How to Flame Polish Plastic




Have you ever used plastic sheet in a project before? It looks really cool, but it can be a pain to make look perfect. This guide will show the basics of polishing plastic using fire. It will create a polished edge that will catch the light in a very brilliant way. All of the tools used in this guide are available at TechShop.

What you will need:

Plastic (I used acrylic) Special Note : Do NOT try to flame polish polycarbonate, it will bubble and will be ruined
An orbital Sander
At least 100 grit sandpaper, I reccomend going up 300
a propane torch (this can be picked up at your local hardware store)
some form of tape that can be used for masking.

Step 1: Preparing Your Plastic

This scrap piece of plastic has no protective film on it. It is important to keep your plastic protected as often as possible to avoid scratches. I used blue painters tape to re-mask the unprotected areas to avoid scratching in the future steps

Step 2: Sanding

Using an orbital sander, gently remove disfiguring marks from your plastic. Make sure to keep your sanding wheel at a 90 degree angle the entire time to avoid rounding out the corners of your sheet. Rounding out the corners and edges of your sheet will cause distortions on your plastic.

Step 3: Prep for FIRE

Remove the film on your plastic or any masking you have applied. If these are not removed, they will burn and adhere onto your sheet ruining it. Carefully wipe down the areas which you are about to flame polish with a micro fiber cloth to remove any debris. Clean plastic is happy plastic!

Step 4: FLAME Polish

Here is the tricky part where some skill is involved. The basic goal here is to essentially use the fire of the torch to melt the plastic, without burning the plastic. Burning plastic is characterized by bubbling and black specs. If you burn your plastic, sand off the damaged material and try again.

Place your plastic onto a non-flammable surface. I used a cleaned welding table. Pull the plastic out so the edge of it is hanging. This will keep it from melting a little bit and picking up the texture of the surface it is resting on. Turn on your torch. Since you are using a propane torch that produces a carbon monoxide gas, make sure you are using this tool in a well ventilated area.

You generally want to flame on your torch to be strong. You want to use the crisp,blue, inner flame to actually polish the plastic, but you should always be aware of the rest of the flame because of its ability to interact with your plastic. Now, with the lit torch, very quickly move over the areas you want to polish. This motion is almost like quickly brushing hair. You want to move fast so you do not burn the plastic. The plastic will retain heat energy, meaning that the more passes over the plastic you do with a torch, the more potential there is to burn the plastic. in addition, because of this energy being put into the plastic, there can be a tendancy of warpage, just clamp down the plastic (away from the areas you are polishing)

You will know when you have done the right thing with your plastic when it reaches its polished finish. I almost looks like a bead of water is running across your material when is it reaching the appropriate melting point. In the final image, i have a picture with what a polished area looks like (on the left) and an unpolished area (on the right). As always, it is best to test your skills first. Grab a piece of scrap where you can refine your skills.

You now have a piece of plastic with a finished edge.



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    10 Discussions


    7 years ago on Introduction

    Torch polishing works but actually polishing achieves optical accuracy. Which is to say it just comes out better. So put down the torch and just grab some polishing compound and do it. It is a bit more work, but the results are worth it.

    4 replies

    Reply 7 years ago on Introduction

    I disagree, the best result come from what tool the user is best skilled with. Plus, fire is way more fun!


    Reply 7 years ago on Introduction

    Your opinion varies from professionally qualified ones. I think I'll side with the pros. In fact I know I am. Flame finishing plastic is a neat trick, but mechanically inferior to polishing. Whether you agree or not is irrelevant.


    Reply 7 years ago on Introduction

    I feel like you are not grasping the point of this instructable, which is not about what type of polishing technique is better, but is only about how to flame polish plastic

    Continuing in the direction of this conversation, I am not sure why you would have to side with a pro on about how to have more fun, but as someone who has worked and continues to work professionally with plastics, I can tell you that fire is indeed the more fun process :)

    In addition, the best result will always come from the tool a person is best with.


    Reply 1 year ago

    well said. ive been struggling with getting this plastic clear (after sanding off the text printed on with 1000, 1500, and finally 2000 grit sandpaper) i can get as good as "hazy" but no matter what polish/compound/wax i use i cannot get that high gloss finish i desire. there is a mini benzotorch here that i was going to use, but i supposed i should just wait to use the larger flame to get it with as few passes as possible. my plastic is about 1/32" thick (so its not thick at all lol)

    additionally, i would push pfred2 to cite where his information came from (and not just say professionala). perhaps the answer for clear plastic lies somewhere in between.

    There is a youtube video that says that a propane torch doesn't get hot enough and you need a MAPP gas torch. Maybe that's why his results were less than optimal.


    7 years ago on Introduction

    Although I haven't seen optimal results from torch polishing, I'd have to agree with pfred2. The best results come from the best tool for the job in skilled hands - your end results (as seen in the pics) do show scratches. You'll (likely) never get better results than using buffing wheels & compound - plus, far fewer ruined material. Yes, fire can be fun, but in this case there's a better way.
    Having said that, if a torch is all you have... fire it up!

    2 replies

    Reply 7 years ago on Introduction

    Meh, my piece I was polishing was some scrap that was only sanded to a 120grit. Had this been a piece of plastic I cared about I would have sanded it to at least 320grit and then flame polished. That makes it look plenty slick


    Reply 6 years ago on Introduction

    I am confused as to why you didn't show or detail this in your instructable, may people just look at pictures would see your end result and think that's not giving a great finish. You may not care about the plastic but you could care about the instructable.