The cut has inconsistant depth across the sheet

[Craig_Johnson]

I noticed this on my old tube, and have the same problem on the new tube. The new tube doesn't seem as strong as the old one, but I'm not sure yet.
The depth problem is from the upper left to the lower right - closest to farthest distance for the beam. I ran 4 passes over my sheet, after the second, the upper left was already burnt completely through. It took two more passes for the lower right to be close to burnt through. Here is the back side of the sheet:

I discovered that the sheet would warp during the cutting, so I weight down 2 sides with square iron bars now. So I have a flat surface and a fixed beam distance now for the whole area.
The sheet is .060 white acrylic sheet with front and back printed label, with lamination over that. So its got two sheets of film on each side.

Could the mirrors be a problem? There is no dense smoke in the box to filter it. I don't have a lot of options for focusing it. Its a rebuild on a FSL MLE-40.
Also- straight lines seem to have uncut areas in the middle. Perhaps the acceleration speed setting in the global options of LaserCAD? Min-Max power settings?
I have them set to the same number. I have no Idea what that does to the tube, maybe I need a Min power lower than the Max?

I'm still trying to figure this stuff out.

Thanks

[Tech_Marco]

You didn't provide any information about how fast you cut or power level you use. Did you enable PPI or not. Focus point and/ air assisted.New tube, old tube....but what power are those tube? 35W,40W, 60W or ?


Marco

[Craig_Johnson]

I have the same problem with or without PPI, new tube or old tube. 10-15mm/sec.
Currently the setting is 35 power, PPI off, produces 14.7mw on a 40w 720mm tube.
I'm assuming its a focus problem. The FSL laser requires a 2in distance from the surface of the sheet, which it has. Perhaps moving the bed up or down a little will help.
That doesn't explain the cuts on lines being better at both the start and end of the line, I'm thinking the min/max setting need to be different instead of the same number?
Is there a part I could purchase that I could actually focus the beam with?

[Tech_Marco]

14.7mW ?? What was that?
Did you mean 14.7mA?

For the 35W tube, the max current should be limited to 18mA. You got to use a current meter to check the current.
2" = 50.8mm, you need to make sure the distance from the lens surface to the object is about 2".

Also, check your beam alignment. It is most possible that you have bad lens/mirror alignment. Make sure laser beam hit at the same spot when moving from up to down or left to right. Plus, make sure the beam is hitting to the center of the lens (concave or flat side facing down)


Marco

[NickWL]

Whenever I've had inconsistent cuts across a workplace it has been down to one of two things:
The bed not being level and the distance from the lens thus changing with distance from the origin 9of the beam),
or
The alignment of the mirrors not being out - the greater the distance from the origin, the more any misalignment is exaggerated.

[Craig_Johnson]

Sorry, that's MA. The 35 power setting was for PPI on, actually used 19 with it off to get the reading under 15MA.

I checked the bed and it seems to be the same distance from the focusing lens in upper left and lower right - right at 2 inches.
Focusing lens appeared fogged. Cleaned it and noticed a tiny spot on it that would not clean off. Need to replace it.

The cutting beam seems consistent with the spotting light across the sheet. I did raise the bed about 1mm and ran a couple tests.
This image attached is at 17min, 18max power, PPI off, 2 passes 13mm/sec.

The problem remains about the same as it was before, even with a cleaner focusing lens. I suppose that small spot could be throwing it off.

Cut job starts at 14.2MA and ends at 13.9MA after 24 minutes. Adding a 3rd pass would cut the sheet completely but adds another 12 minutes to the time.
24 minutes per sheet is tolerable but 36 is not. Would lowering the bed be better than raising it? I really don't want to replace the mirrors yet - they seem fine.

[Tech_Marco]

I think the white acrylic take more power to cut through than a clear acrylic. 0.06" = 1.5mm. With lamination, it take more power to cut through. Remember that a fine tuned K40 can cut through 3.5~4mm good grade acrylic with about 4mm/s. Air-assisted is in used and current is 18~19mA

By the way, the 2" focus distance is from the surface of the lens (not from the laser head tip) to the surface of object being cut. Double check your beam alignment as it must be straight and collinear from closer to farther location. That said, by firing a laser the leftmost and the rightmost, the target on the laser head entrance hole must be exact. If it is off even by 1mm, it make a lot of power lost.

But I don't think it is very bad in your case. It is just that the speed was set to fast for acrylic cutting. I will go for 5mm/s instead. Remember that the tube is really a 32W (35W max) but not a 1m long true 40W. And while acrylic is harder to cut.

