Plug Thread Binding
Plug Thread Binding
(OP)
We have a large diameter (11") bearing cap that is binding in assembly. It is threaded with 2" of Acme-3g with a pitch of .25 (11-4 ACME-3G) and I think we should go to a larger pitch. It is loaded, and holds the thrust bearing in place. Is this thread too fine for the diameter? The machinist's handbook shows a 5" diameter is commonly threaded with a .5 pitch. Is there anything we should consider when moving to larger threads? This is my first time dealing with acme threads and I wanted to ask to see if anyone has greater experience with this topic.





RE: Plug Thread Binding
The two most likely causes of binding are lead error and eccentricity. The manner in which the binding occurs might provide a clue. E.g. lead mismatch in perfectly round parts will cause the assembly torque to rise steadily as the thread is progressively engaged. Conversely, if the required torque peaks at certain angular positions and falls off at other positions, something is not as round as it needs to be.
There are only a bazillion other things that could be wrong, but you need to eliminate those two as a start.
It's time to buy some serious inspection tools and/or services.
Mike Halloran
Pembroke Pines, FL, USA
RE: Plug Thread Binding
RE: Plug Thread Binding
Don
Kansas City
RE: Plug Thread Binding
RE: Plug Thread Binding
You will need a set of pitch wires or balls to check this, but it is esential for quality control on threads.
RE: Plug Thread Binding
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It's worth the eight bucks.
Don
Kansas City
RE: Plug Thread Binding
RE: Plug Thread Binding
Careful! Screwman said "or" not "and" !!! It makes a difference !