On 26 Sep, 17:21, jkn wrote:

* * I'm starting to think about building a bike workstand - the sort
of thing with a pivoting frame clamp

Never had a use for such a thing - as frames are also long and thin,
it's not really practical to "turn" the frame like this, nor do you
really need to. Easiest way to invert is unclamp it, flip the frame
and reclamp.

What you do need is a clamp. A clamp that holds well, is quick to
apply, fits most frames and doesn't damage them. The "stand" part is
easy.

The "community bike workshop" design is scaff-pipe and scaff or kee
clamps. C shaped frame on the floor, one or two uprights and a short
horizontal of scaff pipe (plans probably on-line too). The "swivel"
can be done with two sizes of pipe, one inside the other. Turn a
reduced ring on the end of the inner pipe and hold it from falling out
with a stub bolt through the outer tube (if you haven't a lathe, angle
grind it) Half-a-dozen holes in the inner tube and one in the outer,
with a tapered reamer and a conical peg to lock it, give you rotation.
For a crude clamp, get a clamp from construction site portable
fencing, weld to the swivel pipe, line the jaws with leather (or vegan-
hyde), weld a long handle to the clamp bolt and slip a coil spring
over the bolt.

The hippy special is similar, but made of wood. This does need to be
triangulated and IMHO it needs to be bolted or weighted down, for when
you're trying to get cranks or BBs out. You can build a lovely
elegant clamp by sawing a length of ash partway down the middle to
give a spring (and an overcentre cam to lock), but some hoodie muppet
can sit on it and break it.

My own is just a horizontal scaff-pipe, swivel & clamp and it quick-
bolts onto my workbench (or engine building stand) when I need it.
Saves storing a stand.

A mate who favours expensive frames doesn't have a clamp at all. His
has a three-padded plywood tripod (frame-sized) at the end and velcro-
strap clamps for each tip. As the frame is held with a longer
effective lever arm, the same couple can be produced by far less force
and no-one's expensive Italian carbon fibre gets chafed.