I'm cutting at 50 ipm with stock 1/8" bit. The cut is just as bad on Depron ($!) as it is on FFF.

Doesn't backlash "cancel out" every time X switches directions? I didn't think it would have a cumulative effect...am I missing something?

The 3/16" problem is mostly on the X axis. The part does curve a little so the Y moves as well but not very much, maybe 2" on Y for 15" of X. I'm going to take another look at the parts and see if I can figure out exactly what's going on.

- Jeff

 

I just tried the circle test that's posted in the thread with the new cncusb settings. My circles look best when I have no backlash setting, but then the final square it cuts on the outside of the circles is off. Y axis measures 4.25 but X measures 4.21 (I am DEFINATELY calibrated okay, just checked for the tenth time with calipers and a meter stick). So I add .04" as backlash and my circles are awful (you can see where the bit cuts into the circle as it changes direction) but now the final square cut is perfect.

- Jeff

 

Every issue that I have had with accuracy, I traced back directly to something that was loose or out of adjustment.

Belts tight?

Steppers not slipping in their mountings?

All bearings turning smoothly?

No strange noises (means something is off kilter)?

Gantry and Z axis ways are smoothly moving? (I use candle wax on all sliding parts)

Stepper pulleys tight (that is where I had the most issues)

Calibrations done correctly? (I went through the procedure about 5 times on all axis before I was satisfied with the results)


I know that most if not all of these issues has been covered, but I can't help but think it is one or more of those things. My printer ended up about 1/8 inch from zero after cutting out an entire airplane.


Good luck!!!

 

You may want to check out my backlash thread

viewtopic.php?p=30319#p30319

I never found that my machine had any backlash. Backlash is when the machine moves an axis one direction let's say .100 then when it is told to move back the opposite direction .100 and it only moves .090, then there is .010 of backlash. When I tell my machine to move .100 it may only move .080 but it will also return .080. So the machine has no backlash but it fails to move the correct amount of travel. If I add in .020 in the backlash setting then the machine will move the correct amount of .100. When I calibrate the machine it comes up correct.
One thing though, adding backlash makes no difference in part accuracy but does make circles and radius's skew worse so, I advise not making any backlash adjustments.

 

When I tell my machine to jog 4" on Y, it jogs 4" to a precision of .000. When I tell it to job 4" on the X, it jogs 4" to a precision of .000. There is no backlash on Y. There is .04" backlash on X (belt is tight). With .04" backlash put into USBCNC software, a 4x4" square cuts accurately; however my circles look like sh**. They look best when no backlash is accounted for. I'll just have to test the fuse sides (and hopefully not waste MORE foam) again with the backlash accounted for, as that's the only thing that seems to be able to cut a 4x4" square accurately.

"One thing though, adding backlash makes no difference in part accuracy"

I believe it does. A part will end up slightly shorter than it is supposed to be...wait maybe it won't...haha I'm too tired to try to visualize this in my head right now. I understand the concept of backlash where the belt basically has a small amount of play within the pulley's teeth, much like a nut can move slightly back and forth on a bolt in between two threads, but, uh yea, ill figure it out tomorrow

- Jeff

 

0.04 is A LOT of backlash. You sure you don,t have a pulley loose? I had the same problems on the y-axis and it turned out to be a loose pulley.

 

Just a comment on your conclusion. If the stepper is designed for a 2.2v ref. , then you should make it so. Use a voltmeter and set up the control board as close to that value as you can. The coils have a particular resistance and will produce a magnetic field of a particular strength when the proper Vref is applied. If you exceed this in the hopes of gaining more torque you are also going to increase the magnetic fields through the windings. If you go too far, the fields will be too large for the intended design and will likely cause erratic motion; such as missed steps. You will also overheat the stepper.

I had a similar problem with the X axis skipping steps. It would jog in the right direction and then randomly jump back almost a tenth of an inch. The CNC board had Vref set to 3.6 volts. I backed it off to 2.2V and have not had a problem since then.

 

Some documentation for all ...

Here is the spec sheet for the stepper motor. The Phlatprinter IIi is wired as a bi-polar stepper as seen in the upper right corner of the spec sheet. In the lower left, there is a not to set Vref to 2.2V for this configuration.

With this setting you are guaranteed the specified stepper performance of 166 in/oz. Increasing Vref will make the motor run hotter and is not guaranteed to get you better performance.



Maybe the real problem you are facing is too much friction. Attached files PK266-02A.pdf (339.4 KB)Â