kerf bending patterns

I recently discovered that kerf bending is perfect for building small cases.

Take a pice of plywood, cut out a pattern along the curve you want to shape and apply some hot water to the outside face of the bend, et voila. The cuts weaken the integrity of the material making it able to bend without snapping. Well, I tried some more patterns…

 

For the transmitter case I tried dashed patterns. Unfortunatly the cuts were too far apart. The bend was under a lot of stress. I decreased the spread and it now bends very well.

pliability: very good
tensile strength: good
torsonal strength: good
normal strength: very good

 

 

 

 

 

This is a herringbone pattern. It does work quite well. I underestimated the waste of the laser so the pattern breaks in some areas.

pliability: good
tensile strength: very good
torsonal strength: very good
normal strength: very good

 

 

 

 

 


Here is a good old midevil cross pattern. It’s a little hard to bend but once it’s in place it holds up nice.

pliability: fair
tensile strength: good
torsonal strength: fair
normal strength: good

 

 

 

 

 

 

This is the diagonal cross pattern. I would’t reconment using it. It bends really hard and breaks very easy. The biggest problem is, it doesn’t evenly bend due to its diagonal grid.

pliability: very poor
tensile strength: good
torsonal strength: fair
normal strength: good

 

 

 

 

 

Here is my favourite one made out of a few rows of space invaders. It is very delicate but in the end it does bend.

pliability: fair
tensile strength: good
torsonal strength: poor
normal strength: poor

 

 

 

 

 

You can actually use whatever pattern you like as long as the pattern isn’t diagonal to the bend. Just tinker around a little. It all works to some extend. The problem with these tests is definetly the size of the bend. The radius is only 8 mm. The space invaders are a little too small for the laser I used. I could see this being awesome in a bigger scale.

 

 

 

 

 

 

If you want to try it yourself here’s the CAD file.

25 comments on “kerf bending patterns”

  1. anglo says:

    Very nicely done ,and the site is almost professional .
    question: Have you experimented with stopped cuts using the laser ( e.g. a slit that DOESN’T go completely through , leaving the surface unmarred ) , rather like this : ————-^-^-^———. or is even possible? ( old wood worker with no laser yet )

  2. Thank you anglo. You should be able to do blind cuts, at least you can engrave things. It’s probably just a matter of focus and/or speed of the laser. Unfortunately the folks at the universities workshop are rather strict about the settings of the machine making it impossible for me to try.
    I guess for “just” bending wood all you really need is a table saw but the laser is perfect if you want to work with graphical patterns.

  3. padde says:

    Yes, it bends!

  4. Brian Queen says:

    So can you tell us the length of each cut line and the spacing between the parallel lines? Can you confirm when you use the water, I presume after the laser cutting? Then do you let it dry in the bent position? Do you think the length of the cut line the spacing between them should very depending on the radius of the bend? I’m experimenting with this technique as the spine of a book, nothing new but one thing I noticed is that the grain must be parallel with the cuts, basis woodworking, but even then I get failure or cracking of the 3mm birch plywood. Of course I’d like the spine to bend for a good long time without cracking. Thank you in advance.

  5. Hey Brian,

    the length of the cuts don’t matter. What matters is the spacing between the cuts. If the cuts are too far apart, it won’t bend, if they are too close, the whole thing becomes instable. There is some math to calculate this but I didn’t really bother. All in all it breaks down to the thickness of the material and the radius of the bend. You could check out the cad file to see how big my spacings are.
    Yes, you would use water for the bending process after you made the cuts. The water softens the fiber of the wood so that it won’t break under stress. Bend it to your likes and let it dry in the bend state. It works even better if you’d use water vapor instead of just water.
    For durability, you could glue some strechable cloth to the backside of the spine (the inside of the book). You could even pick your favorite color 😉

  6. Timo Rybicki says:

    Hi, thank you for the pattern experiment and the file. I will try the pattern from your transmitter case on a 1,5mm aluminium sheet for a little case I´m building.

  7. Hey there! I guess you wouldn’t really need kerfbendig for metal. (it will bend on its own)
    But it sure will look great! Please send me some pics when you are finished 😀

  8. Stafford Flood says:

    Hi there thank you for the info its been a great help to me.
    When one bend a piece of wood that has kerfs, what radius does this take? I guess the outside would be stretched but the inside would be compressed. So therefore the centre of the wood would remain the same length. Is my assumption correct?

  9. George says:

    Hi, I’m trying to make a curve of 50mm in radius, the problem being that I can’t import the PDF file into the cad (2D Design) thanks.

  10. Hey George,

    it should be no problem for your CAD program to import PDFs.
    (What software are you using?)

    Maybe you can convert it to something you can use with inkscape?
    https://inkscape.org/en/

    But if you really have a specific bend in mind you might as well go ahead and design your own CAD file. I just added the pdf as a reference. 🙂

  11. Nataly Riquelme says:

    Hi,
    Did you create all these patterns?

    Thanks for sharing your work, I’m collecting design patterns for an investigation of my thesis . I apologize for the translation. I’m from Chile 🙂

  12. Hey Nataly,
    yeah I created those patterns.

    What’s the topic of your thesis? Will you publish your work later? I’d love to see what you found out.

    Cheers from cold germany 😀

  13. Dave says:

    Working with 3.6mm Birch Ply, with straight cuts like the top photo, sideways separation 1.5mm, end to end separation of 3mm, I have managed 180 deg bends with internal radius 12mm (round a former to help shape it). About 10% of them snap if I’m not careful. The piece is 100mm wide. Also works well with 3mm mdf. Perspex tends to shatter.

    Any ideas how I can get a smaller radius with ply and mdf?

    Thanks.

  14. Hey Dave,

    steam it! Should be working great for plywood: https://www.youtube.com/watch?v=e4CoTNeoa98

    Not so sure about MDF though, since it’s mostly composed of resin binder.

  15. Greetings,
    awesome technique can i use this to bend a 6mm plywood i need to create a short booklet of size 16mm x 21mm when folded. could anyone please help me figure it out i m running out of time and need to submit it ASAP

  16. Kim says:

    Thank you for sharing this information! Thank you for the detailed explanation and answering the questions!! Can’t wait to try it with my laser!!!

    Laser Engraving by Kim (on Facebook)

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