Autopilot pin - what metal?

[Goldie]

Like Vyv, I would have been very surprised at anything other than austenitic SS, prob. 316. However the OP has had early failure of such a replacement which doesn't inspire confidence.
How did it fail, Shear perhaps and at the run-out of the threaded section?
If the bits of the original, long-lasting pin are still around it would be interesting to see if it's magnetic. If it is, then it's something more exotic than 304 / 316.

Non-magnetic and yes, failed at the end of the threaded section.

 

[Goldie]

If you do go that way, the thread will be rolled, not cut, if the original failure was at the thread?

Thanks, but can you explain that for a non-engineer please?

 

[Goldie]

A picture paints…..

 

[PaulRainbow]

Non-magnetic and yes, failed at the end of the threaded section.

You don't say what size thread ? Perhaps it's undersized for the job ?

I would copy the basic style of pin used by Raymarine, Raymarine Linear Drive Front Anchorage Pin - K065

If you make the unthreaded portion of the pin that goes through the tiller arm as big as sensibly practical and make it a snug fit in the tiller arm, it should be more than strong enough, the threaded portion could be M12.

Edit: you posted the pic as i was typing, looks like M10 ?

 

[vyv_cox]

A picture paints…..

That looks like a classic under tightened fatigue failure. I would have no hesitation in continuing to use 316, maybe add a washer to move the contact with the bore up a little and check its tightness regularly.

 

[Blueboatman]

Wheel steering R36 with quadrant , ( big old transom hung rudder ) the standard Raymarine pin taking the st6000 ram has never given the slightest indication of overloading . If anything I can ‘induce’ leveraged flex movement in the quadrant before any other component . Bn 40 isn’t that much heavier on its displacement and rudder loads under abuse I would guess

 

[Goldie]

That looks like a classic under tightened fatigue failure. I would have no hesitation in continuing to use 316, maybe add a washer to move the contact with the bore up a little and check its tightness regularly.

Thanks very much indeed Vyv and I have already done exactly as you suggest. Fortunately, I’d had two spares made ‘just in case’. As I have no further spares (yet!) I shall be checking regularly!

 

[Daydream believer]

Neither the Jefa nor the Raymarine pins thread into the arm/quadrant. I don't know why but the manufacturers usually have reasons..

Examples of the Jefa and Raymarine ones below in case they give ideas as to construction.. I do appreciate the fact that the Raymarine one has a removable R clip so that it's quick and easy to disconnect the drive in a hurry should it ever be necessary.

Jefa linear drive tiller pin

Raymarine linear drive tiller pin

At £ 46 plus VAT I would expect the Raymarine one to be made of solid Gold

 

[vyv_cox]

[QUOTE="vyv_cox, post: 7792270,

The difficulty with colhel's suggestion is that the material would need to be in an appropriate heat treated state, which may not be easy.

There's a danger this thread could become over complicated for a pin. But you'll have to explain that to me. I've just asked a supplier for, ie. 17-4 and it arrives ready to use and to spec.
[/QUOTE]
Does not apply to 316 of course but in some cases the base stock comes in the untreated form. This is normal for alloy steels and many others. Don't know about your 17-4PH but if you were, for example, going to carry out a stamping operation on it you would want it in the non-heat treated form. Equally, a case hardened steel would need to be heat treated after it was formed.

 

[Goldie]

You don't say what size thread ? Perhaps it's undersized for the job ?

I would copy the basic style of pin used by Raymarine, Raymarine Linear Drive Front Anchorage Pin - K065

If you make the unthreaded portion of the pin that goes through the tiller arm as big as sensibly practical and make it a snug fit in the tiller arm, it should be more than strong enough, the threaded portion could be M12.

Edit: you posted the pic as i was typing, looks like M10 ?

Thanks Paul. It’s an unusual (non-metric ?) size at a smidge under 12mm. I don’t know what the thread is, but it’s a good tight fit in the female thread of the tiller arm.

 

[vyv_cox]

Thanks, but can you explain that for a non-engineer please?

In threaded components that are likely to suffer fatigue failures it is common practice to cold roll the thread rather than cut it. This produces a less acute angle that might be the initiation point for fatigue but also puts the surface into compression, reducing the likelihood of crack initiation. It is done on large bolts on big machines and, the application I am most familiar with, reciprocating compressor piston rods.

