How To Attach The Tube (Cont.)

Here's a diagram of a simple to build tensioner for nylon webbing, stainless steel strap, or even belts.

The fixed side attachment doesn't move; I tap this side of the C-channel for a 1/4"-20 bolt.  Depending on the strapping material, I may need a large washer to distribute load across more surface area.  For nylon webbing, I would triple the layers for this attachment point.

The adjustment side attachment consists of a 1/4"-20 tapped hole and a bolt (probably a thumbscrew) with two nuts locked in position at the end of the bolt.  The way that I have found works most easily for this is to drill through a hex head nut into the bolt, tap the hole for 6-32 threads, and use a 6-32 set screw to lock bolt and nut together.  The strap goes through the slot in the side of the C-channel, and is held by two washers inside the captive nuts.  The strap can rotate between the washers, so it isn't a tight fit there.  You have to the get the length of the strapping pretty precisely correct for a snug fit, and then you turn the thumbscrew to clamp everything down.  This also gives some room for strap stretch over time.  If you reach the limits of the bolt, you can redrill the holes on the fixed side attachment, but I am considering this a short-term solution to the problem.

Limiting yourself to a thumbscrew not only simplifies tool-free adjustment, but also reduces the change of putting so much force on the tube that it damages it.

UPDATE: Good news: I asked my pastor this morning where I would steel strapping material on a weekend.  He just happened to have a 50 foot roll of .030" thick, 1 inch wide steel strapping material.  I started work on the device above to use some of this.  I discovered that the vertical mill definitely works better with the longer screw holding everything together; I also discovered that once again, the single most important factor in milling is getting the workpiece really well clamped in position.  Anything that lets it jostle in the vise is a problem.  I also discovered that the 1/4"-20 thumbscrews I had...were something metric, not 1/4"-20.  I guess I will buy two of those tomorrow.