Flanges. Oh, how I love flanges.
Step 4. Drill and tap holes in the flanges for mounting the speaker and Buna-N rubber sheet. The reasons will become clear in later steps, but I’ll just describe what holes I drilled. One flange will be welded to the tube itself, so it will have nothing but tapped holes (flange on the right). I chose 6-32 as my size. The other flange will be used to hold down a thin sheet of Buna-N rubber to seal the tube. This has 8 countersunk holes for countersunk screws and 4 through holes for the screws which will be used to mount the speaker.  I drilled one of the flanges first, then transferred the hole locations through using a punch. This way my holes don’t have to line up to an absolute location, as long as they line up relative to one another.   Locating these holes before cutting out the rings is a better option. But, I got ahead of myself. Whoops.
Welded flanges are even hotter.
Step 5. Weld the flange with the tapped holes onto the tube. Make sure to make an nice tight seal with the weld bead. The propane won’t be under a lot of pressure, but you still don’t want too much flammable gas coming out in a place you don’t want.
In the next installment I’ll get the propane-input side of the tube ready and prepare the seal for the speaker end. Once that’s done the Rubens tube is ready for a test!
Not too bad of a weld, if I do say so myself.
Continue on with the final part.