Laser for wood cutting- genaral questions

[adamchapman]

Hi,

I built my first CNC machine about a month ago, pretty much the same as the one at http://www.buildyourcnc.com.

I built it all from MDF because I can't afford the extruded aluminium that a lot of machines are made from.

Trouble is, when Im cutting along some wood the router tends to twist to the left. This is because the cutter is rotating anti-clockwise and a force exists between the cutter and the wood, etc. My only solution at the moment is to cut extremely small depths, with many slow passes until finished. Not ideal.


Im looking into using a laser on the gantry my router is currently attached to. Seen some 40W C02 laser tubes for about £150, which seems affordable.


I guess you can work out the laser cut depth by dividing the drilling rate by the feed rate. Drill rate is calculated at:

http://alumni.media.mit.edu/~yarin/laser/physics.html

but quite a few thermodynamic properties to look up for your material. Boiling point or melting point of 3/4" pine anyone?!?!?!?

I have 2 questions:

1. If the laser only cuts half the thicknes of my wood, could I just pass over it again to complete the full depth i require?

2.Could you use fibre optics rather than mirrors to direct laser energy from the source to the gantry?

Thanks for any help offered.

Regards
Adam

[MacGyver]

You're not going to cut 3/4" of wood with 40W and have anything recognizable come out of it... it just isn't going to happen. You also won't be able to use fiber with the wavelengths of a CO2 laser... you need to go to YAG wavelengths for that.

[LaserImage]

I cut 1/8" wood all day long with my 30 watt machine, 40 won't cut much more than that though. Unless you have 100-150 watts you won't be able to cut anything thicker than 1/2" or so. You can take multiple passes to cut through something, you will need to refocus every 1/16" or so and the result will never be as good as if you had enough power to cut through it in one pass.

My laser uses a printer driver to control the power and speed. I went through quite a bit of testing to determine the best speed/power settings for any given substrate. You won't find anything out there that will allow you to put in a substrate, laser power and speed and have it give you suggested settings, it just ain't out there... If it was, the person who created it would be very rich! That is the most difficult part of learning how to laser.

Gary

[LaserNOT]

This may fit in here, maybe not....
HEY ZAX! Ol buddy..... Big Spring again....
Been playing with a lot of wood and am liking it!
Anyway, I build up a vector file from a bmp and it turns out swell, very detailed. I really love this ENGRAVED and probably even better RELIEF engraved, if that is the correct word. The box "around" the image is engraved away, leaving the image "raised". More correctly, at the same surface height as the rest except the 'relieved" area.

Now, my question. So far, I have only been able to get the "rectangle" box shape. I don't know if it is possible, but can we change the "shape" of the "cutout box" ? (or the relieved area) to say an oval or something else?

The rectangle will work, but you know, oval's would be swell. Doing some custom gun grip/stock work and a customer wants an elk sillouette with oval shaped background. I warned him that unless my PAL ZAX knows a way, and nobody knows it like you, then we will be stuck with the rectangle shape.
Or maybe a workaround....
Thanks again. I see you are as always very busy helping everyone else around here. I wonder if you ever have time to do you own stuff....?
Also, been having fair luck with the metal marking spray, although whenever I re-supply I will get the "paste" version. Just too much waste with the spray...
Still works great though, I've done stainless, brass, aluminum and some kind of coated aluminum, can't say it was anodized because the laser wouldn't touch it. After I appied the spray, worked perfect. I was half expecting the anodize to "discolor" like all the little tag things do, but didn't even touch it at full heat.
Anyway, thanks again, look forward to your message....
JT

[zax15uk]

Hey JT...

Well sure you can have any shape you like, does not need to be oval or rectangular. When you create the .bmp image just fade out to either black or white (depending on your method, normal or reverse engraving). If you prefer to put a nice border on it you can do that too in any shape, just add it in your photo editor.

I am traveling on business, in Taiwan for a couple of weeks right now after spending last week in Japan, so no time to 'do my own stuff' unfortunately. The business keeps running without me though, mainly CNC stuff and vinyl lettering but I am sure the laser isn't sitting idle either.

The paste version is much more economical, and works great even diluted 2 or 3X the recommended amount. I also found it needs less power when thinned more, and the mark is still very clear. It seems to work best on stainless to me.

Zax.

[LaserNOT]

Originally Posted by zax15uk Hey JT... Well sure you can have any shape you like, does not need to be oval or rectangular. When you create the .bmp image just fade out to either black or white (depending on your method, normal or reverse engraving). If you prefer to put a nice border on it you can do that too in any shape, just add it in your photo editor. Ummmm as usual, way over my head. I'm using raw newlydraw and checking the box "reverse" to get the engraving, heat level determines depth...again the only choice I seem to have is the "sizing" box that is used by the engraving menu. This particular setup gives me a "deep rectangular box" with the image "raised" surface level after engraving. Now I think you said to use my external program to edit/play with the bmp file. I've already made the image a vector (assuming I HAD to...) file. I am traveling on business, in Taiwan for a couple of weeks right now after spending last week in Japan, so no time to 'do my own stuff' unfortunately. The business keeps running without me though, mainly CNC stuff and vinyl lettering but I am sure the laser isn't sitting idle either. The paste version is much more economical, and works great even diluted 2 or 3X the recommended amount. I also found it needs less power when thinned more, and the mark is still very clear. It seems to work best on stainless to me. .k Zax.

Didn't know you could thin like that...NOW it may start to get affordable for a change. Am doing mostly stainless, just tested with the other stuff mostly. What kind of heat setting should I be using? I've found that I need about 7 turns for a pretty good tatoo mostly

[zax15uk]

Originally Posted by LaserNOT Ummmm as usual, way over my head. I'm using raw newlydraw and checking the box "reverse" to get the engraving, heat level determines depth...again the only choice I seem to have is the "sizing" box that is used by the engraving menu. This particular setup gives me a "deep rectangular box" with the image "raised" surface level after engraving. Now I think you said to use my external program to edit/play with the bmp file. I've already made the image a vector (assuming I HAD to...) file. Didn't know you could thin like that...NOW it may start to get affordable for a change. Am doing mostly stainless, just tested with the other stuff mostly. What kind of heat setting should I be using? I've found that I need about 7 turns for a pretty good tatoo mostly

Oh ok, well if you're using a vector it's a slightly different process. Just create it in reverse, you won't need to select the 'reversed' checkbox but the result will be the same except you have control over the outer shape. It isn't possible to feather it this way though, but it doesn't sounds like that's the look you want anyway.

You certainly don't have to use a vector, in fact if you want grey scale shading and pseudo variable depth the only method on your system is using a raster file but of course the setup may be more work.

Regarding the Cermark. It depends on the quality of stainless, the better quality actually seems to take the process easier. I use between 6 and 9 turns, but my tube is losing power - on it's way out. I should have mentioned, I use the LMM6000 which is alcohol based (and typically mix it 1:6). I haven't had such good luck with the LMM14 product. I use a small airbrush setup and the water based product seemed to separate and clog the nozzle resulting in a non-uniform coating - which is essential for good results. The thinner coating seems to laser easier and produces the best results.

Zax.

(someone posted here a while ago the instructions to make your own, I never tried it but would be interested in the results)

[vivinar]

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