Chris's New Steering Engine

[cnr6400]

  Don't forget to drill the starboard ports when you do the port ports, will ya?  (worst pun this week)   

[crueby]

Don't forget to drill the starboard ports when you do the port ports, will ya?  (worst pun this week) 

Engine is not done so can't  use it to steer the shop into port!   

[Kim]

Steam chests and glands are looking good! 

You're moving on quickly with your steering engine.

Kim

[crueby]

And today was port and passage day!  Not sure where the cruise is to, so I stuck to the workshop and played!   

Started with the ports. This engine is using the 4-port style of D valve, which allows for both forward and reverse with one eccentric, by swapping which port the steam comes into the valve, and which port the exhaust leaves. It does the same thing as if there was a spool valve that was swapped between inside-admission and outside-admission, which is how the first steering engine worked. Diagrams of things are at the end of this post. So, after laying out the port positions and making a chart of moves and hole depths, first job was to spot and drill end holes for each port. These ports are 1/16" wide and 1/4" long. Two go deeper than the others to connect with the passages to the cylinder ends. The other two are shallower to allow those passages to pass by underneath. These two connect to passages out the side of the steam chest base, where there will be a manifold over to the control valve.

Then used a 1/16" end mill to connect the holes and take the ports out to final width. This end mill is short, so the slots are only 0.1" deep, the drilled holes go deeper.

Then drilled in from the side of the steam chest for the passages from the manifold/control valve. Over on the left, you can see a third hole laid out that just goes partway into the base. This one is the steam inlet, which always has pressure going in to hold the valve slider down to the port face. The other two holes alternate between steam inlet and exhaust outlet, depending on where the control valve is. When stopped, neither has pressure. The constant pressure on the larger outside of the valve slider keeps it in place against the port face. There are also two more holes at the far left and right - these are the mounting holes for the manifold.

Final set of holes was from the cylinder ends down to meet the deeper ports. All these holes required some careful measurement of the part to know how deep to drill, so the holes did not break through where they should not!

And then these end holes were connected to the cylinder end with an end mill:

The edges left by that milling step were eased with a file to let the piston ring slide past during assembly. So, that finishes up all the ports/passages/holes/milling/shaping/etc on the cylinders!      Its all gone pretty quickly, all the engine practice is paying off! Here are all the parts so far, ready for making pistons and valves and gaskets:

 
For those who have not seen this style valve before, here are some diagrams to explain them. They come from my steam shovel book, so this is a sneak preview!



At the top in each diagram is the valve slider in green, with the four ports below it. The layout of the passages in the steam chest base and cylinder are how they were in the Marion steam shovel engines, in this steering engine I went with just straight line passages. If you look close at the slider, it has the usual shallow opening in the center of the bottom face, but it also has a passage above that, with a wider opening at the left end. The left two diagrams show it with the steam (red) coming in from the left hand passage, and the exhaust in blue-green going out the passage to the right.


In the first diagram on the left, the slider is all the way to the right, sending steam into the left end of the cylinder. The upper passage in the slider has pressure, but it is not lined up with any port. The piston is pushed to the right. In the center diagram, the slider is all the way to the left, sending steam around the upper passage in the slider to the right hand port, sending the piston to the left.

Here is the cool part: if the throttle/control valve position is changed, now steam is coming in from the right hand passage, and exhaust is going out the left one in the block. With the slide valve still all the way to the left as it was in the center, now the steam is going to the left end of the ccylinder from the small center opening in the slide valve, so the piston is pushed to the right instead of to the left! Same reversal happens when the slide valve moves to the right. So, by changing the routing of steam/exhaust back at the throttle/control valve, the engine runs the opposite way. Quite a clever setup. It was invented in the early/mid 1800s, and was used on almost all steam shovels later on. I don't know why it was not used much if at all on marine engines or locomotives - all the reverse linkages and extra eccentrics are not needed, and the engine gets more compact.

Hope all that makes sense, let me know if you have any questions!

[cnr6400]

 

[PaulR]

Too much port on a long passage = piston broke 

Beautiful finish on those cylinders.

[crueby]

The pistons were up next, turned them from some 303 stainless round bar. The end was turned down just under the bore of the cylinders, then came back with a parting tool to cut the o ring slots. Some people always ask what groove dimensions to use for o-rings, I like to just get close then do test fits with the ring and the cylinder (leaving the piston part in the chuck), and sneak up on a nice sliding fit. For pistons, you don't want the same tight fit that you would for a stationary set of parts, you want the piston to be able to slide easily but still seal. So, I just do test fits and take anouter thou off, testing with a drop of oil on the rings to eliminate stiction, till it feels right. Moves without a lot of force, but doesn't wobble. If I go too far and the fit is not good, I can just move down the bar and try again. In this picture, rings for both pistons worked out well, so shallow grooves were also made to use as a guide on the bandsaw to part off the pistons:

After sawing, the parts were chucked up again to true up the faces and cut a shallow recess for the nut to hold the piston on the rod.


Then I moved on to the crossheads, turned down some bearing bronze bar to fit the guides. This bar is long enough to get both crossheads out of, will cut in one on each end then part them off and finish the other ends. The center hole was also drilled from each end, tap size for the end of the piston rod.

Over to the mill, and held the blank in a collet to start milling the shape in. The sides of the crosshead get flats. For all these steps, the part was left in the collet, and the square collet block turned around in the vise as needed to do each side.

Drilled/reamed for the wrist pin...

and then stood the collet up on end to shape the base end, where the conrod will go in.

and finished up the milling with the collet angled in the vise to do the extensions at the end:

One crosshead up to this point:

I'll turn the blank around in the collet, and do the same steps on the other end of the bar, then cut them apart and finish shaping that end...

[cnr6400]

  You found it! there WAS a crosshead hiding in that nice bar! 

[crueby]

You found it! there WAS a crosshead hiding in that nice bar! 

It kept trying to hide behind the vise!   

[steam guy willy]

Hi Chriss , Starting to feel better and lots of swarf generation happening here ?? just a quick question ..although you are using brass , there is quite a lot of copper colour in the pictures ?? 

Willy

[crueby]

Hi Chriss , Starting to feel better and lots of swarf generation happening here ?? just a quick question ..although you are using brass , there is quite a lot of copper colour in the pictures ?? 

Willy

Hi W8lly! Glad you are doing better.


The cylinder parts are brass, but the flux from the silver soldering left some copper color. Also, the crossheads are bronze so that is a darker color.

[Kim]

I assumed the copper color came from the pickle solution.  My parts always come out with a thin layer of copper color after sitting in the pickle vat.

Kim

[crueby]

I assumed the copper color came from the pickle solution.  My parts always come out with a thin layer of copper color after sitting in the pickle vat.

Kim

The pickle leaves an all over copper cast that a wire brush gets rid of pretty well. I notice that where the flux was is a lot worse.

[Kim]

I assumed the copper color came from the pickle solution.  My parts always come out with a thin layer of copper color after sitting in the pickle vat.

Kim

The pickle leaves an all over copper cast that a wire brush gets rid of pretty well. I notice that where the flux was is a lot worse.

Interesting.  I'll have to see if I notice that correlation too...

Kim

[crueby]

I assumed the copper color came from the pickle solution.  My parts always come out with a thin layer of copper color after sitting in the pickle vat.

Kim

The pickle leaves an all over copper cast that a wire brush gets rid of pretty well. I notice that where the flux was is a lot worse.

Interesting.  I'll have to see if I notice that correlation too...

Kim

I wonder if it varies with the flux - I am using the Harris Black flux, nice long working time at temperature.