When engraving cups using aMansfield Customs rotary, he rotary we seems to be delayed when we start engravings. It won’t rotate for the first couple of passes which means that for images that have a rounded circle or oval around them and start with a curved edge, that edge is instead flat at the beginning. It finishes fine on the other side of the logo at the end with a nice curved edge but has ruined several cups now. What could be causing this?
Welcome to the forum…
Is this a new rotary?
Does it plug into the Y axes?
Will it do the ‘test’ in the ‘Laser Tools → Rotary settings’ properly?
I’m still not really clear at what’s happening…
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Looseness at a start position can be mechanical backlash.
Place a tumbler in the rotary, watch the motor shaft and wiggle the tumbler to see if anything is loose in the drive mechanism. If you can’t see the motor shaft perhaps you can feel a small amount of backlash.
Backlash is expected in gear driven machinery but it’s rarely seen in belt driven equipment.
When you start your next attempt, open the Move window and using the Jog arrows Jog 5mm away from the direction that the engraving will proceed - then Jog back 5mm in the same direction that the engraving will proceed. This will take the backlash out of the rotary device and your start lines should be evenly spaced when you proceed.
Test this with one of the ruined tumblers.
If this doesn’t solve it, we could be looking for something like bounce-back. If the max speed settings are high and the engrave speed settings are low the backlash at the start point can be affected.
How many of these ‘belt’ machines have adjustments for backlash and is used… mine is…
On the rotary in question… I couldn’t tell you.
How much backlash do you maintain in your machine? I would think that the objective would be to adjust tension or take-up (the working length of the belt) until backlash was acceptable. Perhaps you have more insight. 
I don’t any more insight than you do in all likelihood, I just know what seems to work on my machine…
I think mine is set for about 0.15mm and only on the X axes…
I know most of the laser machines use belts and the discussion is backlash. I think anything you have that’s mechanical will show some backlash as it must have ‘clearance’ to operate. The more clearance the more backlash.
The way I check my belt tension is running it and looking at the ‘line’ it produces.
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FWIW, since your profile says you are using a ruida controller, there was a big thread on this problem in the RDWorksLab forum a few years ago. Unfortunately, a person deleted much of the history from the forum, so I don’t know if the information/thread is still there, but you might want to do a search of the remaining archives to see if you can find some useful information.
We occasionally get folks here that delete information when they solve stuff.
As a moderator I ask for the solution and ask if i can roll it back to the previous version as the version history is often available.
If you could make the ask on the RDWorksLab forum an administrator might be willing to roll the posts back. If it happens please share a link over here. That would be greatly appreciated.
Unfortunately, it is gone for good in this instance. A moderator went maliciously rogue and intentionally deleted a huge and valuable archive of information that many people spent many hours contributing.
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