Flame Finishing and working with Acrylic Edges

Hello,


After putting together a sump, having made many cuts on acrylic, I flame finished my edges. I tried Butane, Propane, and MAPP gas. I'd like to share what I learned through trial and error during my first go round so that others may not have to struggle as much:


Make cuts on thin pieces with a acrylic sheet cutter, and thick pieces with a table saw (they make special blades if you want to be picky, other fine tooth ones will work). If you want to stick pieces of acrylic together use an acrylic solevant as glue is not going to hold properly (IPS Weld-On #3 or similar). When your done file & sand the edges, then flame finish!


Here We Go: Flame Finishing:


I've tried Butane, Propane, and MAPP gas now. I've come to the solid conclusion that if anybody is looking to flame finish "heat treat" the edges of cut acrylic (aka Plexiglass) MAPP Gas is hands down the way to go! As a side note this Flame Finishing process is specific to acrylic and does not work typically well with other types of plastics. MAPP Gas Burns over 2000 degrees hotter than Butane & Propane. Yes 2000 over degrees! Now I'll explain why you should use MAPP Gas instead, and what you may expect if you use Butane or Propane, or even if you do not flame finish at all.


First: Why?.. You should flame finish your edges if you care for your wallet and the longevity of your piece because if you do not, small cracks or fractures may appear and although these may not initially show up, they may over time, plus if any stress is applied your risk increases! Flame finishing is a method of prevention, its not just for cosmetics, and is almost a must for drilled overflows! My research into the topic has indicated that any weakness or imperfection in an acrylic piece will be prone to the development of a crack. Cracks originating from cut corners on the inside of material, or from holes cut or drilled within the material will progress in the direction of the nearest other source of imperfection. So speaking specifically about drilled overflows this is typically going to be the corner joint or an edge. So it makes sense that if imperfections do not exist in the first place cracks will be less likely to form in the long term.


In regards to the flame finishing process specifically (How to Tips):


You will notice that unless your edge is sanded to a fine jewel (not 100% necessary but sanding is very helpful) there will be imperfections which will show up as "white" areas on the piece. If your working on a saw cut edge these are typically the areas where your saw blade took its next step. You should carefully touch up these areas, but should not intitially slow down when you notice them. (IMPORTANT) With any type of gas go back to them right away after you've finished the majority of your edge especially if you use Propane or Butane, do not allow the edge to cool down! NEVER HOLD THE TORCH STILL ON THE EDGE, always be moving!


Flame Finishing:


The instant high heat of MAPP gass at 3670 degrees F, needless to say "heats" acrylic very fast. MAPP gas is over 2000 degrees hotter than Propane which only slightly hotter than Butane. You will find that it's actually this extreme heat that its easier to achieve the desired finish without "burning" the acrylic. The desired finish of an acrylic edge is smooth and transparent, free of imperfections. If with any method your piece catches fire you should always blow it as close to instant as possible as bubbles will result and your edge shape will be altered.


Yes! Butane and Propane can get the job done and I will cover them as well.... but please do yourself the justice of obtaining a MAPP gas torch to treat your Acrylic (Plexiglass) edges, your results will be obtained much faster, be much more consistant, and save you from frustration!


YOU NEED: MAPP gas torch (and two cookie sheets handy)


You can expect the following results by following the provided suggestions:[/b]


The thicker your sheet, the longer it will take (have patience and don't get carried away). With sheets less than 1/8" you can and should progress VERY quickly! You should hit the edge head on flat to the edge of your piece, and therefore holes will be the most difficult areas to finish as you may not always be able to hit the edge straight on. Always aquaint yourself with your material on a scrap piece if possible, if not possible, start by keeping your distance, do not hold your flame in one place, always keep it moving along your edge. The reason for head at the proper distance is that otherwise one side of your edge is going to heat faster than the other and therefore it will be difficult to be consistant.


Propane or Butane: You will have to move along very steadily and will have to make several passes over a several minutes time, to do it right it took took me about 5 minutes, maybe more to finish the sanded edges of 1' of 3/8" acrylic, results were not nearly as consistant as MAPP Gas. You should NOT attempt to use Propane of Butane without carefully smoothing your edge with sandpaper, it will likely not work, will cause the edge to burn easily, your results can get ugly.


MAPP Gas: You should move as consistantly as possible, the piece will get very hot quickly and results will develop visably within seconds. Due to high heat a warping of your material is more likely to occur (especially on thin strips or material), so long as force is not present in that direction and it does not apear severe, it will straighten naturally as it cools without need for major concern. Note that if the warp remains after cooling its not likely you will be able to return it to perfectly flat. If warping does apear to be a concern, address it right away!! Definetly be prepared with two cookie trays, set one on a flat surface like your counter and sandwich your piece inbetween two cookie sheets until it has cooled.


Watch this short youtube video about working with Acrylic (Plexi) it will demonstrate the fundementals of flame finishing with MAPP gass, cutting thick pieces (with a table saw), and other ways to work on your edges (bevel, polishing, etc).





There are also many more videos on youtube about working with acrylic, check them out too!


Best of luck!

 

This is why we have a good discussion forum, thank you for your corrections! There's lots of people who say a lot of different things and coverage of this seems spotty outside groups of acrylic professionals. I have not personally seen the long term effects of flame finishing. I've only read others opinions. But I did go through the process on the pieces to my sump and it seems decent. Haven't done the overflow yet and and will take your advice. I unfortunately don't think my original post can be edited to recommend otherwise.

 

Which will crack or craze first: flame finished or no finish because if flame finishing is bad no matter what I feel like this should be deleted. Further your advice posted instead with a note explaining not to flame finish in such circumstances so that others are not misled.