Re: 1939 120 firewall grommet

Posted by HH56 On 2011/3/23 9:42:18

One other way to make very clean holes in rubber that thick is to use a piece of thin wall brass tubing in appropriate size in a drill press or drill or even a lathe.

Bevel one end with a reamer, grinder or sanding belt so it has a reasonably sharp chamfer all around the diameter. Mount the straight end in the chuck. Place a scrap of wood under the rubber and drill away using slow speed. I use a foot pedal on my drill press for ease and can just hold the rubber but clamps can be figured out if wanted and don't distort the rubber.

With slow speed and a little water or other lube if needed the tubing will neatly cut a hole. After one hole is made, remove the tubing and push out the scrap piece from inside before making another.

I have done this with rubber bottle stoppers an inch or so thick many times. Can go to a half inch diameter or the max size of your drill chuck. Larger if you want to get fancy and figure out how to solder or connect different size tubes together so one end fits the chuck.