Thread Pitch

[deere2210]

I'm tinkering around trying some internal threads on the lathe. Drew up a simple 2.0" diameter by 1.25 tall container with a wall thickness of .1 as a test. I want to build a top to screw down on it.. Something like a pill bottle you see at the drug store or a waterproof matchstick holder.

What thread pitch would you use for something like this? I was thinking of a 16 pitch which I believe translates to .0625 (1/16).. More threads the tighter the seal? Hope this makes sense..

 

[A_Pmech]

4-start 16 pitch Stub Acme with Higbee Cuts.

 

[jxxxoxxxe]

4-start 16 pitch Stub Acme with Higbee Cuts.

I'm lost....LoL....






since this is a thread about threads...when cutting a fine pitch thread on a lathe, do you always used the same sized 60* tool? So would I use the same tool for 6 tpi as i would use for 16 tpi? my thought is 60* is 60*...not matter the size....

 

[Hammer1963]

Personally, I would go with something in the 24-28 range. I prefer the fine thread. It will help sealing properties

 

[hunter1151]

4-start 16 pitch Stub Acme with Higbee Cuts.

LOL..................I did cut some quad-lead 1/2-8's the other day though

 

[fredybender]

Number one thing you need to check is helix angle of the thread compared to the flank releif of the tool;

The fact of having the right clearance angle will make, or break your threds...
Use the following pages to help you out.
If you need more info PM me...
(this is my job )

 

[Jack Burton]

I'd think fine threads would work best but the interface between the bottom of the cap and the rim of the container is far more important.

I believe something like a Maglight(Aluminum) has a one-lead fine thread on the battery end with O-ring. Whereas, a beverage bottle(plastic) has a multi-lead coarse thread with plastic ring seal. The fine threads would cross-thread and wear out too quickly in plastics, and the coarse multi-lead threads in a metal would make turning the cap too difficult.

So I think the thread should be suited to the material and the actual sealing interface needs to be considered in your project.

Also, even tapered pipe threads need a sealant applied to them.

 

[deere2210]

Thanks for all the replies and input.. I had not even thought of the helix angle and clearance.. Spent an hour reading through different online articles. If I understand correctly, I am doing a 1.75 by 20TPI thread so it shows a shim of 0. I ended up on the lathe cutting internal thread/cup this afternoon... However, I have to admit I messed it up.. I pulled the major/minor out of the Machinist Handbook and for some reason I thought of the major as the initial size to bore out and then cut the threads.. So I bored the cup to 1.75 and realized I should have bored to 1.7 as the minor.. I had major in my head as the starting point like an external thread.. Anyway, I'll do it again tomorrow and post some pics.. Another learning experience..

 

[agoins]

He has a good idea of practicing on PVC.