Stuart Number 9 Engine

delalio · Sep 27, 2024

I've been following this build very closely. I recently built my first steam engine, a Stuart 10V, and I've a Stuart S50 awaiting starting too.

I have the same new project nerves you do! So I've been doing almost every other job I can think of instead...

jcreasey · Nov 21, 2024

Part 9 - Making the Piston

First job was to clean up the casting.

Despite what the plans specified I decided not to rely on the thread for alignment and machined a small rebate into the piston. This will be a tight fit against the piston rod.

Now that the piston is cleaned up it was time to make the piston rod. I didn't want to rely on the three jaw chuck but I also did not want the 4 jaw chuck to cause any damage to the piston rod so I made a small fixture from some brass to clamp the rod.

This allowed me to dial in the concentricity very closely before single pointing the 2BA thread and the matching boss for my piston. The boss is a very tight fit.

I used the piston rod as a mandrel to finish machining the piston to size. Hopefully this will ensure everything is as concentric as I can possibly get it.

I ground up a little stubby parting tool to cut the slot for the piston rings.

Once I had the piston done I reversed the rod to machine a thread on the other end for the cross head guide. It took quite a bit of messing around to get the piston rings fitted with just the right amount of clearance.

A bit later I drilled two blind holes in the end of the piston and made a pin wrench to suit so that I can easily remove the piston from the cylinder. This makes life much easier when fitting the cross head guide.

Steamchick · Nov 22, 2024

A proper job!
Recently, trying to drill a 1.25mm hole - using the 3 jaw chuck to hold the drill on my 8in lathe, I found the chuck runout was to great for the drill too not be true. So had to resort to the 70-year-old Unimat SL.
Maybe my 3-jaw chuck has some swarf where it should not be, so it needs a strip and clean? - I was OK less than a year ago...
But I like your fastidious approach to precision of concentricity.
What dimensions are the piston rings? Expanding them over the piston must have been a nervous moment!
K2

Richard Hed · Nov 22, 2024

jcreasey said:
Part 9 - Making the Piston
First job was to clean up the casting.
View attachment 161386

Despite what the plans specified I decided not to rely on the thread for alignment and machined a small rebate into the piston. This will be a tight fit against the piston rod.
View attachment 161387

Now that the piston is cleaned up it was time to make the piston rod. I didn't want to rely on the three jaw chuck but I also did not want the 4 jaw chuck to cause any damage to the piston rod so I made a small fixture from some brass to clamp the rod.
View attachment 161388

This allowed me to dial in the concentricity very closely before single pointing the 2BA thread and the matching boss for my piston. The boss is a very tight fit.
View attachment 161389

I used the piston rod as a mandrel to finish machining the piston to size. Hopefully this will ensure everything is as concentric as I can possibly get it.
View attachment 161390

I ground up a little stubby parting tool to cut the slot for the piston rings.
View attachment 161391

Once I had the piston done I reversed the rod to machine a thread on the other end for the cross head guide. It took quite a bit of messing around to get the piston rings fitted with just the right amount of clearance.
View attachment 161392

A bit later I drilled two blind holes in the end of the piston and made a pin wrench to suit so that I can easily remove the piston from the cylinder. This makes life much easier when fitting the cross head guide.View attachment 161393

I suggest you make an ER holder. YOu can use your 4-jaw to hold it.

Propforward · Nov 23, 2024

Nice approach on that custom collet in the 4 jaw. Top work.

jcreasey · Nov 28, 2024

Steamchick said:
A proper job!
Recently, trying to drill a 1.25mm hole - using the 3 jaw chuck to hold the drill on my 8in lathe, I found the chuck runout was to great for the drill too not be true. So had to resort to the 70-year-old Unimat SL.
Maybe my 3-jaw chuck has some swarf where it should not be, so it needs a strip and clean? - I was OK less than a year ago...
But I like your fastidious approach to precision of concentricity.
What dimensions are the piston rings? Expanding them over the piston must have been a nervous moment!
K2

The rings are about 1/8" wide and 1/16" thick. They were supplied with the castings and there was no issues stretching them over the piston. They are probably overkill for a model but it's nice to put them to use after they have been so patiently sitting in their box for so many decades.