Thread in a Polymer

[djw2k3]

Hi,

I have an application where I would like to put an M12 thread into a polymer.

What I would like to know, what polymers hold a thread well? It will not be heavily loaded at, just half twist past finger tight when bolt is inserted ;-)

Have been told acetal could be a good option. Am wanting something relatively cheap.

Dave

 

[strokersix]

Do you plan to mold the thread or cut it?

Reinforced polymers may be better if you are molding the threads. Neat polymers probably better if cutting the threads.

Do you have room for an insert? Helical wire inserts don't take up much room and would me much stronger and more durable.

Mike

 

[djw2k3]

Hi Mike,

Yeah the thread is to be cut into.

Excuse my ignorance "neat" polymers? I take it these are homogeneous without reinforcement.

Dave

 

[strokersix]

Dave,

I used the term "neat" in reference to no reinforcement fibers. I think it also means no other fillers (glass beads, PTFE, etc.)

Do you need to use standard 60 degreee threads? If not then there are other thread profiles the can be stronger in polymers. Basically they have smaller included angles such as 40 degrees instead of 60. This effectively weakens the metallic screw and strengthens the polymer hole.

Mike

 

[plasgears]

The neat thing about plastics is that you are not limited to stds. You have the freedom to machine a buttress thd if your load is directional. Also, you can specify your own thread angle. I have had success with a reinforced nylon acme actuation nut for auto seat application.

 

[djw2k3]

Thanks for the comments guys, I will look into the thread angles and size and various fasteners

Dave

 

[RichLeimbach]

We use self-tapping brass inserts quite a bit. They can be installed into either reinforced or non-reinforced plastic holes with a simple driver and are easier and more reliable than trying to thread the plastic with a tap. There are a number of standard thread sizes available. You should be able to pick them up cheaply from Grainger or McMaster-Carr among others.

 

[plasgears]

Don't overlook the opportunity to introduce flats at the parting line. With flats you don't need to unscrew the part from the mold; just separate both halves of the mold. This is commonly done in zinc die castings with threads.