For preface ive done many cuts and never had this issue til this started randomly happening, ive made several boxes, including a smaller one of this box from acrylic before and also wood boxes.
Putting this question up because ive already wasted 2 sheets of acrylic tring to figure this out and 8 hours so hoping someone has some insight.
For some reason when i cut this piece and only this piece it shrinks and i dont know why. All the other pieces of this box fit together perfect except this one piece. I have cut it 8 times trying different angles, different acrylics, redesigning the piece in adobe and importing it in and still it shrinks every single time and doesnt line up…
I changed t he color only to help see which piece im talking about but they are all on the same layer and cut the same.
Have you measured the parts to confirm it’s the one piece getting smaller than the other pieces getting larger?
It’s odd that even recreating the piece reproduced the same issue so likely something in the design. I’m noticing that the piece that you’ve identified as smaller is on a different layer than the other pieces. Is it possible you have a kerf or some other setting for the green layer that’s creating the issue?
Otherwise can you upload the .lbrn file here for review?
I don’t see anything obvious in the design. Was this the exact design that you burned?
I suspect what’s happening is that all the parts shrink but that this part is shrinking more because of its geometry. This is the only one with much of the inner portion removed. The other parts are likely shrinking at roughly the same rate whereas this one is the outlier. Measuring the actual dimensions can help verify this.
As a test, I suggest you burn this to paper or cardboard and see how the parts fit. That will help isolate where the discrepancy is being introduced.
well ive made the same box of this in acrylic that has a smaller version and it worked… since this is the only one with the center being hollowed out do you suggest maybe i try putting the outside cut and the inside cut on two different layers? then cutting only one layer at a time?
I’d suggest you first take measurements to understand what is happening and to what parts. Take note of the relative percentage shrink for the various parts removing any change caused by kerf.
Then if you’re satisfied that it does seem like a shrinking issue confirm it by burning the design to paper or similar. That will be quick and will confirm whether or not you’re dealing with an issue of shrinkage or something else.
Then you could do what you’re suggesting. Cutting only the outside first to confirm fit, then cutting out the inside. But I suspect it will shrink once the inside is cut. If that’s the case then you could literally scale the design in the appropriate directions to accommodate for the shrink.
so i do know kerf is happening cuz i did 8 hours of testing yesterday… but heres the thing so i did a A B part kerf test where u have the outer tab A then all the little sqaures that make up b, cut it and measure their relation subtracting A-B / 10 to have the kerf. The problem is the closer i get those numbers together it starts messing with the measurements of the smaller pieces… For example the piece im trying to cut has all those little tabs correct, well when i in put the kerf settings to try to accomodate, it will make the overall size of the piece accurate to what lightburn says BUT it also increases all the little tabs so then those are not accurate in size
Inside and outside kerf need to be handled separately. So you would need to have any inside cuts on a different layer than outside cuts.
If you are indeed getting shrink in the actual acrylic measuring kerf this way won’t work. Or rather, it will be skewed because you’re including the shrink in addition to the actual kerf in the difference.
I’m not sure what the ideal way to measure kerf on acrylic but perhaps just cutting out a square of known dimensions and comparing actual dimension to design dimension. The larger the piece the lower the error.
You may be able to do this more simply by just taking the direct percentage size difference and scaling up accordingly without consideration for kerf. It would be very close regardless.
ill try more tests, yea kerf happens differently on different materials which is hard cuz acrylic isnt cheap so doing alot of tests is hard but i will continue and update if i get any results
Divide by ten, gives the kerf for each cut. Then divide by two for the kerf to apply to each side. The kerf here is .164, so I set the parts for inside/outside kerf of 0.082
Looks like the material is getting hot and melting around the tab holes…
There are two things to keep in mind. Kerf is only applied on a closed path. Some of the kerf will need to go outward, holes inward.
You say the size changes. I don’t know if you mean the overall size of the part or just the hole tab sizes…
When you cut something the laser follows the line in your artwork. With the beam in the center, 1/2 of the beam (kerf) will cut into the material. That line will be 1/2 the beam (kerf) size smaller. If you set the kerf to 1/2 the beam width, it will cut 1/2 beam width away from the artwork. The cut will be in the same place as your artworks line.
This is another thread about this… The Lightburn staff responses are probably the best examples of using and how it works.
i meant the over all size of the piece and the tab sizes… ive done more tests today and trying it out hopefully it works if not gonna take a break from acrylic cuz its just costing me too much money wasting sheets on so many tests… I know someone else said to test on other materials but you cant with kerf kerf can very material to material and is rarely the same which sucks…
I don’t think we have the entire picture. The size of the item would only change by the kerf width or there abouts. I can’t see a physical difference in the photo, but I can’t ‘hold them’ to see how far off they are.
The drawing I looked at has the tabs larger than the holes… as I posted.
