Chris's Marion 91 Steam Shovel

[Ye-Ole Steam Dude]

Hello Chris,

After several rounds of Guiness, I would strongly suggest to NOT get near your work 

Have a good (hopefully a better day) day,
Thomas

[crueby]

Hello Chris,

After several rounds of Guiness, I would strongly suggest to NOT get near your work 

Have a good (hopefully a better day) day,
Thomas

Absolutely not!
Got the axle parts disassembled, looks like I can save the axle by just extending the keyway slot over to where it should have been. The key pried out of the slot okay, so it can be re-used too. I am now updating the drawings to make it clearer where things sit on the axle and bearing holders - top/bottom views get confusing too easily!

[Kim]

Derek, just went and checked, turns out the grit I have for my airbrush type grit blaster is aluminum oxide, so I ran a test on half of one side of some scrap brass. Interesting effect, slightly gray, looks like a cast surface but still some brassy tint to it. Then taped off half the piece and sprayed on the same paint used on the gears as a comparison of how the paint looks next to and on both shiny and gritted surfaces. Will post pics in the morning...

Here is how the test piece looked - started with one of the wedges from cutting the gear spokes, and grit blasted the narrow end, halfway out, then painted a half from the tip back. So, the lower right quadrant is the raw shiny brass, the lower right is gritblasted with aluminum oxide, and the upper half is those two surfaces painted the gray I have been using. The grit definitely got rid of the shine, and looked a little grey at first, but that was only till it was wiped off - at that point the grey went away and it was just dull brassy looking.

I'm unclear from your description here.  From this picture, I can't see much difference between the blasted side and the machined side, once painted. Was there more of a difference in person?  Or is it worth the effort to blast it?

Inquiring minds need to know!
Kim

[crueby]

Once painted, the blasting side looked identical to the unblasted. The only visible difference is in the unblasted and blasted areas at the bottom left and right. Overall, it did not make much difference and does not appear to be worth it. The grey appearance that Derek thought would show from the blasting did not happen, that was the main reason for the test.

[Flyboy Jim]

I had good luck by sand blasting my P & W cast parts after machining:





I'll look at them closer now that they're painted to see how they look.

Jim

[crueby]

Jim, what coarseness grit (grit number?) did you use on that? The airbrush-style gun I have won't take larger grit sizes, so the finish is still pretty fine, looks like you were able to get a coarser finish.

[crueby]

This morning the mods to the axle, to move the small gear and clutch over to the proper position, were done and the parts assembled back on the model. Here is a shot with the clutch disengaged:

and engaged:

The hand lever on the control station floor has enough travel to move the clutch in and out, though I think the parts need a little oil to get them to slide easier on the axle. One thing I noticed was that the operator may have been able to look down through the hole in the floor and see where the clutch fingers were, and that would probably have made it easier to line things up and engage it, moving the main engine slowly till the fingers lined up close enough. The jaws on the real one were squared off at the ends like mine, but there is an inch or so of 'slop' in the fit, which would help getting them engaged.

Next up is the forward gear holder, which I mentioned has been silver soldered up, ready to machine. I have not attached the taller side plates yet, that will be done after the slots have been milled in - otherwise there will not be enough reach with the end mill past the plates. The slots are curved at the bottoms, so that the gears clear the slots. Cutting those slots is going to be interesting. I could mount the part to a faceplate, and use the rotary table in vertical mode to mill the curved slots, though that mounting would be tricky to get right and solid. I think I will try the math approach, and calculate out the lengths of the slot at each depth and do sort of a reverse-3d-print approach (Kvom will be chiming in on how easy it would be with CNC, I am sure!)
Here is the roughed in part. The square bit on the end is for the overhang they put on the one gear, my guess is to keep rocks and dirt from getting into the teeth from above.

[Don1966]

That is just awesome Chris........



 
Don

[ddmckee54]

An air-brush style grit blaster is designed for "light" etching work.  Touching up minor boo-boos on a previously blasted part without having to re-mask everything, delicate glass etching, paint removal from small areas without damaging the substrate - that sort of thing.  If you are trying to simulate the look of a sand casting on a machined part then you want something that will tear up the substrate a little bit.

