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I'm trying to fit a shaft into a hole in an acrylic piece that is 5mm thick to cause an interference fit. The shaft has a max. diameter of ⌀5mm and a min. diameter of ⌀4.988mm. I have access to a laser cutter with a precision of 0.2mm. This basically means that i have to cut the hole in the acrylic to a diameter of less than ⌀4.788mm, to ensure an interference fit right? Lets say I cut the hole in the acrylic, using a diameter of ⌀4.788mm, the diameter could be as low as ⌀4.588mm. Would the shaft of ⌀5mm even fit in this hole? Given the material and uncertainty in the laser cutter, what diameter do you think is suitable? Thanks

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  • $\begingroup$ laser printer? A device used to apply toner in image form on paper? Laser cutter? I did not want to edit it without a clarification. $\endgroup$ – fred_dot_u Mar 22 '18 at 13:53
  • $\begingroup$ Apologies. Yes, a laser cutter is what I meant. $\endgroup$ – Yogi12 Mar 22 '18 at 16:06
  • $\begingroup$ Did you take into account that laser cutters dont make straight holes. but the sides are allways a bit angled. 0.2 mm sounds awfully inaccurate to me. $\endgroup$ – joojaa Mar 23 '18 at 16:57
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There are a couple of issues. Firstly laser cutting may well not provide good enough tolerances or surface finish to reliably produce the fit you need and you woudl probably be better off drilling the holes, possibly using the laser to create a reference mark or pilot hole.

Secondly poly-carbonate and acrylic don't really like this sort of interference fit and the advice is generally to give holes decent clearance as the stresses involved tend to cause cracks, especially if the holes aren't polished and chamfered.

You would probably be better off drilling a hole with adequate clearance and using an adhesive to secure the shaft.

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  • $\begingroup$ Your post brings an oversight on my part. Temperature changes will be different with two different materials, perhaps resulting in the cracks you describe, if the fit is too tight. $\endgroup$ – fred_dot_u Mar 22 '18 at 16:38
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Presuming laser cutter and not laser printer, the project you suggest would be most effectively approached by creating test pieces. With 5 mm thick acrylic, there are enough variables to make it difficult to provide certain answers.

Cast acrylic behaves differently from extruded acrylic. High power lasers are able to use higher travel speeds than lower powered lasers, changing the characteristics of the hole.

A 5 mm diameter hole is small enough that high travel speeds are not likely regardless of the performance of the laser. Laser cutters typically slow for circles and curves and especially for right angle corner cuts. This changes the profile of the cut and the surface rendered by such a cut.

If your project allows for creating test pieces, consider to use a variety of hole sizes and cutting profiles, testing your holes with pin gauges or with the shaft to determine correct settings.

Kerf settings in the software that create the laser job can be adjusted to provide more precision for inside dimensions, but I suspect the tests would give you simpler results.

With such a thick material, a low power laser may have some divergence as it nears the lower edge of the material and may create a non-cylindrical hole. The variation may not be a factor in your project, but the above suggested tests will ascertain that consideration.

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