Scroll Saw Bowl Re-Reborn (Re-incarnated?)

An idea I’m toying with for regular owners is a two part file. And basically have all the half rings have a puzzle joint in the centre. If the split is with the grain as opposed to cross, it should be mostly hidden or not noticeable. That way you could get a 20inch bowl no problem.

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I think it can if you are in a hurry. Two passes apparently gives nicer edges on acrylic. Perhaps it stops the heat from spreading as far laterally.

It can cut 1/4" fine. I do it often. Different materials require different settings though. While you can make it through acrylic in one pass, it’s a lot cleaner finish if you do it in 2 passes. I can go through poplar like butter in one pass with no charring. 1/4" ply however takes a lot more power. Crappy ply takes even more than that

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Thanks @palmercr, very interesting (there goes my theory)

Good to know as well.

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I’m not sure where that came from - maybe 0.25" single sided? We’ve said that.

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Isn’t 0.25 equivalent to 1/4?

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:heart_eyes::heart::sparkling_heart::boom:

Hang on, let me check with engineering.

The difference I was highlighting was single sided (no flip), vs single pass (how many times the laser moves over the material).

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Pretty awesome. As to alignment, I’ve also been thinking about the bathymetric maps as well. Would small circles cut out at the center of each point and the center of each arc allow a small dowel to align? I’m thinking in the case of the baths metric map, holes in all but the top layer would allow perfect alignment. Perhaps we need a GF Think Tank. Ha though I guess we already are. Amusing ourselves as we wait. Ha

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Gotcha

Classic Dan statement! Yes, that might be where it came from.

It probably isn’t much disadvantage doing it in two passes because presumably each pass is faster. As long as it can cut all the way through and give nice edges it’s good enough for me.

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Sure. Only I was banking on the fact that if it can cut 6mm in a single pass that means we might get 12mm with 2 passes… not 4 passes. Multiple passes is bound to mess edges up at some point.

But alas, the wallnut experiment gives me hope.

I don’t think it is a simple relationship like that and I don’t know why multiple passes would mess up the edge as long as the positioning is repeatable.

The GF seems to have as much cutting power as any 40W or 45W laser. I expect it gets the deepest with full power while moving very slowly but that is not the best way of cutting to get nice edges and might start a fire with some materials.

Wood and acrylic are very different. With acrylic you are melting and evaporating. With wood you are burning.

With acrylic the aim is to get a smooth flame polished edge. With wood it is to get the least charring. The former needs as little air assist as possible and the latter as much as possible.

When drilling acrylic I peck drill to avoid it melting and when CNC routing it I do multiple passes with very small Z steps.

SarbarMultiMedia on Youtube has lots of interesting videos about edge quality with a cheap laser cutter.

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Milling acrylic? Fascinating I’d never thought of it. High rpm or low? I know in metals you can cause work hardening by running too many passes across the surface does the brittleness of the acrylic make milling operations a pain? Or do you take such small bites out of it with each pass that you typically don’t have to worry about it. Sorry for the derail everyone

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When drilling use low RPM and peck drill so you keep clearing out the swarf. When milling if you try to do deep cuts moving slowly it melts, gums up the bit and likely snaps it. Going quickly with high RPM taking shallow cuts spreads the heat over a large area so it doesn’t melt. Not that acrylic has a low melt point, it is actually higher than most plastics. It has a high coefficient of friction with metal so heats very quickly when machined.

I think it lasers well because it has a high melting point. People say other plastics like ABS are melt too much when lasered. But I expect it you do a deep cut slowly the heat gets time to spread laterally but if you go fast and make two passes you spread the heat around, just like milling.

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Ah I bet the heat generated from the friction helps keep the surface stresses from cracking the material then. All of this makes sense, thanks for the details

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Depending on whatever you are using linearly for a Z axis (As this dictates your DOC). If it’s rigid enough you can go full depth with acrylic or lexan with a single flute end mill. Most CAM packages do a helix bore then use a 2D strategy to widen it out (Also a full DOC with a little left on the floor so you can do a spring pass/cleanup). The key is chip evacuation. This is where single flute shines. With a multi-flute endmill (i.e. 2 or 3 flute) what you see melting is the chips that have not been removed in the path of the endmill. In turn recuts them and generates even more heat then melts. This is bad for the surface finish, the cut itself and for the endmill.

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I have single flute up-cutting endmills that I use for 3mm DiBond where I plunge and cut full depth. I have never been brave enough to plunge them through acrylic though as they are only 2.4mm diameter.

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I use 2 flutes or a single point flycutter. The best surface finish needs high speed steel honed to a razor edge. Tool geometry and sharpness makes a huge difference in acrylic.

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