Threaded Inserts - Standard Thread or Acme Thread?

[Meesh Bono]

I have taken over a project halfway through (which is never an easy thing), and I need to get a threaded insert to place inside a steel piece that a threaded rod will move through. The original person working on the project wanted to get Acme threading on the inside of the insert and standard threading on the outside of the insert. The rod has Acme threading and is made from carbon steel.

I am wondering why the insert needs to have Acme threading on the inside though? The original guy thought it would be able to withstand more force, but if the outside thread is standard thread than does it really matter what the inside thread is? If the outside thread can only take so much force before it fails then it won't matter how much force the inside thread can take right?

Is there a force equation I can use to calculate when the threading will fail on the inside and outside of the insert? Maybe I can get a standard threading on both sides of the insert instead of trying to find a custom product.

Also, I've had another engineer tell me the insert should be made of bronze because he thinks the assembly will bind. But I thought the insert should be made from the same material as the main parts and the threaded rod (which is steel or carbon steel).

Any advice will help, I'm an electrical engineering student with a mechanical job!

Thank you!
Meesh

 

[billy_joule]

If the outside thread can only take so much force before it fails then it won't matter how much force the inside thread can take right?

The inside thread is of a smaller diameter so will have greater stress.

Presumably ACME thread is being used as it's a lead screw and standard thread won't meet the spec. Low friction is important for lead-screws hence your fellow engineers suggestion of selecting a material with lower friction.

If you can't find what you need need off the shelf you could have them made or redesign.

 

[phinds]

Uh ... from what I've seen of the Road Runner cartoons, I'd be real careful about those Acme products :D

 

[Meesh Bono]

The inside thread is of a smaller diameter so will have greater stress.

Presumably ACME thread is being used as it's a lead screw and standard thread won't meet the spec. Low friction is important for lead-screws hence your fellow engineers suggestion of selecting a material with lower friction.

If you can't find what you need need off the shelf you could have them made or redesign.

I've called many places looking for this part or someone that can make it, but no luck! If anyone knows of a company that makes ACME threaded inserts please share with me!

 

[billy_joule]

It might be cheaper to buy an ACME tap, here's one place that sells them:

http://catalog.tapcotaps.com/category/acme-taps-2