Stuart S50 - Replacing mild steel shafts with stainless steel shafts.

[Sarah]

After a bit of advice please.

I have a Stuart Progress and a S50 to refurbish. All the shafts are corroded and I want to replace them. Is there any problem in replacing the shafts with Stainless Steel, rather than mild steel?

Thank you

 

[GreenTwin]

I think many use stainless for shafts, especially piston shafts on steam engines, to minimize corrosion.

There are various grades of stainless steel, and some is more corrosion-resistant than others.

.

 

[kf2qd]

If stain;less is in contact with steel and water it will corrode. Electrolytic action.

 

[Nerd1000]

Common austenitic stainless (grades 304 and 316) is much more prone to galling than mild steel, so I'd be wary of using it for heavily loaded shafts running against metal plain bearings (plastics are fine, and metals under lighter loads are ok too).

You can use grade 431 martensitic stainless to avoid this, but it corrodes more easily.

 

[Steamchick]

Regular oiling of the engine helps resist rust... But eventually, as a University Professor quoted:
"The oxidising properties of ferrous materials can be summed-up thus: Steel rusts!"
It is the Engineers' equivalent of the religious quote: "Dust to Dust" - often used by astronomers to explain how the dust of the universe combines to form stars, planets, - and even Humans - then returns them all to dust - eventually. - and many engines outlast their makers...
K2

 

[Sarah]

Common austenitic stainless (grades 304 and 316) is much more prone to galling than mild steel, so I'd be wary of using it for heavily loaded shafts running against metal plain bearings (plastics are fine, and metals under lighter loads are ok too).

You can use grade 431 martensitic stainless to avoid this, but it corrodes more easily.

Thanks for your reply.

Would any of the common grades of Stainless Steel still be prone to galling when running against/in cast iron, as opposed to miospd steel.

Regards,

Sarah

 

[Bob Sorenson]

Grade 303 is the best for machinability. It is available "ground and polished" from McMaster Carr. Very precise in dimension and smooth. Won't wear out packing.

 

[Nerd1000]

Thanks for your reply.

Would any of the common grades of Stainless Steel still be prone to galling when running against/in cast iron, as opposed to miospd steel.

Regards,

Sarah

Cast iron is going to be a much better partner than mild steel, but it isn't immune. This is for example why internal combustion engines normally use bronze valve guides if they have stainless valves, whereas cast iron guides are extremely common in engines that have regular steel valves.

It depends a lot on the load and lubrication conditions, with very lightly loaded bearings you can get away with a lot of things assuming lubrication conditions are good. For example, I would expect a piston rod to be ok, it only really slides against the gland on the bottom of the cylinder anyway. On the other hand I wouldn't dare to use austenitic stainless for a crankshaft running in cast iron bearings, that's a bad combination. You might get away with it on a model engine simply because the operating stresses are so low (the engine isn't driving anything, and running at very slow speed) but my inner engineer would mad with me for violating good practice. I'd use carbon steel for this and keep everything well oiled to stop rust.

Austenitic stainless will run acceptably against bronze under moderate loads, so another option would be to install bronze bushings in any part that runs against your more heavily loaded stainless parts.

 

[Steamchick]

Thanks Nerd, I have learned something useful there.
K2

 

[Sarah]

Cast iron is going to be a much better partner than mild steel, but it isn't immune. This is for example why internal combustion engines normally use bronze valve guides if they have stainless valves, whereas cast iron guides are extremely common in engines that have regular steel valves.

It depends a lot on the load and lubrication conditions, with very lightly loaded bearings you can get away with a lot of things assuming lubrication conditions are good. For example, I would expect a piston rod to be ok, it only really slides against the gland on the bottom of the cylinder anyway. On the other hand I wouldn't dare to use austenitic stainless for a crankshaft running in cast iron bearings, that's a bad combination. You might get away with it on a model engine simply because the operating stresses are so low (the engine isn't driving anything, and running at very slow speed) but my inner engineer would mad with me for violating good practice. I'd use carbon steel for this and keep everything well oiled to stop rust.

Austenitic stainless will run acceptably against bronze under moderate loads, so another option would be to install bronze bushings in any part that runs against your more heavily loaded stainless parts.

Thank you so much your your reply, I appreciate yours and every one else's comments.

I'll follow your advice and I'll do stainless for the piston rod, that's the most exposed shaft as well. For all the other shafts I'll use mild steel, though I might have some nice shiny silver steel rod in my stores.

