Not holding focus or shape across the cutting table....

[Bernie_of_CPE]

Recently I have been having issues with my LS6090 with totally baffling symptoms that have taken me a month to resolve.

The laser began to lose focus across the full run of the table (600 x 900 mm in my case) it would cut well where the laser enters the cabinet but as soon as it moved towards the opposite corner the beam would lose focus to the point where it would stop cutting to depth and lose focus scrapping the part to be cut. Initially this would happen randomly but soon escalated to the point where a circle became an oval and we were running the laser at 99% power almost all the time to cut even thin materials.

I noticed that the edge of the last acrylic part we cut had lost it's smooth polished look and there seemed to be a saw tooth pattern of steps with a very noticeable taper to the cut. We tried running the same part several times to complete the cut but this produces a horrible rough edge quite capable of cutting the operators fingers. The machine was brought down whilst we tried to analyse the problem. We had been through the usual issues of mirror alignment and lens cleaning but this was a worrying situation as work had completely stopped.

During an alignment test I had fired the laser from the control panel once in each corner of the bed and compared the results, each resulting hole in the test piece was different in shape and depth. I decided at this point that there was no problem with the tube or power output from the laser as it was well capable of making at least one satisfactory hole. The issue had to be mechanical with some issue preventing the alloy beam and laser head from moving freely across it's entire length. I brought the laser head towards the front left of the cabinet using the manual position keys on the keypad and noticed that it was making an odd noise. Then I noticed a screw lying in the left upper side of the cabinet enclosure. I fished around and found there were actually two screws and washers that had fallen from the belt clamp on the left side of the machine that held the alloy beam to the drive belts. In effect it was only being pushed and pulled by the rubber belt from one side. I can only assume I was just very unlucky and on my machine these were never tightened correctly during manufacture.

The net effect was the alloy beam could move in an arc especially when the beam changed direction of travel in the forward and backwards plane. This would also move the mirror alignment decreasing the power as the beam passed across the target mirror from it desired 90 degrees sweet spot. Yesterday, I managed to refit one screw with a star washer, it is a devils own job to get the second screw in as it is right over the beam assembly and I suspect we will need to strip the machine down to refit correctly.

Apart from a faulty door switch, this is the only problem I have had with this machine in it's 2 years life with us. I will change the washer from a plain face to a star type to prevent them coming loose again. I may also change it for a nut and bolt as the screw actually passes into the the alloy beam which has a threaded hole and is potentially a weak design, it's very easy to strip the thread unless extreme care is taken with tightening. Our first test of the laser produced a promising result with a test panel cut is 6 mm Acrylic as sweet as a nut, perfect polished edges and an accurate profile. I tried to cut a large 300 mm circular part last thing but had a very disappointing result as we seem to be accurate in profile but still down on power with the laser set at 99% power and 12 speed taking 3 passes to complete the cut.

I must be a worlds expert in mirror alignment by now and could do this in my sleep, so today I hope this will be the last issue I need to address. This has been an unusual problem to fix but it may affect other machines and is worth checking from time to time. To recap, the symptoms seem to be:

Small tooth or steps in the finish of the cut with an increased bevel. Uneven cutting power across the full range of travel of the cutting head with a loss of focus and cut depth (maybe random). Lose of profile, circles becoming oval or other anomalies in the cut shape (maybe random) and an unusual noise as the beam traverses in one plane usually when moving from back to front of the machine.

I would be interested to hear from anyone who has had a similar problem or has reset their machine after this fix.

Bernie

[PhillyDee]

I get a sawtooth effect as you say. Never gave it much thought. The edges are still polished, but have ripples along their length. Everything seems tight, I have no backlash, and sometimes the accuracy is questionable. I am trying to find the time to troubleshoot, but have a very busy time at the moment!