The ability to cut intricately designed parts go hand-in-hand with CNC machining. Popular among these pieces are “inlays” – parts that are carefully cut from one type of material to be fitted into another part. Regardless of the material you use, cutting a high-quality inlay is not as easy as it seems. Many aspects of machine construction, programming and operation can affect the outcome.

When done properly, they can be very impressive and long lasting. Take signmaking, for example. When inlays are cut to fit a series of letters cut from a colour like red acrylic into a background panel that’s black, your sign is going to pop and get noticed. Does this sound like something you’d like to do? Then follow these tips to get the best quality inlay possible.

1.    Invest in a high-quality CNC machine

Best results will be obtained by using a machine that has ball screw drives for zero backlash and strong, rigid bearings for straightness and squareness. On any of the Pacer range of machines, it’s possible to cut inlays in any position on the machine bed to achieve that perfect fit. Pacer machines use high quality ballscrew drives and bearings and are driven either centrally or on both sides of the machine to ensure squareness.

                   The AXYZ Pacer Heavy Duty CNC Router

2.    Use an Automatic Corner Radius feature 

For a professional finish, it’s important that the parts fit together perfectly with an even fit all around. Depending on the materials, a small ‘gap’ needs to be left between the inner and outer parts so that they can be assembled. If working with acrylic, a typical gap will be approximately 0.1mm. Using a good machine control system can save hours of filing. If it has an Automatic Corner Radius feature, the machine will automatically cut the correct radius on all the outside corners of the inner section so that the parts will fit perfectly.

3. Measure tool diameter for correct offsets

If the cutter you’re using is not accurate, you’re going to have problems with the fit of the two parts. This is usually a result of the cutter’s diameter not being what it should be, so adjusting the offsets is required to get the parts to fit properly. If the cutter is not exactly the diameter it should be (and this is quite common) then the offsets will have to be adjusted accordingly so the parts can fit properly.

4. Adjust offsets using the right software

If we’re using a 6mm diameter cutter, do we just need to cut the inner part of the inlay with an outside tool offset of 3.05mm and cut the outer part with an inside tool offset of 3.05mm? DEFINITELY NOT! This isn’t going to work because the outside corners on the inner part will be sharp whereas the corresponding inner corners on the outer part will have a 3mm radius – its impossible to cut sharp internal corners with a routing cutter!

Alternatively, a good procedure to use is to cut the inner part of the inlay first and remove it from the machine. Then, cut the aperture in the outer part, with the tool offset set a little larger than you think it should be, and leave it on the machine with the vacuum bed still holding it firmly in place. Now you can test the fit of the inlay and if its too tight, the machine can be run around the job again with a slightly smaller offset to open the aperture up a little before re-testing. Once the correct settings have been determined the rest of the job can be cut with confidence. Of course, this approach is only really feasible if you have the toolpath generation software running on a machine control PC next to the machine – like with Pacer’s XMC-E where adjusting offsets and re-cutting takes only a few seconds.


  1. Cutting an aluminium inlay
  2. Cutting an acrylic inlay


If you need further information on cutting inlays or any other CNC application, call a member of your Local Customer Care Team.