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.

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[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.

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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.

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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.

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

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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.

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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.

[Dave Sheldrake]

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.

It's an Laguerre 01 profile Rich, not unusual

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

very much so ;)

cheers

Dave

[Steve Morris]

just a thought but has the operating/ambient/chiller temperature changed recently?
could impact power output

[Rick Underwood]

Thanks for your input guys, I'll retry the focal length and play with the power/speed of the cut. I wonder if the new lens I put in has anything to do with it. I noticed the one I took out had a convex side and a very gentle concave side, and the one I put in has a convex side and a flat side. From what I've read that makes a wider cut and is less focused. I'll also invest in a Mahoney 100 watt laser power probe.

And of course I'll let you know how it all goes. Next laser cutter I buy I think I'll buy new so I can get some support with it.

[Dave Sheldrake]

Meniscus is curved both sides (the best type of lens) the other one is a Plano-Convex, although a slightly less defined beam shape it won't affect things in a noticeable way at anything under 500 watts or so.


I'll also invest in a Mahoney 100 watt laser power probe.

Save your money Rick, they aren't very accurate and only really provide a *best guesstimate*, good for comparing a tube when it's new to later on in it's life but for actually measuring power they are pretty dire (not a quality issue as such just that they can be affected by a lot of external factors)

Failing that, make one yourself using Dr Lindsay Wilsons instructions.

http://imajeenyus.com/optical/20130423_measuring_laser_power_thermally/index.shtml


Next laser cutter I buy I think I'll buy new so I can get some support with it.

If it's a direct import from China don't bet on support being much better :(

cheers

Dave

PS:


just a thought but has the operating/ambient/chiller temperature changed recently?
could impact power output

Very valid point and can make a big difference

[David Somers]

morning Dave!

I was curious about your suggestion on the power meter. I had pondered getting one for use someday when a laser actually shows up at the house. My thought was to wait a few weeks till I have some time on the tube and it has settled in, (an EFR tube) and then make a few measurements to establish a baseline power for the tube when new. That way I had a point of reference if I had problems later in its life. If I am reading you right, that was how you were suggesting a meter had some value as opposed to looking at a discreet power level reading taken out of context? Or do you think it is not worth the dollars even for that use?

I was not looking at it as a tool that would give a single discreet measurement, but one that might provide a trend overtime. In the way that a BP cuff is not really accurate in a single use given all the externals involved in getting a measurement, but is pretty good at looking at longer term trends.

Dave

[Dave Sheldrake]

but one that might provide a trend overtime.

pretty useful for that my friend, trends rather than outright measurement of power. For pure measurement of raw power you would need a power wizzard wand or an Ophir set up (my Ophir was just under $5,500 so not cheap)

cheers

Dave

[Rick Underwood]

just a thought but has the operating/ambient/chiller temperature changed recently?
could impact power output
Very valid point and can make a big difference

Actually I had to replace the water flow sensor recently and couldn't find one that was an exact match and lets the water through at a greater rate. Could that have anything to do with it? The temperature hasn't changed much.

[Rick Underwood]

I've played around with the settings - and are still continuing to do so. I've also played with the focal lengths and worked out what works best. It seems with the lens I put in a difference of just 1mm can affect the cut.

Now I've cleaned all the mirrors and the lens again it is back to doing a good cut on the Y axis and a poor cut on the X axis. Frustrating.

The pic below is of the back of the 1.8mm chipboard and the test rectangle below is 45.5mm by 7.1mm. As you can see the Y axis/horizontal cuts fine.

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I'm starting to wonder if this laser is just a hobby laser and we shouldn't be trying to make a business from it, just like you wouldn't start a printing business from a home printer.

[Rich Harman]

My next two guesses;

1) The beam is not perpendicular to the table. Easy to test - fire a dot, lower the table several inches, fire again. Thermal paper makes this easier.

2) The travel speed is not the same for x and y.

[Dave Sheldrake]

I'm starting to wonder if this laser is just a hobby laser and we shouldn't be trying to make a business from it

I had one of them otherwise known as the LS6840, bomb proof machines and usually very reliable.


The travel speed is not the same for x and y.

quite possible if the step count has been badly adjusted or changed in the past by the previous owner

[Rich Harman]

The travel speed is not the same for x and y.



quite possible if the step count has been badly adjusted or changed in the past by the previous owner

...or the max speed on the y axis could be set lower such that it is not allowed to go as fast as the x. I think the head being out of perpendicular is the thing to check first.