"Phil Kangas" wrote in message ...


"Bob La Londe" wrote in message On 6/11/2019 6:49 PM,
Jim Wilkins wrote:
My home made sawmill uses L095 Lovejoy couplers to connect the engine
to the transmission, and their set screws loosen unless I pull very
hard on a long hex wrench. The cause may be the large inertia of the
bandsaw wheels, which are from a motorcycle. When the
vee-belt-tightening drive clutch is loose the belt slips freely over
the pulleys, but when stopping the belt still grabs enough to spin the
engine after it's shut off. Thus the couplers see torque in both
directions.

This suggests that adding a second set screw to lock the first does
help.
https://www.hobby-machinist.com/thre...-screws.36903/

What's your experience?




I remember something like that being done for an air metering screw on a
PCP air rifle. First set screw obstructs the passage, and the second one
backs it up and locks it in place.

It takes two screws in the thread to obstruct passage. They
push against each other so both sides of the groove are
sealed. Plus, the screws lock each other in place even if
the inner one is not in contact with something. phil k.

***

In this case, no. The set screw protrudes into a passage way and that is
the passageway that is obstructed or cleared by adjustment of the screw.
The passageway the set screws are in is incidental for the purpose of having
a place to put the screw. Even if it was not sealed the air loss around the
screw would be incidental or parasitic at worst. It would not be major.
Some guys are eliminating the second screw and just using vibratite on the
first screw so they can adjust the gun easier.

However, my whole point was that I had an example of how two set screws are
used to lock themselves in place. I can tell you that it does not work
quite as well as hoped. Its possible to drive the first screw with the
second in a case where its not stopped up against an object. You have to
have a "feel" for it and know when to stop so as to not change the
adjustment of the gun.

We are talking about sudden discharge of a small amount of high pressure air
(3000 psi to start) with a hammer and a knock valve. (I think knock valve
is the right term.)