Very impressed(and flattered) by you barrel
rockbiter. Both from cost and durability and ease of construction.
The 2 ended Fernco cap defied me because I could not get by the band clamps sticking out and hitting the shafts.
You will solve that by making a step in the shafts for clearance, damn why didn't I think of that !!!
It is the HDPE fittings that cost so much. Pipe is super cheap. Contractors have a hard time disposing of left over HDPE pipe sections. The dumps hate the stuff.
Those 6 inch Fernco's are some serious hunks of thick rubber. Lot's of bang for the buck. They will last a very long time with the most aggressive silicon carbide.
With one on each side you will have double protection from gas blow outs.
The 6 inch Fernco can bulge up to 2 inches without blowing off when only using one band clamp.
I think you will find the silicon caulk to be short lived, this should not matter. It is the last coarse grit run before doing 220 that counts most for grit breakdown.
On the last coarse silicon carbide addition you can simply remove both caps and clean them thouroughy to remove any hidden particles and do the last break down run.
Make allowance for lateral barrel movement when(not if) the caps bulge so that the steps in your shafts don't hit the band clamp screws.
Especially if you are running 2 or more barrels against each other.
Are you aware that SDR 11 and SDR 8 pipe is really thick ? Like an inch thick.
It would be interesting to turn steps down on the end 2 inches of the thick pipe using a lathe and buy a smaller Fernco to fit on the steps lowering the band clamp screws from hitting the shafts.
Fernco makes all sizes of end caps for clay pipe, cast iron pipe, various schedules of pipe, etc.
Check out my friend's thick walled HDPE. Lots of meat to cut a step on the ends and loose the 8 screws, go to your Fernco trick.