View Full Version : silver solder

charlie coghill
09-21-2002, 11:22 PM
Good evening people;

Can stainless steel be silver soldered to monel?

I have a boat prop with a 1.750" bore and need to fit it to a 1.500" monel shaft. My thoughts are to silver solder a stainless steel sleeve on the monel shaft and mount the monel shaft in the lathe and machine the stainless sleeve to fit the bore of the prop.
There is a .375 key way in the prop. Cutting the key way will cut through the stainless steel sleeve. An existing thread and nut will hold the prop on the shaft.

What is the best procedure for machinning monel?

I am open to any other thoughts on getting the prop on the shaft.

Thanks for any input.

09-22-2002, 12:21 AM
How long is your monel drive shaft?

09-22-2002, 12:52 PM
Have you considered just getting the correct prop, or are we talking about non-available being the problem?

I would bush the prop myself and leave the drive shaft alone.

09-22-2002, 03:34 PM
I don't know about boat props and shafts, but the general rule of thumb in gunschmidt'n is work on the cheaper part, just in case Murphy lends a hand.

charlie coghill
09-22-2002, 10:46 PM
Thanks for the replays people.

The prop shaft will be about 7 ft. long. The prop it self is stainless steel 22" in Dia. with a 32" pitch.

I don't know what the prop would cost new and I don't want to find out.

09-22-2002, 10:58 PM
Dear Charlie,
I don't know how much silver soldering you've done, but that 7 foot shaft is one helluva heat sink. You'd have to heat the whole piece up to nearly red heat before you'd get anything to happen with silver solder. Perhaps some kind of brazing with a welding torch will be more appropriate, but you'd still have to deal with the heat loss problem. It might be safer to work on an adapter boss to fit inside the prop, which you could machine out of bronze, brass, or even cast it out of aluminum.Any of these would be safer than the heat method, and besides, you don't knoe the shear strength of that joint, you might end up miles from anywhere without a prop. If you can find an old shaft that fits the inside of the prop, there's half the job finished right there!
Good luck, Richard, aground in LA

09-23-2002, 01:55 AM
Some food for thought. I would sleeve the shaft with monel not cres as the prop and cres sleeve will gaul(sp) and be a bear to take apart. Avoid any other metal type between the prop and the shaft to avoid galvanic corrosion, e.g. aluminum will go by-by real quick. As to joining the sleeve to the shaft visit a good braze/weld shop.

Neil Peters

09-26-2002, 02:04 AM
Just my 2 cents charlie coghill,

I would go w/ brazing a sleeve on the propeller and then broached the key way so that the old keyway matches the existing keyway in the sleeve. After wards you just have to use a .375 x .500 key which you could make (even w/ a hand file). Match the SST of the prop and braze. Make sure upon install that you have a bond (different from ground) on the shaft to the zinc. Been in a similar situation before.

09-26-2002, 10:38 AM
Why not go with weld buidup on the shaft?

Neil Peters

charlie coghill
09-27-2002, 12:29 AM
Thanks for the replys fellows; guess this one I will have to think about a while longer although the weld up may be the answer.

09-28-2002, 07:18 AM
Before you weld or bush anything, here are a couple of things to keep in mind.
#1, prop diameter needs to be ALMOST the aperture size (formula needed here)
#2, prop pitch prevents engine from over-revving
The dimensions you gave for this prop are very aggressive. It sounds like a high RPM, high horse power prop. The main idea is to match the hull to an engine to a prop. Any prop will work, although not efficiently or cost effective. A little figuring will tell you if this prop is a waste of your time and money or not.
Need to know:
Engine horsepower
Engine red line
Hull type-size
Reduction gear
Previous prop size


charlie coghill
09-29-2002, 11:40 PM
Dave, This is geting deeper. The prop will be used on a steam boat that I am building. The boat is a WW2 life boat off of a liberty ship,it is 22 ft. long. The engine is one that I machined from a set of castings, it is a 3X5X4. The problem is the porp has a 1-3/4 bore but the shaft I have for it will be too short. I have another monel shaft of 1.5" diameter that would be long enough. I though that I might combine the two shafts by the use of a bushing silver soldered to the monel shaft. I am sure that replacing the SS. shaft with the correct length shaft will flatten an already flat pocket book.

For these steam boats the engines usually are not of a high RPM,some where between 200 and 500 rpm, some are higher of course. Most of the people that I know that have steam boats use this type of a prop.

Thanks for the replys guys, maybe befor I get to the point that I need to make a decision I can find a shaft that will work.

09-30-2002, 12:25 AM
I thought that was a steam wheel!

If both the prop and shaft have the standard
taper, adaptors are readily available to make
up the difference...if the prop has a straight
bore or the shaft doesn't have a taper,
consider the torque of that compound rocking that key back and forth...

If your shafts are long enough to put the
joint in the boat (rather than in the water),
try using an intermediate pillow block
as a thrust bearing, and use a chain-type
coupling w/ taper-loc bushings. of different
sizes. See mcmastercarr.com for examples...

We're just back from a pleasant three days
steaming in the SF Bay delta w/ our 19'
steam launch Otter - see my web page for
boat details.

Bart Smaalders

09-30-2002, 06:01 PM
My mistake! I assumed something very different.The low RPM and horse power lets you get away with almost anything! Lot's of our shafts are stainless 316 which would do just fine for your application. I might have the stuff you need for free if you give me time to scrounge through the yard.Let me see what I can find. What's your time schedule?

09-30-2002, 07:10 PM
Having never messed with steam props , After doing a little digging, I have to agree with barts. Looks like a steam prop.
Also agree with his recomendations about McMaster Carr and their taper-lock bushings.
I might still have an old shaft of your correct length-size given enough time to scrounge. Onward!

charlie coghill
10-01-2002, 08:15 PM
just a quick message. I will get back to the people that need answers on Wed night.

charlie coghill
10-02-2002, 10:32 PM
Good evening;
Dave thanks for the offer. Being retarded ops thats retired I don't realy have a time table. This week end I hope to get the shaft log installed. Than I can get a true length for the shaft, but at this time it looks like the shaft will have to be about 8 ft long.I will let you know how things are comming along.

Bart I thought about a coupling between the two shafts. I guess that with the thrust bearing between the coupling and the hull and the bearing at the prop end, it would not hurt if there was a little play in the coupling. What I had though about was a solid coupling that I could machine.

The silver solder was an idea that I wanted to get some feed back on.

Yes you and Idletime and scookum were steaming around on S.F. Bay I am here at home busting my buns trying to get the boat ready to paint hopfully before the weather sets in. Glad you people enjoyed your selves.
Thanks for the input.


10-03-2002, 02:06 AM
With a proper .003" or so clearance, 60% silver
solder develops 45kpsi of shear strength or so;
it's not that different than mild steel!

So silver-soldering a coupling on would work,
but make sure to get some real surface area.

- Bart

Bart Smaalders