Did you get the laser tube from us or from somebody else. If you got tube from us, then probably you may need to pay attention to other parts as I'm confidence that our tube is great. When doing acrylic cutting, you need to use full power like 18mA


Marco

[waltfl]

hi
just my experience:
I cut 3mm acrylic with 15mA and 10mm speed on my (40W , 700mm) tube my focal lens is a 38.x mm and I use outside air assist.
with 5mm acrylic I use 15mA and 4mm/s speed
just let you know
greetings
waltfl

I think the white acrylic take more power to cut through than a clear acrylic. 0.06" = 1.5mm. With lamination, it take more power to cut through. Remember that a fine tuned K40 can cut through 3.5~4mm good grade acrylic with about 4mm/s. Air-assisted is in used and current is 18~19mA

By the way, the 2" focus distance is from the surface of the lens (not from the laser head tip) to the surface of object being cut. Double check your beam alignment as it must be straight and collinear from closer to farther location. That said, by firing a laser the leftmost and the rightmost, the target on the laser head entrance hole must be exact. If it is off even by 1mm, it make a lot of power lost.

But I don't think it is very bad in your case. It is just that the speed was set to fast for acrylic cutting. I will go for 5mm/s instead. Remember that the tube is really a 32W (35W max) but not a 1m long true 40W. And while acrylic is harder to cut.

Did you get the laser tube from us or from somebody else. If you got tube from us, then probably you may need to pay attention to other parts as I'm confidence that our tube is great. When doing acrylic cutting, you need to use full power like 18mA


Marco

[Craig_Johnson]

I bought the tube from a different supplier for 2 reasons: 1 they are in Chicago, I'm in Lansing. It still takes them 4 days to deliver - so I'm not impressed. 2 the delivered cost was $196.00. If you are going to snap the anode off, its best to not pay a lot for the tube! I will likely try the Light Object tube next, not sure this one has the same power - they advertized 1800hrs at under 12MA. From what I've seen 12MA will take all day to cut thru a sheet.

I had to move the cutter to my factory space, so I have to be there to use it. In the garage, I could set it up with a timer and come back when it was finished. So, cutting time is a lot more important now than it was. I accidentally set the power to 35 with the PPI off and got 20.1MA for a 12 minute cut job. It still needed another pass, and I'm hoping to find a setting that will do the job in 2 passes, in 15-20 minutes per sheet. I'm afraid that slower speed and higher MA will deform the edges of the lamination. I've already seen some problems with that. The PPI on seems to reduce that problem.

The FSL laser came with a 2.25in plexiglass square to check the height. The focus lens measures 2in from the surface. I checked after disassembling it and cleaning the lens. I will check the alignment tomorrow. I assume there are 4 variables - upper left and lower right, and the line from the first mirror to the second and the second to the third. Rather than moving the mirrors, can I adjust the rails instead? Perhaps the ends are not at the right height but they are at the start?

Thanks

[Craig_Johnson]

OK, the beam to the third mirror is 3mm lower in the lower right than it is in the upper left. Dangerously close to the edge of the opening. Certainly not hitting the focus lens in the right spot either. The second mirror doesn't seem to have a problem. Yellow post-it notes aren't the best thing to use for this, any suggestions? They burn thru too easily and the dot is 3mm by itself.
Looks like I can adjust the 2nd mirror instead of the frame, in fact, adjusting the frame up would be backwards to what I need. I really didn't want to mess with the mirrors, but it looks like I have to.

[NickWL]

Yaaaay! you've got it!
And adjusting the middle mirror is something you'll get used to doing, eventually you'll be able to trim it all first time!.
There are several templates for beam targets on the interweb - can't remember but at least one (probably more) of these sites has them, just print onto lightweight card:
Lightobject
Instructables
Thingiverse

Good luck,
Nick

[Tech_Marco]

"Post-it" is my favor to be used for laser beam alignment test. You don't want to use high power to run tests. 8~9%should be sufficient

It is definitely alignment issue. I belt you a cup of cappuccino.


Marco

[Craig_Johnson]

The Focusing Lens arrived and I calibrated the first and second mirrors last night. The laser cut thru the material on the first pass across the entire sheet!
I do like the results using PPI better than not. Got things adjusted so I can do 2 passes at 200 PPI, 95/94 power, and it takes 15 minutes to cut a sheet at 25mm/sec.
runs 15-16MA, never seems to hit 17MA. The tube said 1800hrs at less than 12MA. I'm hoping to get 1000hrs at these settings because time is more valuable.
Besides I'd have to run 3 or 4 passes at 11-12MA anyway and that would put twice as many hours on the tube. 1000 hours would be 4000 sheets, based on what I sell the sheets for and the cost of material, I'll be very happy. Might even afford to pay myself for the effort - which would be a first!
Thanks for the help!