If you have not reduced both the acceleration and speed for the axis driving the rotary, the tumbler may be slip-sliding away as the direction reverses on each pass.
Try reducing both by a factor of 100 or so, perhaps to single digits, and (if that solves the problem) work upward from there.
Put down the Vise-Grip, step away from the laser, keep your hands in view at all times … 
Several folks have used rubber bands around tumblers and or rollers to increase traction. You may be willing to sacrifice a small amount of accuracy for traction. Speed and acceleration are most likely the #1 cause.
ps. (btw. Best title ever!.. I dropped everything to read this thread.)
I also was title-driven to pop in. hah.
Hello Ya’ll
Thanks for the input on speed. I’ve seen several vids on that. I have my speed at 60mm per seconds… I also have my tumbler weighted inside with a jar of wood paste, that fits in nicely in the top of the tumbler.
I’m not sure it’s slippage.
Good crab -vs- bad crab
https://drive.google.com/file/d/1tzPNkHSJrhKuzH0flRwPYYICmvlMxfKy/view?usp=sharing
https://drive.google.com/file/d/1vO-NZFIoOE3UeSOagnN4SPmJa-W7USF6/view?usp=sharing
The only way I can get this guy to engrave almost 100% is change the setting from Black1 to Font
Got it, but part of his left arm is missing. Take a look at the preview screen. I have 1 for Black0, and the good one that works at Purple7 Font.
Preview window
https://drive.google.com/file/d/1xZziJ9VmKbY9fqrgfFOkw-7xXaGwEODm/view?usp=sharing
Are graphics handled differently than straight up text?
Seriously, reduce the speed to 6 mm/s and see what happens. You may also need to reduce the acceleration for that axis, because an abrupt start (= high acceleration) can cause the tumbler to skid; we’re not talking high traction tires here.
You must also reduce the power to avoid torching the wood.
The key difference is between Line and Fill:
Line traces along each line or curveFill scans back and forth between linesOther than that, it’s all about speed and laser power.
Ah-Hah! More balloon than mush.
I suspect you’ve got an offset for Kerf that’s Huge compared to what’s actually happening. It moves the line outward to make the finished cut piece fit into place.
It’s used for cutting boxes and doing marquetry. You’ll find that switch in Cuts / Layers and you’ll likely have success turning it off.
Here’s a better explanation from a while ago. The switch you need is likely similar.
There are two… start speed… this is the actual speed it will start turning… So you can lower that and the acceleration…
I believe I mentioned to @SayCheeze to keep Machine settings for table and rotary… along with my accelerations speeds are in the single digits…
Saying that, I think I have to side with @JohnJohn on a setting. The object doesn’t look like it slipped or has ‘moved’… All lines connect…
I think you’ll have more success scanning on these… I don’t know how many of these mugs I’ve tossed attempting tight vector graphics, especially small ones… My house has too many reject now, so I toss them 
This is more indicative of slipping… with a vector.
I actually did a small test one day based on a video from Rich at Lahobby’s forum with regard to Kerf. I did a red heart with a black insert. I had that dialed in perfectly for a match. In my head I can’t relate kerf to my crab comparison, but that’s ok. I did get the grab to cut somewhat cleanly other than missing part of a piece in his arm.
Let me throw one other question off topic If I may. I really want to quit working with my vice grips and duct tape on these tumblers.
I downloaded an image from my bosses files. When you look at it on the screen in Light burn it looks correct. Reading from left to right, and right side up. It also previews correctly.
When I burned the image on my test piece, it was backwards and upside down. I’m assuming it’s some type of origin issue? Correct? Is it a machine origin, job origin, or something entirely different?
I’m doing a search on the forum to see if I can find info I can read and relate to.
I can take the text and just drag it on the working area in LightBurn, to make it look backwards and it will engrave OK, but I don’t really like that solution.
Here is an EXCELLENT video where we all of can pick up a few tips on the subject of engraving drinkware.
For a quick fix, change ends of the rotary in your machine…
If it’s working with your table, it should work on the rotary.
I’d guess that the phases are reversed, ‘A’ phase wired to the ‘B’ phase.
Mine came that way… Ran it a while ‘swapped’ on the table and finally fixed it at the plug.
