New Kozo Shay Crankshaft material

[Bruce]

Hello, everyone, I'm still working on my Kozo Shay in 3/4" scale and am at the point where the next step is to turn that crank in one piece. Kozo suggests "free cutting" stainless steel or "free cutting" steel. I'm assuming that would be #303 stainless. I've never heard the term "free cutting steel" and don know what that is. I'm intimidated by this project and am wary of the stainless. My supplier here in LA has cold rolled and hot rolled 1 1/4" bar stock. Which one should I use if I go with steel? Is there a number that designates "free cutting" steel. I just saw an article about how unstable cold rolled can be so am wary of that. John Caldwell wrote an article for DLS magazine and mentioned that he could not get a good finish with stainless but found a "mild" steel and got a "mirror finish" directly off the tool. John is in England and you know, they have a different language over there so I'm not sure what he meant by mild steel. Any help would be greatly appreciated. Thanks.

Bruce

[Harold_V]

Something to ponder.
Stainless doesn't make a great bearing, as it readily galls. It is also not a hard metal, although it can be if heat treated. That, of course, excludes some of the alloys, including all of the 300 series. However, there are grades of stainless that would serve quite well, and, as luck would have it, one of them is the best machining of all the stainless grades. It's 416. I would not recommend 303 S or 303 Se, as they would be more inclined to gall.

Free machining steel is typically (but not always) leaded. An example might be 12L14, but there are others. If you'd like to explore, look for screw machine stock, as it is formulated to be free machining.

I'd encourage you to explore Stressproof. It machines beautifully, has great tensile strength and has wonderful qualities for parts that won't get heat treated. If the project was mine, I'd choose it, or 416 stainless.

Mild steel, or cold or hot rolled material, known as 1018, 1020, are common, but do not machine well. They are inclined to tear, leaving a less than desirable finish. It can be polished, which helps, but they are frustrating to machine.

I won't try to confuse you with other choices, as they won't provide any benefits that you won't get from using Stressproof.

Harold

[10KPete]

I'm new to this board and this is, I think, my first post. So hello!

I'll second Harold on the Stressproof. I've used it a lot and love the way it machines, finishes and the great strength
it has.

Pete

[kvom]

I too like stressproof. 12L14 is also a very common "free machining" steel.

[joneg]

you may want to consider assembling it from pieces of pre hardened 4140 ground shafting and cold rolled steel bars for the crank throws. press or loctite throw assemblies on a long shaft and taper pin the joints then cut main shaft out of crank throws

[daveb]

Hi Bruce
Can't speak to the stressproof but I used 12L14 for my 3/4" shay. It really machined well. It took me 4 tries to get she shaft done, because of operator error, not because of the 12L14. The attached is of three of the disasters. The 4th is on the shay. The only consolation is 12L14 is cheap Incidentally, there was a thread on another site showing how to build the shaft in multiple pieces. I think I would have used that method if I had been aware of it.

[Bruce]

Thanks to all, I got exactly the information I needed. I am choosing Kozo's one piece turning as I'm intrigued by the method. Dave B thanks for sharing your mishaps as I have a box of "spare" parts that are off-dimensions and full of holes drilled in the wrong places. I'm sure there will soon be a crank added to the heap. I know this is going to be tricky and as I'm a true amateur, in over my head already. When I look at the trucks, cylinders etc., I can't believe that I made them.

Bruce

[Bill Shields]

Stainless....would not consider it...even free-machining.

Stressproof is a very good way to go.

This is what we are using for the tom thumb article, which will also be showing a very unique / different way to make a crankshaft.

[daveb]

Hey Bruce, you can't believe what you're done, wait until you get that beast to run on air. It's a great feeling.

[Wolfgang]

I'd strongly recommend stressproof steel, formally known as 1144 steel for the advantages described by Harold.

I've machined 2 small twin cylinder crankshafts with the throws at 90 degrees and the streesproof steel machined well.

One observation I'd like to pass on: During the machining operations the embryo crank shaft will distort a fair amount, therefore I found it best to take small cuts off all diameters in turn to sneak up to the finished diameter. The final two cuts were only .002 to .003 thou deep resulting with a very true running crank shaft.

Because the steel is so strong, over 100,000 psi yield strength, it can deflect quite a bit without permanent deformation. This property is useful for those small dig-ins which are unavoidable for the beginner.

Finally, the steel is quite hard without any additional heat treatment, providing excellent bearing surfaces with a small amount of polishing with fine abrasive cloth.

Just be sure you drill all the centre holes in the right location on each end.

Good luck and let us know your progress with this exciting venture.

One-piece crankshaft: yeah!

Wolfgang

[Harold_V]

One observation I'd like to pass on: During the machining operations the embryo crank shaft will distort a fair amount,

That is a topic I rave about on a regular basis, and one that appears to be overlooked by many.

In the shop, it's called "roughing". One does not machine features to size until the majority of material has been removed. That's particularly important when cuts are assymetrical, such as when machining a crankshaft.

By properly roughing, the part in question will have been allowed to relieve the vast majority of internal stress (the result of being rolled), with the material remaining being of sufficient amount to permit corrective cuts. It should be noted that too much stock should not be left, as that is an invitation to further movement when finish cuts are taken.

There are occasions where parts may require a roughing, semi-finishing and then a finishing operation. A crankshaft could certainly qualify.

Harold

Edit:

Stressproof ® is LaSalle's tradename for 1144 steel.

[shayloco]

Here's my 1-1/2" scale "old" Kozo Shay crankshaft. I mentioned making it in stainless but a machinest handed me a piece of steel and said "use this". So I did. Took two weeks of evenings carefully machining as per Kozo's directions regarding order of operations and using nuts/bolts/washers to stiffen throws as they were machined. Follow Kozo's directions, take your time and you will do fine.

What you will need are some right and left turning tools that can reach into tight quarters. I removed my square tool post and used the lantern toolpost and tools for this part. In 3/4" scale you will need some small cutting tools to get in there.

This crankshaft has now been in use for ten years and is still working well. Once you have completed the crankshaft you will have the confidence to machine any part on the Shay. And have no concern about eccentric adjusting or slipping.

-Larry