New to laser cutting... some questions

Hello,

Previously I’ve used Sculpteo for all my laser cutting needs. I’m a twisty puzzle designer, here is my latest design:

And I want to cut 3mm or 1/8" acrylic to make tiles for it. As some of the tiles will be very small I’m afraid they will fall through the support grid Sculpteo uses in their cutters and not make it to me. So I’m looking to do the cutting myself. This is currently the cutter I am looking at:

I’ve been watching Youtube videos and reading what I can find to try and educate myself and I had a few questions.
(1) The unit I am looking at has some features that I don’t see on some others but I’m not certain they are all good features. For example it has an integrated fan. Elsewhere I read that many upgrade the blower right away and throw away the one that comes with the unit. Being integrated into the unit then may be a bad thing. Should I be looking at a different unit?
(2) I want to add air assist to the unit and I see this one already has a cable chain to the head in place so I think that will make the process easier. Would this unit be compatible with this head?


(3) I’ve read that the appropriate settings (power, speed, anything else?) depend on the thickness and color of the material being cut. I want to cut and engrave 3mm and 1/8" white, yellow, red, orange, blue, and green acrylic. How does one go about finding the optimal settings for each of these materials? Any suggested starting points and tips for how to tune from there?
(4) Any questions I should be asking that I don’t currently know enough yet to ask?

Thanks,
Carl

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@Nedman does good work with a relatively stock K40.

For other things to think of, here are two that come to mind:

  • That unit doesn’t look like it has an analog ammeter. It’s worth looking for one that does have an analog ammeter, or expect it to be an upgrade you’ll want.

  • Consider getting a mild steel plate and supporting the acrylic a centimeter or so above the steel plate, to avoid problems with pieces dropping out.

I strongly suspect that blower isn’t going to be very effect especially with the addition of an air assist. Cutting acrylic has a very strong odor so good ventilation is essential. You could get a unit with a external fan which would probably be better, but as you mentioned most people end upgrading the fan anyway.

The cable chain is a nice addition and will definitely make adding an air assist easier. That air assist head would be fine for a k40. THe stock lens is usually 12mm in diameter. That head accepts upto 18mm diameter lens which is an upgrade I would suggest as you will have a bigger sweet spot on the alignment. Also the stock mirrors are usually crap so new mirrors is another suggested initial upgrade.

Power / speed settings for K40s are very machine dependent so it’s hard to give exact recommendations. Usually people create test files for each material and do engraving / cutting at different settings to see what works best for their machine. To be honest I haven’t heard of different colored acrylics having significant differences in cutting settings.

You will need to establish your exact focus point by doing a ramp test for best cutting. Optimum cutting is typically achieved by setting height of your material so that the focus point of the laser beam is halfway into the material being cut.

So initial recommendations are to add an air assist, upgrade the lens and mirrors and probably get a better exhaust fan. Most people go with large pond type air pumps to run their air assist.

Unit ordered as well as an analog ammeter. Thanks.

I’ve ordered an 8"x12" plate of A-36 steel. Why support the acrylic above the plate? And as the acrylic is only 3mm thick, if its supported above the plate by a centimeter I believe I could still have pieces dropping out. Did you mean a millimeter or so? And if so, I’m not aware of what the issue is with having it in contact with the plate.

Thanks again,
Carl

Upgraded lens and mirrors, new exhaust fan, and air pump ordered. Do you have a link you could point me to for the procedure used to establishing the exact focus point? Is this trial and error just to see where you get the best cutting?

Thanks for all the help,
Carl

My understanding is that if the acrylic fumes are trapped, they can catch fire. 1 cm or so I have seen recommended so the beam has room to defocus a bit before hitting the steel. I’m not an expert here, though, it’s just a hint that has come up here from those who (unlike me) know what they are talking about… :grin:

This is a decent video on doing a ramp test to determine the focus point.

The problem with cutting directly on a solid surface is that you can get bounce back burn from the laser on the underside of the piece you are cutting. Also you can get residue from wood or acrylic accumulating on the surface and potentially maring your piece or catching fire. You may have to play with spacing to figure out what works best for you.

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Another question… how critical is it that the coolant is DI water? I have a reverse osmosis system in my home and I’m hoping that is good enough. If DI water is needed were do most get the DI water?

Thanks,
Carl

Someone else asked fairly recently about acrylic and fire:

It might depend on which of the various kinds of reverse osmosis systems you have? DI water can be produced by reverse osmosis, but not all reverse osmosis produces DI water, as I understand it.

You can search this site for “deionized water”, “distilled water”, and “laser water additives” like so:
https://forum.makerforums.info/search?q=laser%20water%20additives

You’ll find references to @donkjr’s excellent site:

That has a link to a short document that is worth reading in its entirety:
http://www.ngceoservice.com/Data/DOC96/SVC-FSB-0008%20Water%20as%20Coolant%20for%20Lasers.pdf

There are lots of recommendations for Tetra Algea Control to avoid algea growth in your water.

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Thanks for the links…

Another question. I’ve been watching this video on mirror alignment:

I notice all his mirrors have these nice protective covers that aid him with the alignment. He tells what you can do if you don’t have these but if you want them, where can you purchase a set of these covers? Here you can see the cover is held onto the mirror mount with a set screw on the left, and the same mirror with the cover removed. So far I haven’t been able to find a set to order.

Thanks,
Carl

Looks like he has a 50w machine. Those have a lot more space than a k40 so there are usually better components. I’m not aware off hand of similar mounts that will fit a K40 but they may exist.