Chinese laser cutter: Designing new tube brackets

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Re: Chinese laser cutter: Designing new tube brackets

Postby xnaron » Wed Jul 18, 2012 12:15 am

TLHarrell wrote:Isn't this overly complex? My laser has the first mirror mount adjustable to center up the beam. The mounts for the tube are metal straps with foam tape.

And it looks like you have about 1/2" to 3/4" of adjustment. You wouldn't need anywhere near that amount. 1/8" tops.


Yeah I know I don't need that much adjustment. I was leaving room for the nuts on the inside of the threaded rod. I just did this up quickly to demonstrate the concept. This isn't the final design. After trying to center the beam in all my mirrors. I think it is absolutely critical to be able to adjust the tube correctly. If the tube isn't "true" no amount of mirror adjustment will get the beam centered in all the mirrors and in all the positions of the laser head.
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Re: Chinese laser cutter: Designing new tube brackets

Postby xnaron » Wed Jul 18, 2012 12:20 am

TLHarrell wrote:Isn't this overly complex? My laser has the first mirror mount adjustable to center up the beam. The mounts for the tube are metal straps with foam tape.

And it looks like you have about 1/2" to 3/4" of adjustment. You wouldn't need anywhere near that amount. 1/8" tops.


And to further elaborate you can't use the first mirror to center up the beam if the laser tube is out of wack. You can of course get the beam in the center but if the laser beam itself isn't parallel to X and perpendicular to Z it will be impossible to center it in the other mirrors with the laser head in all positions. With the tubes being as long as they are it is extremly easy to introduce a small error with translates to big trouble trying to align the beam.
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Re: Chinese laser cutter: Designing new tube brackets

Postby xnaron » Wed Jul 18, 2012 12:47 am

a little more tweaking
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Re: Chinese laser cutter: Designing new tube brackets

Postby mattrsch » Wed Jul 18, 2012 4:49 am

xnaron wrote:
TLHarrell wrote:Isn't this overly complex? My laser has the first mirror mount adjustable to center up the beam. The mounts for the tube are metal straps with foam tape.

And it looks like you have about 1/2" to 3/4" of adjustment. You wouldn't need anywhere near that amount. 1/8" tops.


And to further elaborate you can't use the first mirror to center up the beam if the laser tube is out of wack. You can of course get the beam in the center but if the laser beam itself isn't parallel to X and perpendicular to Z it will be impossible to center it in the other mirrors with the laser head in all positions. With the tubes being as long as they are it is extremly easy to introduce a small error with translates to big trouble trying to align the beam.


As long as you can hit the center of the first mirror you are good to go. The first mirror can adjust the beam angle up/down and in/out, so you can get it parallel to the Y axis by only adjusting the mirror. My tube is visibly not parallel with the X axis and I don't have any alignment problems. I do agree that if you are going to include any adjustment in the bracket you might as well include plenty. As long as you can still solidly hold the tube there is no need to cut down on the adjustment just because you might not need it.

Honestly I think your original design would work just fine. The water jacket in the tube is not very large, and a tube full of water is not all that heavy. I don't have any issues with Bart's design for the tube brackets. except that it could have been a little easier to install the tube. Your two piece solution takes care of that nicely. If you plan on moving your laser with any frequency at all I would definitely lean toward your second design, since a 3 point metal on glass solution needs to be opened up if there is a chance of frame flex.
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Re: Chinese laser cutter: Designing new tube brackets

Postby iGull » Wed Jul 18, 2012 3:40 pm

mattrsch wrote:As long as you can hit the center of the first mirror you are good to go.


If only that were the case - the whole firing system has to be orthogonal over the whole table - that's all three axes.
On a wee table of 300mm or so, its not such a huge problem to achieve - over 1200mm + 600mm it is an issue.
There's no guarantee that the beam will fire exactly coaxially to the physical confines of the jacket either.
To get the z axis perpendicular to the focal plane over the whole table requires the tube to be adjustable. Hitting the centre of mirror one is insufficient - to be honest, hitting the centre of the mirrors is unimportant - what IS important is that mirror three always fires vertically through the centre of the final lens and your beam doesn't touch any part of the other hardware at any point. Putting the beam in the centre of the mirrors only allows you some leeway for maladjustment.

Before even starting beam alignment, the stage mechanics must be completely orthogonal in three axes otherwise you will never achieve correct alignment.

Then you screw on your air assist nozzle and it goes right down the middle - if only :D

New brackets look fine to me - try using silicone baking sheet instead of foam tape 'though - foam tape tends to compress and stay that way - the adhesive also fails very quickly. It looks like you would have to adjust the position using locknuts though - that will be a pita :D

Cheers

Neil
EMOs are a sign of weakness ...
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Re: Chinese laser cutter: Designing new tube brackets

Postby macona » Wed Jul 18, 2012 6:53 pm

You dont need to go crazy with the mounts. The plastic ones from china look pretty good.

I used silicone foam tape on my tube:

http://www.mcmaster.com/#silicone-foam-strips/=ignrr8
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Re: Chinese laser cutter: Designing new tube brackets

Postby xnaron » Wed Jul 18, 2012 7:23 pm

Thanks for the input guys. Here is my latest version. I switched to 10-32 threaded rod and am going to put some thumbscrew adjusters in the slots. Printing it out now.
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Re: Chinese laser cutter: Designing new tube brackets

Postby xnaron » Wed Jul 18, 2012 8:51 pm

Some pics of the print...note 2 zipties used to hold tube
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Re: Chinese laser cutter: Designing new tube brackets

Postby mattrsch » Wed Jul 18, 2012 11:08 pm

iGull wrote:If only that were the case - the whole firing system has to be orthogonal over the whole table - that's all three axes.

This is my last post on this because I don't want to hijack xnaron's thread.

The ONLY alignment characteristic that truly matters is that the beam travels parallel to each axis of motion as it travels along it that specific axis. When the beam is parallel to y, the movement of Y does not change the strike point or angle of incidence on the X-Y mirror so the starting point (and angle) of the beam for the X axis is constant. The adjustment on that mirror can get the laser pointed parallel to the X axis regardless of the angle of incidence to the mirror, because that angle will always be the same.
Laser Alignment.png

This is a simplified drawing in the XY plane, but it is also true for the other planes.

Note how changing the angle of incidence to the first mirror does not cause issues in the next mirror. The XY mirror does not care what direction the light is going in when it starts its journey, as long as the light hits the XY mirror in the same place and at the same angle throughout the travel of the Y axis. In other words, the beam only needs to be parallel to the axis it is traveling down at the time.
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Re: Chinese laser cutter: Designing new tube brackets

Postby xnaron » Wed Jul 18, 2012 11:16 pm

Here is the pices with the adjustment knobs. I have to say they work much better than I thought they would.

http://www.co2-lasers.com/blog/wp-conte ... ection.pdf

Here is a doc on aligning the laser. It expects that you can adjust the tube to hit the first mirror in the center. This is something I am lacking at the moment with my non adjustable mounts. The dot is not in the center.
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