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One screw two directions, same time

Interesting gear

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John McNamara31/01/2012 12:32:07
1340 forum posts
126 photos
Hi All
A while back I photographed this while across your pond.
I was tempted to make it a mystery item as it is located at the Mystic Seaport museum. Connecticut USA Anyway here it is:
Maybe it is well known among the boat builders here, I had not seen the mechanism before.
A single shaft with two coarse pitch threads running in two directions engaged by two half nuts. Turn the shaft in one direction and one goes up while the other down. perfect for chain or cable driven rudder gear.
Rather neglected I am afraid.
Speedy Builder531/01/2012 18:40:26
2615 forum posts
212 photos
The top of most fly press machines have both the coarse pitch for raising/lowering the press tool and a fine thread for the 'nut' which limits the travel of the tool.
Stub Mandrel31/01/2012 19:43:58
4315 forum posts
291 photos
1 articles
It would be an interesting exercise to make one of those.
Clive Hartland31/01/2012 20:08:47
2820 forum posts
40 photos
Thats an interesting device, it seems it is able to maintain tension in the two chains/cables as the spoked wheel is turned.
This is the only way to stop the rudder flapping about.
I would think its off a barge or a small tug type boat.
Richard Marks31/01/2012 22:18:00
211 forum posts
8 photos
I used to have a fixed spool fishing reel that had a reversible handle, you screwed in onto the reel on the left hand side turning it to the left, if you wanted it on the right hand side you tightened it by turning to the right, left was a LH thread and right was a RH thread, the screw thread on the handle was not biased to either thread, unfortunately I disposed of it a few years ago so no photos im afraid.
Andrew Johnston31/01/2012 22:30:44
6603 forum posts
701 photos
Be simple enough to make the thread on a 4-axis CNC mill.

There are similar looking threads on some glider winches to allow the cable to be wound onto the drum in alternating directions for each layer. Most modern winches use narrow drums, thus obviating the need to lay the cable in alternating layers.

Best Regards,

mgj31/01/2012 23:02:07
1017 forum posts
14 photos
The Rarden 30mm cannon has a similar device. One thread winds the gun back to cock and feed, and the other winds it out to battery - part of the unjamming drills. But there is a third mode - when you have wound the gun back and "cocked" it, it shot forwards under spring pressure to battery along the gaps in the diamonds. How that one worked I don't know, but somehow the nut could slip between the point of the threads, and not when you wound the handle?
JohnF01/02/2012 00:14:56
1152 forum posts
190 photos
On most modern multiplier fishing reels with a line laying device they use this system which auto reverses at each end to travel back and forth over the spool..
BERTO01/02/2012 01:04:34
46 forum posts
The screw thread looks an awfull lot like an Archimedes screw to me .
I could be wrong but the level wind on my overhead fishing reel has something very similar to move the line across the spool as i wind the handle .
Stub Mandrel01/02/2012 21:40:03
4315 forum posts
291 photos
1 articles
Berto is right - I knew I had seen one before! My nan used to have two fast acting push to turn screwdrivers back in the 60s taht had the same 'shallow diamond' pattern on the shanks. they were reversed by flicking a small button.
Sorry Andrew, I think you could do it on an ordinary screwcutting lathe and be cutting metal while you were still waiting for the computer to boot
Ian S C02/02/2012 01:01:00
7468 forum posts
230 photos
Gray, Same with a wheel brace over a battery drill. I do have an 18V cordless drill wired into my workshop low voltage supply.
I have one of those screws of an old fishing reel, been trying to work out how I can use it for rudder control on a boat. Ian S C
Eddie02/02/2012 08:42:42
56 forum posts
Hi I have seen something working on the same principal.
The one side runs on the lefthand thread and the other side runs on the righthand thread. it changed a damper position. Release one side and taking up the slack on the other. The shaft looked like a Yankee Screwdriver with two halfnuts sitting on either side of the shaft.

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