Inconsistent circle cutting.....

[Stephen Lynch]

I've read all the other circle posts, and tried all the tricks.. Unfortunately, My problem is that repeated cuts of the same file will yield inconsistent results..
Sometimes they close, sometimes they’re perfect!.. I don’t get it!
Belts are nice and tight, there seems to be no play in the head, I adjusted backlash on Y to .25 which seems to generate perfect circles with no perceptible start / end point, but if I run the same file 20 times, several will be absolutely wonky… I lubricated the rails, and even checked square… everything is dead on.

Here’s a photo… you’ll see that most are dimensionally perfect, whereas I can put the cutout back in the hole and rotate it freely with no binding… but then there’s a couple that don’t close, and even one in the middle which is oddly misshapen.

This is a brand new problem, and I’ve been playing for about 8 straight hours now, and just can’t seem to make heads or tails of it.

What could cause inconsistent cuts like this? The top row is playing with various backlash settings on Y. the bottom 3 rows are all the same 1" circle file run over and over one at a time.. (with .25 backlash comp on y axis)

I'm running lightburn, but can confirm that it does it in RD works as well.. If I enable backlash repay, it makes an offset on both sides of the circle (so it looks like a hurricane icon)

Thanks so much for your insight dudes! (and dudettes!)
!

eXtRpAFA.jpeg

[Pete Cyr]

Have you performed the following?

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I have listed the steps to adjust the step length. A vernier caliper that will read in mm makes this process easier. (and you really need to enter dimensions using 2 decimal places 0.00 mm)
I prefer to cut a thin piece of wood 100mm x 100mm to ease the data input - if you cut a larger square you must correct the value entered into the block shown in the pic because it is really a percentage....so using a 100mm square removes the need for additional math.
If you perform this process 2 or 3 time you will find the accuracy gets better and then worse. That is a function of the machine trying to over correct for an accuracy that exceeds capability of the steppers/servos/belts etc. when you get to 99.94mm or there about I recommend calling it good(the error at that point is 0.0023" for those that use the old system-like me).
You might be able to get to 99.98. But with a beam size of 0.004 -0.006 you are not likely to see the difference.
Don't forget to READ and then WRITE

Adjust Cut Length to be = to design length.pdf

[Gene Uselman]

Pete beat me to the draw again, it is not hard.-

I would start by checking to be sure the lens is seated and tight in the lens tube. Hard for my old eyes but some look to be perfect? I have always wished for a entry in the profile for how much use the machine has had, I have had the set screws [grubscrews in Russ' side of the ocean] on my geared pulleys loosen up, providing a similar issue. Seems most have two setscrews at right angles, often hard to see/access.

[Pete Cyr]

Addtionally - read page 60-61 of the revised manual - This checks the precision factor for cutting

This sets the primary mode of cutting. There are 5 choices; Slow cutting, Precision cutting, General cutting, Speed (Fast) cutting and Super speed cutting (Very Fast). Select your primary cutting mode and click on “OK” to save or “Cancel” to exit without changes. This will change the speed settings of your “Cut parameters”.

[Doug Fisher]

Definitely follow Gene's suggestion about set screws if you haven't done so yet. They were the solution to my circle problem when I first got my machine. As Gene said, there are usually two per shaft/cog/pulley.

[Stephen Lynch]

Hey Pete!

I calibrated the machine a couple months ago, and checked it again yesterday... It was a hair off on the X, but the gantry is still square as square can be... I have a big bed machine, so I did big test cuts and small, with some Gator Board I had laying around... I have consistent 100 x 100, as well as 1000 x 1000 squares, so I'm satisfied that the size is correct. i did not however do multiple test cuts... I did two and got the same result, so I moved on... I may run a bunch of 100 x 100 and see if any come out wonky.

What's happening is this: (.....and I do a ton of CNC work with My Camaster, and I also build 3d printers, so I'm pretty aware of how a pully or pinion gear can get loose and haunt you.) I've checked and checked my pully assembly... I also thought that it was simply slipping, but I made an 8 1/2 x 11" burn on a piece of wood, and burnt concentric circles into it. Then I put a piece of copy paper with a Rifle scope target on it, and ran the same cut about 20 times... If it were slipping, the cut should Migrate... it doesn't... it's pretty much cutting on exactly the same line. it's just that some will come out perfect, and some have aberrations. You can see in my photo, there's one in the middle that is just horribly disfigured..

It's not just circles either... It seems that since yesterday, shapes just aren't closing every time.

Am I correct in my thought process? If I had a slippy gear, the cuts should not all line up when overlaid, right?

I've been able to learn what ailed this machine since it showed up from China in it's wholly inoperative state. I've pretty much re-built the entire thing, including wiring, and some major structural parts. She's been a good girl up till' now. There is one belt driven gear I cannot get to without taking a major section of the gantry off, so I have avoided it so far. Only because I was pretty confident that it was not spinning out on the shaft.

Thanks so much for taking the time to respond... I'll check my repeatability this afternoon.

[Stephen Lynch]

Well, Turns out I was "China'd!" Upon multiple visual inspections, and hex Key checks, I decided "screw it!" and tore the entire gantry down... long story short... They stripped out one set screw, so they used loctite, or cyanoacrylate.. either way, it took a torch to melt it, then it simply fell out... so set screw one was cosmetic.... Set screw 2.... this was a 2mm set screw in a 3mm hole drilled through the stepper shaft, and once again "Glued" in place with loctite! well, that sheared completely in half.... The pully was being held in place by glue! because I could not see it, and could only wrench on it under the panel, I didn't see the Half-assery that was at play.... It"felt good", but apparently the stepper is capable of more torque than my upside down, and bent backwards hand...

Ugh! Anyway, I milled a keyway, and used a piece of square stock to lock the pully in place, and re-tapped it with a 1/4x 20 set screw on each side...

Back to perfect dimensional accuracy, and perfect circles!


Thanks for helping me decide my plan of attack... My gut was right, I just Needed to dig deeper.

Thanks Pete and co.

[Pete Cyr]

Wahoo - glad it is fixed.
Which camaster do you have - I have a stinger II 3x4 with 1.7 spindle.
I do lots of navy plaques and ships crests.

[Stephen Lynch]

I remember ya' from the forums from way back. I had a stinger 1 4x8, then a stinger 2 4x8 with a 2 kw. Now I've upgraded to a new Panther with 7kw spindle, vacuum table and phenolic top... It's an unbridaled money maker, and it runs 24/7 so my wife is actually the one who pushes for upgrades... Toying with getting a tool changer soon. I do it manually now, and it works fine, but according to her: "the less time you spend watching your cuts for tool changes, the more time you have to stay busy!" Slave Driver!

[Pete Cyr]

The panther looks pretty sweet. I am sure it is a big step up from the previous models. Agin glad all worked out.