Axle pin question – choice of material and possible need for case hardening?

[barryblundellParticipant @barryblundell]

I’m not sure if this is the correct thread in which to post this question – so my apologies if it’s in the wrong place.

A question has come up in connection with my current project, and advice would be much appreciated. I’ve attached a photo in which you’ll see two very small ‘axle pins’. These are 1.8mm to 2mm in diameter, and approximately 1cm in length. The axle pin which is closest to the ruler is one that I’ve made today, and the other axle pin is the old one.

The axel pin should come to a point at either end and this allows it to fit between the two sides of the brass capsule that is also shown in the photo. On either side of this capsule there is a small ‘dimple’ in which the ends of the axle pin are housed.

You might notice from the photo that in the case of the old axel pin, one end does not come to a point – it’s blunt, and so cannot be properly housed in the capsule. Hence the need to make a replacement.

In fact I’m needing to make 85 of these axle pins, so I want to be sure that I get them right. Any suggestions you can give with the following would be really appreciated:

1. Given that the axle pin was made from mild steel, and the capsule is made out of brass, do you think that I need to case harden each axle pin? If so, I’m worried that this may not be entirely straightforward as I’ll need to avoid overheating the important points at either end of the axle pin.

2. Is there a particular grade of mild steel that I should be using – and is there any way of buying this in small quantities? I don’t have access to a lathe, so I would need to buy rod of the appropriate diameter.

The loading on the axle pin is not great – it is basically a pivot and moves back and forth through an angle of around 60 degrees – and is not continually in motion. For the axle pin I made today I resorted to using a piece of the shank of a nail which just happened to be of a useable diameter. However I suspect this may be a little too soft. On the other hand, I can’t use for example stainless steel because I’m simply creating the points by rotating the metal in the Proxxon MF70, and gently working on it with a fine file.

Many thanks for any advice.

[alecsParticipant @alecs]

Rub a file on the old pin to see if it is hardened or not. If it is hardened, the file will skid across the surface without cutting into it. If it’s not hardened the file will cut into it and make mark in the normal manner.

If you need to harden the pins, your best material would be silver steel, available from model engineering suppliers. It has higher carbon conten̈t than mild steel or stainless steel and so can be hardened quite easily by heating to a dull “cherry” red and quenching in oil. Then tempered at a light straw colour.

To avoid over heating the tips, apply a small flame to the centre of the pin and let the colour run out to the tips. Or heat the pin or pins on a bed of brass swarf fragments and apply the flame to the brass. See videos on YouTube by Clickspring for this technique, or on his own website of the same name.

Out of curiosity, what are these pieces from? A church organ or similar?

 

[Bill PhinnParticipant @billphinn90025]

A 39” length of 2mm silver steel is currently £1.99 ex VAT at Cromwell Tools. You could get all your 1cm-long pins out of that. Hardening can be done with a very small torch and tempering done in a domestic oven if you don’t fancy judging the straw colour by eye using a torch. The ends can be tapered by putting each pin in a Dremel (or similar) chuck and running the tip against abrasive paper until the desired tip profile is achieved.

What’s not to like?

…well, the cutting, the hardening and the tempering.

As an alternative then you could buy 2x10mm through-hardened dowel pins (pack of 100 currently £7.79 ex VAT at Cromwell)

If hardness isn’t so much of a necessity but corrosion resistance is, you could buy A2 or A4 dowel pins the same size. A2 pins this size cost even less than the hardened steel ones: A4 ones a little more.

[Russell EberhardtParticipant @russelleberhardt48058]

Silver steel is good but you might find the hardening and tempering a bit difficult if you haven’t done it before.  An alternative would be to use blue pivot steel.  This is supplied ready hardened and tempered and is used bu clockmakers to make pivots without further heat treatment.  It can be obtained from clockmaker’s  suppliers.  For example: https://www.cousinsuk.com/product/pivot-blue-steel-by-size

Russell

[barryblundellParticipant @barryblundell]

Hi Alecs,

Many thanks re suggestions. Following your suggestion – the original pins do appear to be hardened. I’d not previously encountered hardening by plunging into oil. In fact, I’ve not case hardened any metals since my school days which were long ago – when Kasenit was used. However, looking online over the weekend it seems this is no longer sold…

In fact, these pins are part of a nineteenth century grand fortepiano that has been very badly damaged. It uses what is called a Viennese form of action which is quite unusual – seemingly simple but reliant on high accuracy. There are 85 keys on the piano and so I’m going to need 85 of the pins.

 

[barryblundellParticipant @barryblundell]

Many thanks Bill,

Following your suggestion I’m currently tracking down some 2mm silver steel. Unfortunately I’m currently in France and I’ve found that Cromwell don’t post to France… However I’m hoping that I might be able to buy the silver steel from Simply Bearings..

[barryblundellParticipant @barryblundell]

Hi Russell,

The blue pivot steel that you suggest would be ideal in terms of hardness, but I’m worried about the practicality of working with this given that I only have access to relatively simple equipment. In addition, I need to make 85 of these pins and I’m not sure and so the blue pivot steel might not be an ideal option. Hence I thought of using softer steel and then hardening.

As I mentioned to Alecs, I’m working on a nineteenth century grand fortepiano which uses an interesting Viennese form of action. This was originally developed towards the end of the eighteenth century or at the beginning of the nineteenth century. I hadn’t realised that case hardening was in place so long ago.

Barry

[barryblundell]

On barryblundell Said:

Many thanks Bill,

Following your suggestion I’m currently tracking down some 2mm silver steel. Unfortunately I’m currently in France and I’ve found that Cromwell don’t post to France… However I’m hoping that I might be able to buy the silver steel from Simply Bearings..

I’m in France too, I get material from this French company who will post it anywhere.

https://www.blockenstock.fr/rectifie-rond-100c6-c102x2607999

The local equivalent of UK silver steel.

€3.00 for half a metre inc vat + postage. He packs his deliveries well and carefully.

[barryblundellParticipant @barryblundell]

Many thanks Howard, that’s perfect – just about to order from them.

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