Bending MDF

I recently purchased a pair of Polk Rti-a9's. These beauties are fairly large and have a curved teardrop shape, as they taper from front-to-back. I like the look, and the bass performance is solid, so I've set out to build 2 matching subs to complement the low end. [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6047.jpg[/IMG]"][/URL]

I've been researching different ways to bend MDF so that I can form arcs for the sides of the enclosures. My budget is tight and tools are limited, so I can't afford too many failed experiments. I've read about kerfing, but I'm afraid that I won't get a smooth outer finish, and that I'll go through several sheets of wood trying to get it right. I've also read about bending several thin sheets then laminating them together, but the only sizes available at the local lumber yards are 1/2" and 3/4" in MDF, and birch is expensive. I've even heard of someone going so far as to cut out the perimeter of a tree trunk to get a rounded finish.

The idea that intrigued me the most came from terryj at home theater shack in his thread http://www.hometheatershack.com/forums/diy-speakers/19571-my-speaker-build-about-time-i-showed-you.html Thanks for the idea. I set a 4X8 sheet of 3/4" MDF on 2 sawhorses. As you can see, the board is very stiff and hardly bends even with about 80 lbs. of weight on it. [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5798.jpg[/IMG]"][/URL]

I used a bottle of household ammonia mixed 50/50 with water and rubbed it on with a washcloth. I applied the ammonia/water mixture evenly across the board until it had soaked about 1/3 of the way through. I flipped the board over and applied the mixture to the other side until it soaked 1/3 of the board's thickness. This left the inner 1/3 dry. Amazingly, the board began to bend! [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5802.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5810.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5815.jpg[/IMG]"][/URL]

I increased the weight on top of the board over the next few hours. I was careful in that I increased the weight in small increments as the board bent, and I spread the weight evenly to keep the bend consistent (a template would have been helpful here). [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5829.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5836.jpg[/IMG]"][/URL]

Drying only took a few hours. I was surprised to find that the board was still smooth to the touch.
The gnap of the wood was still in tack and sanded as smooth as the other panels on the subwoofer.
Performance wise the arced side panels actually feel stiffer than the flat panels! This is amazing considering that they are also the largest panels. After bracing, I can't feel any vibrations coming from the side panels while producing heavy bass passages.[URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG5857.jpg[/IMG]"][/URL]

The pics below are of the finished product. I have applied cherry veneer and wood conditioner, but they lack stain and finish. Thank you for reading my thread. [URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6027.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6034.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6037.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6040.jpg[/IMG]"][/URL][URL="[IMG]http://i1099.photobucket.com/albums/g382/fokakis1/CIMG6030.jpg[/IMG]"][/URL]