Is this any help ?

**LINK** https://www.smithmetal.com/pdf/engineering/en8.pdf

MichaelG.

Hello ifoggy, yes you can use an anaerobic adhesive for the pinions. John Wilding even recommends it.

David

Joining the dots:

All steels can be hardened more or less, but not necessarily easily. It's important to understand the time and temperature characteristic of the particular steel and what needs to be done to stop it warping and cracking etc. Much depends on the size and shape of the object; generally small objects are easier to harden than big ones. (Very handy in the workshop!)

• Low carbon steels like EN1A are so difficult to harden it's considered impractical. (They can be case hardened though.)
• From the spec, EN8 is a medium carbon steel that's moderately difficult to harden, requiring the temperature to be held in within a 30C range and then oil quenched. Certainly not impossible, but easier to do with a thermostatically controlled oven and all the data than with a casually waved blowlamp. EN8 can be case and induction hardened.
• Silver Steel is specifically formulated to be easy to harden in an ordinary workshop. It's forgiving: neither timing or temperature are awkwardly critical. Not the most machinable, or strongest, or toughest, or hardest or cheapest steel possible, but highly convenient and more than good enough for most needs.  Tends not to be used for large objects and production runs because of the cost: when a lot of steel is to be hardened, it's cheaper to invest in the equipment needed to reliably harden cheaper steels.

The value of hardening a clock pinion is reduced rate of wear: clocks with hardened pinions run for much longer than clocks with unhardened pinions. Hard brass wears better than soft steel, and hard steel is better hard brass. Jewels are harder than the best hardened steel.

Is it worth putting the effort in? I think so, Having gone to the trouble of making an attractive clock that keeps reasonable time, it seems a shame to spoil a potential heirloom due to a load of soft pinions grinding to a halt after several years. Though we might all be dead before then!

Dave

Edited By SillyOldDuffer on 05/06/2022 10:36:32

Apart from buying a hardness tester you can use these to get an indication of the hardness**LINK** Niko.

Edited By speelwerk on 05/06/2022 13:03:08

EN24T is the other suggestion. Supplied hardened and tempered it will machine well and needs no further heat treatment. Incidentally silver steel is I think generally supplied half hard and annealing before pinion cutting will help both with the ease of machining and with surface finish.

As to the question harden or not, my understanding is that French clocks had hardened pinions whilst englissh clocks did not. The pertinant question to ask is why? At first glance you would assume that the reason was to make them wear resistant. However clock pinions do not run at high speeds and are generally lightly loaded but are however not lubricated. If you examine a clock that has run for a considerable time you will find that the brass wheels have cut into the steel pinions. The mechanism of this is that the brass acquires embedded dust in the surface of the wheel leaves and the brass leaves then act as a lap against the harder steel and gradually erode the pinion leaves. As this is a grinding process I don't think that hardened pinions would help much. Far better to ensure a closed dust free case or a protective glass dome.

My opionion of the reason for hardening and then "polishing" is to reduce friction, something of the greatest desire in clockmaking. Although hardening does not change the co-efficient of friction much in steel generally it is assumed that harder matherial have less friction than softer, I think the hardened pinion will take and hold a polish better than the pinion in the soft state and will be much less likely to pick up any of the lapping material used in the polishing.

The above is to an extent speculation on my part as I have no experimental evidence for all this so I would be interested in the comments of fellow and perhapse more knowledgable clockmakers.

regards Martin

Would I be throwing a spanner in the works by mentioning blue steel?

**LINK**

As for which will wear more, here's an old chestnut. Back in the 50’s I removed the substantially worn and scored gudgeon pin from a small 2-stroke petrol engine.

The replacement pin was a near perfect fit in the small end (bronze?) bearing.

In a similar vein, tests on a lawn mower spur gear made from HDPE (high density polyethylene) meshing with a similar steel gear resulted in the steel gear wearing out. Lapping comes to mind.

Sam

Edited By Sam Stones on 05/06/2022 21:09:23

.

I think that sums it up nicely

Martin makes a good point about polishing, but ultimately what you need in a pinion is toughness.

MichaelG.

Sam Stones Blue steel ( pivot wire ) will not be large enough diameter for making pinions. It only goes up to about 3mm Ø

Roy

I thought it was a confidently known fact, but re-reading Britten's (which isn't bang up to date), I'm not so sure. The part definitely claimed to benefit is the pivot; reduced wear plus low-friction after polishing. The teeth aren't mentioned. Thinking about it, a clock gear pivot takes most of the stress and movement, whilst wear and tear is shared between several teeth. Leaving teeth slightly soft might even be an advantage by allowing slight imperfections between teeth to be worn down. Do clocks improve after 'running in'?

Now I wonder if the pivot is the reason for hardening, and the rest of the pinion is only hardened as a side-effect.

When I said EN8 was difficult to harden, I should have said 'difficult to harden properly'. The spec mentions holding temperature within 30C. This is difficult to judge. Then quenched in oil, not water. The effect of getting it wrong is either it stays soft, or – worse – turns brittle a full of micro-cracks. Sounds like your experiment with EN8 was over-hardened; brittle and weak. Micro-cracks can't be fixed by tempering.

I'd try again except quench with motor oil. Oil has a slower cooling action, and is less likely to cause microscopic cracks.

The advantage of silver steel is it's specifically formulated for low fuss hardening in an ordinary workshop. Other steels are more demanding. HSS is the fussiest I know of: it's proper heat treatment is remarkably finicky, requiring various cycles of accurate temperature and timing control. I don't think HSS can be hardened in an ordinary workshop because it requires carefully following an elaborate timed process through a series of temperature controlled ovens.

Dave