Laser not cutting properly on horizontal/X axis

[Rick Underwood]

Hi all,

I've had my second hand JSM6540 Chinese laser cutter for about a year now, and this week it's decided to do something weird. It doesn't cut properly on lines or curves that are on the X-axis (horizontal). I've rotated the image 90 degrees to check and it's still the X axis (different lines now that I've rotated the image) that doesn't cut. It cuts most of the way through, but not as good as the Y axis which is perfect. Curves that start on the vertical/Y axis cut ok until they hit the horizontal/X axis and degrade.

It happens no matter where on the worktable I am cutting. I've checked and cleaned the mirrors and replaced the focal lens. I've checked that the laser beam is as near centre on the focal lens as I can get it.

I'm cutting 1.8mm chipboard.

Stumped! Any ideas?

[walter hofmann]

check the belt if it is not tight you get no straight cuts. a picture would make it easier to see the problem
greetings
waltfl

[Dave Sheldrake]

Stick a piece of ply or paper in front of the tube Rick, burn a light mark onto it and post the picture...just something i want to rule out

cheers

Dave

[Rick Underwood]

Hi Dave,

would 1.8mm chipboard be ok? If so here is a pic.

20141116_094628.jpg

[Rick Underwood]

Walt, here are some pics:

From the front - this is typical of what we cut out of 1.8mm chipboard, scrapbooking/paperart stuff.

20141116_095326.jpg

From the back, rotated the way it's cutting on the bed. As you can see the horizontal lines are only cutting partially, you can see some dots where some pulses made it through.

20141116_095347.jpg

The belt tension seems ok but I'm not sure I would know if it's not unless it was really bad. I've moved the head around using the arrows on the PAD and there's no slippage, the X axis motor seems to move the head at the same speed as the Y axis motor.

Thanks for taking an interest guys.

[Rich Harman]

Your focus looks off - the cut line looks really wide to me, and you seem to have issues in both the X and Y directions.

Have you verified that your focus distance is correct? How big is that piece?

[Dave Sheldrake]

Gotta agree with Rich, that kerf does look awefully wide.I'd move the focal point or do a ramp test to verify.

I wanted to make sure the mode of the tube hadn't go awry (if it does sometimes it will cut better in one axis compared to the other) but the spot looks fine to me.(it's unusual but does cause the problem you have)

cheers

Dave

[Rick Underwood]

So the ramp test tells me I was good with my focal length, working out to 5cm from the lens (although I'm measuring to a flat point on the head at 4.3cm because I can't measure exactly to the lens itself), which is what I was using before.

20141116_160655.jpg

So I did the test cut again and from this side it looks fine..

20141116_160003.jpg

But from the rear it's terrible, in fact I think it's getting worse. As Rich says its now having issues in both x and y axis.

20141116_160246.jpg

Up until now I normally cut this at speed 35, power 45, corner power 35 and it's cut fine. Even if I ramp it up to speed 35, power 90, corner power 80 it doesn't cut much better but of course the burn marks are much worse. All I can think is that the laser tube is degrading somehow. The laser tube is about 5 months old and isn't used daily, maybe a couple of times a week, sometimes for a couple of hours, sometimes longer.

I'm tempted to play with the machine settings config file but I don't really know what I'm doing, and of course the downside of having a Chinese laser cutter is there is a dearth of information online about my particular brand (JSM6540H). I could try sending the manufacturer an email I guess, even though it's a second hand machine they might know and be willing to tell me.

[Keith Colson]

Have you checked your mirrors and lens to make sure they are looking "sweet"?

Cheers
Keith

[Rick Underwood]

Hi Keith, yep they align well, although not in the exact center of the mirror, but the beam hits the same spot on each of the mirrors no matter where on the bed the head is moved to. When I check the head where the beam comes out of the .. nozzle?.. it's right in the middle of the hole.

I've cleaned all the mirrors and replaced the focal lens with my last spare. I could order and replace the tube but that's quite an expense.

Just trying to read up on what might affect a laser tube's power - age and use is one. I probably need to get some kind of meter that tells me what power the laser tube is putting out.

[Keith Colson]

Hi Rick, its nice to know you have checked the optics. If I were looking into the laser tube, yah big bucks! it would be a good idea to measure what current it is consuming. This will tell you if it is running right and if the power supply is okay too. If you were worried about the nozzle alignment, you can run a small cut with the nozzle off and clean the lens after (if it got dirty).

Cheers
Keith

[walter hofmann]

hi there
for me the cut looks pretty wide not what to expect from a laser it should be thin like a pencil strike.
it looks like you already to low and the beam is in the lowest cutting power
greetings
walt
change the focal length ether higher or lower.

[Dave Sheldrake]

hummm could be the tube but a couple more things to try first, check the drawn current as Keith says, then have a look at the positive end of the tube, check for any signs of bubbles in the end chamber as they will cause spot heat leading to power degradation.

At this point I'm thinking tube or PSU but get the current measured first then go from there, also make sure the lens in the negative end of the tube is clean.

cheers

Dave

[Rich Harman]

The burn test you did in post #4 looks non-ideal to me. Could be that it always looked like that but the ring around the center might be an indication of tube failure.

The piece is smaller than I thought but still, the lines look too wide. I expect that the less than ideal beam profile is the cause, along with the necessarily slower cutting speed.

[Rich Harman]

I'm tempted to play with the machine settings config file but I don't really know what I'm doing,

I think there is nothing to be gained by that, and a lot to be lost.