Reverse Kerf?

Beyond the Manual
#1

Hello Everyone,

I am trying to make an acrylic cover that attaches to another object using magnets. I have done at least 50 different test engraves with various settings to try and etch out a nice “hole” for the tiny magnet.

Working with Proofgrade Medium Clear Acrylic

The issue is, that the kerf messes with the size. The magnet is 3mm in diameter, and i have a hole that is 3.1mm that i set to etch from the acrylic. The issue is that the top of the engrave is fine with a very small “gap”, but the bottom work out to something like 2.7mm because of the kerf.

I tried setting the material thickness to 0.1 mm to attempt to get a negative kerf going, with no luck. I also tried increasing the thickness to 8mm even to see if i can just elongate the kerf itself to make it less noticeable. Neither one of those methods seem to work properly.

I want to avoid making a 3.5 mm engrave as that would be too much gap near the top of the magnet, but would allow it to sit nicely at the bottom since it would then be approx 3.1mm at the bottom.

QUESTION: Has anyone done anything like this to try to achieve a ‘negative’ kerf?
kerf_question

**This would actually also be useful for inlays as well, just on a smaller scale.

#2

There will always be some hour-glassing that is the nature of the beast but you can take control of it by controlling your focal point in the GFUI. I don’t know how well that will work for engrave but works well for cutting.

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#3

I’ve done it as a two-step, first engrave and then score the outline with focus set midway down the hole.

Test and measure by creating a sequence of holes with various settings and then slicing then in half. You can then easily see and measure the effects.

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#4

This is exactly what I did, but I found that the high quality score settings distorts the acrylic around the hole then… Almost makes it a bit wavy from the heat.

I will give it another shot. Do you remember if it you accounted for laser width on your score layer? Say if you needed 3mm hole, did you engrave 3mm and then score 2.9 mm from center?

#5

This is what I meant by me setting the material thickness to 0.1mm and also 8mm but they both seem to have the same results.

#6

Use lower quality then… Just go manual and take full control.

I definitely accounted for kerf. I can’t find my notes, but I think I scored the same size shape as I engraved, just focused deeper. Not strong enough to cut through though!

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#7

I think you included instructions for doing this with your Ancillary Mode Dial, didn’t you?

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#8

Yeah, probably so!

1 Like
#9

Thanks guys I will take a look

#10

Having a set of files about will make it fit perfectly, for a lot less work than you have already spent, a flex shaft or dremel can solve really tricky bits. I see the glowforge as amazing for laying out complex details but rarely have I had it do all the work.

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