How to polish hairspring?

[Roger HartParticipant @rogerhart88496]

Trying to make a hairspring for an escapement experiment – 0.1mm thick by 0.63mm wide 9 turns so about 13mm dia. Polished flat steel wire – OK. Coil 4 strands interleaved OK. Soap well to avoid scale, bring to red hot and quench OK. Seperate springs OK. But very hard to bring to a good polish before bluing. Outside coils can be done on a wooden cone but the inner face of the coils is 'very difficult'. Also made special tweezers lined with wood + diamantine – workable but have to be v. v. careful not to distort spring.

So ideas for polishing the hairspring please – or how was this done commercially – I cannot believe this was done by hand except in the very early days. Alternatively is there a really good way of tempering but keeping the polish? BTW, I know I can buy hairsprings – but making one seemed more fun – till now.

[Roger HartParticipant @rogerhart88496]

How to polish after it is coiled and ‘set’ or how to avoid need to polish it.

[David ColwillParticipant @davidcolwill19261]

I don't really know if this would work but…. if you can use an oven for the tempering you could try feeding an inert gas into it (mig welding shield gas should work) this would stop any oxidation while it was heating. Good luck anyway.

David

[speelwerkParticipant @speelwerk]

Would it not be possible to use tubing with a inner diameter a little smaller than the outside diameter of the coil, then wind the spring just enough to place it in the tubing so when you release it, it stays in place and you can polish the inside of the coils. Niko.

[Michael GilliganParticipant @michaelgilligan61133]

Roger,

There is a link to Saunier's description available on this page.

Whilst you are there, have a browse through the rest of the site.

… Wonderful stuff, but way-beyond my skill.

MichaelG.

[Roger HartParticipant @rogerhart88496]

Thanks all for ideas. @DC – I had thought of using an inert atmosphere but quenching seemed a bit of a problem. @Niko – mmm, will think about that. @MG – Thanks very much for the Saunier link, I had remembered the conical former method but had forgotten the pegwood/cork block method. Tried it out with an upturned placemat and a pencil and diamantine – works very well and not all that difficult. Also your link is very impressive – that chap has some very nice kit.

Also checked out the bluing method (on earlier tryout) – used a brass block 6.25mm thick with a 1.5mm hole in the side for a thermocouple – cheap digital voltmeter type – then sat block on kitchen electric cooker and wound up the temperature (Mrs R not looking….). Once got to 340C turned down the power and looked carefully – voila a nice blue colour – grab with tweezers and wave in air – job done.

[speelwerkParticipant @speelwerk]

Sorry, had the wrong idea of the shape of the hairspring, that is what you get when your understanding of English is poor. Niko.

[ronan walshParticipant @ronanwalsh98054]

Roger , have you considered electropolishing ? My old job used to send stainless steel parts used in the pharma industry out to be polished. Might be worth looking into.

**LINK**

[Jack Hobson 1Participant @jackhobson1]

I've never done anything like this so no idea if it will keep the finish on the spring. I'd like to try it though…

If you have a good polish before hardening then you could try hardening in a small pot of LoSalt which works as an inert atmosphere for hardening. High temp salts are dangerous if spilt or any water gets near them so give full respect, but as you need such a small container then the risks seem acceptable. Do on a dry stone floor. Make sure the spring is completely dry before you put it in the salt. You probably need to rig up a mini furnace to get the salt pot up to heat (i.e the salt melted) before you put the spring in. Use a thick walled metal container, ideally stainless, or the salt may eat through and spill. Split salt at 800C will immediately ignite anything flammable, like wood, hair, bone etc Wear safety specs and a hat.

Blueing salts can be used for tempering and even quenching.

1 Heat LoSalt till it melts. It should be red hot. 2. dip spring in salt pot until it takes on same colour as melted salt. Keep head well away when you first put spring in. 3. quickly move spring from LoSalt to heated blueing salt for some seconds – I'd guess 15 should do it. 4. dunk in water briefly then let air cool. 5. Once cool AND DRY, temper in the blueing salt.

 

Edited By Jack Hobson 1 on 01/01/2014 14:12:04

Edited By Jack Hobson 1 on 01/01/2014 14:12:26

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Roger ,

Engineering method is to heat the spring using an electrical current passed through the actual spring .

Very little current needed for such a tiny thing so small battery plus rheostat should do it .

Safer not to use anything mains powered and no need anyway .

Experiment on scrap first to get idea of current needed .

For actual job increase current gradually from very low until required redness colour is seen .

Maintain current whilst quenching thus metal hits coolant at exactly right temperature without undesired cooling off in transit . Turn off current while spring still immersed .

Optionally play small flow of safe inert gas over top of coolant pot and do heating of spring in place so as to exclude air throughout .

No air and no flame should mean no scaling at all .

Temper if needs be using same method .

Also works for small tools using higher currents and can be applied selectively to zones within workpiece .

Regards ,

MikeW

Edited By MICHAEL WILLIAMS on 01/01/2014 14:52:04

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

You can also use the same method to set curvatures in small wires and strips for clocks and instruments .

Bend strip or wire to required shape and secure – possibly using simple Tufnol jig .

Very short burst of current and strip or wire is set to shape .

MikeW

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