LED Sign Help Needed

[fred ruppert]

XXray, borrowed a unit and tried MAP gas, quite pleased with the results. Went and got a couple cheep buffing wheels for my 6 in bench grinder. Need some advice on buffing - the first couple of sides went well, but the fourth looked like I melted/removed some surface and the surface was not smooth. Is it possible when buffing to overheat the acrylic and melt the surface? After messing up that one side, I have had repeated instances where it looks like I have trapped some of the buffing wheel in the plastic, particularly on the corners. Even at that, when I kept moving around the part to keep it from overheating, it seems to be a slow process to achieve a smooth surface. Any observations on what I could be doing that I should not?

Right now MAP gas seems to be the easiest for me

[martin54]

Yes Fred it is possible to overheat the material when buffing, friction will always generate heat
How good were the edges once you had finished machining? Really you need them to be pretty good before you start buffing so if it doesn't have a good edge when it comes off the machine then some sanding may be required. I use gas for edge polishing when I do polish the edges, quite often I will leave them with a frosted look though because that is how I like them personally
If you are using gas then something to watch out for other than melting the acrylic is stress fractures/cracking which can occur

[Xxray]

Don't have much experience buffing with a standard bench grinder.
No buffer will work miracles, heavy scratches and gouges must be sanded out first [not clear if you are doing that or not].
I'd say sure, excess heat could have undesirable results - But that kinda heat is nothing compared to MAPP.

Make sure you use a buffing compound, one wheel for rough [usually reddish color] and one for finish [usually white]. That right there will reduce friction and add quite a luster.

[fred ruppert]

I bought a couple of buffing wheels for my 6 inch bench grinder. The first edge polished up nice, but by the fourth edge, it looked like I had removed the surface from the edge, created a step, and the buffed part looked terrible. Is it possible to overheat when buffing and melt the acrylic? Buffing apparently isn't an 'all ya gotta do' solution either. Since then I have buffed small areas and kept the edge that was in contact with the buffing when limited in time before I moved away and worked on another edge. Very slow however, and still not happy with the results. Any suggestions?

[fred ruppert]

Missed your reply - didn't use any buffing compound - perhaps that is the issue

[fred ruppert]

Martin, I started to buff without touching the surface from the router, but buffing wasn't going to take the roughness from routing. So I used 150 grit sandpaper to take care of the router chatter, then 320 grit to smooth out the 150 grit marks. Then back to the buffing wheels (without buffing compound). More to learn...

When you left a less than polished surface, did you at least polish the edge that was going to be directly over the LED's, or can you get by with that surface less than polished, I would guess that the light that transmits through that surface would be less than a polished edge.

[martin54]

Fred, I don't have any roughness off the router, I get a slightly frosted edge but it is perfectly smooth, I use bits that are designed for cutting acrylic & they are relatively expensive.
I have never polished the edge that sits against the LED's, l was told long before I ever owned a CNC machine that the edge the LED's sat against should not be polished as you got better light transmission, I don't know enough to be able to say if that is true or not but I can see how it can be possible, the frosted edge could very well act as a diffuser which may not give a brighter light but certainly a more even distribution of light
All the panels I have personally made have been small, no larger than A4 (landscape) & the lighting has been very good on them all so there has been no need for me to question that or look for a way to increase the amount of light.