You are probably going to have to use a more manly-man type grit blaster.  For the size work that you're doing one of the "Horrible Fright" hand held grit blasters might get the job done without blasting too big of a hole in the pocketbook.  Anything that's much bigger than that and you'll spend a lot of time masking off the areas you DON'T want etched.

Don

[crueby]

An air-brush style grit blaster is designed for "light" etching work.  Touching up minor boo-boos on a previously blasted part without having to re-mask everything, delicate glass etching, paint removal from small areas without damaging the substrate - that sort of thing.  If you are trying to simulate the look of a sand casting on a machined part then you want something that will tear up the substrate a little bit.

You are probably going to have to use a more manly-man type grit blaster.  For the size work that you're doing one of the "Horrible Fright" hand held grit blasters might get the job done without blasting too big of a hole in the pocketbook.  Anything that's much bigger than that and you'll spend a lot of time masking off the areas you DON'T want etched.

Don

Sounds right - though the cost of the blaster isn't so bad, then I would need a larger compressor, should have a booth for it....  Nah!
 

[crueby]

More done this afternoon on the front gear holder. As I described before, the curved slots for the gears to sit in were milled in, using a set of depths and lengths calculated out. The distances needed are basically a set of chords on a circle - as the cut goes deeper, the chord gets farther out on the circle, so it gets shorter. Here is a diagram of what I mean:

The circle with radius R represents the size of the gear, plus room for clearance. The distance D represents the depth of the cut to be made, from the center of the circle. The chord C shows the length of the cut to be made at that depth. If a series of deeper cuts starting at distance D and ending at the radius R are made, then the result will be an approximation of the curved slot - the shallower each cut is, the smoother it will be. For this part, I chose an increment from one depth to the next of .025", mainly since that is a half-turn on the column at a time so easy to do, and it gives a step size easy enough to blend in with a rotary tool.

So, started by drilling a reference hole along the centerline of the slot, down to the depth of the slot. This is 'R', measured from where the taller sides of the part will be, since that is where the center of the gear will be. This hole gave me a reference to bring the cutter back to after milling the horizontal area, and also a safe place to lower the cutter between cuts.

I then plugged in the values for R and D into the formula for the chord length of a circle, which is C = 2*SQRT((r*r) - (d*d)). This was easily done in a little spreadsheet, with the value R constant and D increasing by .025 on each row. The value C is the length of the chord, and I want to move that distance out from the center each time, minus half the width (W) of the cutter, so the result of the formula was modified to get the length to move:  L = (C / 2) - (W / 2).
Sounds like a lot of kerfuffle, but its a couple simple formulas that give the depth and length to move. Here is what it looked like after a series of moves on the first slot:

As I said, it leaves a lot of steps in the shape, but those will get blended with a rotary tool later.
The same was done for the larger slot for the bigger gear on the other side:

A test fit of the gears:

Last thing to mill on this part was the overhanging block, took that down to match the slot inside using several cuts with the part being rotated in the vise between cuts.

Here is the part with the taller sides set next to it, to show where this is going. The axle bearings will be on the end of that taller side, with the gears hanging down into the slots. The slots are just there for clearance. In this picture, I have taken a tapered grinding wheel in a rotary tool, and smoothed out the steps in the slots.


Next step is to drill/tap some holes to hold the side plates onto the center block, and then I can make the bearings and caps to hold the axles. There will also be some overhanging rib plates that extend the base of this part, used to attach it all to the bottom of the main frame.

[Don1966]

Chris if you have my spreadsheet on Coordinates Calculation sheets the tab Cavity Radius pickup table does it for you. I will post it for those who wish to have it but it is in plaans and drawings. Nice work again Chris you are the tops.....

Don

[crueby]

Chris if you have my spreadsheet on Coordinates Calculation sheets the tab Cavity Radius pickup table does it for you. I will post it for those who wish to have it but it is in plaans and drawings. Nice work again Chris you are the tops.....

Don

Thats perfect - I have used your spoke calculation spreadsheet but had not noticed this one - thanks!!

[cnr6400]

Chris I imagine you needed some special math "hogarithms " to do all that hogging out in the big brass chunk. Nicely done as always.

[crueby]

Chris I imagine you needed some special math "hogarithms " to do all that hogging out in the big brass chunk. Nicely done as always.

Or a Nogarithm to Nibble the slots!