Making a miniature leaf spring.

I want to make a small leaf spring for a catch of my own devising. It needs to be in the form of a U about 1/4" high with maybe 3/16 between the arms and around 1/8 'front to back'. None of those dimensions are set in stone - they're just to give an idea of scale.

I tried a bit of 10 thou shim steel, which seemed springy, but not springy enough. Sadly when I tried to stiffen further it by heating/quenching it ended up softer.

Maybe bits from defunct electrical sockets? Cheapo feeler gauges?

Any suggestions would be welcome.

Robin

A bit of Clock Spring would seem the obvious choice.

MichaelG.

Plus one for the clock spring but 0.010" is quite thin, in any event you will have to temper the spring after hardening to a dark blue in daylight.

If you get a piece of clock spring ready heat treated you may well be ok just cutting to size and make the 3/16 dimension slightly wider as a start then compress in the unit you have made, the set will probably reduce slightly on 1st compression.

John

Edited By JohnF on 27/12/2019 23:42:17

Edited By JohnF on 27/12/2019 23:43:45

"Band-it" strapping is a good source of thin spring steel. Also useful for shimming lathe cutters

Paul

I save knackered junior hacksaw blades for leaf springs. The serrations file off easily enough.

Mick

Reeves do annealed spring strip ( may not go that thin) which will be easy to bend and cut unlike an existing spring, then once bent and shaped can be heat treated to give it some spring.

.

Good point, John

... perhaps something from a retracting tape measure would be suitable ?

MichaelG.

Edited By Michael Gilligan on 28/12/2019 08:14:21

If the springiness is across the U-arms in compression then how about just using a piece of rubber?

pgk

Phosphor Bronze strip is often used for electrical pickups on model train locomotives and is usually very thin (10 thou approx) and quite springy. Suggest you try some of the specialist model railway suppliers who cater for the scratch-builder or alternatively the specialist non-ferrous metal suppliers.

Yes agreed, it’s handy stuff. Far too good to throw away with an empty crate!

You might also find good spring material in a (used) seat-belt system. The bit that bolts to the car floor will have a long clock-type spring inside, about 10mm wide. Not much demand for used seat belts, either so finding one should be easy.

Cheers, Tim

Retracting dog leads also contain a lot of spring steel. Eventually the end breaks off, but the rest of it is useable

Thanks for suggestions. I had thought of clockwork, but not having anything suitable from which I could scavenge a bit of spring I discounted the idea. However following MichaelG's mention of clock spring material I Googled and found Meadows & Passmore . Good Lord, they've got everything!

I like the suggestions for 'repurposing' blades from retractable rules and knackered junior hacksaws.I tried with the latter, but unsurprisingly it snapped before I could bend it tight enough. Which leads to my next question...

Meadows and Passmore supply the right stuff in annealed form, which they say has to be heat treated after forming, but they don't give details. Likewise I would have to anneal the hacksaw blade to form it, then re-harden. How does one go about that with such thin material? In my experiment with shim steel I heated the metal over the gas hob in the kitchen then chucked some water over it which simultaneously cooled the metal and extinguished the flame. But there must be another way less annoying to the wife!

Thanks also for other scavenging suggestions which I shall bear in mind.

Robin.

.

In the absence of a super-duper thermostatically controlled oven ... a metal tray full of brass filings [or swarf] is an excellent bed for controlled heating.

MichaelG.

Workshop Practice Series ... Book 1 has some pertinent advice

Hardening Tempering & Heat Treatment, by ‘Tubal Cain’

MichaelG.

Robin, a quick run down on the basics, after annealing and shaping heat to red hot and quench in oil - now comes the tricky bit - tempering !

In the absence of a temperature controlled muffle etc you can improvise

You can "blaze off" the oil by hovering the part over and not in the flame, the oil will catch light and burn away and hopefully your spring will be tempered, this can work well for small and thin springs such as yours but experience is all !

Alternatively as Michael suggests polish the spring to bright and heat in a bead of fine degreased brass chipping's until it turns dark blue in subdued daylight.

Another method if its a thicker spring is place it in a small tin with a small quantity of oil and heat the tin until the oil catches fire then allow the oil to burn away more or less until its all gone, apply a little extra heat if the flame starts to extinguish before most of the old has burnt away - again your spring will br tempered

John.

Thanks for further replies. I have a copy of the 'Tubal Cain' book somewhere but can't lay my hand on it the moment. My problem isn't so much to do with annealing, but initial hardening. It's not easy to get such small parts from the flame or furnace to the quench before they have cooled too much. I think TC touches on this, but doesn't give advice beyond 'you've got to be quick'. That's from possibly faulty recollection though. I do remember his discussion of the 'blazing off' method for annealing though, now I'm reminded - thanks John.

I wondered if horologists (who presumably do this kind of thing routinely) had some cunning method for initial hardening unknown to TC....

I've made some experiments with hacksaw blades, they're a bit too thick for what I want, but I'm getting there.

Thanks for advice, Robin.

.

Here’s a relevant page from a useful transcript of Abbot’s revision of Saunier, Robin: **LINK**

http://www.kirxklox.com/project/ebooks/0004/whb_pt4_pg02.html

... and a link to the home-page: **LINK**

http://www.kirxklox.com/project/ebooks/0004/whb_index.html

.

2020 seems an appropriate year for hindsight [*]

MichaelG.
.

[*] ... but there’s a lot to be said in favour of Electricity 

Edited By Michael Gilligan on 01/01/2020 08:43:55

Robin, when hardening very small or thin items I just suspend the item with thin iron wire, the type that florists use is ideal, don't use galvanised, I heat it in close proximity to the oil quench with a large flame and dunk it immediately into the oil. Never had a problem with hardening this way.

John