RH or LH Thread- how about both?

[Robert Atkinson 2Participant @robertatkinson2]

While catching up on the excellent first war Peerless rebuild (link below so not to divert you but worth a read) there was this link

The guy machined a bolt with a 10 start thread in both RH and LH
Thinking about it this is what a Yankee pump screwdriver shaft has but coarse and square.

The ongoing Peerless restoration thread

https://hmvf.co.uk/topic/35087-ww1-peerless-lorry-restoration/

and completed Thonycroft thread – 10 years worth

https://hmvf.co.uk/topic/9672-ww1-thornycroft-restoration/

They do use a Myford but this is NOT model engineering

Robert G8RPI

[Robert Atkinson 2Participant @robertatkinson2]

[Nigel Graham 2Participant @nigelgraham2]

I think the pump-action screwdriver is a single-start thread in both directions. The lead is very coarse to allow the screw be driven by the nut – a lot less efficient than the conventional way round.

It is a very old idea, used in the Archimedean-type drill, probably pre-dating the 'Yankee' screwdriver, which I think was a trade-mark used by the American wood-work tool-makers, Stanley. I have such a drill, and found it useful for making pilot holes in hardboard for panel-pins when assembling a flat-kit book-case.

A development is the reversing-screw drive that oscillates something at constant speed (apart from a very short deceleration and acceleration at each end on the change-over). It consists of a pair of opposing square or Acme threads engaged by a cylindrical or pivoted rhomboidal follower that simply leaves one thread as it enters the other for the return trip.

Two applications I have known:

– Very short screws, only 2 or 3 turns, on a small lithographic printing-press, for oscillating the ink and water feed rollers against each to distribute the fluids evenly;

– Much longer ones operating the laying-fairlead on a winch built for handling what are called " towed arrays " – long hoses containing strings of hydrophones, used in naval defence and marine surveying. The hose has to be wound accurately to avoid damage, so the reversing-screw, parallel to the drum and geared from its drive, would have a lead (also pitch) equal to the hose diameter.

Although giving constant stroke length and speed, I have wondered if a reversing-screw could be one way to fit a power-drive to something like a manual shaper or planer, provided you have the equipment for milling hefty threads. Its advantage is that it would need only a simple motor and reduction-drive – no need for a reversing-switch, nor for stepper-motors and electronics.

[egaParticipant @ega]

On the subject of the Yankee screwdriver, I believe the original was by North Bros and a passable copy was made by the appropriately-named British firm of Spiralux.

[peak4Participant @peak4]

Here you, there might be just time to make one of these before Christmas.

Bill

[John HaineParticipant @johnhaine32865]

There's a classic wood lathe that has opposite handed threads at each end of the headstock mandrel, the lhs being for bowl turning. It has to be opposite hand so the faceplate won't unscrew itself. I believe they do a faceplate which is double threaded lh and rh so it can be used on both ends.

[Howard LewisParticipant @howardlewis46836]

Right and Left Hand threads are found on Turnbuckles to tension wire ropes, and on the scissor jacks that used to be used on motor cars for support when changing wheels.

Multiple start threads suggest that the aim is to produce a lot of axial movement for a small rotary movement (Akin to focusing threads on camera lenses )

The combination should produce a lot of linear movement for small rotary travel.

What was the arrangement meant to adjust? (This would seem to be reverse of the adjustment required for brakes or clutch on a vehicle ) A seat adjuster, perhaps?

Howard

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