To adjust for kerf or not to

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I think you’ll find from my posts over the past 11 months that I do not rank my Glowforge feature preferences to the exclusion of what others believe their needs may be. I do not attempt to rationalize why there’s are any less important than mine. I do not try to aggressively to defend selective feature choices or business model decisions made by the Glowforge principals/(and/or VC’s) that I am not privy to first hand. I am on the “live and let live” train while still trying to challenge things that may not make perfect sense to me, but which I believe are of benefit to the community at large, yet never to the exclusion of others.

But that’s just me. . .

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@smcgathyfay, could you go into much more detail about when to use the kerf adjustments and the ramifications when you do. This is something that I am having trouble understanding. :slight_smile:

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Being aware of the kerf is important and it would be really nice if the Glowforge software automatically compensated for it. Frankly, I was under the impression that this was a planned feature from the beginning. I suppose we all hear what we want to hear… the lack of an easily referenced listing of expected features is only making this phenomenon worse (or better, depending on your perspective).

As @jdodds said, adjusting for kerf is a fundamental aspect of CAM software. Also, it sounds like the Glowforge software is no exception - it sounds like it includes kerf compensation functionality already… but only for Proofgrade material.

I share @jdodds’ incredulity. The Glowforge software is surely able to compensate for the kerf of Proofgrade material because each Proofgrade SKU has a corresponding kerf value attached to it.

  • 1/8" clear acrylic = 0.0035"
  • 3/8" high density foam = 0.0120"
  • 1/8" solid maple = 0.0050"
  • etc.

Sure, it may be more complex than one number for each material but, eventually, the software seeks out a number and then uses it to compensate for the kerf. As long as the programming already exists to grab a number from something I don’t think it’s too much to ask that we be able to supply the number manually.

I thought Glowforge was suppose to be all about eliminating “the laser operator’s little black book”. I thought the idea was that it was going to let us focus on designing, not recording and referencing data.

Although it would be entirely possible to add a kerf-compensating offset to a 2D sketch in Fusion 360, those extra lines could be very disruptive with more complicated models. If you were to make the kerf-compensation lines affect the geometry, changing from one kerf value to another may wreak havoc with the joints in an assembly. If the lines are construction lines that would make exporting them more complicated. You could have one set of construction lines in every sketch, then project those out into another sketch, but that would mean you’d have at least two sketches for every body in your model. Also, modifications made to the original sketch may not always link properly with the added outlines (what if you delete and redraw a source line - Fusion 360 isn’t likely to treat the new line exactly the same way as the old one). Mirrored/arrayed geometry would need to have sketches added so that those features can be properly compensated-for as well (unless Fusion 360 has a way to mirror sketches along with geometry). Not to mention that bodies that are connected to their mirrored counterparts would have overlapping kerf-compensation lines. Also, managing all the relations between the sketches could be tedious - you could create a named variable for the kerf compensation value, which would make it easier, but you’d want to make sure you created that value early-on in the design process because retrofitting a drawing to utilize a defined variable can be tedious. Plus, sharing the compensated sketches would then only work properly if the person receiving the files is using the same material (or, a material that cuts with the same kerf).

I think it’s better to compensate for the size of the tool that will be used to manufacture an object after the design has been finalized.

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Going back to original question - To kerf or not to kerf…that is the question.
:smirk:

Keep in mind that the kerf on this thing is going to be as wide as a sheet of copy paper is thick. It’s not going to have any impact on most materials, and if it is an issue (say that you want to create one of @smcgathyfay’s cool inlay style objects out of acrylic, and you don’t want to use glue to keep the pieces in place), then you can avoid the issue entirely by simply buying the proofgrade material.

If you know you won’t be using the proofgrade material, and you absolutely must have a tight fit, then just adjust the size of the holes and shapes to compensate for the kerf when you design it in the first place.

The Offset Path tutorials that I just posted show how to do that for irregular shapes in Inkscape, Illustrator and CorelDraw. Skip the Auto-Trace part and just do the Offset or Contour step on your vectors.

It’s even easier to do in Fusion 360, just assign the correct dimensions in the sketch. Or create a little formula that lets you adjust it no matter what the kerf is.

(You don’t have to put two sets of lines into the sketches in F360, you can just set up a parameter that changes the size of the parts automatically. Everything gets laid out flat when you design for laser - it cuts 2D.)

Or…we are still going to have to take the sketches out of Fusion 360 into either Illustrator or Inkscape to convert them anyway…you can just do a big batch offset in there if you prefer.

One time and boom - they’re all done.

I’m not trying to make light of the kerf question, because I have thought about it, and figured out a couple of ways around it.

I’ve also decided to wait and see if it’s even an issue. I’m betting that for most of the stuff that we do, it won’t be.

