Z Axis ignorance

General discussion of laser machines

Z Axis ignorance

Postby hutchcj » Thu Dec 24, 2009 1:41 pm

G'day all. I'm new to this forum and I am very interested in building a laser cutter.

I've had a look through the buildlog and it's quite nice to see such detail. It's very helpful.

My question is about the Z-Axis. Does the Z-Axis actually move while cutting or is it just to focus the laser? If it's just to focus the laser, then surely if you always cut the same thickness materials then you don't need to change the height of the table and you could skip the Z-Axis part? Or am I missing something?
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Re: Z Axis ignorance

Postby bdring » Thu Dec 24, 2009 2:28 pm

Yes,

You got it. The laser has a fixed focus point. You either want to the top of the material at that point for engraving or in the middle of the material for cutting. Some people just have a fixed table and shim the material up. That gives them a little adjustment, but no complexity and little work it the material never changes.
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Re: Z Axis ignorance

Postby Art » Mon Apr 19, 2010 3:24 am

New here but I have built an indexer that will turn wood columns 18" by 10' and a 4 by 4 router. Both driven with Mach 3. My site is http://www.turningaround.org . I am planing a 4' by 4' laser engraver and first question is wheatherto have a Z axis with 6" clearance or use an adjustable table? The big disadvantage of the 6" Z is the extra mass that needs to be moved.
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Re: Z Axis ignorance

Postby bdring » Mon Apr 19, 2010 11:17 am

Art,

If I were to build one that size I would probably still build a moving table. Look at the post of Alvaro's machine. He has a large moving table and it does not look too complicated. I would also do a least 12" of movement. 6" or 12" does not make much of a difference mechanically and it would be a lot easier to get a big piece of material in and out with more clearance.

My second choice would be to make a manually adjustable Z axis lens adjustment. There is no real need to motorize it and it would make the head a lot lighter which will make the rest of the system easier.

At some point I plan on making a bigger machine and I really want to mount the tube on the gantry. This would vastly simplify alignment because you remove one axis from the problem. At the size you are talking about, alignment and divergence start becoming real issues. This would make a heavy Y axis, but all engraving could be done in X axis only. Normal cutting, could still be done in X and Y.
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Re: Z Axis ignorance

Postby thechoochman528 » Thu Aug 05, 2010 1:38 pm

bdring, in your z-axis design why do you use a NEMA 23 and not a NEMA17 for the z-axis?

At first I thought load, if you have something heavy on the table, but then thought about it some more and decided that the load on the rod threads wouldn't require that much tangental force applied to turn...well at least with any load that i would be putting on the table. I guess if I was putting marble or granite slabs on the table I'd want a NEMA 23.
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Re: Z Axis ignorance

Postby bdring » Thu Aug 05, 2010 1:51 pm

You are probably correct.

I started the project with 23's that I already had. I changed the X and Y to 17's for weight and fit issues. I did not want to order an additional 17 for the Z at the time. I should look into putting both motor bolt patterns on the Z setup. The difference in cost between 17's and 23's is not that much though.
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