Author Topic: Chris's Marion 91 Steam Shovel  (Read 248548 times)

Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2610 on: December 09, 2018, 05:51:20 PM »
Today I got started on the crank discs - the cylinders on this engine are outboard of the crankshaft support (which is the same thick support that holds up the slew drum), so the crank is a simple disc with a side pin. The discs are .24" thick and are 1.875" diameter, so they will act as a small flywheel also. I cut a pair of discs out of the same 303 stainless bar used on the track end wheels, thick enough to leave room for chucking them up. I turned the face and took it to diameter, then drilled/bored the center hole for the axle. The axle hole is a snug fit, and will get a set screw through the rim of the disc.

With the part still in the chuck, moved the chuck over and bolted it to the mill table to drill/tap the offset hole with a M7x1.0 thread for the crank pin, which will have a shouldered end. Since the axle/pin holes and the face were all done with the part chucked throughout, they should wind up nice and perpendicular to each other.


One more disc to get the same steps, then I will turn them around in the chuck and turn them down to final thickness.

After that, on to the eccentrics...

Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2611 on: December 10, 2018, 07:50:07 PM »
Both crank discs are turned to thickness, and I have turned up the crank pins. Decided to thread the inner ends to a shoulder, undercut the threads at the inner end so the pin would snug up all the way to the disc face. Next steps are to drill for the set screws and loctite the crank pins in place.


Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2612 on: December 10, 2018, 09:03:27 PM »
Drilled/tapped the rims of the crank discs for some 10-32 stainless set screws to hold them to the crank shaft - still want to mill in some small flats on the shaft for the ends of the set screws.

I was just about to loctite the crank pin threads into their holes, when I real quick hit the brakes -  :wallbang: - I am going to want to be able to test fit the pins into the bearings when boring them out, and cannot do that if they are already fixed into the discs! So, that will come later. First, will mill the flats on the shaft (I carefully aligned the discs so the set screw holes are in the same plane when the discs are back to back, so if I mill the flats at 90 degrees to each other, the crank pins will be at 90 too).

Offline cnr6400

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Re: Chris's Marion 91 Steam Shovel
« Reply #2613 on: December 10, 2018, 10:32:35 PM »
Cranks and pins look great Chris, good catch on not Loctiting things until after assy tests. Been caught on that myself a few times.

Offline Don1966

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Re: Chris's Marion 91 Steam Shovel
« Reply #2614 on: December 10, 2018, 11:21:34 PM »
Well thatís a good thing Dog now you wonít be backtracking like a coonass crawfish! Looking good Chris.....now did I say .........I..........like....... :Love:


 :cheers:
Don

Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2615 on: December 11, 2018, 09:11:58 PM »
Thanks guys!
Today moved on to working on the eccentrics for the hoist engine. Normally on an engine with enough room on the crankshaft I like to make the eccentrics in two pairs, each of the pieces having a seperate set screw, which makes it simpler for me to individually tweak the timing on each cylinder in each direction. However, for this engine, there is only 0.350 of shaft length for each pair of eccentrics, so I compromised it down to having one set screw for each pair, each pair being made from one piece. Also, since the followers are so thin, I switched from my usual preference of having a rib in the center of each cam to keep them centered to having a lip on the outside of each cam.
In order to machine these parts without having to do interrupted cuts with the parting tool (which never goes well for me), I am starting out by turning the blanks out of a piece of 303 rod stock long enough to have a shaft out each side, so I can turn the parts around and turn them from either end. Later on, the shaft on one side will be trimmed to final length, and the other one trimmed off completely.
Here things got started, turning the shafts out either side and drilling/boring the holes for the axle in the center of each blank. The blanks only needed to be made out of 1" bar, but the closest I have on hand is some 1-1/4" bar, so they look a bit large to start (since they are too large to start!). After turning the two blanks, the first one was offset for the throw of the eccentric, using a dial indicator and the 4-jaw chuck.


Then the cam on one side was turned in, taken down to the OD of the outer lip with a normal turning tool.

At that point I switched to a parting tool, and took it down the last .050 from the lip, to form the inner slot.

Then, you guessed it, turned the part around to do the other cam. Before removing it from the chuck, I marked the centerpoints of the part where they hit the center points of the jaws in the offset direction. That way I could index them from the other side. On these engines there is very little lead/lap, since they only ran in short bursts from dead stop to normal speed and off again, so saving steam like a loco would on a prolonged run is not neccessary. So, the cams are 180 from each other.

