shell mold update

the first mold i made was very inconsistent, the only way to make the arched surfaces smooth and level is by using a wood rasp or sanding the heck out of it. now doing that wont guarantee the arc to stay at the correct radius so i better redo the mold before i actually use it. let's just call it alpha version.

wonder how i made the alpha? well, first things first, shells are 1/8" undersized so if you buy a 14" you actually get 13 and 7/8" so they say over at forum.drumshed.org. kellers are done this way.

so my target size is for a 10" tom with a shell thickness of 2/8". that would give me 9 and 9 7/8" outer diameter and 9 and 3/8" inner diameter. why not 9 5/8" you say? because we are talking about diameter and you have to subtract the thickness twice. here's an illustration:


you just divide the inner diameter by 2 to get the radius for the mold. but i converted to the metric system (in millimeter to be precise) so i can easily and accurately measure the arc. i drew the circle on a piece of paper and cut it out as a template for the wood block. this method was actually suggested to me by massimiliano signori, he's italian and he's the one who showed me how to do the shell. although we never met personally before, we had a series of email exchanges along with it an english version of a how-to guide he made for me to follow.

now back to the paper template, well you just use the paper as a template and draw on the wood blocks. then use a power jigsaw to cut along the lines, glue the blocks together to form the mold. what you get is exactly on the second pic of my last post. simple isnt it? the first problem is getting a consistent and repeatable cut. remember you have to cut several blocks for the depth you want and its a pain in the poopoo to do it freehand. there's got to be a better way of doing this!

well, as i mentioned before, i have a day job which a do nothing for 9 hours so i did research on the internet and saw a couple of pics for inspiration. now comes the beta mold...this alpha-beta stuff is way overused, sounds corny, anyway...i created a compass-like thingy using some scrap wood to hold the block in position and the jigsaw mounted on a plywood upside down blah blah blah. you'll get the idea on these pics below:

here are pics of the thingy:


the jigsaw and the base with graduated holes


the base and the arm, you can see that the holes are marked for 10, 12, 14, 16, 18, 20 and 22 so i can cut molds for those diameters too by just moving the screw to the appropriate holes =)


here's a solo of the arm. i put a 1"x1" stopper for easy alignment of blocks. i'll just screw the block tight and its ready for cutting


here's the thingy in action, cutting a 10" mold


look, clean convex cut


here's the whole block and the convex part removed from the arm


cant wait for saturday...