I’m often asked for suggestions on how to get a clear routed edge finish on acrylic.  ZThis is usually an application for displays, awards, and advertising specialties where the edge of the product is exposed.  It needs to have a smooth, fully transparent, glass-like appearance. 

This can be achieved if you follow these steps:

1. Cast vs. Extruded Acrylic

Start with cast Acrylic.  Extruded Acrylic will have an opaque edge finish.  Cast will have a crystal clear edge, but it will cost more.  However, cast Acrylic also has the following properties that make it a more desirable material to work with:
•    Thermal stability, meaning less melting and clogging of tools
•    Solvent Resistance, allowing less crazing when exposed to cleaners
•    More scratch resistance
•    Available in more colors

2. How Fast for RPM Settings?

For best results, you should be using an HSK Tool Holder, or better, for routing this job. This tool holder provides far less chatter which means smoother results. 

An rpm setting of 32,000, or higher, gives the routed finish a smooth and clear appearance.  Make sure the bit is solid carbide and made for Acrylic.  I’ve seen excellent results with a single O flute up cut bit. Check with your tooling vendor for the best selection.  

If this job can be done in one pass at 32,000 rpm, polishing will probably not be necessary, depending on the quality you are trying to achieve. Unfortunately, most spindles have rpm limits of 18,000 or 24,000. Therefore, polishing will be necessary.  Because of its thermal stability, flame polishing is a bit challenging with this Acrylic. The best method is to use a polishing bit to finish the job at the router.  The polishing tool path needs to be set at 16,000 to 18,000 rpm.  Again, check with your tooling vendor for the best settings and polishing bits.  The polishing bit should cut into the material .1mm -.2mm.  You also need to overlap the tool by 1mm.  

3. Watch the Feed Rate

The best feed rate for Acrylic is anywhere between 75 and 300 inches per minute.  This depends on the diameter of the bit (to prevent it from breaking).  A 1/8” bit should be set somewhere between 75 – 100 ipm.  A 1/2” bit can be set between 200 – 300 ipm.  Again, because of its thermal stability, cast Acrylic is less likely to melt, even at slower speeds, like extruded Acrylic has a tendency to do.  

4. Depth Setting? Times Two

Setting the depth follows the same general rule as always. Set the depth approximately 2 times the diameter of the bit being used.   When routing in multiple passes on thicker materials, there will be a line in the finish for each pass you cut through the Acrylic.  This requires a polishing bit to finish it off even if you can set your rpm to 32,000.  

5. Deionize Before Starting

The chips, particles, and dust created from routing Acrylic, have a very strong static charge.  This debris will adhere to the cutting edge, material surface and bit while routing.  If it is possible to configure the router with a deionization unit, this will neutralize the static charge on these particles and allow the dust collection system to remove the debris much more efficiently.  This prevents particles from being reground, or melted into the cutting surface, allowing for a smoother and clearer finish.

I would love hear your ideas or questions on how to improve routing acrylic and other plastics.


Lance George is Plastics Division Manager at Biesse America. www.biesseamerica.com
 

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