Y Axis Troubleshooting

[Doug Fisher]

As I posted in another thread, my new Chinese laser doesn't always cut circles well. I have tested and found that it doesn't cut straight line cuts in the Y direction consistently with the same accuracy. The length can be off up to 1 mm short. Sometimes circles have flat spots or when the laser comes around to close the cut on the circle the cut line is inside by less somewhere less than 1 mm. Often .3 to .5 mm. If I am cutting 5 circles in succession as test run, often the first circle is the worst. The X axis does not seem to have the length problem. Any suggestions to troubleshoot this would be appreciated.

Here is one example:https://www.dropbox.com/s/dahvdciqvg73m8a/Bad%20Circle%20Cut%202.JPG?dl=0

Here is a group of bad examples:https://www.dropbox.com/s/wfexy4to5xaj0gz/Badly%20Cut%20Circles%201.JPG?dl=0

Here is what the machine sounds like when it is actually cutting circles. Sounds much different that when cutting lines but that could be normal:https://www.dropbox.com/s/ecjnum55ptt3ob3/Audio%20of%20Cutting%20Circles.m4a?dl=0

Notes:

I have applied a thin coat of white lithium grease on all the rails.

I measured the distance between the two Y Axis rails at the front and then the back of the machine and they seem to be even or less than 1 mm of difference. I am not sure of the best way to measure the X axis.

I have done the test cut of a very large square (at least 400 mm), measured and then put those numbers into the RDWorks software where they allow you to input the numbers and it computes a correction factor. This does not help.

Plenty of cooling, mirrors aligned, table shimmed to be flat, set the cutting height with the gauge

[Mark Sipes]

I would be on the phone with my local rep.........or in your case the manufacture.

.

[Bill George]

Ditto what Mark said, ask the people you purchased from that question. It could be a lot of things, and the fact that its brand new and not working would make me a little upset.

[Doug Fisher]

Yes, thanks, I have contacted them and am waiting for their reply. I just wonder if others had dealt with a similar problem and knew of things I could be checking/testing on my own while I wait for a response from the company.

Thanks.

[Kev Williams]

Forgive me if this sounds like a dumb question, but I had a similar issue not long ago: Are you using air assist, and are you sure it's not moving the material around?

My air assist (which I rarely use but was this day) was moving the piece of 1/8" x 6" x 6" or so Romark around as I was cutting it.

Aside from that, you may have some set screws loose on the Y rods or the stepper that rotates the drive rods...

[Doug Fisher]

Thanks for the reply. I wonder if air assist could be a factor since it goes first goes into the cutting head nozzle and then straight down through the hole where the laser shoots out. It is a pretty weak stream.

The suggestion about the set screws is something I need to check. I am not familiar with the set screws and where they are located but I will have to get in there and learn!

Thanks!

[Joseph Shawa]

Check your lens. Make sure it is tight.
What happens if you rotate your circle and then cut it again. Does it finish wrong then?
Rotate your head. Still in same place?
Have you tried 1% speed? 100%?

[Dave Sheldrake]

Not unusual on the KeHui machines, they are clones of the Redsail X700 and X900 and the stepper pulse distances aren't always set up very well. (KeHui otherwise known as "the ebay red & black")

Try all the ideas above Doug then let us know if that hasn't worked and it may be pulse distance adjustment time

[Monten Pierre]

Look at the gears and belt, mayby there is a screw loose on the gear from the stepper motors.
Succes

[Doug Fisher]

Thanks for the replies.

Joe, the bad spot where it missed correctly connecting/closing stayed in the same place repeatedly.

Kev and then later Monten, you both were on to what I believe to be at least part of the problem. The gear drive for the left Y rail back near the laser tube had set screw issues. One was completely missing and the other one was very loose. I tightened the one up and a quick test did produce a much better circle. I will reserve judgement until I can get a second screw to totally lock things down. I tried to find set screws at Home Depot but they of course didn't have the size I need. I am hoping Ace Hardware will have them when they open in the morning but my guess is that the set screw is metric which could be difficult to find. I can measure the overall width and length with my digital caliper but will have to guess at the thread pitch if I have to order from McMaster or wherever.

Again, thanks to everyone who took time to reply. I appreciate the time you took out of your busy day.

[Doug Fisher]

>>it may be pulse distance adjustment time<<

I will have to research that one!

Thanks.

[Bill George]

They are metric set screws, my guess hard to come by if you find they carry just purchase a few extra. Also check eBay for a metric set screw assortment?

[Doug Fisher]

Just for reference in case there are other US-based owners of Chinese lasers that find they have a similar problem with missing set screws and need to scramble for replacements:

There are different size set screws on different shafts within the laser but my particular problem one (Y axis back under the exit end of the laser tube), which seems to be a common problem point according to multiple other threads I have read, is a 5 mm long M4 with a sharp point for high holding ability. Using a digital caliper, it actually measured 3.79 mm wide versus 4 mm.

Home Depot does_not carry metric set screws. I doubt Lowes does either but they changed their closing hours to 9 pm even though their website says 10 pm so that was a wasted stop (no, I wasn't annoyed!).

Ace Hardware stores carry M4 (measures 3.8 mm wide) set screws in 5 mm length for $.53 each (at least mine did) BUT they are the black metal ones and they have the cone tip that flattens at the end versus the cone ending in a sharp tip. I think it will get me through for a day until the correct part arrives. FWIW, my Ace did_not stock anything smaller than M4 and I know there are some set screws inside my machine that are smaller than M4 because I tried to tighten them all last night.

McMaster Carr sells what appears to be the correct stainless set screw, part number 91217A110, here: http://www.mcmaster.com/#91217A110 . At the time of this posting it was $2.68 for 25 of them plus shipping. McMaster carries as small as M3.

[Kev Williams]

Try Cal Ranch if you have one nearby. I'm amazed at the weird hardware they sell--

[Rich Harman]

...is a 5 mm long M4 with a sharp point for high holding ability.

Just FYI;

http://www.atlanticfasteners.com/tech-tips/set-screw-point-styles-and-their-use/

[Doug Fisher]

Good information.