Leveling Bolt Detail 1

[dozer]

A vendor is proposing the following arrangement to allow a skid to be adjusted up and down.

A rod which has an unthreaded portion at the end and then is threaded the rest of the way up goes through a hole in the base plate. The threads actually bear around the perimeter of the hole. It's not threaded into the lower part mind you. This seems like a really bad idea to me. Not sure how you would compute the bearing stress on where the underside of the threads bears on the lower portion. I just had an idea as I was typing this. If you reduced the diameter of that unthreaded rod and the hole it goes in a bit to give yourself a shoulder to bear on that might not be so bad.

Has anyone ever seen a detail like this? If so, how do you prove the threads won't shear or fail in bearing? I've pretty much convinced myself it needs a shoulder just in the process of writing this but I'm still curious if this is something that is not uncommon outside my tiny little world.

 

[MintJulep]

About a million commercially available solutions available for purchase. Why reinvent the wheel?

"Leveling feet"
"Leveling screw"
"Scaffold jack"

 

[Tmoose]

In principle I agree about requiring a shoulder of sufficient area and accuracy.

Will the skid live on these leveling screws forever?
Is rotating machinery involved?

 

[dhengr]

Dozer:
You are spot on with your first impressions of that detail. That is some CAD monkey’s idea of how to make things difficult, expensive and unworkable; all because his CAD software will allow him to draw it without him having any idea what he’s actually doing. At first, you have some small portion of the circumference of the rod thread bearing on the plate, until the thread or the pl. start to yield and bring more (new, yet to yield) thread into play. You’ll just have a progressive shearing failure of the rod thread. The bearing pl. has been thinned by the counterbore, right where the load is applied. It is not loaded in bearing, but rather bending in the pl. and shear at the edge of the counterbore. Finally, how do you keep the rod from tending to turn when you try to turn the leveling nut? Ask to talk with an engineer or the boss at the vendor’s shop, not a drafter, to clear this up.

 

[dozer]

It will live on these leveling screws forever but at least it's not rotating machinery. I'm in the US, this was designed across the pond. Here, we might have used adjusting screws to set the height then grouted it and backed the screws out when cured. At the risk of being politically incorrect they seem to like to do things more complicated over yonder. Dhengr, you understand exactly what's going on. I was afraid I might have zoomed in too much and made it unclear. Thanks for reinforcing what I already thought. One thing you're not seeing is there is a set nut on top of the rod. Once you twist the rod to set the height you then tighten the set nut (locking nut, whatever you want to call it) to keep it from rotating (you hope).

I kind of did the same thing as this design only in reverse recently. I was pulling a steering wheel and I just put the tapered end of the puller right in the threaded hole. Not too smart. When I saw metal peeling out I decided to back off and put a socket between the puller and the shaft. Worked like a charm. Kind of the same thing as adding a shoulder to this contraption. Still an overcomplicated design in MHO.

 

[JohnRBaker]

You're overlooking the obvious as I suspect that this design was probably chosen based on the cost of production. The main part of this can be easily manufactured by turning-down and adding a groove to one end of a piece of 'all-thread' or threaded-rod. Granted, they could have started with a larger threaded-rod and turned it down so as to include a bearing-area or shoulder, but again I think they were trying to keep the cost down so that stuck with minimum sized parts.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[chicopee]

I agree with all above responders and in essence it is a lousy design.