threaded rod design and static load control

Hi,

I've been trying to design a heavy duty threaded rod in Solidworks but
without a lot of success. I know there is a cosmetic feature. I'm
wondering if this cosmetic feature is used when you put a static load
on it using cosmos.

I would like to know if the thread will hold.

I have to design a movable carriage wich can hold a load of several
tons and wich can be moved on a 0.1 mm precision. I fear that an
hydraulic system can't perform on such a precision and therefore I want
to try a threaded rod design.

Best regards,

Geoff

 

If you need thread geometry for FEA, it should be modelled.

I only use cosmetic threads for fasteners. If the threads are
functional (like feed screws), I like to have them modelled.

 

If you model them, which function do you use? I've been working with SW
for +1 month now and I'm not familiar with all of it.

Regards,

Geoff

 

Go to the "Help" Menu option and work through using the "Thread" items
where you will learn to use the "Helix" and "Sweep" items.

Bo

 

Thanks

That helped me a lot.

But when mating two parts together with cut-sweep and a boss-sweep I
can't mate the thread.

I presume I have to mate the thread to do some FEA afterwards.

Best regards,

Geoff

 

I do NOT think there is any technique to allow mating of thread faces,
one against the other, or at least I've not heard of any. Doing a mate
that allows a FEA stress analysis would be tricky in that situation.

Collision detection will work on threads, but that doesn't establish a
mate.

Maybe someone else knows more.

Bo

 

Are you saying that you cut threads on the outside of the rod with a
sweep and then you cut the same threads on the inside of the nut and
then you had two swept surfaces to attempt to mate together? I'm not
sure if two such surfaces would mate.

Something that you may try first is to apply the forces to the cut
thread surface. This may not work. But, then you could try cutting a
series of annular rings with the same pitch as the threads. It
probably won't make much difference if the rings are not connected
because approximately the same amount of material should be involved.
What is nice about the annular rings is that you should be able to
apply forces in COSMOS to only the number of rings that would be
engaged in the length nut that you have and the approxomate distance
from the end of the rod.

In the end, this may be one of those problems where the answer may be
easier to estimate from a handbook. Probably along the lines of
something like the mean thread diameter x pie x effective nut length
divided by 2 x (some fudge factor like) .9 times the worst case
expected tensile strength of the mateiral and since the failure is
probably in sheer the resulting value should probably be divided in
half....(which I'm not sure that COSMOS takes into consideration. But
you should definately look this up and verify a calculated estimate
agains COSMOS. Which is always the best practice.

And if this is a critical application, (like holding up a bridge or a
beam in something like the new World Trade Center Building) you will
probalby need to do a fair amount of physical testing.

The other alternative for this is to contact a supplier of such
fasteners and get them to tell you what the specs are.

Just a few ideas...
hope this helps

Ed
Now if this works then