I realize that after a long time of not blogging that I simply forgot to blog about finishing my Rubens Tube.  Besides, I need to show the final piece in action.  Sorry about that!  Here are the first three blog posts about this.  One, Two, Three.

One hole drilled for a pipe thread, the other for a 1/4" OD tube.

Step 6.  Prepare the plate for the propane side.  I drilled and tapped a 3/8″ NPT for the brass fitting.  The other smaller hole is for a tube which I’m welding in for an attempt at a pilot light.  If you’re building your first tube, you can ignore this, as it may not work well.

Welded and plumbed

Step 7.  Weld the plate into place.  I also had to weld my pilot tube through the plate and out through the top of the tube, so it as a bit of juggling.  I then plumbed it with a brass flare fitting that mates with my propane hose.  The plate isn’t very thick so it’s easy to strip out the few threads of pipe thread.  Always use two wrenches to tighten/loosen the flare fittings to prevent over-torquing these relatively delicate threads.  A better solution might be to braze or silver solder the flare fitting to the steel plate.

Cutting the rubber is as straightforward as it gets.

Step 8. Seal the speaker side of the tube.  I use a thin rubber that is rated for exposure to propane (caution, not all rubbers are equal!).  The rubber I found is Buna-N rubber that I got from McMaster Carr.  It comes in a big sheet and I’ve been using the same one for all of my tubes.  I poked the screw holes through the rubber so this plate can hold the rubber sheet against the flange that is welded onto the tube.  The speaker is then installed over the whole package.  The speaker never touches the propane.  The frequencies can easily transmit through this thin rubber.

Fire at last!

Step 9.  Fire it up!  After sealing the flanged end with rubber, I was ready for a test.  The tube may take a while to fill with propane (which is heavier than air), but eventually you can light the flames.  I adjust the pressure on the propane bottle with a regulator to get a nice small, even flame across the entire tube.  It’s then easy to see if you have slightly clogged holes.  I usually just use a drill bit by hand to clean out clogged holes.  The result speaks for itself.

I hope you enjoyed these instructions.  If you have any questions, don’t hesitate to ask in the comments down below.