Cutting birch plywood with an LED laser (some 40W drawn, most likely about 5W - 6W output) and why it's called "can't be done".TL;DR:it is possible.
But one has to have strategy and take certain steps to be able to perform this arduous task.
The Long Story:You need to be able to make following tasks:
1. make the machine take a predefined zero point (to zero the machine) reliably even it has no limit switches (which make it immensely easier)
2. make the piece take the very same position it was in when processing started (this can be hard but it is very important too)
3. check the outermost path with the actual laser that will cut it set on to least possible power and ran along so you can check it fits the piece you prepared
4. set the job into layers - strategy is: smallest holes, then recesses and possibly sections of key cutouts - only a few at once, then the outline as last operation.
5. try use a program that allows to select more or less shapes to be cut (i used Light Burn and paid the $40 for it as i see it worth it)
6. get potent air assist - i've ran up to 1 bar and it makes thing a LOT easier and cleaner
the process:
1. once you have figured the layout and PCB and everything - get your layout (most likely from the famous
http://www.keyboard-layout-editor.com/) make certain it matches your particular key set and switches - you most likely will revisit this moment (i know i did (oh boy!))
2. paste it to the cutout helper:
https://plate.keeb.io/ and select the desired parameters (kerf for laser and birch can be as low as zero, i have cut without any radius (works) and with 0.5 mm radius just the same, used ALPS, MX switches, the stabs work right and are of good quality and consistency (5mm means 5mm, 3mm means 3mm thick plate, et cetera) and save the output(s) (i used svg, but you might find DXF more useful for your own work flow, i used
Inkscape and
Lightburn.
3. next you need to align the cutouts with your plate outer shape - be it some matching you housing or PCB or whatever - you need t mate the cutouts and that shape before you can burn it out of the plywood board.
3b. I cut from the back side - i mirror the board so all issues and errors remain on the back, should there be any
4. i import the layout to Lightburn next, and try match the position of the layout with most favorable place on the lasers bed. I take my time and experiment here a lot
5. first pass is usually just to trace the outermost outline and check if the board and the layout match and fit each other.
6. i affix the board so i can use quite a force during cutting and to make the board flush with the nail bed - birch warps too easy and that can rise issues with focusing it.
7. once the board is in place and flush, check and adjust the focus height so it is about 1/3 or higher of the board cutting depth - a focus on the top of the board will be quite dispersed after 2mm deep, and we go 3.2 to get thru (i could not find thinner birch plywood) so i set it to about 19 of needed 20mm focal distance, YMMV depending of the lens on your laser
8. check the height on several places and adjust to be in between the worst cases
9. if there are too many nodes or "eyes" on the plywood i'd advise taking a different piece - it is hard enough already without them.
10. my first pass is the outer most contour at 1000-2000 mm/sec and 15-25% PWM just to scribe the line
11. it is wise to run the whole layout next tha same way - so if the piece ever moves it will be next to trivial to align it with running the laser at 1% and tweaking until it fits.
12. next i do the smallest holes first (as appetizer really) with 5 passes x 400 mm/sec @85 PWM - going too slow will make charring more pronounced, going faster will reduce it but produce more smoke stains - keep the air assist at a high enough rate. Repeat with 2 more passes until cut thru
13. make sure the air assist extinguishes the wood - don't let it char the edges too much - put more air into the cut, make sure it always hits the point of laser burning the wood.
14. if you plan to etch some wood away (i did outline filling with 0.15 step) now it is the opportune moment to run it: 500 mm/sec @ 80% should bite about 1 mm away on a single pass (or less) - i used it to etch the 5 mm stabilizers on the bottom of my 3.2 thick plywood.
15. next i cut the first 5-7 passes off of all the key cutouts - some will fall out some will stay in - don't worry just yet!
16. now set the layer to 2 passes and set to cut only selected shapes - select the numblock for example, remove the cut thru ones from selection and let it work - few more will fall out.
17. selecting ever less key shapes keep repeating until they are all done, repeat for F key row, nav-pad and space row, do the alpha block then, the right order depends only on your preference.
18. if you manage to fiddle with the cut out pieces and find the board has moved - check points 10 and 11.
19. for the end cut the outer most contour: 6 passes x 500 mm/sec @85% - repeat 3 more until the whole perimeter is free or less than 5% remains uncut even after 9 consecutive passes.
20 once removed from the laser, cut any remaining contour with a sharp blade in multiple passes - avoid splintering it uneven - sand it to final dimension
21. take a fine flat file and remove any imperfections from the keys, watch not to file off any material needed for latching the keys!
22. post feedback and pictures and consider painting it with PU or something to lessen warping and potential spill damage.
I found the 85% setting to be more productive than 100% on my laser
I found the 4-5 passes vs single slower pass chars the cut significantly less and produces a quite acceptable cutting surface
This is ongoing research and I am open for advice and feedback.