 

[PaulRainbow]

Thanks Paul. It’s an unusual (non-metric ?) size at a smidge under 12mm. I don’t know what the thread is, but it’s a good tight fit in the female thread of the tiller arm.

If you drill the threaded hole out in the tiller arm, going up a size or two if possible, you move the threaded portion further down and all there is within the tiller arm is a straight section of steel subject to a sheering force, the threaded portion just holds it all in place.

 

[Moodysailor]

Having looked at the image and read again the OP, I think the issue is that this is tapped into the quadrant/tiller arm.

Usual practice is for there to be a hole right through the tiller arm, then the threaded portion would be tightened with a nut & washer from underneath. This would greatly reduce the shear load on a weak point in the system, and would work much better.

I would definitely advocate (as others have mentioned) to drill out the tiller arm and through-bolt so that the wider section with flats on it is flush to the top of the arm.

 

[Moodysailor]

Thanks Paul. It’s an unusual (non-metric ?) size at a smidge under 12mm. I don’t know what the thread is, but it’s a good tight fit in the female thread of the tiller arm.

If it's definitely not metric and less than 12mm, then it's probably 7/16 UNC

 

[DownWest]

If you drill the threaded hole out in the tiller arm, going up a size or two if possible, you move the threaded portion further down and all there is within the tiller arm is a straight section of steel subject to a sheering force, the threaded portion just holds it all in place.

The catch there is the hole in the rose joint on the actuator ram. If a bolt of the same imperial size in ss could be obtained?

 

[penfold]

If it's definitely not metric and less than 12mm, then it's probably 7/16 UNC

It looks metric and measuring from the picture the thread pitch is 1.75mm, which is standard metric.

 

[PaulRainbow]

The catch there is the hole in the rose joint on the actuator ram. If a bolt of the same imperial size in ss could be obtained?

The section of steel going through the tiller arm can be bigger than the pin that goes through the rose joint.

 

[Iliade]

If you are getting one/some machined, you could also consider having a broader shoulder at the top of the thread thereby putting the thread into tension rather than bending.

 

[colhel]

[QUOTE="vyv_cox, post: 7792432,
[/QUOTE]
Does not apply to 316 of course but in some cases the base stock comes in the untreated form. This is normal for alloy steels and many others. Don't know about your 17-4PH but if you were, for example, going to carry out a stamping operation on it you would want it in the non-heat treated form. Equally, a case hardened steel would need to be heat treated after it was formed.
[/QUOTE]

You've baffled me.
The OP asked for recomendations for a stronger material to machine a pin, which I did. The only time you'd case harden something is after you machined it and then you'd normally grind it (in some cases it can be re-machined but very rare).
So where does "forming", "stamping" and heat treatment come into it?
You seem to have dismissed my perfectly reasonable and straight forward answer ??. Probably the same answer you'd get if you walked into any machine shop.
I'd hate it if this were to turn into never ending forum argument but I do feel I need to defend my answer.

 

[vyv_cox]

[QUOTE="vyv_cox, post: 7792432,

Does not apply to 316 of course but in some cases the base stock comes in the untreated form. This is normal for alloy steels and many others. Don't know about your 17-4PH but if you were, for example, going to carry out a stamping operation on it you would want it in the non-heat treated form. Equally, a case hardened steel would need to be heat treated after it was formed.
[/QUOTE]

You've baffled me.
The OP asked for recomendations for a stronger material to machine a pin, which I did. The only time you'd case harden something is after you machined it and then you'd normally grind it (in some cases it can be re-machined but very rare).
So where does "forming", "stamping" and heat treatment come into it?
You seem to have dismissed my perfectly reasonable and straight forward answer ??. Probably the same answer you'd get if you walked into any machine shop.
I'd hate it if this were to turn into never ending forum argument but I do feel I need to defend my answer.
[/QUOTE]
I think you are misunderstanding. I am not criticising you in the slightest, only pointing out that many metals are sold in the annealed or normalised condition so that after whatever activity they undergo during manufacture of the finished item they need to be heat treated.