Chris's Marion 91 Steam Shovel

[zeeprogrammer]

Given all the other hard work in this, I need to do it right.

I don't know what's right...but I know you want to be happy/satisfied.

(P.S. right = steel.  )

[Baner]

Looking at the part, brass or steel seems like a moot question - I don’t think I could machine something that complex in any material! It looks plenty difficult enough that I don’t think steel will make it much harder. If anything steel might be more resilient to cutting forces.
Excellent work all round by the way.

Dave.

[crueby]

Looking at the part, brass or steel seems like a moot question - I don’t think I could machine something that complex in any material! It looks plenty difficult enough that I don’t think steel will make it much harder. If anything steel might be more resilient to cutting forces.
Excellent work all round by the way.

Dave.

I think I agree - some of those narrow fingers might be too flexible in bras under the cutter when doing the final faces. The hinge fingers would be a lot more durable in steel.

[crueby]

Today I got the rest of the top-half track parts milled to shape. Here is a shot of the bin full (82 of them, including spares) with a couple out front to show the shapes. Quite a pile, the bin weighed in at 4.2 pounds.


To take off the small burs at the edges, and to even up the appearance of the raw vs milled areas, they are currently taking a long soak in the vibratory tumbler with some pyramidal ceramic media, a medium cut grit that will remove a little material and leave a coarser finish. This is the same media that I used on the tracks for the Lombard, and I liked how that looked. Just checked after 20 minutes of running, the burs are gone, and the finish on the flats is about halfway to blended in, so I'll check again after a full hour, which is I think how long I let it run on the Lombard parts.

In the meantime, I have cut off a handful of blanks for the bottom halves of the track segments, to test out the holding jig and make sure the sequence I am envisioning is going to work out before committing too much metal.


These bars are the same 1.5" width as the tops, but are 3/8" thick vs 3/16" for the tops.

[crueby]

A very productive day so far. This morning I went back to my Fusion model of the holding jig, and made some notes about the order I had worked out for milling the shapes into the lower half of the track segments. These next couple posts will be very detailed, I want to capture the order of things well so I can refer back to it myself as I do the mass quantities of parts to come - I am going to make just one part to test out the sequences before starting the rest, to make sure I am not going to paint myself into a corner.

So, I got started by milling a slot down the center of the part, which will form the seat for the top half parts I made first. The slot is .125 deep to match the tops, and extends out to within .250 of each side. To leave room for holding the part, I first cut the center and one side, then turned the part around to finish the other side. The initial cut was made in shallow steps, then once to depth it was just a matter of back/forth passes to widen the slot.

Then I set up with a 1/8" radius round over bit. Now, these come with the lower part of the cutter extended a bit (amount seems to vary by brand) to allow cutting right to the vertical portion. In my case, I want to have the round part end at the bottom of the slot, so I had to carefully grind off the bottom few thou of the cutter (slow speed grinder, fine wheel, plenty of water dipping to keep it cool) so that the cutter ended at the end of the radius portion. Then, just a matter of a pass down each side of the part at the edge of the slot.

With the cutter at the same height, moved out and did the same cut on the outside of the part on both sides:

Quick test to make sure the slot and curves would mate with the top piece:

Good fit, so a little  and moved on!  The next step was to move the holder vertical, and mill the finger slots for the hinges. I did not do the wider areas to the sides, since I need those to hold the parts in the jig for the center cuts. These slots are a few thou wider than the fingers to let them pivot freely - they are not holding the hinge up like a door hinge does. First did the one slot in the center on one side, making a center cut then moved the part over each way to widen the slot to final dimensions:

Note that I did not go all the way through, not needed since the bottom portion will be milled off thinner later anyway. Then turned the part over and did the two slots on the other side.


Then, turned the part up vertical into the deeper slot, and milled off the side areas in several passes:



Then it was time to drill for the hinge pins, the pins are 1/8", but I used a #30 drill (.128) to let them swing freely.

The drilling could have been done earlier, but doing it now meant that the hinge slots would act as places for the chips to escape, so I did not have to peck at the hole to keep clearing chips.

