[SEL] NC or NF thread

[Curt]

Gene,
Sorry about taking so long to respond but I have been doing the jury 
duty thing. Not done yet as I have to go back this afternoon. :-(
Yes both are RH threads. Pick 1/2" rods. Fine thread will be 20 threads 
per inch and course will be 13 threads per inch.
As you rotate the turnbuckle 1 turn, the fine thread will advance 1/20 
inch and the course thread will advance 1/13 inch. The difference is 
.027" (7/260 inch). So for every rotation of the turnbuckle you change 
the length of the pullrods by .027". That's some pretty serious 
mechanical advantage!

If you really wanted some pull you could make special threads. Say 20 
threads per inch and 19 threads per inch. One turn of the turnbuckle 
would advance the pull rods by .0026" (1/380 inch). You might get tired 
of turning, but you could pull just about anything.

Back to the standard screen door turnbuckle with the RH and LH threads. 
Generally they are 1/4-20 threads. For every rotation of the turnbuckle 
each rod will move 1/20". However, these are additive not differential. 
So the real rod movement per rotation of the turnbuckle is 0.10" (1/10). 
This has only about 1/4 the mechanical advantage of the first example 
above. In reality screen door turnbuckles are pretty poor mechanical 
devices. But they work OK so no one has marketed a better one.

Curt Holland
Gastonia, NC

Gene Waugh wrote:

>Curt, could you go into this a little deeper, or possibly send me to a site
>that can explain this turnbuckle more for me??  I can _sorta_ see how the
>two tpi could give a differential, but both with rh threads?--that is the
>part I cannot visualize.  In Ron's example, the winds are opposite, which I
>can see where it would provide a compound action.
>
>TIA---and Thanks also for the pictures & write-up of your piston sequence!
>
>Gene Waugh
>Elgin, Illinois USA
>
>
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