How to cut a thread at the end of quality piano wire

[Danny Fenton]

I have often wondered how to cut a thread at the end of piano wire. I have never tried it as I thought the wire was hardened. Is there a way to anneal the piano wire to allow cutting a thread, then re hardening?

 

Or.... Am I over engineering this, do I just cut the hardened stuff. Don't want to damage my dies

 

Cheers

Danny

 

[Biggles' Elder Brother - Moderator]

Danny, you can buy a specific tool for this. I think Dubro do it and its available from SMC and the likes. Its basically a very hard die, with a knurled handgrip. I'll try to look it up and post a link.

 

BEB

 

PS You could anneal it by heating and then letting in cool slowly in the air. Tap the thread, then heat again, but this time quench it under running cold water which should reharden it.

[Martin Harris - Moderator]

As I understand it, piano wire isn't heat treatable and gets its hardness from work hardening during the drawing process.

 

I'm not a metallurgist but although I believe quenching will restore hardness it will be extremely brittle. As far as I'm aware it isn't possible to temper it by any heat process as can be done with ordinary carbon steels and restore its original properties.

Edited By Martin Harris on 07/11/2010 00:27:46

[Lee Damms]

You might have problems doing this, I came across this thread which may help http://www.rcuniverse.com/forum/m_9112583/printable.htm  scroll down to the section Heat Treating Music Wire - by Roy Vaillancourt and good luck

[Danny Fenton]

Hi Guys very interesting, that thread featuring the Roy piece on re-treating carbon steel piano wire is interesting. I wonder if the annealing is enough to allow a thread to be cut. I did find something somewhere saying that pushrod piano wire has the thread rolled on the end.

 

I was toying with being able to use nylocs to hold tailwheels, spinning them straight onto the end of piano wire. I can of course solder a brass tube and thread that I suppose.

 

Cheers

Guys

[Peter Miller]

The trouble with anealing and rehardening pianot wire is that it goes brittle. I doubt if you could cut a thread, even in anealed piano wire.

 

You talk of solerin on brass tube and threading that. Possiblbe but why not try this.

 

Mmake the axles short, solder on the brass tube and drill across it and then use a split pin. That would even be scale for some WWI aircraft.

 

I think that push rod wires are much softer meterial. You wouldn't roll a thread in the piano wire weuse for undercarriages etc.

[Tony Smith 7]

If you harden carbon steel by heating and quenching, normally that's followed by tempering at around 250 degrees or so to avoid that brittleness.

[Danny Fenton]

That thread by Roy says exactly that, let it air cool to anneal then controlled heating and cooling to get the spring back without making it too brittle.

 

I have tried the pin through the end route and it works but you then have to hide what you have done if it isn't WWI  Many WWII types use a nut and thats why I wanted to do likewise.

 

I will see if I can get some thick walled brass tube.

 

Thanks chaps

[Steve W-O]

Although springy, is piano wire that hard?

 

It cuts easily with a file or hacksaw, so I imagine it would thread OK, though probably not with a cheap die

[Bert]

Posted by Steve W-O on 07/11/2010 09:22:58:

Although springy, is piano wire that hard?

 

It cuts easily with a file or hacksaw, so I imagine it would thread OK, though probably not with a cheap die

 

'Real' piano wire is very hard - if you know a (very) friendly tool maker they could spark erode a thread in it for you!

 

Bert

[Tim Mackey]

Crikey this sounds like its getting awfully complex  - isnt there a simpler method you could use Danny!

[Steve W-O]

If you want it to look like a nut, why not take a piece of hex bar, drill it for the axle, then in one of the flats drill and tap for a grub screw?

 

The grub screw could face down, so it won't be seen on the ground.

[Danny Fenton]

Hi Steve, it was really a general question on how to put a thread on piano wire. I haven't a specific task for this. The need often comes up and I have always gotten around the problem.

 

Cheers

Danny

[Braddock, VC]

Posted by Steve W-O on 07/11/2010 10:12:24:

If you want it to look like a nut, why not take a piece of hex bar, drill it for the axle, then in one of the flats drill and tap for a grub screw?

 

The grub screw could face down, so it won't be seen on the ground.

 But you'd see it in the air

[Steve W-O]

Posted by Danny Fenton on 07/11/2010 10:18:47:

Hi Steve, it was really a general question on how to put a thread on piano wire. I haven't a specific task for this. The need often comes up and I have always gotten around the problem.

 

Cheers

Danny

 Sorry, yes it was a bit off the original question, I saw the split pin suggestion and went from there

[Bob Cotsford]

Hi Danny, I threaded the axles for my Jungmeister by heating the end 1/4 inch of the wire to cherry red then cooling slowly.  It didn't do the die much good, taking off a few teeth, but I bought a cheap tap and die set from Aldi for a couple of pounds just for this job so I didn't really care.  It worked allowing nylock nuts to be used to retain the wheels.  As you only soften the very end of the axle there's no real need to re-harden it.  The die still works as long as you don't want anything too accurate, and the remainder of the set have paid for themselves time and again.

