Laser Kerf Allowance?

Laser
#1

When I’m designing parts in Solidworks, my strong preference is to design the parts to their actual finished dimensions and adjust for tool kerfs on whatever tool I’m using to produce the part.

I recently cut a part on the laser and on my particular material it looks like the kerf width on the laser is about 15-20 thousandths, maybe a bit more.

Is there a way to correct for this without modifying my design? Perhaps a way to tell the laser to cut on “this” side of the line by an arbitrary distance that I provide?

Thanks!

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Laser Precision Design and Cutting Advice
#2

What is dimensional tolerance? This creates a tolerance band you’ll be striving to fit into and if additional processing is needed. But think tolerance band and trying to put upper and lower edges inside it.

As long as you are concerned with the minimum dimension - which would be the kerfed out edge at the bottom. Outside cut dimensions would be correct at bottom but not top, inside dimension, say hole would be smaller in diameter by .030"- .040".

Walls would still be sloped. However, when cleaning up the walls to be perpendicular , a second process step, it would be dimensionally as designed.

What is you tolerance ±? Skew it towards the dimension you want: say tolerance is .010" for and outside dimension. Nominal dimension is 10.000". So tolerance band would be 9.990" to 10.010" for acceptable part.

Do offset of add .008" for outside cut. Finished upper section will be 10.016" or .006" oversized, bottom 9.986" or .004" undersized. Can you live with that?

If tolerance is equal to or larger than kerf, then you can make the offset from top to bottom fall inside tolerance band. (assumes laser cuts at nominal dimensional - will have to add or subtract laser variation).

Fit up of edges will determine acceptability without further processing of edges or if some is needed - then skew adjustment as needed.

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#3

i believe Lightburn software lets you choose an offset, This allows for the kerf, at least in theory. I’ve haven’t used that feature, but I remember seeing the option.

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#4

Key is deciding which edge (top or bottom of kerf) is the most critical, split-the-difference, or clean-up afterwards.

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#5

These are parts that mate with other parts and the acceptable tolerance is more about aesthetics than anything else. How close do I want it? As close as I can reasonably get it. I’m less interested in focusing on what’s acceptable than I am in just finding a way to tell the software to simply cut outside my line rather than on it :slight_smile: I can get it where I want it if that setting exists somewhere. I just don’t want my solid model to try to be something it’s not :smiley:

@Photomancer Good point about the beam spreading. I am okay with one face or the other having the dimensions I’m looking for (part is symmetrical and can be flipped).

@tomthm I’ll have to dig around for the settings.

Thanks, guys!

#6

According to this post by @LightBurn kerf offset was added to v0.5.10 under “cut settings”.

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#7

kerf will vary slightly with focal length and lens and between the lasers, and how much it is noticed depends on material.

You will have to test.

I remember one member that did a lot of testing say on the original Thunder the kerf was .04mm, which is 10x less than what you saw. But interval settings are measure 100ths of mm. ymmv.

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#8

Wow, 0.04mm - one and a half thous. That’s amazing and wish it was what I saw. Being a novice, I had my settings a little too fast and had to make two passes to cut my material (1/4" acrylic). That could have had something to do with it. My plan is to come to the laser committee meeting and the maintenance day afterward - I’d like to learn more about keeping the lasers in-tune and eventually be able to help with that. A tuned-up laser seems the best place to do some kerf testing.

#9

My machine has a .002 kerf so mating parts are made .004” bigger. The Chinese brands don’t seem to have as tight a beam so I use .005” on those. You can always cut a 1” square and measure both the square and the hole to determine the kerf

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#10

If you find a way, I’d sure love to know! Many of my (tiny) parts are such that the kerf makes the difference between working vs. not. I always modify my design, which is a serious pain in the butt.

I routinely cut a one inch square as a kerf test. I measure it after cutting to determine the exact kerf on that material, with those settings, on that particular day. Typically I get about 0.008" on wood or acrylic < 3/16" thick. What material are you cutting that you’re getting such a huge kerf?

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#11

Chris -

It is 1/4" acrylic. I tested on a different laser yesterday (closest to outside door) and got that .008". I dialed my speed back to 5mm. On the earlier run I, not knowing what to use, cut at 20mm and needed to make two passes, which might have changed things.

But again to those responding, I’m not as interested in what the kerf should be as I am in knowing how to correct for it (if perchance I need to) without modifying my design file. I saw that reference to lightburn above but I’ve never used it and last time I tried there was some licensing issue. I cannot find a similar setting in RDWorks.

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#12

One suggestion I’ve heard works but never used is to use the “sew seam compensation”…

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#13

This is probably the best advice, as the machine tolerances can change based on the use (and possibly the abuse) they’ve recently been subjected to.

When I cut tabbed boxes in 0.2” plywood, I don’t offset at all and the tabs work fine - for wooden tabbed boxes. If the precision is needed, I would get an accurate, up-to-date estimate of what today’s specs are and go forward from there.

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#14

Do you find that your tabs are extremely loose? Because that’s what I get when I do tabbed boxes on the laser. They fit, but they’re by no means snug. Being able to correct for the kerf would help alleviate that problem.

#15

I’m happy with the snugness, once glued with Titebond. I made some simple boxes for storing Dutch Ovens, so the threshold was not very high.

#16

I found it in RDWorks. It’s called “Sew Compensation” (?!). It seems to be a setting associated with individual layers, which I assume without looking means the cut color layers over on the right side of the screen.

And oh hell, @jast already posted this!

image

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#17

For the sake of those who use the laser after you, please reset obscure settings like these back to the default when you are done.

I believe RdWorks will “remember” the change and apply it to the next person’s job, which can be quite vexing to debug.

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#18

Will do. Will do again.

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