I’m afraid I don’t follow the question?
To your earlier point, unfortunately, MDF is a great example where material from different vendors (and even different batches) can vary immensely in settings. For example, I bought some 1/4" MDF from Home Depot that I couldn’t cut through on my friend’s 100W machine! But I’ve found other 1/4" MDF that cuts just fine on a Glowforge.
Good point (esp with MDF I imagine as it is pressed fiber with adhesives). What I meant by settings was - on almost all laser instructions/sites they say things like " for 1/8 acrylic use 30% power, 100 speed - for anodized metal use 20% power and 80% speed, etc (those values were pulled out of the air - not necessarily correct). While I could never do that on my K40 with just a rotary dial and speed set in mm/s (not %)., every other laser (epilog, universal, trotec,etc) that use laser software let you set in the software speed and power manually - I’m assuming the GF would let you do that - is that correct? Even with PG , what if you wanted a lighter engrave, or darker - can you override power % in the UI ?
It is a good question.
If there is a parameter field that allows one to select certain cut lines (perhaps by color) and provide a direction and offset, then I could see that being useful if arduous. I would get annoyed pretty quickly if I had to do that EVERY time I wanted to cut that file.
If I could set some kind of global parameter where a given color was associated with a set of focus/speed/power/kerf comp settings then that would be better, but then I would need some kind of complex interface to manage those settings. I would also need to know the exact color set so that I can prep my file correctly.
Finally, I would need to know that the file I am cutting does not ALREADY compensate for kerf, and if it does I would have to have access to a setting(s) that does no compensation.
I don’t know what the folks at Glowforge at intending to do, and I try not to guess (since I have been wrong so many times). 
Lol. I’m out of likes for the day so…here❤
I view a kerf setting the same way I would use a blade or bit setting. I put my design into the machine as a 4x4 square and use a 1/8 blade parameter and the machine off sets the blade appropriately I don’t put the file in at 4 1/8 x 4 1/8 because the blade will take1/16 from each side. Heck when I manually cut something I don’t measure 4 1/8 I measure 4 and but the blade where it’s supposed to go
Okay…I think i now understand why there are a few folks who are so concerned about the impact of kerf, if they are coming from a CNC environment, where the tools are much larger, and cut away much more material.
Designing for the laser is no different from designing for the CNC. If you want a 50 mm hole, you go ahead and design a 50 mm hole.
If you want something to cut as 4 inches by 4 inches, you design it 4" x 4".
The actual size is going to be cut as 3.9921" x 3.9921" if you do not account for the laser kerf.
If you do decide that you want to account for that kerf, there is a remarkably easy way to account for that in Fusion 360 parametrically, and I’m working on a quick tutorial for it.
There is probably also a very easy way to do something similar in other CAD programs, by creating a variable parameter for it, so if that .0039" gap on each side of your tabs is important enough to you, see if you can figure out how to do it in your program. (I know Solidworks can do it, it shows up in @Hirudin’s video.)
It is entirely possible that my response to this topic is based on my stubborn nature and my distrust of authority. I rarely want someone else to take over doing something for me once I learn to do it myself. Other than folding laundry. I hate folding laundry.
Cutting with the laser just feels a bit different then, say, running a part on my mill.
The kerf has a slight angle, acute corners react oddly, the material has a (relatively) large effect on kerf size, material consistency matters (hence the existence of Proofgrade), etc.
However I would be happy to be proven wrong, and if the answer is a simple as a .004 offset then I will just shut up and push go.
I’m afraid I don’t see a major problem here. Auto-kerf is apparently built-in for Proof Grade material so why is there a problem letting users manually select a kerf allowance? The feature is already there, presumably using a built-in table of kerf setting for the ProofGrade materials so all that is needed is an input box for the user to enter a kerf setting for their 3rd party material. It should also be pretty simple to make the use of kerf allowance user-selectable via a checkbox in the UI - enable it if you want it, disable it if you don’t.
As many of the CNC router and machine tool users have been saying this is one of the most basic aspects of CAM software for CNC machine tools and the GF UI is essentially the CAM for our GF laser cutter. I have no objection at all to users that want to manually fiddle with their designs as much as they want to get them to fit, but I really want a way to automatically adjust kerf much like I adjust toolpaths in CAM so that my machined parts come out precisely as they were designed in CAD.
I think some of the issues we are seeing in this thread stem from the fact that there are so many different backgrounds, experience levels and understanding of terms and techniques.
One solution is not going to be correct for all…
Not all techniques will work for all either.
Ultimately each of us will decide on what techniques will best work with what we plan on creating with the Glowforge.
Arguing about which option is better is becoming pointless…especially when its hard to confirm anything without having the finished Glowforge sitting in front of you.
Let’s just agree to disagree on some of these points and move on…m’kay?
Stupid cap on likes again for the day…so here is a manual like.
Perhaps it’s time to ask @dan if he’d care to let a staff member care to comment on how the auto kerf works? Early on I remember comments about being able to mark which side of a line was good and which was trash and just have the laser shift into the trash side to make the measurements exact on the material you want to keep. I suspect things are far beyond that now.
If you asked me a few days ago if a topic on kerf would become a hot button issue with over 100 comments in a day, I would have called you crazy.
Swarf on the other hand, that’s where things can get nasty. 
When I am milling I don’t have to specify which side to cut on. Holes have the opposite winding order to outlines, so the CAM program knows which is which.
Absolutely could not agree more.
But for those coming more through a CNC CAD/CAM route, the absence of an option for manual input of a numeric value for kerf offset would prohibit those user’s techniques from being implemented. Not really any different than not having manual input values for speed and power settings.
I agree on both his agreeing with @smcgathyfay and agreeing on what he says.
I am a total newbie to any kind of mechanical construction and the way our local firebrand @jdodds explanation is on how his machines and software work sound much more logical to my brain.
When I design I just want to do the exact measurements I know I want and not have to do that bit of math to adjust because that would annoy me heh.
If the Glowforge could just cut like in @Hirudin video in the Solidworks simulation thing of just telling it to cut on the left/right of a cut mark to account for kerf would be ideal.
So I’ve read through “most” of this thread now… and I can’t believe I’m going to say it, but I kind of agree with @jdodds!
It seems, that since this machine is replicating a manufacturing method, and utilizing many of the same aspects of said method (CNC milling), that the software at it’s basest level should account for something like kerf, particularly when existing machines that utilize more basic software already do the same function and have done so for years.
I fully understand the problem with having the software automatically determine the value based on the material given that materials can vary greatly (see @dan’s MDF example above), however, the ability to manually add in a value seems like it should be elementary given the history of the same exact feature in CAM software as mentioned above.
Do existing laser-cutters have ways to adjust for kerf? Or do they have to be accounted for in design?
As I brought up in the other kerf discussion, I had thought there was a way to pick “inside”, “outside”, or “on” the line within the UI for cuts? Is that not the case?
All that said… I would still rather have the GF in December without a manual kerf adjustment, than to have it be delayed because of it.
Existing laser cutters act very much like your printer…you send the file to be printed as is…the laser is merely a peripheral.
That is very interesting. In my head I just assumed that the first laser cutter was simply a CNC router with the router replaced by a laser, and that the software would simply follow suit. However, I suppose that I should have known otherwise given that the box-maker sites adjust for kerf.
Live and learn as they say.
Thanks.
Nope…a bit more to it than spinning a bit
That’s hilarious.