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Message No. 20402, Started by kevinh673 on 03/11/09

I have an assembly in which I must translate torsional force (a torque from screwing in a piece), that pushes against a silicon ring, which pushes against a metal piece. I'm interested to see if the piece will deform or fracture.

I do not have the specs for the spring constant for the silicon ring. I'm just going to do calculations assuming the piece that is being torqued is directly pushing on the metal piece. I'm not entirely sure on how to go about calcuating this.

I know of the torque to axial force equation that is:
F=.2*D*T
However, this does not account for pitch....

I've included a hand calculation my boss did. I'm not sure if it is correct or not...

I will include the hand calculations with an illustration, as well as two pictures of the assembly modelled in CAD if it helps.

The torque is 15 in-lbs. The thread is a 7/8 - 32 pitch.  

 http://files.engineering.com/getfile.aspx?folder=8c14c6cb-205e-4fd0-9fc0-7191b347cd14&file=TorqueCalculations.pdf

http://files.engineering.com/getfile.aspx?folder=81720060-fa98-4db6-a30a-e9a6eb50bb0f&file=TorqueAssembly.pdf

http://files.engineering.com/getfile.aspx?folder=c4501c09-d563-407b-a6ae-ed7b95b8031d&file=TorqueAssembly2.pdf

Some sites I've found:

http://www.roymech.co.uk/Useful_Tables/Screws/Preloading.html

MIL-HDBK-60 Threaded Fasteners - Tightening to Proper Tension, available free of cost here:

http://assist.daps.dla.mil/quicksearch/  

 

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Follow-up Messages (13)
I am just curious, is this a 60 degree Unified series thread   or s...
No. 20421, Posted by gerdb on 03/14/09, 00:10 PST.
It's 7/8-32. It is not common, I agree.
No. 20416, Posted by kevinh673 on 03/12/09, 12:37 PST.
maybe we're talking two different things:  .875 (7/8) has two threads ...
No. 20415, Posted by apatelct on 03/12/09, 12:34 PST.
Yes, I am sure. We used it on the old design, and are using the same size o...
No. 20414, Posted by kevinh673 on 03/12/09, 12:18 PST.
Are you sure on the thread size?  I've never heard of a .875-32 thread...
No. 20413, Posted by apatelct on 03/12/09, 12:15 PST.
I ave that book. I used it to find the data for the pitch and thr...
No. 20412, Posted by kevinh673 on 03/12/09, 12:11 PST.
Hmmm, according to this I'd have over 3,000 lbf.   if T = 15 in-lbf,...
No. 20411, Posted by kevinh673 on 03/12/09, 12:01 PST.
correction: Q=force, lbf T=Torque, in-lbf p=pitch, in
No. 20410, Posted by apatelct on 03/12/09, 11:52 PST.
T=in-lbs R=lbs p=in
No. 20409, Posted by apatelct on 03/12/09, 11:49 PST.
Thanks. What units are the equation for? I noticed there is a con...
No. 20408, Posted by kevinh673 on 03/12/09, 11:23 PST.
REF Machinery Handbook (26th Ed.) Pg 135   T=Qp/6.2832 Where T=torq...
No. 20407, Posted by apatelct on 03/12/09, 11:15 PST.
Get a book (remember them?)  Specifically Machinery's Handbook.  ...
No. 20406, Posted by twirly on 03/12/09, 07:14 PST.
KEVIN673:  The F=.2Dt equation you mention is for tightening a bolt or...
No. 20403, Posted by cessna on 03/11/09, 11:32 PST.
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