General limits of laser cut acryllic

[Choidebu]

I don't believe this has been discussed before, so here goes..

I have 5mm acryllic sheet laying around which I'm looking to laser cut a bracket/enclosure that have pretty tight tolerances.

I've done this before through a shop but it was just a big logo to be glued somewhere so I wasn't really thinking about how accurate my design came to be, quality etc.

Obviously every shop will differ depending on their softwares and machine, also on material thickness I suppose... but do we have like some general guidelines on design tolerances (curvature, edge/corner), dos or donts, parts tolerances (for assembly) etc?

I'm asking this because I'm working with big holes with 1mm material between them, ventilated panels, and parts that interlock with keys and slots. While I do have pretty big material so I don't need to worry about the cost of that, the cutting fee is quite high so I don't want to do a double take or more of possible.

I am also considering 3d printing (there are people offering the service in my area) but afaik domestic hobbyist grade 3d printing needs careful tuning to be dimensionally accurate.

So I thought that on top of having to learn 3d design from scratch I'd still have this back-n-forth with the prototypes, fixes, etc, I'm better off with laser cut acryllic for the moment.

Pinging @K888D , @owliwar

Please help!

Thanks!

 

[Choidebu]

Note to self:
Cannot add tags to thread after first post.
Search is broken on mobile at least - keyboard closed by itself in 3 secs.

 

[Thehack]

Laser cut tolerances are tight. Usually accurate to 0.2mm. But you have to keep in mind of two things:

1. Kerf. The width of the cut: http://www.cutlasercut.com/resources/tips-and-advice/what-is-laser-kerf
2. Cut angle. The laser has a focal point that will cause the edge to not be 100% straight: http://www.cutlasercut.com/resources/tips-and-advice/focal-length-and-thicker-material-edge
3. Material width. Acrylic has a large variation for its material width. It is usually a spread of 0.4 mm. Compare this to metal, whose difference is about .1 mm.

I'd just get a sample cut from your local guy to dial it down exactly what you need. If it's a bigger company, like Ponoko, they may have a design document with the exact specs to follow.

For general cut guidelines, I'd avoid sharp internal corners. Give them either a chamfer or fillet. Acute inside corners can develop cracks. I'd ensure that there is at least 2-3mm material width between ventilation holes.

For interference fits, it is probably 0.1 mm to 0.2 mm real clearance between the panels. For clearance fit, probably .3-.4mm.

I've only worked with acrylic a couple times but that was my experience. The cuts are very accurate due to the laser process, but the variation in material width and need for a thicker material hurts.