Chris's Build of Steering Engine

[crueby]

Time for the follower on the control nut. This looks a lot like a eccentric follower on a crankshaft, but the hole needs to be elongated to let the follower slide as the crank arm turns, and instead of an arm up to the valve there are pins on the sides to connect to the crank arms. Started out with a disc of bronze, flattened both sides on the mill then chucked up in the lathe to turn the pins:

Back to the mill to cut in the shoulders where the screws will go through the top/bottom halves,

and drilled the screw holes. Clearance size down to where the cut between the halves will be, tap size the rest of the way. These holes were drilled/tapped for 1-72 threads.

Back onto the lathe, to bore the center hole. This was done in two operations, with the part shifted in the 4-jaw for the second bore, to make the two overlapping bores to form the elongated hole.

That shift left a peak in the sides where the circles overlap, so that was flattened out tangent to the two arcs on the mill

Last bit of forming was to round over the ends, using the old trick of positioning the part in the mill vise with a rod through the hole, and making a series of cuts with the part turned slightly for each cut. That leaves a series of small flats along the arc concentric with the center hole. Only takes a few cuts either side of center to make a convincing arc. Here it is with the arc cut on the left, in progress on the right side.


Here is the finished part ready to cut the top/bottom halves apart. Well, almost halves, the cut needs to be made below the pins.


Then a fine jewelers saw was used to split the two halves. Here is the finished part screwed back together and test fit on the model. I had to do a little cleaning up on the groove in the control nut, but is a good fit.

Next will be the crank arms that the follower hangs from, connecting it to the upper crossbar. The end of the crank that will stick out will have links down to the control valve that will mount on the front wall. Thanks again to Michael for those extra details on this part of the engine!

[cnr6400]

 

[Kim]

Great progress, Chris! 
It's really shaping up.  Lots of little complexities on this guy!

Kim

[crueby]

Great progress, Chris! 
It's really shaping up.  Lots of little complexities on this guy!

Kim

Sure are. Still need to make the indicator follower, gears, and needle, end stop mechanism, control valve and links, two steering wheels, and THEN can actually start on the engine itself!

[Michael S.]

Chris, very good.
Now you are one step further. I like the "eccentric" ring.
And there are still so many exciting parts to come.

Michael

[crueby]

The arms for connecting the follower ring to the upper crossbar are made - started with a piece of flat stock, drilled the pivot holes, and cut it out with a small end mill.

A little cleanup with the belt sander, and filed some relief next to the holes so it would not catch the side of the follower ring, here is a test fit on the model:

All appears to move smoothly, the next step will be  to make the drop links that go from the end of the crank down to the valve rod. After that, um, er, have to look at the plans and decide! Probably start in on the end stop and/or the rudder indicator linkage...  For now, the temperature is getting very comfortable outside, time to head out and enjoy a sunny fall day!

[crueby]

Got to work on the rudder indicator mechanism today. There is a threaded block that rides on the threaded section just inside the front wall, that block moves forward and back as the steering wheel is moved. Attached to the block is a gear rack which then turns the indicator needle up top. So, lots of little bitty pieces!  I started with the block, which I made in one piece with the gear rack holder:

The two screws on the section going to the right towards the front wall will hold the gear rack. The two screws on the top above the shaft will hold a rod that keeps the block from spinning.
The gear rack was cut with a M0.6 cutter onto the side of a strip of brass:

A pair of holes to match the ones in the block were drilled and elongated to give some adjustment to the mesh of the gears. Here it all is test fit on the upper shaft:

Still need to make the rod that keeps it from spinning as the shaft turns.

Next made the pinion gear (photo taken while cutting the gear teeth came out too blurry to use, sorry). The center hole is tapped 4-40, and the outside turned down and milled to just leave one side of the gear teeth:

Here it is after parting off:

Still a number of parts to make for this subassembly - the indicator dial and needle, the pivot post to hold the spur gear onto the needle shaft, and also need to cut slots in the front wall for it all to fit into...

[Michael S.]

Hello Chris, great pictures again!
Here are pictures of the big machine for comparison.
At that time I didn't have such a nice gear cutter and I made a shank cutter myself. Luckily I didn't have to mill all the way around. The threaded rod is guided with a groove in the frame. I didn't scale the table for the pointer. I think there were lines there. Maybe also letters for O , port and starboard. You still have artistic freedom 🙂


Michael

[crueby]

Thanks Michael!
I used the length of the threaded sections to estimate the total travel, and used that to pick the number of teeth on the spur gear (14), so that it gives me about 35 degrees of travel each side on the indicator. When it comes time to make the wheel for the chain to go around back at the rudder post, I'll size that to give about 40 degrees either side.  My engraving skills are pretty crude in metal, but the rotary table should make it easy to scribe an arc and lines in the top plate.
 

[cnr6400]

Great looking mechanism Chris! 

[Michael S.]

Hello Chris,
I just looked at your drawing of the flat slider again.
You drew him rectangular.
but it is a trapezoidal shape.
I think it was done that way because it's a full pressure steam engine.
Like almost all high-speed working steam engines. This is perhaps due to a softer start.
You would have to see in practice whether it is necessary on the model.

Greetings Michael

[crueby]

Hello Chris,
I just looked at your drawing of the flat slider again.
You drew him rectangular.
but it is a trapezoidal shape.
I think it was done that way because it's a full pressure steam engine.
Like almost all high-speed working steam engines. This is perhaps due to a softer start.
You would have to see in practice whether it is necessary on the model.

Greetings Michael

Ah, yes, I remember you mentioning that before, I forgot to angle the edges on the valve slider, will have to change that. I remember seeing it in your photos too. Thanks!

[crueby]

For everyone else, here is what Michael and I are referring to. This is a picture of the flat D valve inside the control valve in the steering engine. This valve is moved by the linkage on the upper shaft that I have been working on this past week, it directs steam into either the center or the ends of the spool valves in the cylinders themselves, so it controls both the direction and the speed of the engine. This picture was taken very close to straight above the valve, as proven by the red rectangle I drew over the center recess.

The outer red rectangle shows the angles on the edges of the slide valve, highlighted by the green lines along their edges. In the photo editor I measured the angles between the green and red lines, and the average between the two is 5 degrees. What this does when the slider is moved past the edge of the steam ports on the valve face is to make a small wedge shaped opening at first, then a larger opening as the slider moves farther. This valve is the control valve for the engine, not the valve in each cylinder, so with a small movement on the steering wheel, this valve could be moved to just open the port to steam a little ways - this would result in the engine running slowly, recentering the valve and turning off the steam. With a larger movement on the steering wheel, the port would be opened farther, letting in more steam and running the engine faster to catch up to the steering wheel. When getting close to center, it would also slow down the engine as the port is closed, so the engine would have less likelyhood of running past center and have to back up again, hunting for center.

An interesting detail - for the model, it may take some experimenting to find a good angle - my guess is that a larger angle would be better at small scale, but that will take a couple tries to be sure. On the Mann Steam Truck I built, they did something a little like this - the slider on the throttle valve itself was square, but the port was angled into a V shape so the increase in area opened on the port was more gradual, that worked quite well, a lot like a needle valve does.

[crueby]

Updated drawing for the valve....

[Don1966]

Dog your work is superb, did you ever think about applying to the Martin model museum? After all you do use a sherline lathe and mill…


 
Don