Author Topic: Self Reversing Screw  (Read 278 times)

Offline Joules

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Self Reversing Screw
« on: September 09, 2019, 12:11:15 PM »
Has anyone cut one on a manual lathe ?   I am trying to work out a way of making one of these, probably in perspex or Delrin rod, milling the groove from the cross slide with a 1 or 2mm ball nose cutter depending on design of other parts.





It's the same mechanism as in the old Yankee screwdrivers.   The final device is very much a work in progress if this can be resolved first.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline Joules

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Re: Self Reversing Screw
« Reply #1 on: September 09, 2019, 03:00:14 PM »
Hmmm that wasn't as easy to draw as I hoped.  It took 3 attempts, thinking it would just be two screw cut passes right and left with some blending where the hard edge meets.  Not so lucky, it needed the intersection blending properly.  The difference between the upper blue tool path and the lower tool path, not something I can easily achieve on the manual lathe.  A 3 axis CNC mill/router would do it with one axis being a rotary, at least the tool path is now generated.   The pitch is 7mm as that's the largest I can cut here, another thought would be to screw cut the shaft, and then 3D print the transition ends. 7mm pitch is still a bit slow and could do with being double that.

Just get doing and make swarf, you can decide what its going to be later.   :thumbup:

Offline mc

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Re: Self Reversing Screw
« Reply #2 on: September 09, 2019, 06:36:48 PM »
I'm guessing these would have originally been machined on some kind of copy machine, as I've maintained them on rope reel units where the original design must date from the 80s, if not earlier, so before CNC was that common place.

They're quite a simple mechanism, it's just machining the screw that is hard.

Offline Pete.

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Re: Self Reversing Screw
« Reply #3 on: September 09, 2019, 06:46:23 PM »
I've got one, but it's huge compared to what you want. It works with three ball bearings. One fixed, the other two can change positions.

http://bbs.homeshopmachinist.net/threads/77796-An-interesting-take-on-the-self-reversing-nut

Offline Joules

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Re: Self Reversing Screw
« Reply #4 on: September 09, 2019, 07:21:17 PM »
Cheers Pete and MC, thatís the one I am trying to make, with the two spring clips that retain the balls so they stay in track at the cross overs then change direction at the transitions, each end.   I think I can print the nut in the same style I did the ball nut.   I am looking at printing the screw, if it works I may be able to use it as a follower if the printed version isnít strong enough for final use.


Pete, the link at the end of your other thread appears to show that a screw cut left and right thread might work if I can keep things aligned.
Just get doing and make swarf, you can decide what its going to be later.   :thumbup: