Chris's Marion 91 Steam Shovel

[Mikem]

Was that a turtle support truck ?

[crueby]

Yup! Carried its radio to the pond, and the broken belt back!     You can see the truck in the background behind the whale in picture 10.

The truck is from the kit you pointed me at - works great on the rough lawn and also gravel paths. A similar crawler motor as in the truck is the one that snapped the belt in the turtle. Just spent some time in Fusion 360 modelling up some replacement parts, thinking of switching the turtle to a single rather than dual gimbal system, and getting rid of the belt drive - would make it all much simpler and more durable. I think the issue on the belt was the idler pulley on the back side was too small, too much flex for a fiberglass-corded belt. Without the idler, the belt does not wrap that far around the drive pulley, and it tends to skip teeth under load. Can't go that much larger on the belt tooth pitch, or it would need larger pulleys on the output shafts, which there is not room for. There is no room in the water tight compartment for a motor per prop shaft, so its either a belt drive or gear drive, and the output shafts are very close to the WTC walls so the final gears would have to be small. A single prop system would require moving one through-hull and plugging the two existing holes, and remaking the gimbal unit.

I've got two weeks till the next pond run to get it reworked however I do it...   

[Roger B]

Still enjoying the steam shovel build and all the distractions     

Do you loose many submarines or is the pond shallow enough to fish them out?

[crueby]

Still enjoying the steam shovel build and all the distractions 

Do you loose many submarines or is the pond shallow enough to fish them out?

We haven't lost any permanently, have had to fish a couple out that got caught in weeds, and swum for a couple. Pond here is maybe 6 feet at the most. Thats the good thing about renting the pool over the winter, much safer place for initial trials on new boats.

[crueby]

Back on the steam shovel this morning - milled the openings in the center floor plates, used a bit of plywood as a spacer on the mill table and clamped down the plates.
Drilled the clearance holes on the plates on the mill, then used the Proxxon mini drill press to drill the tap holes through those holes into the webs of the frames, and tapped/screwed them down with some 1-72 hex heads.
Here are the installed floor plates:The opening at the rear is for the firebox grates, the narrow one in front of the backstay takes the boiler front support cradle, and the large one in front of that is where the gear trains and winding drums will sit. The large hoist engine cylinders will run down either side of the large front opening.
This render shows where everything goes on the inside - 100 tons in a 50 ton bag!
Next up I think I will get the front track supports made - the cap on the corner of the frame, then the links and triangular assemblies that hold the tracks. Those should be a challenge, quite a complex set of shapes.

[crueby]

Pondering time!
This is one of those parts that I knew from the start would be a tricky one to make (and I need two of them). The front track supports:

The bottom tube, which holds the axle for the track assembly, is easy - it can be turned and silver soldered in place on the rest of the assembly. That 'rest of it' part is a pretty complex shape - one time when a casting would be a great place to start from. Or a big block of rectangular bar. The thickest section at the bottom is 3/4" thick, with the rest looking more like combinations of I-beams. It would be possible to piece up those areas like the I-beams were, but pretty tricky to hold it all in exact positions for soldering...
 
 
 
 
 
 
Hmmmm....
I do have some 3/8" thick flat stock that could be layered up to form the part, and mill it all out....
One thing I've never looked into would be to make a wood pattern (mill it from one big block) and get that cast. Is that practical, and economical? Could still be left as a block to mill from, I guess...
 
 
 
Thought about getting it 3D printed and cast at someplace like Shapeways, but at this size I would guess expensive, and from what I've heard from others the cast alloy is a tough one to machine....
 
 
 
 
 
Suggestions, ideas, thoughts, all welcome!!!


EDIT: just checked on Shapeways for the heck of it - prices range (for the upper section only, had to remove the lower tube for overall size) from around $30 for plastic to $90 for steel (infused with bronze) to over $300 for brass! Thats each... Gack!

[crueby]

More thoughts...
Looked at getting some thick aluminum bar, could get the size needed fairly cheap but the lower tube would have to be machined in or bolted on rather than silver soldered (ali does not silver solder as I recall).

Then looked at some 3/4" brass bar, could piece it up from 3 bars for the upper section plus the rod for the lower tube. Price on that is not bad, getting some 3/4" bar from Stoner on eBay. I did a similar piece up on the boiler support bracket for the Lombard, made a notched connection at each join and silver soldered, then machined that assembly.

So far that seems like the best approach for cost and strength. I think....       This part has to support a lot of weight and take some torsional stresses too....
 

[Gas_mantle]

Looking great Chris 

You sure are the expert when it comes to machining the big stuff on relatively small machines

[Farmboy]

Just thinking how I might attempt those track supports 

Could you cut the triangular webs out of one piece of flat plate (maybe overscale, say 1/8" for more strength), then bend up the inner and outer flanges from 3/4" x 1/16" strip. Might be easier to hold it all together for brazing with only three separate pieces.

