Mirror Alignment
My machine came with a video that shows how to align the beam after changing the laser tube but, as everything seemed to work right out of the box, I didn't think to check it until I read on a forum that the alignment can affect the power of the beam. When I did check it I found that the beam was not hitting the centre of the mirrors and had it been any further from the centre of the hole where it enters the cutting head, it would have missed entirely. Thus I spent a frustrating couple of hours adjusting the mirrors, followed by a cleaning session (instructions on the video), and was pleased to find that the machine seemed about 3 times more powerful as a result.
Other people have been less fortunate with the initial alignment of their mirrors and these are indeed difficult to adjust... so I thought I'd write up a few notes about it. But before we get on to making fine adjustments of the mirrors there are a couple of other issues to address:
The image above shows the ideal path of the laser beam. Observe that the mirrors change the directoion of the beam though 90 degrees and that until the beam hits the last mirror, it should be moving entirely in the horizontal plane; the same plane as the cutting bed.
This is NOT how it was on my machine which was initially set up such that the beam travelled downwards between the 1st and 2nd mirrors and then upwards between the 2nd and 3rd. Consequently the beam hits the last mirror in different positions depending on where the head is located. This results in the beam hitting the lens, and thus the work piece below the head, in different positions depending on the position of the head i.e. it causes inaccurate cutting. Over the distance of a few centimetres this is hardly noticeable but over the full extent of the cutting bed it results in an inaccuracy of a millimetre or two.
An additional issue was that the beam was hitting the upper half of the first mirror.
I solved these problems by lowering the laser tube, and raising the second mirror.
Lowering the Laser Tube
The laser tube is held in place by two padded straps and I observed that there was additional padding, about 1/4" of the stuff, under the tube.
Having measured, as well as I can using the simple tools at my disposal, the diameter of the laser tube and the arcs on the metal blocks on which it sits, it is my belief that designer intended for the tube to be installed without padding, and that the padding is an afterthought (which raises the height of the tube). So I unfastened the straps, replaced the padding with something much thinner (I didn't fancy trying it with none at all, or machining the blocks to accommodate thick padding), and VERY VERY CAREFULLY fastened it back down. This, followed by some adjustment of the mirror assembly itself, resulted in the beam hitting the centre of the mirror, which I was then able to adjust such that it travelled in a horizontal path to the second mirror.
Raising the second mirror
The second mirror is mounted on a bracket attached to the end of the gantry along which the head moves. Ever wonder what that little round cover plate on the left hand side of the machine is for? Well so did I until I came to thinking about how I was going to access the screws holding that bracket in position. All that was required here was to loosen those screws make sure that the assembly was as far as high as it would go.
A Modification to the Mirror Assembly
The previous image shows the second mirror assembly as it was initially on my machine. It's not easy to see from that image but essentially there are thumbscrews in three corners of a rectangular plate (which 'push' forwards) and two other screws that (that 'pull' against the others). Whoever thought this up should, in my humble opinion, be taken out and shot because it's a ***** of a thing to adjust.
Of course what we'd really like is to have just two screws: one for horizontal and the other for vertical adjustment. But such a mechanism would be significantly more complex, thus, expensive, and this is what we have so we may as well just get on with it and accept that it's going to take some fiddling with.
A crucial point to realise is that you'll use the screws in combination i.e. slackening a pulling screw before tightening a pushing screw. If it starts to feel tight then slacken something because otherwise you'll chew up the threads and then you really are f***ed.
A relatively simple adjustment that you can make to this mechanism is show in the image to the right. It's difficult to explain so for the most part I'm going to leave you to study the photo and figure it out yourself. But essentially what I've done is to modify the way the two "pulling screws" work by adding a couple of little springs. This mean I can now adjust the thumbscrews without having to slacken/or tighten the "pulling screws".
Fine Adjustment of the Mirrors
Well if you've read all of the above and understood it then you probably don't need to read this bit... so it's really just here for the benefit of those who have skipped down the page wanting some advice on how to adjust the mirrors on their newly acquired machine. To those people I say: by all means read this first but then go back and read the stuff above because there are a couple of easy modifications that you can implement that'll make this a hell of a lot easier.
Okay, so, finally:
When it comes to adjusting the mirrors you need to start with the one nearest the laser tube.
I stick a piece of masking take over the front of the mirror (it only touches the mounting frame not the mirror itself). Then with the power setting down low: test fire the laser. Note that we're not looking to burn a big hole in it. Just the merest indication of where the laser is hitting tape is all we need. (Note that even with that we're probably going to need to clean vapourised glue off the mirror before we continue.) Hopefully it's hitting as shown below, otherwise you have some adjusting to do; to the padding under the tube as described above, and/or to the position of the entire mounting.
Note that the beam is hitting the masking tape slightly to the right of centre... because the tale is in front of the mirror surface. Think about it: as shown the beam will hit the centre of the mirror. ;-)
With the beam hitting the centre of the 1st mirror we can now think about adjusting its angle such that it reflects the beam at right into the centre of the second mirror... so of course we now remove the masking tape from the 1st mirror and stick some over the 2nd.
Got that adjusted? Good, now for the bad news because if you hadn't realised it already: you have to check that the beam is hitting the centre of the mirror when the gantry is at the back and the front of the machine. If it's not then you have something out of alignment. As I said way back at the start of this page, I found that with my machine it was running out in the vertical plane and I had to adjust the height of the second mirror assembly and the laser tube itself to correct this. You could also find that it's running out in the horizontal plane in which case the most likely cause is that the entire support structure for the gantry is not square in the cabinet (it's held in place by some bolts that you can see underneath - have fun).
Having got the 1st mirror directing the beam at the centre of the 2nd mirror you now need to adjust the 2nd mirror to fire it into the centre of the hole in the head assembly such that the 3rd mirror (no adjustment needed) can bounce it down through the lens.
Having achieved this you should feel at liberty to wear your underpants on the outside... but I still wouldn't try stopping any speeding trains or leaping over/off buildings. Seriously though, getting this initial alignment sorted out can be a first class ***** of a job but it has to be done, is worth doing, and the only way to do it is to spend however long it takes tweaking, tweaking, tweaking, until you get it right.
Have fun. ;-)