, I can turn the motor couplers with my fingers and move the X & Y axis.

Tonite I put a 2" DI on the X-axis and I've slowed the accel, start vel and max vel way down. 75 Start, 750 Accel, 2500 Max. That seemed to have made the difference. I measured the backlash to be .0035" and set it to that. Using a 2" DI, I can go <alt-g> from 0-1" and it will move 1.000". If I go 0-.5", it really goes to 0.48" if I go 0-2.0" it really goes to 2.002". So I'm short .002" on a .5 " move and .002" over on a 2" move. Is this normal error? Any way to correct for it? When I go to 0" from whereever I'm at, it does return to 0" each time on the DI.

Previous settings were 1000 Start, 3000 Accel, 9000 Max, this was causing missed steps.

[ger21]

What voltage arre you running those motors at? What the rated current of those motors? I looked at the torque charts, and depending on which model you have, the torque drops to less than 100 oz-in by 200-300rpm. What is the model? 296-02BA?

[strat]

not sure if this is touching base with your prob or not i had a sim prob i was using a star as pattern a couple ot the legs of it were wavy shaped now for the answer ........i had a lead screw that wasn't straight replaced the lead screw for the x axis and prob dissappered not sure if it your prob just an idea to check

[HobbyCNC]

Originally Posted by rustyolddo I did check the voltage on the port, with the laptop it was 3.3V so I went with a desktop computer. Same results. I've got Vexta PH296 NEMA 34 motors. I checked the gibs, Im using 5/8" ball screws, I can turn the motor couplers with my fingers and move the X & Y axis. Tonite I put a 2" DI on the X-axis and I've slowed the accel, start vel and max vel way down. 75 Start, 750 Accel, 2500 Max. That seemed to have made the difference. I measured the backlash to be .0035" and set it to that. Using a 2" DI, I can go <alt-g> from 0-1" and it will move 1.000". If I go 0-.5", it really goes to 0.48" if I go 0-2.0" it really goes to 2.002". So I'm short .002" on a .5 " move and .002" over on a 2" move. Is this normal error? Any way to correct for it? When I go to 0" from whereever I'm at, it does return to 0" each time on the DI. Previous settings were 1000 Start, 3000 Accel, 9000 Max, this was causing missed steps.

What voltage are you using with what steppers? Performance seems awful low.
Dave Rigotti
HobbyCNC.com

[strat]

"I measured the backlash to be .0035" and set it to that. Using a 2" DI, I can go <alt-g> from 0-1" and it will move 1.000". If I go 0-.5", it really goes to 0.48" if I go 0-2.0" it really goes to 2.002". So I'm short .002" on a .5 " move and .002" over on a 2" "


are you talking on the the indicator or on the program??? if you program is showing right and your indicator is off ....... this shows more of a prob of the bent screw

[rustyolddo]

Originally Posted by hobbycnc What voltage are you using with what steppers? Performance seems awful low. Dave Rigotti HobbyCNC.com

Dave: Using a 28V P/S. 15A

ger21: PH296-02 steppers that are 5.5V 1.25A. They are rated at 174oz holding. If you have a link to the torque curves, let me know.

Strat. The error shows in the DI not what the software indicates. Software is functiong fine. I won't rule out bent lead screws or screw error but they were new Roton stock and I turned the ends in a Hardinge collet lathe. Roton hand fitted the ballnuts. Using motor oil for lube, not any heavy grease. I have a teflon light white grease I'll apply when I'm done. Oh, I made new gib strips from Si/Al bronze.

When I"m checking the backlash, I just set the jog increment to .0005 and jog left & right & tweak the software until there is ever so slight movement in the needle. (.0001" or less) I'll stick a DTI on it and fine tune it better than that when I've worked the other bugs out.

I did have my feed rate in the test program set to F10. It seems that the letters like 'S', 'G' that had alot of interpolation were the ones getting compressed. That error had to be missed steps. Haven't run the program since I've been playing with reduced speeds. Does the accel rate get taken into account on every move? I didn't have any success with the G28 Home command and it may be because the Max speed was too high and the Start & Accel don't get taken into account on a G28 command?

Thanks for all the help folks!

[ger21]

I misread your pevious post and thought you had PK series motors. I think those motors just don't have enough power, and need to use a much higher voltage to use the power they do have. I couldn't find a torque curve for those.

Max speed is used for rapid moves only. Unless you try to cut at an F faster than the Max speed. Yes, every move accelrates and decelerates. You might want to try a much lower start speed, say, 25, and a then slowly increase the acceleration until you notice missed steps. You may be able to increase the max speed as well.

I think the bottom line, though, is you need more voltage and / or bigger motors. More voltage alone may not be enough. Perhaps Dave can give you more info.