 

Bob

[Bob Cotsford]

ps - hold the wire in a vice with just 1/2 in. exposed, the vice acts as a heat sink so that the annealing is localised. 

As for rolled threads, they are normally on softer wires not on piano wire.  The act of rolling the thread work hardens the wire.

[kc]

I reckon an unthreaded 'nut' drilled for a tight fit and Loctited on would be easier.

For pushrods use a soldered on threaded end from SLEC.

[Brian Parker]

 

A couple of points..

Annealing of carbon steel is done out of contact with air, eg.  In pre-heated dry sand.

 

Cooled slowly in air carbon steel is normalised (de-stressed) not annealed.

 

 As a guide when heating carbon steel … the point of carbon alloy transformation is when the steel no longer attracts a magnet. The required hardening temperature is just  higher. This temperature should be held for a few minutes.

 

 To temper after hardening, polish with wire-wool then heat to a straw colour and immediately plunge in cold water and agitate. As a guide, this is approximately the melting temperature of lead-free solder.

 

[Danny Fenton]

Hadn't thought this was going to create the response it has thanks very much chaps. Bob do you think a decent die would have been damaged the way your cheap one was?

 

There seems to be a bit of a mixed bag as to what to do, but apart from Bob nobody has tried to do it.

 

Very interesting, thanks again for all your help.

 

Cheers

Danny

[Bob Cotsford]

Not sure Danny, but it definitely wouldn't do it any good.  Depends on what you are trying to acheive, all I wanted was enough thread on the end of the axle to take a single nylock nut.  If you wanted a longer thread, I suspect you could have a bit of a game on your hands.

Actually, the tap and die set I bought turned out to be of reasonable quality, certainly plenty good enough for general modelling use.  The 4mm die is still useable, but takes some care to start the thread as the lead-in suffered.

 

Brian, I bow to your knowledge, it's 40 years since I was at college, and these days I'm more involved with bytes than pearlite/martensite (good god, I'm amazed I can still remember those).  In practical terms, getting the wire red hot did soften the wire enough for what I wanted. 

 

Bob

[JOHN THOMPSON 5]

Piano wire can be threaded quite easy , any good quality split die is usually made from heat treated cobalt steel whch is harder than the piano wire,

 

you need a proper 3 screw die stock , back off the outer 2 screws , screw in the middle one thus openiing up the die , enough to put a half cut on , lock the die up with the outer screws and using ep 90 gear, oil start cutting the thread , then using a threaded bolt of the desired size , reset the die , and very carefully cut the finish cut, you must always use oil as the main  reason for loosing die teeth is high pressure caused by the two surfaces siesing up , this can be done in multiple cuts , you get a feel for this when you,ve done a few ,

 

incidentally if you anneal piano wire and cool it in an uncontrolled fashion sub surface micro fractures can occur especially directly beneath any thread or bend that has been done, the micro fractures will go un detected until the u/c fails too late then.

 

hope this is useful JOHN

[Bob Cotsford]

Hi John, that's certainly the correct way of doing things and the way I was taught as an apprentice, however the cheap dies and supplied stocks that come with them are not adjustable!   

[Danny Fenton]

Thanks John and Bob, very interesting indeed. Will take a look at my dies and see what type they are.

 

Cheers

Danny

[J.N.]

Posted by Danny Fenton on 07/11/2010 22:59:33:

Hadn't thought this was going to create the response ithas thanks very much chaps. Bob do you think a decent die would have been damaged the way your cheap one was?

There seems to be a bit of a mixed bag as to what to do, but apart from Bob nobody has tried to do it.

Very interesting, thanks again for all your help.

Cheers

Danny

Yes I had the same problem some time ago in how to hold wheels in place on 1/8 inch spring wire undercarriage using a Fit and Forget fitting. I decided forming a thread on the wire and using a nyloc nut or 2xnuts would be the answer. After ruining a Goliath HSS die, cutting 2 x 3mm thread I decided to think again. I tried softening and annealing piano wire then gave up to take advice from Presto and Dormer. The font of knowledge suggested that cutting a thread on piano wire by a mere mortal such as I was to be avoided if at all possible. However if I must, then the die to use is a HSS Solid Circular Gun Nose (Cobalt) with Rocal Cutting Compound and when buying thread cutting tools, you get what you pay for. No matter, I have achieved a successful result by forgetting to cut a fully formed thread on 1/8 inch piano wire. I now use a No 5 UNC HSS die which leaves a partially cut thread on the piano wire. 5 UNC is far too big to form a full thread and will only leave a partially cut one thereby allowing the die to cut without bogging down. The die skims the outside diameter of the piano wire allowing a 3mm nut to be used and when the nut is tightened with its female metric thread onto a male 5 UNC thread the result is a secure fitting that can be adjusted/reused.