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Old 11-01-2015, 09:34 AM   #21
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Rudder shafts are usually specked with a huge safety margin.

Turning 1/8 or 1/16 off them will not change their service life.
I kind of thought about that too. I agree there may be a margin. But rudder stock loads are dependent upon the type, size, and arrangement of the rudder and (number of) bearing. It will have inherently different mechanical loads than a prop or pump shaft.

Depending on the age and hereditary of the boat, calculations may not even been involved in its fabrication or sizing.

Other options to consider.

If there is adequate strength with the remaining diameter, one could consider skim cutting and using a Belzona (1111 super metal is common) build up instead of weld filler.

A good machine shop may also be able to machine off and shrink a sleeve on as well.

Thermal metal spray (HVOF, HVLF) build up is another option.

All of these have the advantage of replacing the corroded area with a non or less corrosion susceptible material.

I thought I downloaded some rudder stock sizing calculations at one time. I'll see if I can dig them up.

Keep in mind, the stuff I am responsible for fixing is industrial, runs 24/7, and is expected to last. There's 8760 hours in a year. I'm trying to get 50,000 hrs out of my repairs. But I also figure, if one is going to all of the work to take it apart and suffer the downtime, it is only incremental cost and time to do it right.

I think that doing a skim cut to a smaller diameter without build up may just lead to leaks or problems later on.
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Old 11-01-2015, 09:55 AM   #22
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I forgot to mention in my previous post to check radial runout before and after the repair. Anyone actually doing this type of work would do this automatically.

And you can also use SAW welding. A pump shop might be set up for that.

I wouldn't use MIG welding as it is pretty low amperage and more susceptible to incomplete penetration and porosity. Just saying that in case a buddy had a lathe and MIG welder at home.
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Old 11-01-2015, 05:33 PM   #23
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I forgot to mention in my previous post to check radial runout before and after the repair. Anyone actually doing this type of work would do this automatically.

And you can also use SAW welding. A pump shop might be set up for that.

I wouldn't use MIG welding as it is pretty low amperage and more susceptible to incomplete penetration and porosity. Just saying that in case a buddy had a lathe and MIG welder at home.
What are you doing next week? I've got some frequent flier miles I can send your way . . .
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Old 02-09-2016, 08:42 AM   #24
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Update

I got the rudder shafts back from the specialty shop yesterday and the work looks to be excellent. They ground away the pitted surface to solid metal and built it back up with Inconel 625. They like this alloy with marine applications, including with graphite packing. Measuring equipment might be able to distinguish a difference in diameters, but the transitions from old to new material feel perfect. Not cheap but not as hard on the wallet as I was expecting. Here are some before and after shots.




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Old 02-09-2016, 10:13 AM   #25
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Inconel 625 is an excellent choice. Sounds like you found the right shop!
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Old 02-09-2016, 10:34 AM   #26
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Inconel 625 is an excellent choice. Sounds like you found the right shop!
I was REALLY hoping you were going to say that. Thanks!
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Old 02-09-2016, 11:02 AM   #27
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I was REALLY hoping you were going to say that. Thanks!
Spy has given you the correct advice for the past few months. Inconel products have been used for this application for close to a century with great success. BTW, Inconel is an acronym for the long lived Inco mining and metals company that became famous for their variety of nickel products including Monel, named after the President of Inco - Monell - in 1906.

I am unfortunately saddled with a degree in Metallurgical Engineering and slobber all over this stuff and the guys like Spy who really make it work. Smart of you to listen to him Angus.
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Old 02-09-2016, 11:07 AM   #28
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looks like beautiful work. Amazing what skilled craftsmen can accomplish
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Old 02-09-2016, 11:14 AM   #29
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Thanks, SC. When Spy talks, I listen. Simply finding a business that catered to heavy industry, vs marine, saved me money.

I have actually been to Sudbury and seen the giant nickel!

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Old 02-09-2016, 01:23 PM   #30
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Damn great to have such a diverse, knowledgeable group of contributors on TF. I'm looking to utilize Ian's truly top tier workmanship company for similar shaft restoration needs as they may arise.


My hat's off to you all!


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Old 02-09-2016, 02:00 PM   #31
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Wow! What a result. So they machine down to good metal and then built it back up to the same diameter? How does that work? Can you describe the process?

I asked about replacing material on my pitted shafts (102") a in the yard last year and the guy said it can't be done. I wonder if it is a balance thing, physical size, or if he just wasn't aware of the process since it is "specialized"? In the end, all we had to do was move the stuffing box a little so the seal didn't ride in a pitted area to fix the problem to avoid replacing two $3000 shafts.
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Old 02-09-2016, 04:17 PM   #32
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Wow! What a result. So they machine down to good metal and then built it back up to the same diameter? How does that work? Can you describe the process?

