Design question... if you all don't mind...

[A.DelNegro]

Since this is such an expert/experienced list I figured I'd ask this
question...



I need to create a height gage for a stack of material. The basic
design needs to be 2 parallel plates with one stationary and one sliding
on shafts with linear bearings. It was suggested that I design this
with 4 posts with linear bearings. I've seen this done a few times
before with 2 posts and there always seems to be a sticking issue when
the plates are not perfectly parallel.



My question is, will using 4 posts with linear bearings be better or
worse than 2 posts with linear bearings? They would also like it
actuated by an air cylinder. For this reason, it makes me think the 4
post solution might be better. Anyone out there done this and can offer
some advice?



Thanx for the help.



Tony



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[KenGawne]

Adding additional posts, I have found, does not keep the system from cocking and binding. What works better is to add an additional bearing on one or both of the posts. It is best to move as close to a square when looking at the extent of the bearing contact on one post to the other post rather than a narrow rectangle. Sometimes three post work well to counter cantalevering of the load in all directions.

Some of the linear bearing manufacturers have some application information regarding this problem.

Are you using 1 cylinder or more?

Ken Gawne

[BobFrindt]

Hello Tony,
I have seen two post designs like this for stamping dies. They are quite
accurate and don't bind. If your bearing length in the bushing in
relation to the post diameter is sufficient, you should not get any
binding.

Here are a few sample die sets, three of which have only two posts.



here is a link to Danley's site