What's the maximum angle a propshaft can be run at without irritating vibration?

Would something in the 6.9-7.9 degree range be okay?

Assumptions: trans output and differential pinion are parallel, u-joints are in phase, speeds up to 70 mph, driveshaft mass is small (solid shaft about 3/4" in diameter).

This is the plan for a shaft made up of two Honda CX500 shafts welded rear to rear (for a trike I'm building):

I would not have thought that the angle shown was excessive at all IMO....

Love to hear some more informed opinions though.

When I was researching propshafts, I came accross a site with a table of prop angles to safe RPM's, the greater the angle, the less RPM is safe (no sh1t sherlock!!)

I cannot remember the site, but it was one of the main manufacturers, I think I just put propshaft manufacture into Google

hooke joints & cvjoints wear out faster if they're perfectly straight - I think you're supposed to have a degree or so at least so all the wear doesn't happen at a single "point".
If the yokes are aligned 2 hooke joints on a prop with parallel gearbox o/p and diff input will give overall constant velocity - the diff end corrects the errors put in by the gearbox end, but the prop in the middle has the wobbly speed thing going on.
Sorry - grannies sucking eggs etc. - just thought I'd point it out.
Bob C

The wear is called Brinnelling and is caused by the roller bearings acting on one spot instead of 'rolling'. With a bit of agle on the UV's, the rollers rotate around the bearing case.

It is simply known as "wiping" where the lubricant in the joint is not distributed over the roller but is cleared from one spot allowing the hardened surface to be breached. It used to happen when cars were delivered by train and rolled forward and back when the train slowed and accelerated and knackered wheel bearings on brand new cars before they got on the road. Little bit of history there.

yours, Pete.

and how did they discover it?

Some american car manufacturer stopped making cars on the west coast. Kept making them in the east and shipping them. All the cars on the east coast where fine, the west coast ones had the problem .... took them a while to realise what was causing it mind you.

a litle bit more history

Angles should be OK but I would be uneasy about having the joint between the two shafts slap bang in the middle -- as suspect the shaft could start to whip at critical speeds.