Where the two cams meet in the center, there was a little rim of metal pushed back by the cutter, this was pulled out with pliers and the burrs on the corner get filed smooth. Here is the first eccentric turned to shape, will do the same on the other one then will trim the shafts out either side and drill/tap the holes for the set screws. Its hard to judge scale in the photo, the center section with the two cams/lips together totals 0.230" thick.




Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2616 on: December 12, 2018, 02:51:22 PM »
And cut the second eccentric pair, and parted both pairs off to length from the shafts. Next will drill/tap for the set screws.

Test fit on the axle:



Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2617 on: December 12, 2018, 06:28:13 PM »
The set screws are drilled/tapped/installed on the eccentrics, and did a test fit in the model. If you were wondering why they have to be so narrow, here is why:



As you can see, there is very little room on the right end, and even less on the left end:



And a shot of them on the real machine, shows how squeezed in everything gets:



And a family shot of the machinery space so far:



Next I want to make the eccentric follower straps. They will be made out of a chunk of bearing bronze (932) bar stock - being so small I wanted the extra strength of the bronze over brass. The bar will be split in half, the cut faces dressed smooth, then will drill/screw them together to start the shaping process. Hmmm... May need to mill the tabs before I can bolt them together.... need to ponder the order of things before I get to cutting.... Maybe mill the tabs with a space left for cutting....  Usually I have made them up out of thin bar stock, this is a different process for me... Something to ponder while mixing up some Christmas cookie dough!



Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2618 on: December 12, 2018, 07:30:01 PM »
A bit of thought, and decided that profiling the tabs in first would make it a lot easier for the following steps - drill for bolt holes down through the tabs, split the stock in two and mill the cut faces back, bolt them together to bore the center holes, then part off the 4 pieces needed (plus a spare or two if there is room, should be plenty) for final shaping.




Offline cnr6400

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Re: Chris's Marion 91 Steam Shovel
« Reply #2619 on: December 12, 2018, 08:29:03 PM »
Hi Chris, the eccentrics look great and that's a nice Slab-O-Straps you have going too. Got another box of  :popcorn: here.

Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2620 on: December 12, 2018, 09:14:59 PM »
Hi Chris, the eccentrics look great and that's a nice Slab-O-Straps you have going too. Got another box of  :popcorn: here.


I just need an industrial strength deli slicer!   :Lol:

Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2621 on: December 13, 2018, 01:18:15 AM »
Hmmmm.... Started laying out the distances between bolts to see how many straps I can get out of the block (looks like at least 6, so a couple spares). But, along the way I checked my fastener boxes and realized that I only have 1-72 screws long enough in brass (2-56 are too thick), though I do have 0-80's in steel. Question is, would the brass 1-72's be strong enough in brass? The steel 0-80's would be stronger, I would think? I can order more (though 1-72 in steel hex head is hard to find, other than AME which is excellent though pricey) but I'd rather not wait to get them....
 :thinking:
 :thinking:
I do have tap/die for 1-72, could make my own from steel, milling heads and doing threads that small is not fun....
 :thinking:
Thoughts, anyone?

Offline kvom

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Re: Chris's Marion 91 Steam Shovel
« Reply #2622 on: December 13, 2018, 01:52:58 AM »
I'd order the AME screws, and work on something else in the interim.

Offline 10KPete

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Re: Chris's Marion 91 Steam Shovel
« Reply #2623 on: December 13, 2018, 02:11:51 AM »
I'd order the AME screws, and work on something else in the interim.

What he said!! Cut yourself some slack, dude! :wine1:

Pete
Craftsman, Tinkerer, Curious Person.
Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline crueby

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Re: Chris's Marion 91 Steam Shovel
« Reply #2624 on: December 13, 2018, 04:03:10 AM »
Thanks guys, I took your advice and decided that I would order some tomorrow, and skip over to the big ends on the con rods while waiting, when just before going to bed I remembered my old workbench in the basement. It has a couple of pencil drawers that accumulated a bunch of stray bits and pieces, including a couple of little tins of screws. Some digging and measuring in there, and I found 14 1-72 pan head machine screws that are long enough!


 :cartwheel:


So, all I need to do is mill the heads to small hexes with the hex collet holder, and I am in business. That gives time to order more screws without any waiting.


 :cheers: