Stresses on Acme threads? 1

[jmccalip]

Hello, I am a new mechanical engineer, and am tasked with designing a heavy duty screw jack. I choose Acme threads over square, since it will only be lifted without load, so extra friction doesn't matter, I just need the extra strength they provide over square threads. Also, the load is extremely high...over 200 tons.

My question: is there any pre derived formulas for the bending, shear, combined stresses on ACME threads? Most I see is for square. Thread anaylsis is not my strongest point, but it seems the only difference is an increased root area and radial force involved. I would rather see this in text before I try my first attempt on a critical item. Any help? Thank you.

 

[KENAT]

Any of these help (not the 2nd one)

http://www.eng-tips.com/search.cfm?...tress&t=&h=&searchSite=2&searchArea=1&d=1&s=1

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Jboggs]

I would enlist the services of a company that specializes in the manufacture of screw jacks. There are many, and all the big ones do one-off specials all the time. Let them design and provide the screw, the nut, associated bearings, etc. You will learn a lot from the details of their design, without having the pain of learning those same lessons from your own mistakes. You say you are a new engineer. Take some advice from an old one: if you don't have the experience, use someone who does. A 200 ton lift is not the kind of project for you to "get your experience" on. I've had good personal experience with Nook Industries and Joyce-Dayton.

 

[TVP]

Yes, there are derived formulas for calculating the stress on a thread (square, trapezoidal, etc.). Google "power screw stress". Here is one link that has useful information:

http://www.roymech.co.uk/Useful_Tables/Cams_Springs/Power_Screws_2.html

 

[3DDave]

One note on RoyMech, front page,

PLEASE NOTE: Roy Beardmore passed away on 9th March 2013. This website will therefore no longer be updated and email contact is now suspended. He is sadly missed.