Pros/Cons of Multi-start Threads 3

[momoneymo]

I know that multi-start threads have a greater lead than single-start threads of equal pitch length, but are there any other differences in function? Is there any difference in strength between a single-start and a two-start thread with the same pitch?

Thank-you

 

[funnelguy]

Multistart threads are not typically used in high stress applications. The slightest errors in lead, geometry or index would preclude equal sharing of the load by each of the individual thread forms. I'm sure these concerns could be overcome, but why add another source of error in a high stress application when it isn't required? Frictional losses while tightening would be higher, leading to a lower tensile load being possible.

Thread stress area would be almost identical, I suppose.

The advantage of multi-start threads is simply a faster lead in a shallower form depth. This could certainly improve the stiffness, and consequently critical speed of a lead screw used for motion control. Luer components, I imagine, use the thread form because of its shallow radial depth requirements and quick connect/disconnect abilities.

There are others on this forum who are more knowledgeable than I and they may correct me on a point or two...

 

[unclesyd]

The amount of rotation for full engagement is a primary consideration for using multi lead thread forms. In the US the a prime example is the multi lead threads is the common plastic milk jugs. Another reason is that, for old folks like me, it takes less force for a tight seal and consequently less force to remove.
I tell a local plastic molder that he wouldn’t be making multi lead threads without the computer and CNC machines. It used to be a bear to generate multi leads so we always fell back on the interrupted thread.

 

[GregLocock]

It's easier to cross thread a multi start thread. This doesn't matter overmuch in the case of milk bottle tops.

Funnelguy's point about load sharing is well made.

Cheers

Greg Locock