curved lead screw 2

[njlee]

Hi All,

Has anyone seen a custom thread design that allows a threaded nut to follow a curved threaded rod (true arc trajectory), like bending a lead screw. can it be done?

I think it might be possible if the nut only has one thread inside.

has eveyone seen something like that? and where?

thanks,
Lee

 

[EnglishMuffin]

Cockroach: In response to your comment, the following comes to mind : After Yul Brynner's character says "I'll be damned" at the very end of the film "Return of the Magnificent Seven", his companion says "I doubt that. I doubt that very much". However, njlee is not so impressed - he thinks this solution is "too expensive" - the story of my engineeering life I'm afraid ! Sorry, no coaching suggestions. I'm afraid I've lived in the States too long ! At least they didn't lose to the USA (although that has happened before too!)

 

[njlee]

HI All,

I got it. The implementation of the curved lead screw is almost identical to the straight screw, except that the teeth are circular patterned on the single ruled arc (the tooth is radially spaced / duplicated about the same arc). I made an SLA protoype and it worked.

Thanks,
lee

 

[bries]

Hello Lee,

I don't know if this helps and it does have its limits. But check out a Patent I have regarding linear leadscrews moving curved members. The main feature is buried in the entire assy. It is the leadscrew nut & interfacing slider.

Patent # 6,038,127

 

[nbucska]

Could you please give me some specification?

<nbucska@pcperipherals DOT com> subj: eng-tips

 

[turboengineer]

Without having read all of the above posts I can't say if this suggestion has been made, but the easiest way to do this is to over cut the threads on the bar and the nut and then bent the bar afterwards to the final radius of curvature along its normal axis. You could play around with the pitch diameters by trial and error if you have the time an inclination, or better yet you can calculate the PD's ahead of time if you know the desired raduis of curvature and thread series that you are working with. Consult "Machenery's Handbook" for the formulas that you will need.

Tim, the turboengineer

 

[strokersix]

Isn't a curved screw used for automotive safety belt systems? I seem to recall a screw in the "A" pillar that moved the seat belt upper anchor into position when the door is closed and ignition switched on. Perhaps something can be learned from this application.