Perhaps the axle tube could have a 1/8" slot milled along the top to take the lower edge of the web?

Maybe the pivot bosses could be added in two halves soldered on after the main fabrication, then drilled and reamed?

I would try a card mock-up first . . . having never actually made anything so complex

[crueby]

Just thinking how I might attempt those track supports 

Could you cut the triangular webs out of one piece of flat plate (maybe overscale, say 1/8" for more strength), then bend up the inner and outer flanges from 3/4" x 1/16" strip. Might be easier to hold it all together for brazing with only three separate pieces.

Perhaps the axle tube could have a 1/8" slot milled along the top to take the lower edge of the web?

Maybe the pivot bosses could be added in two halves soldered on after the main fabrication, then drilled and reamed?

I would try a card mock-up first . . . having never actually made anything so complex

Thats possible, I think. Thicker center web would be stronger too. Bending that center flange would be the trickiest.  Hmmm....


 




Thanks for the idea.   

[Swarf Maker]

I see this as starting with a section of flat material 3/4" thick. Mill all the channels out from both sides with a bull nose cutter (small radius corners). Drill for the outside diameter of the two cylindrical parts at the corners. Make these holes smaller so that collars can be fitted either side and be brazed in later. These holes can be used to locate in a jig while the triangular hole and outer profile are cut. Jig can be tilted to profile the cross section taper. The main bearing housing is again a seperate item which can be located for brazing if the triangular brace has a corresponding rebate milled into it. Might be a few fiddly bits but I think that is where I would start from although I would probably see the error of my thinking if the job were in front of me! An absolute cracking job you are making of this so all respect to you.

[crueby]

I see this as starting with a section of flat material 3/4" thick. Mill all the channels out from both sides with a bull nose cutter (small radius corners). Drill for the outside diameter of the two cylindrical parts at the corners. Make these holes smaller so that collars can be fitted either side and be brazed in later. These holes can be used to locate in a jig while the triangular hole and outer profile are cut. Jig can be tilted to profile the cross section taper. The main bearing housing is again a seperate item which can be located for brazing if the triangular brace has a corresponding rebate milled into it. Might be a few fiddly bits but I think that is where I would start from although I would probably see the error of my thinking if the job were in front of me! An absolute cracking job you are making of this so all respect to you.

Thats where I started, but it would have to start with a very large block, trying to save some money on it. Best bets so far appear to be a piece per arm plus the tube, or the many piece like the I beam builds. These parts are quite large, probably biggest of the model.
I have found some reasonable prices on thick brass on ebay, am leaning towards that approach, a soldered up triangle then adding the bottom tube.

[Swarf Maker]

As an ace fabricator I am sure that you will come up with a good solution! When faced with the need for chunky bits of metal I have often found that it is cheaper to buy a length of round stock that will encompass the finished item, rather than buying flat stock.

[crueby]

As an ace fabricator I am sure that you will come up with a good solution! When faced with the need for chunky bits of metal I have often found that it is cheaper to buy a length of round stock that will encompass the finished item, rather than buying flat stock.

Thanks!  I have done that a number of times, this one would need about a 3 1/2 or 4 inch bar, so I have ordered some 3/4 square bar and some 1/2 inch square, should do the trick.

[crueby]

Getting caught up on posting from the last couple of days - I made up the U-shaped pieces that go on the front corners of the frame, which both reinforce the corners and give it some protection from getting hit by the bucket and/or rocks. On the real machine, the front sides of these are all scored up from the bucket getting too close when digging to the sides. They were made from 3 pieces of flat bar, temporarily screwed together and silver soldered. Here is one side attached, the other one ready to go on:
On the lower horizontal plate of those braces will be a support that holds a rod that angles back to the ends of the track supports that I have been talking about recently. Made those from a length of rectangular bar, first milled a slot in either end of the bar:

then drilled the cross holes


and then cut them apart and rounded the ends:

They still need to be soldered to a base plate to bolt them to the front corners with. At the back of the track support is another of the angle rods - for whatever reason they shaped these differently. I was about to mill them out of some flat bar, then Swarf Maker's comment about milling out of round bar reminded me (thanks!) that I have lots of round bar, and they would fit in a length of 5/8" bar. Also, using the collet block makes it easy to rotate them 90 degrees at a time to shape each side. So, started by milling in the outer dimensions:

then shaping the block at the end that will take the rod:

then milling in the 'legs' of the piece:

drilled the hole for the support bar

and tapered the two side legs:

Here are the rear supports after cutting them off to length - they also need to be soldered to a base plate still, and get the tops rounded off around the hole.