2-D (spherical) kerf bends in MDF and Plastic

Using a laser cutter to create 1D bends is well known. But to make a bend in two axes simultaneously is a tough mathematical challenge.

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My main goal here is to make spherical or parabolic shapes. This is very difficult to do using kerf bending because of fundamental mathematical principles ruling flat and curved geometries, but I've had some descent success so far. I've written some basic code in C to generate .svg files, and cut out some successful prototypes on the 60W(?) Trotec laser cutter at Xerocraft.
  • First success in UHMW PE

    David Lesser07/24/2014 at 21:57 0 comments

    Last night I had my first success in forming an UHMW sphere section.  I made a 10" diameter circle from 1/8" (3mm) stock.  The center is roughly 1-1.5" proud of the edge.

    My main difficulty was simply with getting good cuts in UHMW- it tends to melt, and the high density of cuts in my part leads to significant thermal warping.  My successful solution was to screw the sheet into a peice of thick plywood for support (four screws around the edges, plus one in the middle).  I also ran the laser cutter extremely slowly (over 5x slower than our settings for similarly-sized acrylic or wood); this basically melts the PE and blows it away with the air-assist.  The kerf is relatively wide, and the surfaces (covered with masking tape) require some scraping to clean off, but the end result is surprisingly good.

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  • 1
    Step 1

    Download the stupid simple code from my server here. It's written in C. It ought to compile and run without issue on any flavor of linux with basic C libraries and gcc.

    At the moment, critical parameters (such as circle diameter and slot length) may be configured by changing the #define statements at the beginning of the code. Ugly, but effective.

  • 2
    Step 2

    The cut out shape is quite flexible on its own.  But to maintain a bent shape, ideally you'd soften the piece (both thermoplastics and MDF soften well with hot water) and press it in a "die" until it cools/dries/hardens.  The form I have in the pictures was made using a very simple CAD solid part imported into 123Make, which generates the files to cut out all the pieces.

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sibasaur wrote 03/31/2015 at 22:29 point

Neat proyect, however have you tried making "lines" along the lines that are the same "z" height, as for example a contour map

That way i think you could kerf any 2d convex shape, at least in my mind =O, try it =D

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David Lesser wrote 04/01/2015 at 06:04 point

Hey Sibasaur,

That's basically what I'm doing, only for the easy case where it's just a simple shape.

The other thing to do is to vary the length of the slits (longer arms are easier to bend) depending on the rate of curvature.

I think it would be super cool to write some sort of code to do that automagically, but the algorithm to do it right (i.e. avoid any kerf overlaps/intersections) seems quite difficult!

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