# Experimenting with 3D printed inlay

This thought had been bouncing in my head for a while, so I had to get it out of my system. The idea behind doing a PLA inlay is that it gives me a lot of creative flexibility given the variety of filaments available. I can have the 3D printer doing the inlay while the CNC is carving the main part. I can sand/finish the PLA surface before using it. One thing I want to try is using “wood” PLA and simulating wood grain with stain.

For this first attempt I used OpenScad to generate the ‘inlay’ (just a letter ‘M’), export that as a DXF for ESTLCAM.

In ESTLCAM, I used the 1/16 flat bit to carve a 2mm deep ‘part’ as a hole, which basically also cuts right outside of the perimeter of the letter. This leaves a gap all around with a width equal to the radius of the bit (as expected). It’s still something I could use (see first picture).

Next experiment (which I haven’t done yet) will be to use the offset and minkowski functions in OpenScad to round the corners to match what the 1/16 mill will do. The code for the inlay would be something like this:

```\$fn = 50; linear_extrude(height=2) minkowski(){ offset(delta=-1.5) scale([2,2])text(size=40,font=“Old Town”,text=“M”); circle(r=1.5); }```

Translation:

• I take my shape (in this case the text) and offset it inwards by the radius of the tool
• Then, I use minkowski to combine it with a circle with the same radius
In ESTLCAM, I'll just do a hole carving with the 1/16 mill (2nd picture - haven't done this yet)

The result is my original letter, but with the outside corners rounded in the same manner as those of the cavity.

I’ll post the results once I finish.

That is a neat idea. As someone who loves 3D printing and cnc, I would be very excited to see the final product.

For most inlays, you would cut each part with a draft angle and sort of wedge the part in, then sand off the excess. If you can get a good fit without sanding though, you aren’t limited to flush on the 3D printed parts. You could add texture or structures to the top. You could even do something fun like inlat the word CASTLE and have the tops of the printed parts have castles or at least castle edges. All kinds of possibilities.

I love it when things work better than expected (which isn’t often).

The fit was very tight, so I placed a block of scrap wood on top and hammered it in. The result is pretty seamless. Couldn’t even fit an Xacto knife between the inlay and the wood (no need for glue, either!)

In my test, I made the milling depth equal to the 3D print height, so after sanding it’s flat. One cool effect would be to make the print taller for a raised lettering effect.

The first picture is after I hammered it in:

[attachment file=107897]

After a quick sanding:

[attachment file=107898]

There are a few white blotches from sanding the PLA. Next time, I may try sanding and painting the PLA before hammering it into the wood.

Finally, I sprayed on some Polyurethane (not a quality job here, just wanted to get an idea about what the end result would look like):

[attachment file=107899]

For reference purposes the letter is 7 cm high (about 2 3/4")

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That is an amazing fit. Super cool experiment!

This came out great, awesome stuff. Did you have to fuss around with print shrinkage to get the fit just right or did you oversize one undersize another a little to get it right?

So to be clear, it’s not a “v” style inlay? If not that’s an impressive fit, lol

When I have some time, I’ll try to do a write-up of the process. It’s not a V-bit inlay. I just use a flat 1/16" bit for the carving. With PLA I have not had an issue with shrinkage. I did a second experiment where I offset the cut by 0.1 mm and the inlay went in without needing a hammer. In that case, it was still seamless, but I would have needed glue as the inlay could come out on its own.

In my second experiment, I used an inlay pattern that was about 150+ mm. Once I fixed a misconfiguration of the steps per mm for the X axis of my 3D printer, the fit was perfect (I measured the sizes produced by the MPCNC and the 3D printer with calipers, and they were spot on).

So, again, I’ll try to write a more detailed explanation/procedure, but what I basically did is use Openscad to generate the DXF for the CNC and the STL for the inlay, and used Offset() to give me a slight margin to make it easy to insert the inlay in the wood (but still not visible to the naked eye), and also to round the outside corners of the inlay to match what the CNC will do.

The biggest advantages I see in this process are 1) the CNC and 3D printer can work in parallel, possibly saving time, and 2) greatly simplifies the overall process of doing an inlay (though it will not be suitable for all situations).

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It will save a lot of material too. If you cut an inlay out of an otherwise useful board (or chunk of plastic), you’ll be left with a lot of waste.