Fixing two parts with a screw

[davidrdguez]

Hi everyone!

I'm working on a design of a small stand for some parts.

This consists basically in a lower and upper support. They are connected with 3 screws. Adjusting them we can control the height and inclination (we want the upper part perfectly horizontal, so they all must stay the same).

Screws are M10. One of them has a small play at the bottom. Adding this to the screws play itself makes the system not so stable or accurate.

I was thinking about placing a 4th screw. When we finish the alignment the upper part with the 3 screws we use the 4th one to fix the position.

In order to do this i would like to ask you which kind of screw I might use to accurately fix everything. thin pitch? bigger or smaller than M10?

Thank you

Regards,
David

 

[davidrdguez]

I got trouble with the picture uploading, here:

http://img696.imageshack.us/g/system01j.jpg/

Cheers,
David

 

[rb1957]

ok, you've got three levelling screws.

you could add c/bores and nuts to the three screws so that you tighten the upper table down onto the rests.

you could add a 4th screw to fix the upper table's position. i'd suggest this would be at the bolt group center of the existing three. two problems with this ... how do you ensure the 4th point on the upper plate is directly above the lower plate ... use an oversize hole in the upper plate ? what about angularity ? will the upper plate be parallel to th elower plate ? maybe use self-aligning washers to take out the small difference ??

 

[Tmoose]

transits and builders levels use center mount bolt, and 4 adjusting screws in opposing pairs arranged so X and Z can be adjusted independently.

http://www.taylorrental.com/images/products/level.jpg

Similarly lamp poles often use 4 anchor bolts with nuts above and below the base plate for convenient leveling.

http://brownbrosasphaltconcrete.com...Detail/7/LightPoleBasePainting_1244652447.jpg

3 screws in theory means no dangling leg, but makes adjustment more hit or miss.

Only Suitable for light duty applications, with no rotating machinery involved

 

[MikeHalloran]

At least they're not equidistant.
( I use three equidistant adjusting screws as a sign of an amateur or neophyte. )
Yes, you can, eventually, adjust the movable plate to any orientation within range, but in general it requires moving two screws at once, which is difficult to do. I.e., the screws interact, and it can take hours to align such a system.

What you need is one fixed ball/pin/whatever to serve as center of rotation, and two adjusting screws that each lie on lines that are orthogonal to each other and that intersect at the center of rotation. I.e. at least move the single screw to a corner of the plate, not the midpoint.

Add some springs pushing the plates apart, and that will take the screw slack out of the system.




Mike Halloran
Pembroke Pines, FL, USA