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Modeling Parts for 3D Printing with Shortcuts

A while back the kerf plate on my chop saw got damaged. It’s not a well known make (at least, not to me, it’s a “Rexon M2500AE” that I got second hand), so sourcing a replacement wouldn’t be trivial. As time has gone on, it’s got more and more damaged, to the point that the saw is getting dangerous to use.

Kerf plate damage

So rather than use it in it’s increasingly dangerous state or replacing the saw, I decided to try and make a replacement on my 3D printer.

First stage is to build a model of the plate. This first required me to reassemble the parts of the plate, which I did by supergluing the parts I still had back together.

Glued kerf plate

Rather than spending ages modeling it from measurements, which might prove a little bit more difficult given the state the plate was in, I decided to speed up the process quite a bit by scanning the part.

Plate on scanner

Not that I have a scan of the part I can import it into Inkscape, square it up and model the outline using bezier curves. In this case as the part is mirrored I could create one half and mirror it. Due to the damage to the center slot it was hard to gauge it’s width (more on that later).

Copying shape with Bezier curves

The outline could then be competed by mirroring the outline.

Outline complete

The bezier curves can then be combined and the internal features diffed from the shape to form the full outline.

Complete shape

Before going any further, the outline was printed on a standard printer and compared to the actual part. The shape could be massaged a bit at this stage to try and ensure a reasonable fit.

Comparing printout with plate

The shape was then converted to STL using the Inkscape extension paths2openscad and opened in OpenSCAD. For some reason the extension adds odd scaling to the part so this was removed (shown commented out in the below screen capture).

Initial part in OpenSCAD

Before printing, I needed to add the recesses to take the screw heads. I decided to do this by tweaking the outline and exporting this separately from Inkscape.

Outlines with and wihout screw recess

I then combined the paths in a single OpenSCAD source file with different heights to fully model the recesses.

Model with recesses

Now that the model was essentially complete it was sent to the 3D printer. I elected to stop the print after the initial outline had been printed and compare the main dimensions it with the actual part. I’m glad I did this as the part was approximately 2% over sized, so I was able to rescale the part and resend it to the printer without wasting lots of filament and lots of print time.

After rechecking the part outline again, the final print was left for 2.5 hours to print.

Orignal and printed parts

The part seems to have come out reasonably well and fitted the hole without any large gaps or fettling to fit the hole. The slot in the middle of the plate turned out to be a bit slim for the blade I have in the chop saw, but this will resolve it’s self nicely when the chop saw is next used.

Fitted 3D printed part

This only took a few hours to complete from start to finish, with a large proportion of the time required being the printing of the part. I think this really shows on the of the strengths of home 3D printing, helping to create parts that can be used to bring life back into broken objects and creating items that just aren’t otherwise available.

23 Feb 2019 #3D printing