3018 CNC Engraving acrylic

I decided to collect in a post the keynotes I learned when I’ve been facing with the problem of engraving acrylic. Most of them came through try and error, others thanks to valuable info found online. I’d like this section to be more of an open one, with comments and suggestions, as my experience with CNC is very limited and has been always goal oriented (merely I started just to achieve better finish of my home cockpit panels and panel cases), so I’m just an hobbyist and by no means an expert!

Material

When it comes to engraving acrylic, the starting point is for sure the material to engrave. In the market there are sheets which have a black face and a white one. Those are the best fit to engrave panels like the one above. They have nice chip removal performance, and milling can be very precise.

Design

Most of the time this step is not even considered, while in my opinion is among the most important ones. A good quality vector tracing is of utmost importance to achieve a good final result. It is definitely the part to which I dedicate more time.

For vector tracing I use Inkscape, it is really a great piece of software and is free. There is a big community, and a lot of tutorials available. A broader description would take us off track, but among the most interesting performance: great point control, possibility to overlay images, great to have a starting point, flexible export, and, as already said, a huge community!

As a general consideration, most of the times one wants to engrave text. Most fonts perform poorly when engraved, because the bit will try to follow the external part of each letter. There are few single pass fonts available, but a versatile way to deal with the problem is to create an offset of the track (to the inside), so to take into account the amount of material that will be removed on both sides during cutting.

When I’m happy with the result I export it to CAM.

CAM

A versatile CAM, is nice to have, but there are some good (free) alternatives on the web, which can be fairly good if the starting file is a good quality vectorial image.

As far as engraving is concerned, there are several things to consider:

• bit : the V-Cutter is a good starting point for engraving text, its angled V shaped bit can be very precise. It is to remark here that depending on the tracks you created (in particular for text), also different choices can do the job (single flute mill for instance). In the landing gear panel above, for example, I engraved the text with the V-Cutter, while the pads of the emergency jettison, down lock release, and hook release, as well as the synoptic representation of the viper, I used a single flute mill for acrylic.
• Depth: that’s a tricky one, as it depends so much on your setup, so take this info with a grain of salt. For my setup, I found that 0.4 mm depth provides a good balance for details definition such as text.
• spindle rpm: we will be removing a tiny bit of material, and usually in one pass. Therefore the spindle rpm shall be chosen so to provide enough cutting force, but the lowest vibrations level possible (particulary true for low cost CNC as the 3018). Adjust your spindle speed and feedrate to achieve the lowest vibrations possible.
• spindle feedrate: the action required to the spindle is fairly low, the material is dull, and only a small amount shall be removed, therefore fairly high spindle speeds can be used.

GCode

As far as G-code is concerned I’ve not so much to add, as I use the default grbl control software.

CNC

As far as engraving is concerned, there are several things to consider:

• bed levelling: we will be removing a tiny bit of material, so it is very important to have the bed levelled, or (better) to use height maps.
• be patient: I usually practice with a small detail / small piece, until I find the combination of parameters I’m happy with.
• step by step approach: particularly true for cheap CNCs, I divide the job in different sub tasks, such as, start with the text engraving, then focus on pads and holes, finally cut. They involve different tools, and most of the times they allow to correct errors.