JACK!!!
You do remember, my previous thread about A+ / A- etc… LOL ?
I’m in no way on gods green earth screwing with that kind of stuff. It’s out of my range of knowledge…
Thanks though.
For giggles though I think I will take out my rotary, reset my laser, and see if I can engrave a piece of wood, and see if she comes out normal.
I may just have to settle on clicking the Mirror Image Vertically before burning the first tumbler. That is one solution.
Just swap ends of the rotary in the machine… then you don’t have to mess with the wiring…
Not going to sweat the upside thing right now.
However, is it possible to engrave powder coated tumblers and end up with a shiny engrave that matches the rim of the tumbler.
Mine are cleaning up fine, but I can see very, very, very, small lines. Am I just being too picky?
I want to provide the best to customers.
Here is a close up with my phone.
It reminds of seeing bean fields after the combine has removed it. You see 30’ wide dark lines in one direction, and 30’ lighter lines in the field, where the combine was coming at you, and then turned and went the other way if that makes sense.
I’m going to set my line interval to what he has at marker 3:20. His was 0.040. Mine was 0.1000
The line interval when scanning is how much the machine will move to make the next pass.
If your li is 1mm it will move up one mm for each scan… so at 0.04 you are moving it by 0.04mm every scan.
It really depends on how big of a ‘spot’ the laser makes on the material. If you can remove it all with 0.1mm li, then if you make it 0.05 li, half of the beam will cover half of the last pass …
It will also take more than twice as long.
Sometimes you just have to burn up a few mugs till you figure out the exact settings.
It’s nice to know how tiny of a spot you can make… gives you something to go on.
Hello Jack. I can see now why folks that do this for a living have multiple lasers in their shops. Of course all I have is time when I come home at lunch, so all is good. I might be able to speed things up somewhat with a Chuck Style Rotary too.
I’m afraid to buy one, because of all the problems I had with their own rotary. That was a nightmare.
I don’t need a rotary chuck doorstop. Yeah, I’ve burned up one tumbler so far testing, but was lucky enough to have bought these from China Direct, so it cost me 4.25.
Funny to read your words “scan”. I never have thought of engraving or cutting as Scanning.
Hope your doing well today my friend.
When you run an image or fill you will be doing scanning as the head will scan the material, much like a TV… This relates to the lines/inch or dpi…
I think there is something wrong about your setup from the output I saw… I think you’d be trading one problem for another…
Might want to get more feedback and see is you can use your head instead of your wallet…
I’m getting it close to be dialed in I think.
My settings are 30mm per seconds Max 15% / Min 13% on a 50w laser. I just burned a couple of letters on my test tumbler.
It cleaned up nicely, with no visible lines showing. I want to dial down the power numbers a bit more so I just burn the powder coat off, and leave the stainless steel along. I’m close I think.
IIRC, somebody had a kerf problem that boiled down to selecting the mixed Inches - mm/sec units (in Edit → Settings), picking a “0.1 kerf” based on the general advice around here, then discovering an assumed 0.1 mm kerf was really 0.1 inch = 2.5 mm.
Something along those lines would account for having your rotary crab get all swoll up like that …
Well folks, looks like Monport has struck again. I’ve just found out this rotary is junk. I can’t get a tumbler to sit square on it as you can see here. It’s not very noticeable if you have one small word. But 3 or 5 words or a large graphic widthwise, and you can see it’s crooked.
Not square:
https://drive.google.com/file/d/1M36WmiHeQaOzmEBQiBWN4XZ0wtk9aLqk/view?usp=share_link
Tumbler walking:
https://drive.google.com/file/d/14eBs-EXyhrST6v8pYqLtl1Ji-3VnkEba/view?usp=share_link
Rear wheels not level with each other.
https://drive.google.com/file/d/1Cnfpcc1zCJUuLOYp4vruh49Nkz0i9tfR/view?usp=sharing
Think of it differently: you didn’t buy a roller, you bought a parts kit with most of the pieces you’ll need to build a real roller.
That’s not quite as cynical as it sounds, because often a cheap thing gets you Good Enough™ parts at half the price you’d pay for them individually. All it takes is finishing the last 10% of the engineering and manufacturing required to make something useful that works the way you know it should:
