Autopilot pin - what metal?

[Goldie]

I need to replace the autopilot pin which is tapped into a steel arm on the rudder quadrant. The pin will be threaded on the lower portion with a ‘spacer’ with machined flats above the threaded portion for tightening. I have a friend with the skills and machinery to produce it, but what is the best metal to use please? I believe that ‘ordinary’ SS is liable to fracture so is there a best grade to use, or should I avoid SS completely? If the latter, what is the best metal to use please? The pin will be approx 12mm diameter and the pilot is a hydraulic ram on a 40ft boat displacing about 12 tons in cruising trim.

Knowledgeable replies would be really appreciated please. Many thanks in anticipation.

 

[pvb]

I'm sure @vyv_cox will be able to advise in due course. I'd probably have suggested unobtanium.

 

[PaulRainbow]

When supplied new, with the drive, they are made from stainless, i would presume 316.

What make of drive ? Is the pin not available as a spare part ?

Edit: Scroll down the list here and there are three pin options: Pricelist Jefa Steering 2018

 

[Concerto]

Have a word with your local electronics fitter. He should be able to obtain a suitable one and fit it.

 

[Martin_J]

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

 

[colhel]

If you want more strength than 316 could try, 17-4 stainless, 431 stainless, ali bronze or duplex.
Edit: nitronic 50 would be good too if you can get a bit

 

[Goldie]

When supplied new, with the drive, they are made from stainless, i would presume 316.

What make of drive ? Is the pin not available as a spare part ?

Edit: Scroll down the list here and there are three pin options: Pricelist Jefa Steering 2018

The boat builder (Bowman) no longer exists sadly, The hydraulic ram is by Smiths Industries but the rose joint will be a generic size and the original pilot was B&G but now Raymarine EV400. The key components relevant to my search - the arm attached to the quadrant and the associated pin - will, I suspect, have been manufactured by or on behalf of Bowman

 

[Goldie]

If you want more strength than 316 could try, 17-4 stainless, 431 stainless, ali bronze or duplex.
Edit: nitronic 50 would be good too if you can get a bit

Many thanks indeed. I think it makes sense to go fir the strongest realistically available. Of your suggestions options, which would that be in this application?

 

[colhel]

If you can get it, nitronic (used to make rod rigging on superyachts). 17-4 would probably be my next choice but 431 would probably be more than likely held in stock in a machine shop.
I'm no metaloligist and fall far short of Vyv Cox's expertise but I've been crawling around machine shops for 30+ plus years working for aviation, mod and superyachts. Take my advice accordingly ?
Edit . I'd add duplex after 17-4 or better still "Super Duplex" (yes there is such a thing) but expect your machinist to swear at you, its a bitch to machine

 

[Iliade]

Do you really want the strongest available? Wouldn't you want it to fail before the ram or something structural if you, for example, backed into a rock?

I'd just get a few made up in 316. R-clip securing is great, but threaded is what you have, so use an anti-seize compound and keep the correct size spanner and the spare pins somewhere obvious (taped/tied to the quadrant?)

 

[vyv_cox]

I would be amazed if it was made originally in any sophisticated material. Strength is far more easily gained by size increase rather than expensive materials. In some cases the materials route is necessary but probably not here. 316 will almost certainly be fine.

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.

 

[DownWest]

A thought, but unless there is a clearance problem, you could drill out the thread and just bolt it?

 

[Blueboatman]

My thinking too
Take the quadrant to a machine shop and have them sleeve or bush it to accept an off the shelf pin

 

[Moodysailor]

If you can provide the specs of the ram it would be easy to see what the maximum load would be, but just based on experience alone a 12mm SS pin will be more than strong enough for this application.

Within normal conditions (i.e not bashing off the sea bed or Orca's ) then the loads will be well within the failure strength for that size of material. There are metals with higher shear loads, but most of those are ferrous, so in my view, SS is the correct material as will not require monitoring and checking for corrosion.

If you want to use the best possible grade, then something like AL6XN, or another "super-austenitic" grade of SS will be superior to 316L (but more costly)

 

[Goldie]

I would be amazed if it was made originally in any sophisticated material. Strength is far more easily gained by size increase rather than expensive materials. In some cases the materials route is necessary but probably not here. 316 will almost certainly be fine.

Thanks Vyv. Any particular 316 - are there variants?

The pin fitted when I bought the boat 5 years ago may have been 20 years old or a few months old, I have no way of knowing. When it failed a year ago, the SS replacement I had made lasted only about 1000nm hence my desire to come up with a longer lasting solution. Replacing the pin is not a massive job in itself, but access is and probably not practical at sea due to the amount of stuff that has to be removed from the lazarette to get at it!

 

[Goldie]

Thanks Moodysailor. I don’t have the ram specs but will see if I can photograph and the read the label - if it’s still legible - next time I’m under there!

 

[Goldie]

A thought, but unless there is a clearance problem, you could drill out the thread and just bolt it?

I’m thinking that that may be a good option - KISS principle! I would have to add a clearance spacer but that shouldn’t be insurmountable.

 

[colhel]

[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.
[/QUOTE]
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.

 

[earlybird]

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.

 

[DownWest]

I’m thinking that that may be a good option - KISS principle! I would have to add a clearance spacer but that shouldn’t be insurmountable.

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