Dog bones was something that was addressed by @jkopel. I remember it, too. Had to do with cutting acrylic or Delrin.
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Chuckle - I’ve never measured mine, but it’s on the extremely thick side. Couple of mm at least.
(And most uncomfortable in the heat down here.) 
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It relieves the strain in corners and keeps the acrylic from cracking if you try to fit it too tightly.
I need to find that app.
I can totally see by that example where you would get the rounded corners concept . When I get back in my office tomorrow I will take a picture of the cuts that I make with my lasers. One has a 2.0 lens like the glowforge will have and the other has a 1.5 lens. The 1.5 lens is a much finer beam for detail and creates a smaller kerf. It seems whatever laser that made that cut was a bit shaky because it’s not very precise or the focal length was way off. I think you will be glad to know with correct settings you can get a much better cut then that. 
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BTW…no need to pull your hair out over this LOL[quote=“palmercr, post:19, topic:2946”]
This is a human hair at the same scale
[/quote]
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No, all shapes (tabs, slots, or otherwise) will only need one kerf adjustment (with a minor caveat, which I’ll explain below). This tutorial shows a quick, easy, and (most importantly) correct way to create a kerf-compensating offset.
The image smcgathyfay showed had a design flaw. The flaw was that the two sides of the box were touching each other. It’s as if the person who created that box design was ignoring or unaware that a kerf would be created when the two pieces were cut apart. With a properly-made design (one that has allowances for kerf in all directions) only one adjustment is needed, the one @Jules shows in the OP.
OK, the small caveat…
Yes, the beam/spot of the laser has a shape. That shape is not square and it does not get altered to conform to the object you’re cutting. For all intents and purposes the shape of the laser beam is round, just as @palmercr said. The shape is a circle and the diameter of that circle, in the context of the Glowforge and this tutorial, is 0.2mm.
When that round beam cuts, it leaves a round hole.
When the round beam changes direction (goes around a corner) it leaves a radius equal to the radius of the beam. The radius of the beam in this example is 0.1mm. That means the radiuses left on the insides of the corners that are cut with this round beam will be 0.1mm.
Although this radius is very small and is hard to see, it does exist. Smcgathyfay is right that it basically doesn’t matter, but isn’t right about it not existing. That radius exists whether the laser changes direction at 90°, 45°, 18°, 179.999°… basically any time the laser changes direction at a corner, a radius will be present on the inside of that corner.
Back to the caveat… Imagine you are cutting an acute angle. This angle is very narrow and very long. You’re cutting the inside of this angle. As you get closer and closer to the point of this angle the distance between the two lines will get smaller and smaller. Basic arithmetic tells us that, at some point, the distance between these two lines will be smaller than the diameter of the laser beam. That is the point where the laser will change direction. And, since we know the laser has a shape, and we know that that shape is roughly round, a radius will be present on the inside of the corner where the laser changes direction. The corner will not be sharp. There will be a radius. This is a fact. The area between the radius and the actual point of the angle you’re trying to cut will not be cut.
This area, however small and potentially insignificant, does exist and it’s important to be aware of these things. If the tolerances of the part you’re making are tight enough that these uncut areas will not be acceptable, you will have to find a different way to cut them. Perhaps a wire EDM may be an option.
So, again, the method shown in this tutorial will work for ALL shapes, regardless of what you call them, as long as the very small radiuses that are left on the insides of corners do not affect your design.
Sorry to repeat myself so much and be so long winded, but I’m trying to nip any further misinformation in the bud.
OK, one more caveat: this information doesn’t account for laser power variations, acts of god, material variations, presence of explosive material, earthquakes, gravity waves, sabotage, uneven cutting bed, temperature fluctuations, or power outages.
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A great Article thank you for posting im really wanting to use Fusion 360. Why argue over the beam size and that tolerance here? he was just trying to be helpful and for most situations we will use the glowforge for it is most any of us will need.
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I use this method all the time for boxes. Most efficient. Less cuts on the laser and less material used. The boxes come out tightfitting everytime.
I think things are being over thought…(thats a mouthful…)
Rarely do I use the same design for different materials so kerf adjustment is not needing to be changed often if ever. Sharing lines in a cut run reduces the time the laser is running as well as uses less material.
More than one way to skin a cat, as my old Aunt used to say.
If you plan to design and sell your plans, it may be good to have parametrics in your design so you can easily convert it for a customer based on the material desired.
If you plan on cutting the same file out, multiple times from the same material, then it may be best to design it once with kerf adjustment, utilizing any sharable lines within the layout to minimize your time and material consumption.
If its a one time design I would say design it however you are most comfortable…lol
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Thank you for letting me know that was okay! (I wasn’t sure if that method was going to be accurate enough.)
