So focusing slightly higher than the surface makes it cut deeper?
I just checked a new board, and there is a substantial amount of warp edge to edge, so y’all are probably correct.
Don’t understand the mechanics but focusing 0.015" higher on this one machine is the difference between a clean cut and not getting through the mask on the material in my basement. I always use strong magnets to flatten material.
I’m out of here. See ya. Going camping.
I think that means the actual focus must be lower than it should be. Moving it above the surface can only reduce the power density at the surface and below.
Have a good trip.
I tried taking out some of the warp by bending it the other way, and that’s reduced it some. I think in this situation, you can either a) cut in the center of the bed, or b) tape down the corner of the sheet you’re cutting at.
From what I’ve been able to determine, the depth of field for the Glowforge is 2.65mm/.104". And depth of field is generally described as 1.4x minimum spot size.
Have fun. Watch out for bears.
Hope you have a great trip!
From the formula here: http://www.parallax-tech.com/faq.htm I get 5.4mm for a 5mm beam and 50mm focal length.
I had another try with the visibly warped board, taping down the nearest corner. This time, the corner piece dropped out easily while the ones near the center were harder to remove, but still worked. So it is definitely the warp that is causing the problem.
I think I read that people are using really strong magnets as hold downs, any recommendations for good ones?
Maybe my maths are all wrong.
Your calc seems to be double mine.
I doubled it because I thought the formula was d in the diagram. Perhaps it is 2d, so I shouldn’t have doubled it.
Since GF can cut 6mm in one pass 2.7mm seems too small but perhaps the power density at focus is far more than it needs to cut so it still cuts well outside the DOF.
I had ran across that link a few days ago and also remember asking the question a while back about what the depth of field was. That’s the first definitive answer I’ve seen.
Meant to make it a different thread at some point. But, I think that knowledge can help you get better cuts depending upon what you’re doing.
I think it helped on the puzzle pieces that I showed in another thread. Moving the focus from top of material to middle, (~.075” material) made an appreciable difference on the bottom of the cut, since I was cutting image down.
But - as it relates to this thread, if the numbers are accurate, that shows how warpage can certainly impact a cut.
It’s all a bit arbitrary because DOF is defined in terms of an arbitrary change in spot size but spot size is defined in various arbitrary changes in intensity.
That’s how I hold down the medium proofgrade and use to register a piece so it doesnt move for jig type operations. These are strong and would work well.
@curt paid me a visit and came bearing some bigger ones as gifts, not sure where he got them.
Those are bigger, but not as strong? 8.3 lbs vs 18.
I use the ones he gave me to hold down corners of warped material, the magnet halfway on the material, so it is sitting slanted on the edge. They are plenty strong… see the spacers between them in the link? If they weren’t there it almost takes a tool to separate them.
I’ve got a question for you magnet guys…I got a bunch of those bar neodiddlium magnets and they must have been about 600 lb. strength. I got two packs - took the magnets out of one and I kid you not, they leapt across the room to the other pack, met, shattered, and there was shrapnel flying!
How the heck do you store the darned things without breaking them? They are so freaking fragile.