How I do kerf

[wenning08]

Made a video on how I do kerf. I’m sure others do it in different ways or styles. I like to get mine really tight fit for no glue.

The Perfect Laser Kerf?

Anyways, just sharing if it helps someone out. Take what you want from it but adjust to the style you prefer.

[deirdrebeth]

I generally go a tiny bit looser as I find that hammer tightness to be almost impossible to assemble if it’s a large number of slots! Maybe my hand/eye coordination isn’t as good as yours!

I do it in a similar way, but if I think about it ahead of time I also remember @evansd2 advice about making clones (in Inkscape) so it’s easy to adjust later

[evansd2]

This is a good explanation of kerf, it’s nice to have a video on the topic. Some people prefer to learn that way.

What you’re doing here is using a single dimension one-sided kerf correction to adjust by .0065“ while not changing the slot widths. This is a solid method, though sometimes kerf varies depending on your settings, material choice, and material thickness. This also leads to a slight asymmetry, such as if you’re doing finger joints, where one set of tabs will be slightly wider than the other. This can cause “handedness” in your designs where you have to be aware of which pieces are kerf adjusted and which are not while assembling.

I understand that this is YouTube and you’re probably shooting for 10 minutes ish to monetize so you probably didn’t have time to include how to determine the correct kerf value for your material. Maybe a good subject for a future video?

This sort of method is manual and destructive — for a simple single slot and single tab that’s the fastest method; with a larger box or with a more complicated design this method will struggle to scale, especially if you need to adjust the slots later. Do you have any tricks for how to handle more complicated set ups?

Again though the video is really good primer for people who have never done kerf adjustment before. If anyone wants more details they can study several of the longer posts that dive into the weeds(e.g. kerf testing, node management, serrated tabs, flip mating, hardwood vs plywood, box generators, stroke to path/offset, clones/modular design, and more. Kerf is a deep topic).

Further reading (and inspo for further videos in the series?)

Kerf testing:

KERF and Proofgrade Materials

Cut some kerf gauges, one out of each material. Then mate the two pieces to figure out what kerf adjustment you need in each material. Like these:

Node management:

Improving kerf adjustment on complex shapes

This is an inkscape-specific thing, but may apply elsewhere. Kerf adjustment is well-trod territory at this point, but I recently decided to see if there was anything to improve performance. The issue: when doing a “stroke-to-path” action on an irregular shape, you can sometimes see deformation of the resulting paths. The solution: add more nodes. The software is making a best-guess estimate, which you can improve with extra nodes. Illustrated: On the left, the original shape. On the righ…

Serrated tabs:

Serrated tabs - no more glue

I love design but I don’t much care for assembly. Why should you have to deal with glue when your Glowforge can make the fasteners for you? I did some experimenting with serrated edges on tabs, and the results have been terrific. Proofgrade plywood is very consistent in thickness, so when using it, you can reliably depend on a design with serrated tabs to go together with a few taps from a rubber mallet. I’ve printed a single serrated design from Proofgrade maple, cherry, walnut, and I think…

Flip mating:

Rounded Corner Box w/ stacked inserts

The thicker the material, the more pronounced the cut profile “sawtooth” pattern will be. This project is a lot like any other layered box with multiple parts per layer, and has the same caveats. Take a more extreme example like my space invaders box: The “pixels” aren’t squares because of the cut profile, and you can see it if you look closely. [IMG_5489] If you zoom in… [image] I flip-mated these layers to eliminate the gap but the misalignment is all down to the inconsistent pixel s…

On kerf and hardwoods vs plywoods:

Inkscape box generator

If you want them to dead line up, set the kerf to zero. But if you want the pieces to fit tightly, then don’t do that. Kerf adjustment intentionally offsets it so you can get a better fit. You’ve been around, so I’m sure I don’t need to explain what kerf compensation is. For most 1/8" woods, 0.006 is a nice place to start, it’ll work out as a tight glue fit. 0.007 or 0.008 will make it veer into “I need a mallet” kind of friction fits, which can be really cool but are hard to work with, esp…

Box generators:

Is there a free box building website

Here is a massive roundup that isn’t GF specific but is definitely what you’re after.

Stroke to path/offset methods:

Making Stencils from Recurring Patterns

This type of tutorial takes a good bit of effort to write up, you’re generous to post it. I think you might find the Inkscape command “stroke to path” (or its equivalent in other programs) very useful. All of the steps that involved exporting to a JPEG and converting it to an svg can all be skipped if you use those commands. Secondly the kerf for the glowforge is about 0.006” for most 1/8” materials. Your estimate of how much to correct for it is about ten times too large (your recommended cor…

Clones and modular design:

"Parametric" design in inkscape

No one: Evansd2: What’s that?! You want a super long Inkscape hack post? ON IT. So before I begin: This post in intended for people who are pretty familiar with Inkscape. If you don’t know how to modify nodes/paths, use clones, or rotate a guide, chances are you aren’t the target audience. That’s not to say that there isn’t something for everyone here, but just keep in mind that this isn’t intended as a beginner’s guide, so I will be moving quickly. My goal: take an older tab-and-slot de…

Gotta love the power of the forum — such a gold mine of information.

[eflyguy]

I test for each type of new material, or a new batch of existing, using a small simple “comb” like test piece. I will also re-run it on a sheet before any large print. I have very rarely run into issues following this practice.

[evansd2]

Yep, that’s what I was referencing in my kerf testing link. It’s a great method. It’s also the only way to really do it when you have two dissimilar materials that you’re trying to join, such as 1/4 inch plywood to 1/8 inch acrylic.

[timjedwards]

When I’m in “pure inkscape” mode I still use the stroke-to-path method. For more complex designs I sometimes leverage fusion360 and there you can define the width of your laser beam; it will account for that kerf when exporting the cut-ready .svg files.