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Old 18-02-2015, 13:44   #1
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Repair by welding? Or find obscure part?

My pin that connects my autopilot to my tiller broke at the bolt end. There is a welder who can drill into the cylinder and slide a new bolt and weld it together. Good idea? I can't find a part number or similar thing anywhere. Advice?


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Old 18-02-2015, 14:23   #2
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Re: Repair by welding? Or find obscure part?

Get a good machinist. Cheaper than getting the part and will renovate your entire rod.
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Old 18-02-2015, 14:28   #3
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Re: Repair by welding? Or find obscure part?

I agree with Newt. Better to build a new one.
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Old 18-02-2015, 14:32   #4
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Re: Repair by welding? Or find obscure part?

Maybe drill, tap and insert a new stud with thread locker. Will be stronger, less rust prone and also be easier to replace if it happens again
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Old 18-02-2015, 14:39   #5
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Re: Repair by welding? Or find obscure part?

Evaluate why it failed; looks like there was a bending moment; figure out his to fix that with new part


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Old 18-02-2015, 15:01   #6
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Re: Repair by welding? Or find obscure part?

I would go with the machinist, but first figure out why it failed. Is the original part heavy enough for the stress put on it? You don't want to do this twice. It looks as though the bolt ends were machined to it's size from what was a solid shaft. If so, leaving a sharp 90 angle, is known to cause stress cracks and the solution is when machining, leave a cove at the base.
I've seen this problem in new vessel construction in matching propeller shafts to the transmission coupling. The supplied couplings had a smaller hole than the shaft diameter. So instead of boring the coupling and re-keying it, or getting one the right size, the foreman decided to turn the shaft ends down to match the coupling. All the boats they built for a period of time, that I know of, broke their shafts at the edge of the coupling.
Without seeing the whole tiller/autopilot, it looks like the large section is really a spacer. I would bore a brass shaft the size and length of the large center and then get a longer stainless bolt that goes all the way thru.
My pop was a machinist and chief marine engineer in the days of steam.
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Old 18-02-2015, 15:04   #7
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Re: Repair by welding? Or find obscure part?

FWIW, I would just weld it back up.

If you were cautious you could either build up the base a bit with weld metal or add some small gussets.

But that's just me.

Alfred E. Neuman

But...out of curiosity, is that from your 46' boat?

I find it odd to be using a tiller pilot on a boat that size.

Or is this on something much smaller?
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Old 18-02-2015, 15:25   #8
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Re: Repair by welding? Or find obscure part?

I'm going to go out on a limb, and ask if that was a vertical stud off the A/P tiller arm and the ram? If so, redesign the system, it'll break again...
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Old 19-02-2015, 05:30   #9
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Re: Repair by welding? Or find obscure part?

It was the pin off the end of the piston ram end that attached to my wheel under the transom

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Old 19-02-2015, 06:03   #10
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Re: Repair by welding? Or find obscure part?

Nah man...

A weld will work long enough to get into trouble... Unless of course the application lets you have a large root, say the diameter of the pin, and then you can start your shoulder area above it... Definitely can't use the broken off pin...

Next best... drilled and tapped for a shoulder bolt...
McMaster-Carr

Best... Have one whipped out by a machinist... A hobby guy could do this in 30 min, and probably 2 beers and $75

Machinist forum.... I had 3 guys respond when I inquired about machining Zboss's main flange...

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Old 19-02-2015, 10:17   #11
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Re: Repair by welding? Or find obscure part?

I would go with all new pipe drilled out and tapped. Harder and/or tougher (depending on the application )bolts are easy to get and cheaper than machining. To get equal hardness or toughness the piece has to be machined and then heat treated, bolts come ready to use. Also heavy wall ss pipe (schedule 80 or higher) is easy to get and tap. Nearly everyone has a tap set, lathe not so common.

YMMV Just what I would do in this case.

But first find out why it broke, maybe something is starting to seize.
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Old 19-02-2015, 10:21   #12
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Re: Repair by welding? Or find obscure part?

I think your plan to drill is fine with a weld to secure it.... but why not drill and tap if you are drilling? Then maybe weld it or better yet Loktite it... then keep a spare threaded rod so you can replace it in the future. You could even go to high strength rod....
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Old 19-02-2015, 10:31   #13
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Re: Repair by welding? Or find obscure part?

If you weld a bolt you'll need to heat treat after to remove localized heat affected zone hardness. It will be somewhat brittle.

It will also need a significant chamfer to reduce the stress concentration that led to the failure in the first place. Think 10mm radius chamfer.

The suggestion to machine a new part is a good option too. The chamfer advice still stands.

If welding (assuming tig only) careful selection of filler can help alleviate the weld brittleness problems. Cheap ss and ss bolts are not vacuum degassed so you get a lot of hard and brittle microconstituents migrating to the weld zone. Heat treatment can alleviate much of this.

Another option is to modify so the bolt will shear and be removable and easily replaced.

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Old 19-02-2015, 10:49   #14
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Re: Repair by welding? Or find obscure part?

Most all of the replies will work, even welding. 60 year welder here. If welding, drill out, re-tap and add bolt. Drill hole perpendicular to bolt and fill with spot of weld. Grind and done. There could be a problem with the system but stuff just wears out and that includes parts that are constantly stressed. They will only flex so long, if only slightly. Having a spare part made is really good insurance, not hard to do.
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Old 19-02-2015, 11:39   #15
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Re: Repair by welding? Or find obscure part?

Quote:
Originally Posted by captlloyd View Post
Most all of the replies will work, even welding. 60 year welder here. If welding, drill out, re-tap and add bolt. Drill hole perpendicular to bolt and fill with spot of weld. Grind and done. There could be a problem with the system but stuff just wears out and that includes parts that are constantly stressed. They will only flex so long, if only slightly. Having a spare part made is really good insurance, not hard to do.
Now this is a good idea, the welder I was speaking with was worried as was I about the dimple of the weld not being flush. By pre taping we can sink the weld into the cylinder part. I think that's what we're gonna do. Thanks! I'll give an update with finished product

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