Troubles with K40 cutting and overall power levels

Community Laser Talk
#1

I hope someone can help. I’ve done a bit of digging through the forum and found all sorts of things to try but none seem to help.

I purchased a K40 from OMTech about a month or so ago. I ordered a Cohesion3D board and Lightburn at the same time. To be honest, I only test fired the laser to make sure it was working before I switched the boards out and began messing around in Lightburn.

My issue seems to be complete lack of power. I have cleaned the mirrors and the lense. I made sure the lense was the right way up(convex side up), I have double checked the alignment (all but perfect coming from OMTech), and reads tons of forum posts and videos trying to see what’s going on. I have tried paper, cardboard and 1/8th basswood so far. I have also tried each power level on the digital readout (I know, ammeter is coming) from 40 all the way up in increments of 10. In order to get any sort of image, I can’t go over a speed of 15-25 and the power has to be up well over 60. Cutting cardboard is a speed of 5 with a power of 100% and it takes 10+ passes to get a cut. These again are at readouts all over 40+. The cut is really crisp and not burnt, but it takes for ever. We’re talking about little 1 inch circles and squares. 4-5 mins per cut.

I have also tried the ramp test to verify where my focus point is. I’m at a complete loss folks.

Any thoughts would be helpful.

#2

does your machine have the digital panel or a potentiometer to set the power level?

The way the power level in software works is a combination of the hardware and software power setting. Set the power level on the hardware to what you want 100% in lightburn to be, then lightburn will modulate the laser in software within that range.

If it’s the digital panel I suggest ripping it out and replacing it with a potentiometer and ammeter, it’s way easier to control and as an added bonus get to know when you’re overdriving your tube.

#3

It is the digital panel and I’m working on collecting the parts now to change that out. But in the mean time, I’ve tried settings on the machine between 50-80 on the board and 100% in the software. We are talking speeds between 1-5 and it’s taking 15-20 passes to cut out anything from 1/8 acrylic or 1/8 basswood. I’ve tried to clean the mirrors and the lens. And that seemed to help a bit. I might try to order new mirrors and a lens to see if that makes a difference. But I"m reading about people cutting 1/8 stock in one pass. Mine is no where near able to achieve that. It’s like it’s working with 20% power or something???

#4

laser test backside
laser test backside810×1080 94.7 KB

Also, to add to this in case it’s related, I get this sort of cut often. Again, this is like 15 passes in, but the top and bottom always burn through before the side. Seems very odd but this is very consistent with all my cuts.

#5

On my K40 90% on the digital display was about 18mA tube current (now replaced the digital display with a 30mA meter and a 10 turn pot)
Looking at the pictures, you are only getting the top and bottom of the circles being engraved, assuming that you have mirrors 1 and 2 aligned correctly (always worth checking again!) I would suspect that the laser head isn’t sitting vertically. I replaced mirror 3 with a cardboard disk to check the beam was hitting the centre of the mirror, then removed the lens and stuck a piece of paper tape over the bottom of the lens to check the beam was hitting it dead centre. (also worth checking the tube is free from debris) if it isn’t hitting the centre you may need to pack the head plate with washers to adjust it.

#6

Well, guys it looks like I figured it out. First, the weird wood patterns were because of the grain direction. I turned the wood 90 degrees and it left marks going the same direction as the grain. Second, my biggest issue with not cutting through or taking 15+ passes to cut through, was due to water temp. Apparently I wasn’t cooling the water nearly enough. So now that it’s 20 degrees cooler, but cuts on the first or second pass. I guess I have to chalk that up to a noob mistake.

#7

Yikes! Check your tube with a flashlight for any cracks. Overheated coolant can cause a number of permanent tube problems, and hopefully that didn’t happen!

For reference, I have a 5 gallon bucket under my K40 that contains 3 gallons of distilled water. I find that’s sufficient to run the machine for a couple hours at a time. I don’t track the coolant temperature directly, but every so often i’ll reach down and feel the bucket. When it’s noticeably warmer than ambient I give the machine some time to cool down.

I’m glad you figured it out!