Re: Questions regarding thread diameter and pitch for special design case wtih limited thread length

John2005 wrote:
> Hi David,
>
> Thanks for your reply.
>
> How would what you suggest compare as far as cost, to threading ? If I
> were not going to use threads, perhaps a slip fit between the rod and
> the hole and the use of loc-tite at the joint would be the way to go,
> but I think threads are probably my best bet, it's just a matter of
> what thread diameter and thread pitch are best.

I agree that threads are probably best IF the motion of the rod is
cyclical. Eventually it will work its way out of the hole if press
fitted. Some mechanism to prevent unthreaded is also recommended or the
same could happen with screw threads. See my replies in
"alt.mechanical.engineering" regarding thread type.

> The rod will have threads on each end.
>
> Also, If I use the method you suggest, where the rod goes into the
> hole, I may not be able to put the full 3/8" OD in the hole, and may
> still have to neck the rod down, where it goes in the hole, due to
> design constraints. Necking the end of the rod down, may also help it
> assemble more straight, since the hole does not have much depth.

This doesn't make sense, except that a shoulder at the neck-down will
help RETURN the rod to perpendicular. Is that important?

> Also, the base plate has bearings in it, and I cannot deform the
> bearing bore with heat, since the bearing bore sizes the bearings and
> bearing radial internal clearances. The rod also has a close tolerance
> hole machined in it center, along it's longitudinal axis.

Does that mean that the hole is used in such a manner that would prevent
the rod from rotating? If that is the case then a shoulder on the
thread does not serve to prevent unthreading (again, see my other posts)
and may not be necessary.

Mark 'Sporky' Stapleton
Watermark Design, LLC
www.h2omarkdesign.com
.

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