Chris's Marion 91 Steam Shovel

[Don1966]

Excellent Dog!.....




 
Don

[crueby]

Excellent Dog!.....




 
Don

Thanks Don!

Todays photo is titled "Used To Be Round".   

Starting the stock prep for the engine block and cylinder for the steering engine. Started with some 1144 stressproof steel round bar (engine block is cut from same stock as the other two engines, but from a horizontal slice this time) and cut the rough shapes out on the bandsaw.

Next step is to square up the blocks...

[crueby]

Yesterday saw the engine blanks milled square, this morning have bored the holes for the crosshead guides. Drilled all the way through the block for the starter hole, then bored out the first inch to size - that gave the chips a place to go.


Next will drill/bore the holes for the cylinders...

[crueby]

A little boring time     later, and the cylinder bores are done...

Parts so far...

Time to whip up an arbor to center the holes on the rotary table for milling the outside curves.

[cnr6400]

 

[crueby]

Hey, pass some of the popcorn this way too!   

[crueby]

Catching up on the work from the last two days - after boring out the cylinders and crosshead guides, went back to take a look the order that I did things on the other two engines, and decided to mill out the crankshaft bay. Started with chain drilling to remove the bulk of the metal...

then finished with end mills. This engine has a slightly different bottom end, there is no ledge sticking up like the others had, the stand will span that gap. So, could just mill in from the end, which made it all go quicker.

Next sections to shape are the front end of the crosshead guides and the cylinder. It is important to get all the screw holes in the proper places, and they are concentric to the bores, so a mandrel was the next thing made. Turned it so it would fit the crosshead bore, and the cap has steps for the crosshead and the cylinder sizes.

The side of the base had to be nibbled back to clear the arc in the corner of the crankshaft bay.


With the part on the arbor, the offset from the centerline was dialed in and the holes drilled around each bore.

Same pattern on the cylinder. Each time the parts were set on the mandrel, the rotary table was zeroed and the back edge of the part lined up with the axis of the mill table - a straightedge along the part makes a good sighting tool.

The cylinder bottom cap plate was also done. Since the bore is so small, there is not much room for screws to hold the piston rod gland in, so I came up with a different way to do it. I made the plate out of two pieces of thin stock, and drilled one side for the o-ring, just deep enough that it gets a little compression onto the rod.

You can see the rings in the plate half sitting in the foreground. The screw holes were tapped and some offcuts of some 1-72 screws that I had hung onto were threaded in to check the alignment of the parts. Note that some of the screws are in the cylinder, some are in the engine block - the top ones come out of the steam chest base, so the nuts have to be on the block side. the rest come out of the guides, so the nuts will be on the other side of the flanges milled into the cylinder edge.


All good! The outer cap will be made next, that one will be clamped to the cylinder and both drilled at the same time.

[crueby]

Cylinder caps drilled for this morning - got out my handy expanding arbor, turned a new lip on the end to fit the bore, and clamped the cap blank for drilling the first set of holes:

Tapped those holes, swapped to the other bore, screwed the cap in place in the first set of holes, and drilled for the second set:

[cnr6400]

Great work Chris!  Sorry about not passing the popcorn. Here's some for you....

Like the expanding arbour. That will come in handy for many jobs.

[crueby]

Great work Chris!  Sorry about not passing the popcorn. Here's some for you....

Like the expanding arbour. That will come in handy for many jobs.

Those expanders come in very handy, simple to make from some round stock, just thread for a bolt, taper the end of the bolt slightly, and counterdrill the hole to just over the thin end of the taper. Slit the body to let it flex. The end can be turned to fit a bunch of parts till it gets used up. I also have one with a split bushing at the end that I used for the cylinders on the other two engines, actually using that one now to mill the sides of the block, pics later...
And thanks for the popcorn!   

[crueby]

This afternoon saw the outside rims of the cylinders milled down to size (the center section between the flanges is still to be done) using the expanding arbor to hold the part, could not use the through-arbor since I wanted to do the cap to match:

Second side coming to shape...

And while the setup is there, did the matching flanges on the engine block, which are stepped (figure they did the step to give a place to pry against when popping the cylinders off the block for servicing them).

Having done all these steps on the other engines earlier is making this go much quicker, very handy to have the writeup to look back through!

[Zephyrin]

there is something puzzling with the crankshaft, as the web look to be set at 180° apart, and not at 90° as it is usual with a double acting two cylinders engine.
Impressive work with these tiny parts, brave enough to use steel blocks, wow !

[crueby]

there is something puzzling with the crankshaft, as the web look to be set at 180° apart, and not at 90° as it is usual with a double acting two cylinders engine.
Impressive work with these tiny parts, brave enough to use steel blocks, wow !

The cranks actually are at 90 degrees apart on these, its just that the center section between the crank pins directly connect them rather than going back down to the centerline and then back out to the next pin. As you say, this is unusual, but it is how Marion made them on these engines. I dont know why they did that, it would make the crank more unbalanced. These engines just ran in short bursts, but seems like that would still be a concern.

In this picture from the other engines you can see the offset better on the one in the foreground. This was taken before the web outlines were cut in, but it shows how the center section just goes direct between the pins:



There patent drawings of the engine show this kind of crankshaft too, but since the patent is concerned with the valving they dont mention why they made it this way. They did make the engine as compact as possible, and there would not have been much room for a center bearing between two webs, maybe that is part of the reason.

As for using steel, the 1144 is cutting very nicely, as recommended by others here on the forum. It is more stable dimensionally than stress relieved brass is, so well worth the extra cutting effort.

 

[Ye-Ole Steam Dude]

Hello Chris,

This little engine is a complete project within itself and as usual your work is beautiful. Cannot wait to see it and the others in action

Have a great day,
Thomas

[crueby]

Today started turning loose the trained steel-eating termites on the engine block, nibbling away at the side recesses. The shop elves were supposed to do this with their hand files, but they are off waterskiing on the birdbath..