Lens alignment

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Froggy
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Lens alignment

Post by Froggy » Sun Sep 25, 2011 4:31 pm

Being new to this group I've been very good and read all of the posts. What a lot of great info and tips. One thing that stood out was how critical mirror alignment is so, I thought I would check mine (if it ain't broke don't fix it should have been remembered). Now, my question is this: is it important for the beam to strike the centre of mirror 1 on both planes. On my machine it is central on the vertical plane but not the horizontal plane. If it does need to be centralised how can I do this because adjusting the 3 larger bolts on that mirror seem to be rather drastic

Thanks in advance, Graham

tweakie
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Re: Lens alignment

Post by tweakie » Sun Sep 25, 2011 4:54 pm

Hi Graham,

The real important part is that the beam strikes the focus lens in it's centre (or pretty close to it's centre) and exits the focus lens perpendicular to the work table. Exactly how it gets there is relatively unimportant and that's probably why they use such large diameter mirrors, to allow for this alignment with such a large range of manufacturing tolerances.

Tweakie.

PhillyDee
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Re: Lens alignment

Post by PhillyDee » Sun Sep 25, 2011 4:57 pm

Acurracy and focus improve, as does the power.

Best thing to check is to have a piece of wood under the exit aperature (directly, with nearly no gap). And record the shape of the point the laser hits. You want a very very brief pulse, and turn the air assist on to keep debris off the mirror. If the mark on the wood is circular, then you are all good. If not, then the alignment is defo out!
http://www.tmbelectronics.com - Electronics, tools, hobby tools, power tools, and much more!

An ex LS3020 user now playing with an LS6840PRO (60W) and an LS1290PRO (80W)

johnb80

Re: Lens alignment

Post by johnb80 » Tue Sep 27, 2011 8:43 am

We had problems from day 1 with angular cuts which drove me mad. I eventually lost my cool with our 6040, yanked it out into the middle of the workshop and decided to sort it.

I set all of the mirrors so that the beam hit dead centre, made a small acrylic target, held in place by masking tape and fired the laser. That done I then fired the lazer down to the bed with the bed high and then with the bed low. The out of focus low position was about 2" out of position, in my mind it should have been in the same position. I adjusted mirror 3 but could not get them to hit in the same place. I removed the lens and fitted a target to the bottom of the tube and found the laser was not hitting the centre of the lens, no amount of mirror jiggling could sort it, it was continually off to the right when viewed from the front.

After considerable head scratching, I raised the laser tube on it's mounts, realigned the mirrors (now the beam was hitting above centre in the vertical plane). I adjusted to ensure at all 4 corners the laser hit mirror 3 in the same position. Checked the exit and it was central, repeated the check on the bed and it was vertical (I would have made adjustments to mirror 3 to get vertical alignment).

When I put the lens back, power could be reduced, speed increased and best of all, almost no angle on the cuts.

Regards - John

tweakie
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Re: Lens alignment

Post by tweakie » Tue Sep 27, 2011 9:12 am

I think I posted this picture before but blowed if I can find it now. (please excuse the quarter, the pic was originally posted on a US forum)

One way to check that the beam from the focus lens is perpendicular to the table is to use a piece of scrap acrylic stood on end, then with a short burst produce a hole. If the hole is perpendicular to the base then bingo. :D

Tweakie.
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Froggy
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Re: Lens alignment

Post by Froggy » Tue Sep 27, 2011 10:38 am

Hi all and thanks for the comments. Because of them some improvement has been made. I can now have the beam hit dead centre of mirror 2 either at its nearest to mirror 1 or at its furthest, but not both. Now , theoretically all I have to do is work on the mean average but somehow that seems impossible to do. Could it be a problem with the alignment of mirror 1 and the laser? Obviously I'm missing something very simple but what? I have improved the beam striking mirror 1 (but am frightened of shifting the laser). I honestly cannot see what I've got wrong but then I've spent a lot of time and been so close to the problem that I am in danger of vanishing somewhere that's not nice. Further suggestions would be appreciated 'cos I'm not going to let this thing beat me (yet)!

PhillyDee
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Re: Lens alignment

Post by PhillyDee » Tue Sep 27, 2011 10:54 am

Sounds like mirror 1 is out. If it was not, then either the bed is not straight, or the mirror is out. I very much doubt it is the bed!
http://www.tmbelectronics.com - Electronics, tools, hobby tools, power tools, and much more!

An ex LS3020 user now playing with an LS6840PRO (60W) and an LS1290PRO (80W)

Froggy
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Re: Lens alignment

Post by Froggy » Tue Sep 27, 2011 11:56 am

Thanx Philly,
I will go right back to the very beginning (a very good place to start) and rather than ABC I'll do 1 2 3. I was under the impression that mirror 1 was not to be moved. I'll get back and let you all know just how many hairs I have left when I've finished tearing.

Graham

PhillyDee
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Re: Lens alignment

Post by PhillyDee » Tue Sep 27, 2011 12:23 pm

Not to be moved if at all possible, but, like you describe, it does look as though it is out of alignment!
Mine has never needed to be touched as it is fine, it hits mirror 2 perfect no matter where the mirror on the Y is.
http://www.tmbelectronics.com - Electronics, tools, hobby tools, power tools, and much more!

An ex LS3020 user now playing with an LS6840PRO (60W) and an LS1290PRO (80W)

Froggy
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Joined: Thu Sep 08, 2011 5:08 pm
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Re: Lens alignment

Post by Froggy » Thu Oct 06, 2011 5:05 pm

Hello all and thanks for all the advice given. Final report is this. I ramble so please bear with me. Laser to mirror 1 is a straight line (obviously),just as obvious is mirror 2 to mirror 3 a straight line. Now the way I now understand is, if those 2 lines are parallel to each other, as they are, it is essential for the line from mirror 1 to mirror 2 to be at right angles to those 2 lines, otherwise if you change the distance you change the position that the beam will strike mirror 2. When I had taken off the rear cover and the front cover and took some measurements it appears that this is not the case with my machine. I have managed to improve the angle by releasing the 3 bolts which secure the plate that mirror 1 is fixed to. At the moment, unfortunately, there is no further adjustment possible. It would seem that somewhere along the line I may have had a part fitted from another model or some other slip up. The next step will be to design a mounting system which will allow me to get the correct alignment and therefore the best results. I'm pleased that I'm moving forward but rather disappointed that something like this should have been the problem. If I haven't explaind it well enough and someone needs help please ask and I'll try harder.

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