Thanks again for your advice, I'll add it my knowledge bank. I'll do a little reading on the different grades of stainless.

Best wishes,

Sarah

 

[Jasonb]

Sarah if you are in the UK then a good shaft material is PGMS - Precision Ground Mild Steel. This has the same sort of finish as stainless and silver steel, is easy to work with and being precision ground runs nicely in a typical H7 reamed hole. Ideal for crankshafts on steam models. Use 303 stainless for the piston and valve rods but give it a rub length ways with worn fine emery cloth or a Scotchbrite pad as in the supplied state the finish runs the other way and will wear gland packing.

Silver steel is quite prone to rust so stick with the PGMS or just bright drawn mild steel such as EN1A or 230M07 in new money,

These three replicas of no longer produced Stuart Engines (Progress, Simples & One-One) all use 303 for the rods and PGMS for the crankshafts, other bright steel is 230M07. Rust is usually down to aftercare or storage not the actual material. Leave moisture on bare metal after steaming or store in cold damp conditions and you will get rust.

 

[Bob Sorenson]

I bet those rods are threaded with British Association (BA) threads on both ends. Unless you have BA dies, you'll have to change out a number of other parts. Maybe contact Stuart to see if they have just the replacement shafts. Andrew at the sales email is a good guy, he'll get back to you.

 

[Sarah]

Sarah if you are in the UK then a good shaft material is PGMS - Precision Ground Mild Steel. This has the same sort of finish as stainless and silver steel, is easy to work with and being precision ground runs nicely in a typical H7 reamed hole. Ideal for crankshafts on steam models. Use 303 stainless for the piston and valve rods but give it a rub length ways with worn fine emery cloth or a Scotchbrite pad as in the supplied state the finish runs the other way and will wear gland packing.

Silver steel is quite prone to rust so stick with the PGMS or just bright drawn mild steel such as EN1A or 230M07 in new money,

These three replicas of no longer produced Stuart Engines (Progress, Simples & One-One) all use 303 for the rods and PGMS for the crankshafts, other bright steel is 230M07. Rust is usually down to aftercare or storage not the actual material. Leave moisture on bare metal after steaming or store in cold damp conditions and you will get rust.

Thanks for your comments, I tried to get some PGMS but it only starts at 1/2" diameter. I will use it on ot her projects though Your three engines look great. Thanks again, Sarah

 

[Jasonb]

Try these people which is where I get mine they go down to 1/4" in imperial or 6mm in metriv. Page 88

https://www.m-machine-metals.co.uk/downloads/Metals catalogue.pdf

 

[Sarah]

Try these people which is where I get mine they go down to 1/4" in imperial or 6mm in metriv. Page 88

https://www.m-machine-metals.co.uk/downloads/Metals catalogue.pdf

Thank you for this link, I'll have a good browse of their catalogue

 

[Lloyd-ss]

If I may suggest a slightly different approach to your material selection conundrum, I will give it a try.

Because most of us are working on models and only need tiny amounts of specialty materials, we are often left with:
1. What can I find?
2. What can I buy?
3. What can I afford?
And finally,
4. Will it work well enough in the application.

We start looking around for dowel pins, shafting, drill blanks, anything that might be at all close. And it usually isn't our first choice of a material for the application.
But after you find something that you can buy, and that might possibly work, look the material up on
www.matweb.com
They have specs on just just about any material you can think off and you might actually be able to find the particular characteristic you need listed and quantified. Some of the common materials have all sorts of properties listed, including the same properties but in different heat treat conditions.. It does eat up a serious amount of time doing the research, but you might find an available materials that checks all of the boxes....... or at least most of them, LOL.

 

[Jens Eirik Skogstad]

The gland rods for valves and piston in stainless steel. And crankshaft can be made of steel or drill rod steel/silver steel. Some time the original cast crankshaft from Stuart in the unmachined steam engine set.

Important to keep steam engines free from moisture: All steel and cast iron surfaces is oiled. Use engine preservative oil in a spray can, which can be bought from marine dealers. After you have run the steam engine with steam, blow all the moisture with compressed air through the main pipe to the steam engine with the drain taps open while the steam engine is running and then spray preservative oil in the same direction into the main pipe and continue blowing until the preservative oil is covered everywhere inside the steamer with the drain taps open while the steamer is running to protect against corrosion. Do not allow the preservative oil to enter the boiler!