Further Refinement of Plexiglass Ground Glass

[Ari]

Hi,
In the past, I would buy a ground glass and have it ground further to get a very fine grind, which I prefer to have for better focusing.
My new camera came with a plexiglass GG; it's very good for aerial viewing, but the grain is quite coarse for my taste.
Can I apply the same treatment and techniques to the plexiglass in order to achieve a finer grain?
Or do I have to be extra careful with plexi?
Thanks in advance.

[Kevin Crisp]

I've had good luck with valve grinding paste, you can get it at auto parts stores, I think Permatex brand in a tube. A 2000 grit boat polish like Aqua Buff might be too fine, but they make 1000 too.

[jnantz]

hi ari
i use an asymetrical sander to sand my plexi, it works but might be not to your taste.

[Peter De Smidt]

The valve grinding paste I tried must've been coarser than Kevin's. I didn't get good results, but I don't remember the brand.

I recently made a couple of plexiglass screens, and it was much more prone to scratching than glass. It's possible that my plexi just wasn't flat enough.... I used 3 micron aluminum oxide. The center ground ok, but the edges did not. Kirk has the screen, I don't know if he tried focusing with it.

http://www.lortone.com/abrasives_polish.html
Aluminum Oxide Pre-polish
#591-021 14 oz. $5.75

[Ari]

Thanks, John, the sander is probably more expedient, but I'd rather use the traditional method.
Kevin, thanks for the suggestion, I'll look into valve grinding paste.

[Bob Salomon]

A lot of guys use to just use tooth paste.

[Ari]

A lot of guys use to just use tooth paste.

I prefer hanging a pine-scented car freshener from my camera.

[unixrevolution]

I prefer hanging a pine-scented car freshener from my camera.

I should try that with my 8x10, it still has pretty bad halitosis inside the bellows.

[el french]

What technique are you using to grind the plexiglass? I recently watched a video about lapping, which unfortunately can't locate now. It showed the difference between lapping where the abrasive was embedded in the lap which was softer than the material being lapped and where the abrasive stayed on the surface of the lap. The later produces a rolling motion in the abrasive grains and each grain produces short cuts. The former made longer cuts. I wonder which would work better for glass and plexiglass.

[richardman]

I see we have the same issue ;-)