Polishing Edges on Acrylic

[Mr. Sign Pro]

I'm having trouble getting a polished edge on acrylic. The material is 1/4" thick clear and we are cutting rectangles out on our router. The router gives us a pretty nice smooth edge but we still do some light sanding afterwards. We then take a propane torch and run it along the edge of the acrylic. No matter how long or how much we repeat this, it's just not getting polished enough. Anyone have any tips? Has anyone went the route of buffing the acrylic with a buffing wheel. I have about 14 smaller rectangles to do and i'm hoping to not have to get Gemini or someone else to do them for me. Thanks in advance.

 

[rjssigns]

I've sanded and polished acrylic the same way I do auto paint. Tedious and messy. Another way is to use a sewn cotton wheel on a stationary grinder and use the same compound sticks for metal polishing. Less messy(somewhat) and a bit safer.

 

[CES020]

It's not difficult, but a propane torch isn't the easiest to use for that. The quality of the edge will be directly proportional to the time you spend preparing it. What grit are you using? 320 is going to be fair, 400, especially 400 wet sanded, will put you in great shape. I never go more than 400 on things I flame polish and I flame polish more than I'd like to. I have a hydrogen micro torch that runs on water, lye, and alcohol. It's very slick and works fantastic for flame polishing.

If you do a lot of it, you might want to look into one of those. In the mean time, sand to 400 or wetsand with 320 or 400 and then polish it.

Just my opinion. Your mileage may vary.

 

[letterman7]

What's "polished enough"? A propane torch isn't hot enough - step it up to a MAPP or oxy/acetylene torch. Just keep the flame moving fast or you'll melt the piece.

 

[dlndesign]

+1 on propane, just keep it moving and you'll get the results your looking for. But always for good measure, have a smaller piece of the same material cut to test it out first.

 

[Techman]

chemical polishing is soo much easier and better. Plus it does not set up crack stresses.

 

[CES020]

chemical polishing is soo much easier and better. Plus it does not set up crack stresses.

Got any links to that? You're talking about something other than the stepped abrasive setup from Novus, aren't you? If so, I'd like to know more. I have a bunch of 1/2" to cut and flame polish next week and I hate sanding the stuff by hand. I'm getting too old for high volume repetitive movements

 

[johnnysigns]

MAPP gas is a must vs the propane if you don't have a heavy duty setup or plenty of sandpaper, a buffing wheel & rouge as mentioned.

 

[Z SIGNS]

We use this.
It is a torch head cannibalized from a neon crossfire.
It runs off propane,oxygen and air and puts out a very hot pinpoint flame.
We scrape the machine marks with a razor blade and then one pass with the torch.
Turns out looking like glass.

You can also scrape with a razor and spray a glossy clear coat on the edges.
Try it you will be amazed how it looks

 

[signsofparadise]

Hydrogen and oxygen

The really serious way to do this is with Hydrogen and Oxygen - this burns much hotter and its a cleaner burn. I had asked Curbell Plastic years ago and I was told the Oxygen Acetylene burns dirty and is impure whereas Hydrogen mix isn't. You can find out more on the Web and Youtube etc...

 

[CES020]

The really serious way to do this is with Hydrogen and Oxygen - this burns much hotter and its a cleaner burn. I had asked Curbell Plastic years ago and I was told the Oxygen Acetylene burns dirty and is impure whereas Hydrogen mix isn't. You can find out more on the Web and Youtube etc...

That's what we use. It's a tiny, very hot flame.

 

[Techman]

ever wonder how they get plastic lenses to be so smooth and clear?

They use a chemical process to polish the lenses. The lenses are ground to the shape they want. The finish is like an opaque sand blasted surface.

They place the plastic lenses into a small tank filled with a specific solvent and let it set for a short while. The surface soon becomes absolutely clear and micro polished. It goes from a matt finish to a glossy water clear optically perfect surface.

However, You must be sure not to breath the solvent. It is said to be safe but. I wouldn't trust it. If it can change plastic it could change your lungs.

Flame polishing polycarbonate fails because there is moisture in the plastic. Flame will cause micro blisters.
Flame polishing acrylic fails because it sets up heat stresses that very easily fail into micro cracks. Add some cleaning solvent to clean it and suddenly you have a ton of cracks on the edge.

This stuff is magic. You make a shallow bath and a cover. Set up something that will hold the part just above the liquid. Nails with points up will work.. Pour in just enough liquid to wet the bottom plus a little more. This stuff evaps very fast. Put a cover on it and wait a short while. Do not breath it.

There are hundreds of ways to vapor polish the edges this is just a suggestion to get started. Once you get it right you will never again flame polish anything.

I recently polished my old headlight covers. They look like new again.

 

[SignDesignExpert]

The Museum Way

I'm having trouble getting a polished edge on acrylic. The material is 1/4" thick clear and we are cutting rectangles out on our router. The router gives us a pretty nice smooth edge but we still do some light sanding afterwards. We then take a propane torch and run it along the edge of the acrylic. No matter how long or how much we repeat this, it's just not getting polished enough. Anyone have any tips? Has anyone went the route of buffing the acrylic with a buffing wheel. I have about 14 smaller rectangles to do and i'm hoping to not have to get Gemini or someone else to do them for me. Thanks in advance.

Worked in museum display business:
Scrape with sharpened scraper (like wood workers use.) Sand with a D/A using stepped grits until you get to 1200 then 3200 grit Adhesive-Backed/PSA Discs. Then the cotton pad with medium then fine polishing compound on it. In the end you will have an edge indistinguishable from the face.

Large cost of setup - not that hard once you get the hang of it.

Anyone interested - I'll send you the name of the company that does this if you need that quality - prices will surprise you compared to buying a sheet and using only a little.

 

[DChorbowski]

One thing i didnt see mentioned: You want to work with cast acrylic, not extruded. The extruded is under pressure like tempered glass I believe. When you sand or polish it and it heats up, you create a heat differential which can cause stress fractures. Cast acrylic does not do this.