Torsion Spring

[Jeff DaymanParticipant @jeffdayman43397]

Hi Neil,

In my experience piano wire does not do well in damp environments. In industry I was involved with two major corrosion related incidents with piano wire parts. One was in valves for hydronic home heating, the other in photocopiers. Both involved severe corrosion in just a few weeks regardless of heavy grease coatings on the wire. Several hundred thousand wire parts failed in the valve case, and tens of thousands in the photocopier case, and had to be dealt with in both cases at huge expense to the firms. The piano wire was mandated originally as a cost down measure vs our design dept's original spec of stainless wire, by the forensic accountants in the purchasing depts. Didn't work out that way! I'm gunshy about piano wire if there is damp conditions, as a result of these experiences.

JD

[Sub MandrelParticipant @submandrel]

Interesting Jeff,

It seems it is good with occasional exposure (dishwasher pokers and model aircraft bits), but can't take sustained life in a damp environment.

Neil

[Ian S CParticipant @iansc]

Would not have thought a photocopier would be concidered a DAMP enviroment. Ian S C

[Jeff DaymanParticipant @jeffdayman43397]

Hi Ian,

Photocopiers are used in all environments worldwide. Some are dry, some are damp, hot,cold etc. One of the big challenges designing that type of equipment is making it reliable in the varying conditions, as the behaviours of paper and static electricity vary widely with environment. The major piano wire corrosion problems occurred in machines primarily in South America, Vietnam and Thailand.

JD

[Sub MandrelParticipant @submandrel]

I've been told that paper is one of the most difficult materials to handle automatically.

Ten years ago, our paper used to come with an arrow on it so you could put it in the machines the right way up, wrong way and it would soon misfeed. It's to do with the curl of the original roll.

Funnily enough the paper we get now ssems to be 'omni-directional'.

Neil

[Rufus RoughcutParticipant @rufusroughcut]

Neil

That's because its made flat primarily in South America, Vietnam and Thailand which are much nearer the equator so dosn't realy know which way to roll.

Barry

Had a go with TIG 1.5mm stainless weld wire at work, for spring warmed it a bit when bent and quenched quick and seemed a sturdy spring, was a blueish hue when i quenched.

[Ian Robinson 4Participant @ianrobinson4]

Posted by Rufus Roughcut on 17/04/2013 21:26:38:

Hi Ian R4

Would you not be better using new on each side of latch bar as per your edited pic, which would unburden the single spring a bit.

Regards

Barry

I think that 2 would better. You have also bent the end which, looking at the photo of the old spring [see album], there is a slight suggestion that this is perhpas how it was. As an alternative to a wire spring, I was thinking that a flat spring might be an improvement to the design – similar to the one at the other end of the lock but not wrapped around the pins – so it has some freedom to move?

[Jeff DaymanParticipant @jeffdayman43397]

Neil – you have a PM

Ian – a flat spring may be less prone to breakage than the wire. You can probably use a thinner gauge of stock with a flat spring to get the same force as the 1 mm dia wire. Several places online have design aids for flat springs. (Google is your friend.) What will retain the flat springs to the lock assy though? it would probably be wise to add some tabs beside the bends in the flat spring to keep them from expanding outward and a) falling off the latch face in the centre b) hitting the sides of the pocket in the door the lock fits in. These could be placed next to the round posts the wire spring is wound around, and shaped like the tabs holding the upper end of the wire spring as today. If you were thinking of maybe using holes in the spring to attach a wire or clip around the round post, I wouldn't advise it – any holes in flat springs are where breakage will usually start. A rectangular strip with no notches, holes or sharp edges/corners will make the most reliable flat spring.

JD

[Ian Robinson 4Participant @ianrobinson4]

THANKS JD & Rufus et al.

The problem with the flat spring idea is that the crown of its arc increases as the latch is retracted and hits the metal plate approx 1mm before the end travel of the latch. Unless the spring can be bent to eliminate this arc it isn't ging to work. I will explore the effects of the bend a little more but it looks as though two torsion springs may be better.

Ian

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