Flame Polishing Acrylic

Intro: 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.

STEP 1: 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

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

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.

Comments

[furtech]

Great Instructable! I had heard about this, but you explain the process really well. I can really use this, too: much better (and cleaner) than using a buffing wheel.

One suggestion: re-do the video and get a friend/helper to film it. Most of the time the process you were trying to show was completely off-camera

[steveastrouk]

Yes, good point. I have to repeat the original project soon, so I'll do it then.

[Bruno153]

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]

Yes, it will work, but on simple flat surfaces Metal polish works very well.

[veryken]

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]

There aren't any flammables around. That's a ceramic paper.

[iceng]

Beautiful table edge.
Our local plastic shop uses a Hydrogen flame.
I use a hot air acrylic welder at low setting.