Now slot sizes, tabs, and nominal thickness - that’s another puppy. If you’re planning to build 3D constructions out of widely differing materials, or if you are planning to sell your designs as files, you will want to look into parametric design, because it saves a whole lot of rework on your model.

My 2 cents…FWIW. :no_mouth:

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You’ve become quite the advocate for F360 and parametric design. This makes me proud.

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I’ve done three now - the first one took a week, the second one took 3 days, the third one took 15 minutes.

Yeah, I’m a believer now. :wink:

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I’m a VERY slow learner. I jump in and start designing and then somewhere down the road I realize things would be SO much easier if it was parametric. Luckily, F360 is so forgiving that most of the time I can just go back and replace the raw numbers with variables and BAM! Everything works parametrically.

So if anyone is asking, two big things with F360. First, create a component before you ever draw your first line in a sketch. Again, F360 is so forgiving that not doing so is not that big of a deal but is definitely best practice. Second, put the “change parameters” icon in the bar and remember to open it and start populating it right away.

Now I need to get those down to a couple of short bullet points, put them on a card and tape them to the top of my monitor!

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You need to do a tutorial. (Hint, hint!) :smiling_imp::innocent:

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I could call it “everything I always screw up using F360 and how not to”… Who knows I just might. I learned many years ago if you really want to master something, try to teach it.

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I’d read it!

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This is disturbing to say the least. While I certainly wouldn’t expect an automatic correction for non-PG materials, I certainly would expect a manual option for adjustment of kerf on our own materials for dialing them in. I thought we were to be given a choice of cutting left, center, or right on any given line.

I find myself confused and demoralized…:confounded:

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Don’t count anything out until you don’t see it. Then work with the cool things provided and learn to work around those that are not. I have never owned a tool or piece of software that worked exactly the way I thought is should. Wearing a pair of shoes for a while is almost as good as getting a bespoke pair.

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Kerf is basically how much material is vaporized by the laser beam.
In the first example below, if you want a 3" circle, then you would adjust the size of your shape larger using the known kerf width to compensate.
(.2" is NOT a normal kerf size but I used here to demonstrate so its easy to see)
This would be an example where auto kerf adjustment in the Glowforge would work.

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Example 2 is when you wish to cut a tight fitting puzzle or inlay.
Using one piece of material, represented in the green, shows the gap made by the laser cut.
The procedure below it shows the correct way.
If the kerf was .2", the blue material would have a circle cut line at 2.8" in diameter. And the plum material would have a circle cut line of 3.2".

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Here’s an example where auto kerf adjustment would not work.
When cutting slots for a box.
The widths of the slots in the yellow material are adjusted however the depth of both are the same as shown with the red line.

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Here is a close up. As the laser cuts away the material of the yellow/orange set, the slots fit nice and snug. However the blue/plum material will not.
I dont see how auto adjust would work in this case since only the vertical lines move. The yellow slots are thinner and the orange tabs are wider.

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Nice post and aptly demonstrates what @Jules has been talking about in regard to parametric. Make notch height one variable and notch width another and then off to the side make a test cut design. A couple of test cuts and tweaks and the whole large project will fit perfectly.

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Brilliant job on this! :smiley:

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The problem is not all design software is able to do parametrics.

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True and why I am further falling for F360. This would be a disaster in Sketchup.

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Thanks, Jim for bringing this issue to light. I am quite concerned about any functionality that is available for proofgrade material that can’t, at least manually, be controlled for other materials.

This isn’t going to play out well in the media, when they spin it as coercion to force Forge users to buy proofgrade material.

Yes, there is a work-around by adjusting cut placement in the CAD software before sending it to the Forge. But kerf adjustment is currently one of the main features they use to promote the machine:

They don’t say, “…but only if you buy our special material!”

I have to wonder if there are similar restrictions to other claimed features?

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I’m totally on that page. What would be very disturbing to me would be seeing manual kerf adjustment as a “pay per use” or part of a set of “premium” features available for an annual subscription fee. I also initially thought the “in the hopper” phrase was very cool place for ideas, but for me, it has lost any aspect of positive meaning having become the most used phrase in the forum, and taken of this feeling of a dumping ground for any feature comment that the team isn’t prepared to address with the community.

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Yes, that bullet point certainly left me with the impression that there would be manual kerf adjustment right out of the gate rather than “in the hopper” as per Dan’s comment on the topic. In my opinion, that feature being built into Proof Grade material but not finding its way into the core product right out of the gate would represent a gross misrepresentation of the product given in the sales cycle. It’s obvious that the Glowforge team could not possible be expected to provide automated kerf adjustment for every conceivable piece of material you could use and therefore the only reasonable assumption is that the user would trial and error their way to a correct kerf adjustment for their material choices.

This one is scary and why people aren’t seeing that is even more so.

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