What if I made the backing ring out of 3/4" MDF, I know it would be quite thick, but that couldn't be a disadvantage, could it? I would just need longer bolts.

At least I have the tools and the materials available to use MDF for the ring.

 

I would say there is good chance you might split the mdf ring when tightening the bolts.

 

Damn! What if I'm generous in the width I make it? Say 3/4" square...

 

Get some 1/8" aluminum, mark it out and cut it with a jigsaw. Then take a file to it and file it smooth. Actually a belt sander will work on it as well.

 

While we're at it, how would you guys recommend actually cutting the sub holes in the face of the plexi/acrylic?

I was planning on using my dremel as a router with a RotoZIP Sabrecut bit:

They cut MDF like butter, but I don't know if it will chip the plexi, they're designed for all woods and plastics... If it chips a little it's no big deal, cause that area will of course be covered by the sub's mounting ring.

 

i would used just a strait Single flute rouger bit.

 

Is something like that available in a 1/8" or less shaft size?

 

not sure, we always used a " laminate trimmer " which is basicly a small router and they had 1/4" shanks

 

Nope, all that will do is make a mess and melt back together. Take it into a shop and have it routered properly.

 

Sounds good, I've already contacted some shops in the area.

Thanks.