If you don’t have a Ma meter, stay below 60% power until you do. Your tube specs should have a working mA rating. Stay a hair below it just to be safe.
Whan I was using my K40 (40ish watts tube) I was cutting 3mm MDF at 7-8 mm/s, running my tube at 14mA, single pass.
Back to your main question:
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Check if the unfinished cuts are always in the same zone? This could indicate an uneven bed that is higher or lower at that exact point, or a problem with mirror alignment.
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Do these unfinished cuts appear after a certain time of work? Check if your water temperature has rised. Tubes lose some of their power as they become warmer.
Finally, make sure your lens and mirros are clean.
Yes, thanks.
I was able to dial in the right settings this weekend. Works great now. Thanks for your help.
I was able to dial in the right settings this weekend. Works great now. Running at 65% power and getting nice clean cuts. Thanks for your help.
I was able to dial in the right settings this weekend. Works great now. Running at 15mm/sec at 65% power with a focal spacing of 7mm and 14 passes.
The unfinished cuts were in random places and at random times. The problem was inconsistencies in the material especially with 3mm Birch plywood. The number of passes have solved this issue and provide consistent clean cut throughs.
Thanks for your help.
I am still concerned about those 14 passes. I don’t know a lot about your machine, but I don’t think it should be performing so poorly, specially compared to a budget K40 like mine
Have you tried doing a ramp test? It should help you confirm if your focal point is actually where you think it is.
It seems to me that your focus is not right or that you may have impurities on your lens and mirrors. With my K40 I cut 3mm HDF, which is harder than MDF, by 28% (8mA) and 450mm / min. Your 900 mm / min is too fast in my opinion. I use 2 passes to be absolutely sure that the topics fall out. My laser tube is approx. 1.5 years old.
Try to check everything and do some tests, it should probably succeed for you.
Treasure chests made yesterday for my grandchildren (3mm HDF)
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Thanks for the detailed info. I did a ramp test and 7mm focal spacing is optimum. On many cuts it cuts through before the 14th pass. However, some cuts require all 14 passes to ensure a complete cut through. This is due to inconsistencies in the material. I’ll try some more tests with the lower speed to see if I can reduce the number of passes without increasing the overall run time for the job.
Any suggestions how to clean mirrors and lens would be appreciated. Thanks again.
I did a ramp test and 7mm focal spacing is optimum. On many cuts it cuts through before the 14th pass. However, some cuts require all 14 passes to ensure a complete cut through. This is due to inconsistencies in the material. I’ll try some more tests with the lower speed to see if I can reduce the number of passes without increasing the overall run time for the job.
I assume you have a 35-40 Watt CO2 laser machine but do not know your optics. A standard K40 has 50.8mm focal length. Something is wrong with your machine, 3 mm plywood no matter how poor quality, must not take 14 passes with a CO2 laser…
Regarding cleaning the lens and mirrors, I clean them when I suspect it is necessary, mirrors 1 and 2 I can see directly if they are dirty, the lens in the nozzle and the last mirror I also check once in a while, but typically only when I think I lack power or when I do not get the narrow kerf I burn with normally. I use technical alcohol, a cotton swab and a spectacle cloth.
I just read the manual from your machine and have to say that it was a significantly better experience that I have had with my Chinese manual. But as you also write, the manual states that the distance from the nozzle end to the bottom of the material is 7mm and the focus length itself is also 50.8mm. I always focus on the surface of the items I work with and subtract half of the material thickness, (49.3mm at 3mm material thickness). But the 1.5mm does not pose the real problem in your case.
Are you sure your laser beam is properly focused, even in the nozzle? and does not hit the inner wall of the nozzle tip?
I cleaned my lens and mirrors. Made a HUGE difference. Now cutting 1/8" (3mm) MDF) in 2 passes at 65% power at 15mm/sec. Nice clean narrow cut.
Since you are more experienced, maybe you could help with my other post in the hardware section of the forum … Why do 2 lenses of the same diameter and focal length behave VERY differently
Appreciate your insights.
I will second beam alignment. All to many of the ‘instruction manuals’ say you need to be centered in your alignment.
The ONLY place you need to be centered is down the lens tube onto the lens. Everything else needs to be PARALLEL and reasonable close to center on the mirrors. Personally, I hit my #3 about 2.5mm high to hit the center of the tube in Z.
I cleaned my mirrors and lens. HUGE difference. Now cutting 3mm MDF in 2 passes at 15mm/sec at 65% power. Thanks for your feedback!
Sorry for the delay, I’m not home at the moment. But to your specific question, I can only say if you have two nominally identical optical lenses, with the same angle on the same side, the same diameter and the same properties of the optical glass itself, the performance of both should be the same. If this is not the case, at least one of the parameters is different. Finally, my experience with deliveries from, especially from china, the products often does not quite match their sales description.
THANKS everyone for your insights. I acquired a 20mm diameter 63.5mm (2.5") focal length. It matches the performance of the original lens, and make flawless cuts and engraving. The owners’ manual is totally wrong about the lens specs. I’m now cutting 3mm and 6mm MDF with no issues.
Unless you’re cutting metal or really thick acrylic, there’s no reason to use this. It delays at the beginning or end of a cut to compensate for beam drag or piercing delays.
You shouldn’t need this either - if that’s in mm, it’s too small to be meaningful, and if it’s in inches it would mean you were focused under the wood or well above it, both of which would be much less effective than setting the focus right at the surface of the wood.
Do you have air assist? You shouldn’t need multiple passes at 2mm/sec to get through 1/8" MDF.
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