blueonblack
04-28-2008, 06:37 AM
Ok, so you're building something (anything) with plexiglass and one or more of the edges will be visible. You need to make it shine. There are a couple of ways to achieve this: flame polishing and sanding.
Flame polishing has a couple of advantages over sanding. It is much faster and once you get the hang of it, much easier. However, no matter how practiced you are at it, you run the risk of badly damaging your project, and no matter how good you are at it, it will never look as good as a sanded edge.
Let's look at sanding. Yes, sanding sucks. I have yet to meet anyone who enjoyed it. Unfortunately, it is all too often a necessary evil. This tutorial will focus on plexiglass, but the same principles apply to any material that lends itself to sanding, and there a great many of them.
Sanding is nothing more than scratching. By moving from lower-grit coarser sandpaper up to higher-grit finer paper, we just make the scratches smaller and smaller until they are no longer visible to the naked eye. One of the most common mistakes made in sanding is sanding too much. Yes, people hate this with a passion and yet many will sand twice as much as they have to. The key is grit.
The grit that you start with will depend on the condition of the original piece. Take the edge I am working with here:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-13.jpg
This is a really rough edge, left by whatever cutting machine the plastic shop I got it from uses. I could have smoothed it out a little with the blade I have on my table saw, but in this case there is no need. I am going to round this edge over for my purposes with a router and a rounding bit:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-1.jpg
Looks better, but still pretty rough. Here is where we determine what grit to start with. One of the reasons a lot of people sand too much is because they start with a grit that is too high for the job. The higher the grit, the smaller the abrasives and the finer the scratches. We want a grit that will cut scratches as deep as the ones we already have, so we can level off the top of the plexi down to the bottom of the mill marks. We can't add material, so we have to take it away. In this case, I chose 150-grit to start, which is pretty coarse. After:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-2.jpg
Notice the scratches are still highly visible, but now they are running the length of the piece, instead of across it? This brings us to another thing that causes a lot of people to sand too much. You should only sand with a given grit as long as you have to. Sounds simple, but you'd be surprised how quickly that point is reached. After some practice, and really paying attention to how the sandpaper *feels* when you're sanding, you'll probably notice that after just a couple dozen strokes it will stop feeling any different than it did on the last couple of strokes. That's the end. Stop. Wipe the dust off of your project and inspect it for any singular spots you may have missed, but overall, you are done with that grit. This only applies if you started with a grit that was coarse enough to begin with, otherwise you are still trying to get those deep mill marks out with shallow abrasives. If the piece is uniform, move on. In this case I moved to 220 grit:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-3.jpg
Much finer lines. That's the point. Follow the above and move to 400 grit:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-4.jpg
Then to 800:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-5.jpg
Then skip a grit to 1500. With plexi you can get away with skipping grits at the higher levels, not so easy with metal. In this case, since I was using wet/dry sandpaper (more on sandpaper later) I chose to use Mother's Chrome Polish as the wet portion. You can use water if you like, but I find that the tiny abrasives in the chrome polish give better results.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-6.jpg
http://i452.photobucket.com/albums/qq245/techreview/Untitled-7.jpg
Looking better! At this point we're done with sanding. We could go on up to 2000 grit, but with the next step it wouldn't do anything anyway.
The last and most important step to making plexi edges (or any plexi surface) really glitter is polishing. I've had very good luck with a buffing wheel mounted on a bench grinder:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-9.jpg
This product is called buffing compound or jeweler's rouge, depending on who you talk to. If comes in a handy solid form, you just peel the cardboard off the outside to get to it. Turn your buffing wheel on and hold the end against it, it's soft enough that it will embed into the buffing wheel fibers. You can see how this one is worn down.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-10.jpg
So this is a tricky part. Turn your grinder on and slide the edge of your plexi along the buffing wheel edge, but pressure is critical, as these buffing pads are not solid, but are several flat sheets sewn together, and too much pressure catching an edge can shred them and cause all kinds of havoc. (Yes, I know.) Gentle pressure, just enough to see the buffing wheel flex a little under the plexi. Slide the work at an agle across the buffing wheel. Once should do it, but twice won't hurt. When you're done there will be some compound residue on it, just buff it off with a cloth or paper towel.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-11.jpg
See those lines in it? That is actually a magnified image of the mill marks on the BACK of the piece.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-12.jpg
And there you can see my finger through 19 inches of plexiglass, even though the back side is unfinished. That's a shine.
A side note on sandpaper, there are three common forms, aluminium oxide, garnet, and silicon carbide. I always use silicon carbide when I have it or remember to get it, as it is wet/dry and lasts longer than the others. Garnet is a second choice, I usually have some laying around for wood projects. One final thing that makes people sand more than they should is continuing to sand with a piece of sandpaper that is sanded out. Sandpaper doesn't last forever. In fact, it doesn't last nearly as long as you think it does. Sometimes it will load up with dust from the project and you can clean it to get a little more use from it, but usually you just need to switch to another piece or another spot on the piece you are using. Feel it with your finger, feel the area around it. If it's dull, move to another spot. Remember, the goal here is to achieve a shine, not to sand as much as possible.
