Official Luthiers Forum!

Hi there! So i own a k40 chinese laser and i would like to know if it can cut shell for inlay work...any experience?

I have no experience with those, but one of the local luthiers has a day job helping students and faculty in a university shop that is packed with CNCs and laser cutters, so I asked him. Here's his reply:

"I have never tried cutting shell with the laser. I have heard of people doing it but I would choose a router 100% of the time, if it was available. The beam needs to be focused very carefully to get an accurate cut and, even when it is done carefully, the precision isn't what you would expect from a nice CNC machine. Part of that is the actual laser and part is the lower quality of the actual x,y,z axis'- both the rails and drive systems.

There is also the issue of reflection, not a friend to the laser! That one is easier to work around as some simple masking tape on the surface can remedy the issue.

And lastly, there is an issue with perpendicularity of the edges. They might be fine, but it isn't a guarantee that the sides will be straight and the thicker the material (and more passes required to cut through it) the worse it can be. The plexiglass that comes off of our machines at school (even 1/8" thickness) usually have slightly wavy and tapered edges. This is an issue with waterjet cutting too, and there are software compensations available to deal with it but I have never seen them available for laser cutters. They might be, I'm just not familiar.

So, maybe possible if you don't have another option but it wouldn't be my first choice for very accurate work. I'd be even less inclined to cut the pocket with a laser- it would almost certainly leave serious burn marks that couldn't be removed without affecting the accuracy and id worry about glue bonding with the charred surfaces.

All of this is with the caveat that I don't personally use the lasers much! But we certainly talk about them quite a bit."

One of the local luthiers has access to a laser cutter at a 'makerspace', and uses it to cut wood veneer inlays into the tops of his guitars. The charred edge on those is a 'feature', akin to the old practice of 'sand shading' for marquetry, but I can't say I like it.

Shell is composed of layers of calcium carbonate (iirc) and protein. It really stinks when you get it hot, and I'd imagine that the protein could 'explode' on a microscopic level and make a very ragged edge. It may not be any worse than the edge you get from hand sawing, but I would not expect it to be much better. Charring of some sort could also be possible.

in a nutshell no
if you only have a low wattage it won't work. Not all shell is the same and with the heat of the lazer it often lets a smoke mark but usually polishes out. I use a cnc machine with a small bit that works much better
The commercial places also use mechanical cnc not lazer

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I have a friend with a 40 watt laser. We tried cutting white MOP. It basically crumbled. I use a CNC. .023" and .010" end mills from Precise Bits. com. They do a nice job with MOP and abalone. - Mike G

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guitarsbygiltzow.com

I was able to cut shell on a laser. You must raster them out, and my laser has the same controller as a K40.



Both inlays, the headstock and the Chinese character is done by the laser.

The way to do it is as follows:

Take a piece of aluminum plate, about the size of the inlay you wish to cut. Glue on (with CA glue) a piece of insulating backing. Can be any scrap wood about 2-3mm thick. The wood is necessary to insulate the shell from the aluminum as the aluminum will conduct heat too fast and prevent the shell from cutting cleanly.

On top of that wood you would then CA glue your inlay piece over it.

Make your design. Do a raster engrave. Use as high of a power as you can safely use. Set speed to something like 100mm/s. 20 passes or more. You must have air assist and you must set the air assist pressure as high as you can safely use (I used about 40psi). MAKE SURE YOU USE THE INVERT IMAGE OPTION!!!

The laser will burn away the part that you don't want. Keep at it until all unwanted shell is burned away. The aluminum plate acts as a weight to hold the piece down and keep it from moving, and also prevents the laser from burning through the backing (it will). Check for any leftover shell. If any is present, then keep burning until it's gone. You will need to do 20 passes, but you may need as much as 40 or even 60 passes. Especially if thin lines are present.

DO NOT vector cut it, you will ruin your shell.

You can also use the laser to cut out the inlay cavity that will fit the inlaid piece. Use illustrator and use the "offset path" option and offset your cavity by about .5mm. MAKE SURE INVERT IMAGE OPTION IS TURNED OFF!!!

You can also use the offset image option in illustrator to create your inlay piece and cavity, in such a way that you won't ruin anything because you forgot to set or unset the invert image option. You can also minimize the amount of wasted laser power on bits that is already burned off.

Be aware that if you are using laser to cut inlay cavity for spruce, it will not work since the density difference between the growth rings are so high, that the laser will burn away the spaces but leave the dense growth ring intact.

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