This gets a little complex - sorry.

The Clearpath servos do have encoders, but I don't know where the encoders are. If they are on the motor itself (most likely), then you can also have backlash in the 3:1 gearbox which is added to the motor. From an engineering perspective, you must have some backlash in the gears to avoid having them lock up and jam.

That said, I suspect that the rack&pinion is far more likely to be the source of any backlash.

Rack&pinion is good for large routers processing large wood panles: you would probably never notice any backlash. But for machining harder materials - from hard plastic to steel, industry uses ball-screws and ball-rails these days. To be sure, older CNC mills might have used ACME threads and dovetails in the distant past, but they always had backlash and wobble. That made getting precision difficult, and these days ACME and dovetails  are only used on low-end manual mills - it's cheaper you see.

Cheers
Roger

Thanks for the information.  My previous version using the same rack and pinion didn’t have this issue but the machine isn’t the same anymore. So with all thats been said and all that ive tested changed and verified, it is the only thing that makes sense at the moment.  So backlash compensation is what ill be adjusting and testing next.  Thanks Roger!

My pleasure. Anytime.
Cheers
Roger

You can easily measure backlash if you have a dial indicator - method is shown in the Mach 3 manual if it isn't obvious.  I have a very small amount of backlash on my mill - ~0.01mm IIRC - and compensation works well.  On my lathe however, which has an acme Z drive with more like 0.3 mm, I have not had much luck as the Mach3 BC algorithm doesn't seem to work very well with larger amounts, and the setup isn't very well documented.  On a lathe Z axis you can usually avoid backlash problems by always cutting towards the headstock just like you do with manual machining.

Also whilst you can compensate from a purely metrical point of view, BC cannot prevent other effects such as the cutting force pulling the work into the cutter as it isn't constrained.

Latest update.  To keep all things even, i've ordered the same servos that are on the Y axis for the X (considering a load issue and undersized the servo).  Tuned with the MSP software from Teknic.  The oblong shape is gone when cutting but definitely seeing, the best way to explain is stuttering.  I'm leaning towards a tuning issue with the clearpaths as i've taken things apart to assure things are tight and straight (assuming some sort of binding).  Then I noted something when homing.  There slight stutters going to it's home position.  Not for the Y axis but for the X.  Once homed i brought the spindle/carraige closer to me and reduced the jogging to 5%.  This made it a bit more noticeable as the carriage is closer visually.  When things were apart, and without the motor used to move the X axis, it moved smoothly by hand.  So at a slow job, it stutters... which is odd.  Even more odd is that I remember seeing this when I was initially tuning.  But others thoughts when using clearpaths would be great.  They are the SD models.  Thanks again to everyone who has provided information.  It is greatly appreciated!!

What you are calling 'stuttering' MAY be marginal oscillation in the servo. The gain setting may be too high, or maybe the differential setting needs adjusting.
This can happen with any servo drive, and may not be a reflection on the brand - just on the tuning.

Cheers
Roger

Will be doing retuning of the x axis.  Also refine my velocity and accel.  Only things I can think of.  Thanks!

Hi killrmodz,

I came across this thread and wanted to offer a suggestion that may help with further troubleshooting.

Teknic's ClearPath SD and MC motors come with a motor setup and configuration software called MSP. The MSP software includes many diagnostics tools that can be helpful when troubleshooting a machine’s/system’s performance. For example, MSP includes a digital oscilloscope which can be used to monitor different application variables in real time. For this application, you could use the scope to measure tracking error (i.e. the difference between the commanded position and the actual position of the servo) to help infer whether the issue is caused by the command itself or by the servo's response to the command.

For more guidance on using MSP and the digital scope, here’s a helpful video that walks you through the software: https://youtu.be/-6JbTaa9EPA?si=Q48qSvLpkz4xkqel

Best of luck with the application. If you have any questions, please feel free to contact Teknic at 585-784-7454 or submit a contact request on the Teknic website (https://teknic.com/contact/).

Aimee F. – Teknic Engineer

Aimee, thanks for this.  Ill have a go at it this week.  Falling behind on projects and need to get this resolved!

You're welcome - I hope the issue is resolved soon. If you have any questions while troubleshooting, please feel free to reach out. We're happy to help!

-Aimee F.