________
Grape ape (http://trichomes.org/marijuana-strains/grape-ape)
Flame polishing has a couple of advantages over sanding. It is much faster and once you get the hang of it, much easier. However, no matter how practiced you are at it, you run the risk of badly damaging your project, and no matter how good you are at it, it will never look as good as a sanded edge.
Let's look at sanding. Yes, sanding sucks. I have yet to meet anyone who enjoyed it. Unfortunately, it is all too often a necessary evil. This tutorial will focus on plexiglass, but the same principles apply to any material that lends itself to sanding, and there a great many of them.
Sanding is nothing more than scratching. By moving from lower-grit coarser sandpaper up to higher-grit finer paper, we just make the scratches smaller and smaller until they are no longer visible to the naked eye. One of the most common mistakes made in sanding is sanding too much. Yes, people hate this with a passion and yet many will sand twice as much as they have to. The key is grit.
The grit that you start with will depend on the condition of the original piece. Take the edge I am working with here:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-13.jpg
This is a really rough edge, left by whatever cutting machine the plastic shop I got it from uses. I could have smoothed it out a little with the blade I have on my table saw, but in this case there is no need. I am going to round this edge over for my purposes with a router and a rounding bit:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-1.jpg
Looks better, but still pretty rough. Here is where we determine what grit to start with. One of the reasons a lot of people sand too much is because they start with a grit that is too high for the job. The higher the grit, the smaller the abrasives and the finer the scratches. We want a grit that will cut scratches as deep as the ones we already have, so we can level off the top of the plexi down to the bottom of the mill marks. We can't add material, so we have to take it away. In this case, I chose 150-grit to start, which is pretty coarse. After:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-2.jpg
Notice the scratches are still highly visible, but now they are running the length of the piece, instead of across it? This brings us to another thing that causes a lot of people to sand too much. You should only sand with a given grit as long as you have to. Sounds simple, but you'd be surprised how quickly that point is reached. After some practice, and really paying attention to how the sandpaper *feels* when you're sanding, you'll probably notice that after just a couple dozen strokes it will stop feeling any different than it did on the last couple of strokes. That's the end. Stop. Wipe the dust off of your project and inspect it for any singular spots you may have missed, but overall, you are done with that grit. This only applies if you started with a grit that was coarse enough to begin with, otherwise you are still trying to get those deep mill marks out with shallow abrasives. If the piece is uniform, move on. In this case I moved to 220 grit:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-3.jpg
Much finer lines. That's the point. Follow the above and move to 400 grit:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-4.jpg
Then to 800:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-5.jpg
Then skip a grit to 1500. With plexi you can get away with skipping grits at the higher levels, not so easy with metal. In this case, since I was using wet/dry sandpaper (more on sandpaper later) I chose to use Mother's Chrome Polish as the wet portion. You can use water if you like, but I find that the tiny abrasives in the chrome polish give better results.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-6.jpg
http://i452.photobucket.com/albums/qq245/techreview/Untitled-7.jpg
Looking better! At this point we're done with sanding. We could go on up to 2000 grit, but with the next step it wouldn't do anything anyway.
The last and most important step to making plexi edges (or any plexi surface) really glitter is polishing. I've had very good luck with a buffing wheel mounted on a bench grinder:
http://i452.photobucket.com/albums/qq245/techreview/Untitled-9.jpg
This product is called buffing compound or jeweler's rouge, depending on who you talk to. If comes in a handy solid form, you just peel the cardboard off the outside to get to it. Turn your buffing wheel on and hold the end against it, it's soft enough that it will embed into the buffing wheel fibers. You can see how this one is worn down.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-10.jpg
So this is a tricky part. Turn your grinder on and slide the edge of your plexi along the buffing wheel edge, but pressure is critical, as these buffing pads are not solid, but are several flat sheets sewn together, and too much pressure catching an edge can shred them and cause all kinds of havoc. (Yes, I know.) Gentle pressure, just enough to see the buffing wheel flex a little under the plexi. Slide the work at an agle across the buffing wheel. Once should do it, but twice won't hurt. When you're done there will be some compound residue on it, just buff it off with a cloth or paper towel.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-11.jpg
See those lines in it? That is actually a magnified image of the mill marks on the BACK of the piece.
http://i452.photobucket.com/albums/qq245/techreview/Untitled-12.jpg
And there you can see my finger through 19 inches of plexiglass, even though the back side is unfinished. That's a shine.
A side note on sandpaper, there are three common forms, aluminium oxide, garnet, and silicon carbide. I always use silicon carbide when I have it or remember to get it, as it is wet/dry and lasts longer than the others. Garnet is a second choice, I usually have some laying around for wood projects. One final thing that makes people sand more than they should is continuing to sand with a piece of sandpaper that is sanded out. Sandpaper doesn't last forever. In fact, it doesn't last nearly as long as you think it does. Sometimes it will load up with dust from the project and you can clean it to get a little more use from it, but usually you just need to switch to another piece or another spot on the piece you are using. Feel it with your finger, feel the area around it. If it's dull, move to another spot. Remember, the goal here is to achieve a shine, not to sand as much as possible.
________
Grape ape (http://trichomes.org/marijuana-strains/grape-ape)