I have done some experiments this morning using the 2d .dxf export from Templot, with the specific aim of testing the 'kerf' settings to attempt to establish a suitable default when laser cutting plywood for the plug chairs. I have (mostly) avoided using any other CAD input as so tried to replicate how someone with no CAD experience might approach the job.
The chairs were straight out of Templot, printed on an Elegoo Saturn with standard Grey resin on default settings.
I'm using 3.2mm plywood as that was to hand.
Here are the results:
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The top loose sleepers were cut with the default 0.2mm kerf using the file straight from Templot. Because they weren't fixed into a fret, they tended to move about whilst cutting as so neither the sockets or timber outlines were cut accurately. I tried cutting the sockets first and it helped, but even so the results were not ideal.
Next up, I took the same file, bunched the pieces together and made a small 'nib' between them to stop them moving about.
I did this in the laser software (not CAD per se.). To do this I drew a .5mm radius circle between the bunched sleepers, deleted the line bridging the circle, and then deleted the circle to leave the nib. I also removed the overlapping lines so that the long edges didn't get cut twice once the timbers had been bunched. I added the kerf legend to the sleepers and cut again (with a .2mm kerf). To reiterate, this was done with the laser software not a dedicated CAD program.
The top-left sleeper plate was the result. The chairs were a bit loose and fell out when I turned the piece upside down.
Next I tried again with a .4mm kerf. This time the fit was good but not tight - I'd say ideal with a little glue.
Next up, I tried .5mm kerf (by increasing the kerf I was closing the socket slightly). This time the chairs were a bash fit and it took quite some force to squeeze then in. A little more than I was comfortable with - although I didn't break any chairs.
Next I tried a .45mm kerf - this time the fit was excellent. They pushed in firmly, but could be removed without damage if care was taken. The outer width of the sleeper was 3.39mm, I couldn't measure the length as I only have a 25mm micrometer to hand. A little over width, but not that anyone would know.
So what has been the learning?
Well, theory would seem to suggest that .2mm kerf ought to be ideal. But variables such as cleanliness of the laser, exact focussing, etc. all come into play. What has been proved is that it is completely possible to produce the data directly from Templot, and that the kerf adjustment is all that is required to produce repeatable results.
There is no need for CAD.
I'm going to produce a test .dxf with different incremental 'kerf' offsets ranging from 0 to 0.6mm in 0.1mm increments. I'll post it on here.
I'd suggest all that one would need to do is use it as a test cut before each cutting session/material - try fitting the chairs and see which works best. Martin, if such a test piece were available within Templot then it would save others experimenting such as I've done.
Secondly, it has confirmed my suspicion that some form of fretting is essential. Not just from the perspective of retaining the pieces from movement during cutting, but also in terms of accurate alignment when they are glued down. If 0.05mm of adjustment is the difference between good and optimum fitting tolerances, then I'd suggest that sticking down individual timbers to that level of accuracy could be potentially difficult.
Of course the 3d printed track bases avoid that worry and are good to go as-is.
I hope that is of some use.
This system is excellent. Martin you are a Genius.
Best,
James
p.s. Yes I know that the chairs on the 0.4 and .5mm versions above are the wrong way round.
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