Posted by John Swensen on August 20, 1999 at 15:10:27:
In Reply to: Porting/Venting posted by Alan on August 20, 1999 at 12:26:04:
If your valves have any tendency towards leakiness, venting holes will make them worse (play with a water key open to get the idea of the resulting sound).
In any case, you may get a whistling sound as slides are pulled with vented rotors, but you are probably the only one who will hear it.
If you try porting and hate it, the hole can be plugged with a drop of (soft) solder, with the excess solder on the inside of the valve carefully scraped down level with the casing wall. You will see the solder spot and the lacquer damage, afterwards.
You only need to vent those valves connected to slides that you actually pull in playing.
The hole should be VERY small (numbered drill in the 60s or 70s), centered between the slide ports of the valve; obviously, the rotor must be removed before drilling the hole, and any burrs inside the rotor casing cleaned up before the rotor is replaced. Usually, there is not enough room to get a standard 1/4" or 3/8" drill chuck anywhere close to the valve where the hole must go, so a miniature chuck on a flexible shaft is usually required (Dremel makes a small, 3-jaw chuck).