Locking an adjustment screw

[kgwhipp]

Hello, this is my first post here and I wanted to thank everyone for creating such a great useful community.

I'm designing a lifting platform with a 10,000 lb capacity and one of the features I'm incorporating is a set of leveling screws embedded into the structure at the four corners. The cut-away view I've attached should explain the idea pretty clearly.

The bolt will be threaded into a 20mm thick steel that is welded to the rest of the structure.

The bolt is going to be used once for leveling then the desire is to lock it in position so that over the lifetime of the lift operation, the platform will remain level to the surroundings (the large area on the left, the frame is slightly raised for clarity).

I've rounded it down to two possible options: a chemical thread locker (loctite) or a less common approach: thread locking helicoils. I don't have much experience with either and wanted to know if anyone had any advice to share.

Additionally, I wanted to get a bit of confirmation regarding my bolt sizing- this is an 18mm coarse thread bolt, a set of 4 are expected to hold a 10,000lb load. I'm having a hard time finding a good resource to obtain appropriate strength numbers, especially for the metric side of things. Can anyone recommend a site and/or share thoughts on my selection?

Thanks!

-Kevin

 

[MikeHalloran]

On a generic platform, you don't control the actual location of the load on the platform. ... so it would be conservative to design for the load case where all of the rated load is carried by just one of the supports.



Mike Halloran
Pembroke Pines, FL, USA

 

[USAeng]

I think I understand your drawing... maybe not worry about locking the threads and instead secure the top of the socket cap screw with something? tack weld, or some sort of locking clasp/clamp/sort of thing... if you decide to lock the threads loctite sells a variety of "permanent" thread lockers that should work ok there like red 277 and a green one and others that are even stronger... loctite website is pretty good too

 

[MintJulep]

The available open time for many of the Loctite products is in the order of 5 to 10 minutes. Can you apply, run the screws in and get the thing level within that time frame?

If not make sure you select one of the longer open time flavors, or do your adjustment dry, then apply one of the wicking types.

 

[kgwhipp]

We should be able to level it within that timeframe (5-10 minutes.) These chemical adhesives seem to be pretty trustworthy then?

Thanks for the suggestion USAeng, while for all intents and purposes this adjustment should be "permanent," I don't think we would want to weld the head just-in-case a decade down the line someone feels the need to tweak it.

-Kevin

 

[cooperjer]

The Loctite adhesives have a lot of versatility. You may want to contact your local Loctite sales rep to get their recommendation.

Regarding the bolt design, I would recommend referencing Fundamentals of Machine Component Design by Juvinal and Marshek. I find this book invaluable for bolted joint designs. The design you have looks to put the bolt in compression and therefore the two failure modes that come to mind are buckling and thread shearing. Look for the equations related to those to failure modes to confirm your bolt size.


Cooperjer
Mechanical Engineer

 

[drawoh]

kgwhipp,

Take a look through some catalogues for opto-mechanical hardware. None of this stuff will be strong enough for you, but some of it will give you good ideas. Optical people have the same problem you do of how to lock their screws down without disturbing alignment.

Search Google for Melles Griot and Newport.

JHG

 

[Duwe6]

The ultimate in locking is a amall weld [tig - GTAW preferred] on every other flat of a hex-head bolt or nut. Figure 15-30 minutes per bolt.

 

[desertfox]

Hi kgwhipp

If you change your leveling bolt to a hexagon headed bolt you can lock it by welding a block to the fabrication and placing the block against against one of the flats of the hexagon.
Your request for a site on metric bolts:-

http://www.roymech.co.uk/Useful_Tables/Screws/index_screws.htm

desertfox