I asked about replacing material on my pitted shafts (102") a in the yard last year and the guy said it can't be done. I wonder if it is a balance thing, physical size, or if he just wasn't aware of the process since it is "specialized"? In the end, all we had to do was move the stuffing box a little so the seal didn't ride in a pitted area to fix the problem to avoid replacing two $3000 shafts.
Heavy machine and gear companies specialize in this activity. I've had bull gears up to 16' in diameter built up and then machined down. As Spy mentioned some months ago identifying the shaft metal to get a good weldment match is important. Where to get this done near you, don't know but I betcha Rick B does.
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Old 02-09-2016, 04:22 PM   #33
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Wow! What a result. So they machine down to good metal and then built it back up to the same diameter? How does that work? Can you describe the process?

I asked about replacing material on my pitted shafts (102") a in the yard last year and the guy said it can't be done. I wonder if it is a balance thing, physical size, or if he just wasn't aware of the process since it is "specialized"? In the end, all we had to do was move the stuffing box a little so the seal didn't ride in a pitted area to fix the problem to avoid replacing two $3000 shafts.
Tom, I'm sure Spy or Sunchaser can do a better job explaining the process in detail. I wasn't able to watch, but I believe they ground down the pitted area using a lathe or grinding tool until they were certain they had reached sound metal. There are a number of techniques, as I understand it, to spray on the new alloy to make it bond molecularly to the shaft. Then they grind it down to match the original diameter of the shaft. If done right, the end result is a perfectly consistent surface with, in this case, an alloy that is much more resistant to crevice and galvanic corrosion. It cost me $900 for two 4-5" areas on both shafts. New rudder shafts, I was told, would be easily more than double that amount.

I have some wear, but possibly not corrosion, on my engine shafts as well. I plan to take a similar approach to yours if possible to move the worn areas away from the stuffing.

Edit: thanks, Sunchaser.
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Old 02-09-2016, 04:26 PM   #34
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There's a machine shop in Wildwood, NJ that does it. They did my prop shaft 4 years ago.


They have a pretty wide service area for all kinds of marine machining.


A lot of commercial fishing boats and big sporties use them when fishing out of Cape may...and what I had heard is their reputation is good enough their work has spread back to many of these boats home ports from NC to Mass.


Not sure why any good machine shop couldn't do it if they do it at all...but like many things, experience in a corner of the market sometimes does have it's benefits.


Funny...my sprayed area actually has a touch of rust here and there and told it was normal.... Spy...any thoughts?
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Old 02-09-2016, 05:29 PM   #35
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There's a machine shop in Wildwood, NJ that does it. They did my prop shaft 4 years ago.


They have a pretty wide service area for all kinds of marine machining.


A lot of commercial fishing boats and big sporties use them when fishing out of Cape may...and what I had heard is their reputation is good enough their work has spread back to many of these boats home ports from NC to Mass.


Not sure why any good machine shop couldn't do it if they do it at all...but like many things, experience in a corner of the market sometimes does have it's benefits.


Funny...my sprayed area actually has a touch of rust here and there and told it was normal.... Spy...any thoughts?
Some shops won't do it for some applications due to the "pit" often being much larger inside the shaft than it outwardly appears as shown in this X-ray of a single pin prick size pit in a shaft.
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Old 02-09-2016, 05:33 PM   #36
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Some shops won't do it for some applications due to the "pit" often being much larger inside the shaft than it outwardly appears as shown in this X-ray of a single pin prick size pit in a shaft.
OOOOUCH!!
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Old 02-09-2016, 06:01 PM   #37
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The resolution of this shot is poor but you can clearly see the microscopic pits on the shaft that don't appear too bad while the inside of the shaft is in exremely poor condition with thousands of much larger sub-surface pits.
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Old 02-09-2016, 06:12 PM   #38
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There is a guy named Adam - ABOM79 on youtube who is a good machinist and he shows how to spray weld metal to build up a worn shaft and fix a keyway.

Here is a link to the video: https://youtu.be/KK9OwDxwJp4

Fun to watch a master.
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Old 02-09-2016, 09:56 PM   #39
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Some questions:
Is a metal adding process also used to revive props?
Different metal? Is a plus of monel non reactivity with other metals?
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Old 02-10-2016, 08:07 AM   #40
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The rudders were probably bought OTS , off the shelf.

There are mfg of "stock" rudders that may be an exact duplicate , or close enough.

Might be cheaper and longer lasting than a "repair
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