Instructables
Picture of Flame Polishing acrylic
As part of a new Instructable, I realised I would need to use a technique I haven't seen documented here before, and that is the flame polishing of thermo-plastics.

Its not hard to do, but requires access to some fairly special tools, ideally an oxy-propane or oxy-acetylene torch.Here, I am using a "Jewellers" scale torch which seems to be fine for my size of work.

Polishing works by locally melting (NOT burning) the surface, and the low viscosity of the melt and surface tension in the liquid plastic does the rest.
 
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Step 1: Preparation.

Picture of Preparation.
You can see here how "frosty" the curved edge of my workpiece looks, after being routed out. Preparation began with a light sanding to remove the more egregrious saw and router marks.

Next, I take a "naked" Stanley knife blade, and use it as a scraper, to plane off the protruberances.

Step 2: Scraping

Picture of Scraping
Just like the very finest wood finishing, scraping acrylic produces a very smooth surface, which is perfect for the final finishing. To scrape the edge, hold the blade perpendicular to the surface and drag.

The noise isn't pleasant, but the work gets the job done quickly. You can see in the picture, the snow like planings coming off the work.

Step 3: Flame polishing

Flame polishing is a fast, steady process. A very tight flame is passed quickly, and at a constant speed down the work. Here's a video of taking a pass down one edge.

Step 4: The final result

Picture of The final result
And finally, here's the result. A fine polish round the whole piece, in a few seconds.

Stages
  1. Preparation: remove saw marks
  2. Scraping: remove prep marks
  3. Flaming: remove scrape marks
Time, for 4 edges 600 x 400 mm (2 feet x 16"), around 15 minutes.
Bruno1539 months ago
I've seen that everyone uses this method to finsh the edges, but is it possible to use the flame to remove some scraches on the normal surface?
steveastrouk (author)  Bruno1539 months ago
Yes, it will work, but on simple flat surfaces Metal polish works very well.
veryken2 years ago
Nice edge. FYI, I polish my acrylic with a regular hand-held propane torch. MAPP gas cylinder gets a hotter flame, but not necessary. By the way, it's good idea to torch away from open cans of liquid flammables and workbench rags.
steveastrouk (author)  veryken2 years ago
There aren't any flammables around. That's a ceramic paper.
iceng2 years ago
Beautiful table edge.
Our local plastic shop uses a Hydrogen flame.
I use a hot air acrylic welder at low setting.