Here are some shots showing the progression so far, from rough blank to trimmed blank to half-finished part, and how they fit to the top piece:





So far so good, next will be to mill in the fingers on the ends and shape the bottom where it fits over the sprocket wheels. The lower part of the hinge fingers will be rounded off as part of that process. But, this is a good place to break and come back when I am fresh.
 

[zeeprogrammer]

But, this is a good place to break and come back when I am fresh.

Hee hee hee. When he is fresh. 

[crueby]

But, this is a good place to break and come back when I am fresh.

Hee hee hee. When he is fresh. 

 

[crueby]

This morning I started in again on the bottom half track prototype. First step was to take the bottom side of the hinges down to dimension:

giving this shape:

could have rounded off the bottom of the hinges now, but I wanted that material there to locate in the jig when undercutting the fingers at the side. That was done with the jig angled up in the vise, and using a 1/4" ball end mill, taking several light cuts down to the point where the ends of the fingers were almost sharp.

Part with the undercuts done:

Then used the same 1/8" corner rounding bit as before to round the bottom corners of the hinges off:

Then, with the jig held vertical in the vise, switched to a 1/8" cutter and cut the openings between the fingers, coming from the flat side through to the curved side in one pass - that way there was maximum thickness to support the fingers as long as possible. After the first pass in the centers of the openings, a couple more side passes got the fingers to width and proper spacing. The spacing is not even, for some reason Marion made one side thicker.

With that operation done, nervous doing it but there was not issues on it (I think there would have been if I had made them out of brass, the fingers are only .062" wide and quite thin at the ends), I moved the jig back down flat and milled the opening in the center to take the idler wheels. The opening was taken out to meet the bottoms of the flanges on either side, which will be tapered next. Note that for the following operations, I put on of the top half pieces in as a support, since there is not as much material backing up the hinge fingers any more and I did not want the clamp to flex the part.


Then tilted the jig up to mill the inside of the flanges, a few degrees more than the sides of the idler wheels so they have some play to center themselves.

To do the taper on the narrow ends of the flanges, tipped the jig up to 60 degrees and took off the ends. For this operation, the part was held back on the top of the jig, which was used for the top parts.

And except for drilling a locator pin or screw hole to fasten the parts together, that completes the prototype of the track segment!   
Just need to repeat this entire process 75 more times....   
Here are the parts:



And set in place on top of the idler wheel:


Time for a cookie and a nap on the porch!   

[zeeprogrammer]

Awesome Chris, just awesome.

You apparently freshen up pretty good. 

[Tennessee Whiskey]

He does give a whole new meaning to “power nap” doesn’t he Zee?

Cletus

[crueby]

Zzzzzzzzzzzzzzzzzz.......


 

[gbritnell]

I certainly don't envy you having to make all those track links by hand. As much as I like hand machining this would certainly be a good place for CNC work.
gbritnell

[crueby]

I certainly don't envy you having to make all those track links by hand. As much as I like hand machining this would certainly be a good place for CNC work.
gbritnell

Absolutely, but at least with the holding jig it goes fairly quickly. Making just the one part, figuring out all the setups as I went, took about 6 hours of shop time. Once each setup is made, though, it is no more than a minute or two per operation on each piece. The top halves took just a few days to make, I figure the bottom halves, with the extra operations, will be no more than a week or two, depending on how much shop time I take per day - when doing these production type things, I'll tend to go in for 1/2 hour to an hour at a time and do a batch, then go do something else for a while, come back for a few sessions like that per day.


 Even with CNC, it would be necessary to be there for just as much time to change parts, clear swarf, etc - less effort but still a lot of time involved. Pohtato, pahtahto.... Its all fun!  And look at all the swarf I'll have to pour down the neck of salesmen! 


So far I have the first 45 blanks sawn off the long bars of raw stock (3/8x1.5 stainless), another 45 minutes should see the rest cut (loving the new bandsaw, very repeatable and fast).

[crueby]

And here are the blanks for all the bottom-half track segments, all 14 pounds of them - will be interesting to see what it weighs once all the excess swarf has been removed...

[zeeprogrammer]

And here are the blanks for all the bottom-half track segments, all 14 pounds of them - will be interesting to see what it weighs once all the excess swarf has been removed...

Might be interesting to see how much you weigh after all that work...and cookies.