I think I’m going to use something like this to adjust my designs up front, even if GF does decide to put a kerf adjustment on their interface…
If I’m working on a design, it’s easy enough to drop the Offset relationships in while I’m working, and then they are there, to be used or not. (Or they can be added once afterwards.)
If I have to change the design - say I want to resize everything on one axis by 10 mm - those Offset relationships, once they are created, don’t ever have to be touched again, and they adjust as I change the original design. I just drop in one kerf number and export the new file ready for cutting. All the kerf lines know where to go, inside or outside of the individual lines.
So if I do it this way, I have to mess with kerf only once.
If I were to just export the original design and it changed, then I would need to reset all of the kerf relationships individually for the all the parts in the GF software again on the revised design.
Six of one half dozen of another. It’s probably going to be about the same amount of work either way for easy designs, since the initial setup of the Offset relationship takes a few more clicks.
But for complex designs, or designs for sale, which might be cut out of lots of different materials with different kerf impacts - I plan to use this, because I think it will be a HUGE time saver.
Parametric is just unbelievable.
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Thank you for the great tutorial @Jules. I think I have been focusing on the 3D elements of Fusion 360 and not enough on strengthening the 2D sketches that are used to build the 3D model. I need to spend some time with the 2D elements and become more familiar with them. My way of thinking says that I need to have a complete 3D model such that I can determine the 2D pieces that will be required to create that model.
I was also kind of freaking out over dealing with kerf adjustments over multiple slots/tabs because in my mind slots and tabs would have to be treated differently. So thinking more about it and seeing the continuing discussion here has helped to put my mind at ease a bit.
Follow-up question for @smcgathyfay. You say that you cut back-to-back pieces all the time and have a tight fit… are you saying that they hold together without glue? Based on the demonstration videos where Dan picks up the outer piece of material, leaving the cut-out piece sitting behind on the print-bed would indicate that a tight fit would not be possible if the pieces are cut back-to-back. Or, does the rotation of the piece to make the box joint, and/or expansion/contraction of the material overcome the kerf?
It is nice having so many people here that already have lasers and are experienced in these things to help us newbs get into the swing of things!
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Sharing a cut line and cutting out a shape and having it fall out as in Dans demo are two completely different things…
Instead of having two boxes…you butt them together and only cut once down the middle.
Kerf adjustement is figured in. This technique would not always work with any auto kerf.
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Hmmmmnnnnn…
Hadn’t given that part of it much thought yet - seems like sharing the cut line is by far the most effective use of your material, and if the material is pricey, that is definitely what I’d want to do. But this method won’t work if you intend to do a single shared line…that is also true.
So i believe that in that case, in order to make both cases work…
But if you need…
Gahhhhhhhh!!!.… (Thanks a bunch guys, i was actually planning to do some laundry today so i don’t have to run around in cat-hair covered clothes.)
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Unfortunately can’t have it both ways…it will ultimately come down to what works best for what you are designing…
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I’m confused a little here. Do you mean just cases where boxes share a straightline border, or are you also talking about more complex shapes like finger joints? (I can imagine that for almost any glue except the thinnest cyanoacrylate an 8 mil gap would be just fine, but not for a press fit.)
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I think I misunderstood the original post then, so I’ll get specific.
This is the design for a box, courtesy of Makeabox.io. It has been adjusted for kerf (exagerated .1" just so it was obvious.) It shares lines where it can, but obviously the slots/tabs can’t share a cut because the offsets overlap.
This is another box courtesy of makeabox.io. It has no kerf adjustment, and shares a cut line. There is only one vector (not two overlapped).
So, my question, if the kerf is as advertised (.008" to .025"), are you saying that cutting the via the shared line in the second image creates a snug fit?
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Give me a second - I’m going to draw something using your picture to explain it visually.
(Okay it might take longer than a second…since lunch might be involved at some point. ROFL!)
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I understand the kerf issue and based on that, I think that the answer to my question is no, it will not create a snug fit due to the kerf.
I’m trying to confirm whether the scenario I’ve laid out is what Stephanie is describing or not. I’m thinking that it’s not, and that I’ve incorrectly interpreted her statement.
Oh, I know you understand, but I want to include it anyway up top for folks who might be coming in later and reading up on kerf for the first time.
It’s a confusing issue. 
The good news is…there might be a way to optimize that center cut parametrically, and I want to play with that next…
best of both worlds.
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If you were really crazy, you could lay the boxes out so that nonmatching edges nested. But the assembly would be interesting unless you engraved marks to identify each matching edge.
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Great job on all of your tutorials!
Giving like that is what makes the community such a rich experience.
Thank you Jules!
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