3/4-inch scale B&O P7d Cincinnatian

[Andy R]

Harold,
You asked: "Would it have been possible to turn the compound...?" Well, yes and no. I did try rotating the compound as you suggested but the geometry would have still required the compound to clear the casting. I even considered trying a tool held in a boring bar to cut the slot, but still had inadequate clearance.
Thanks for your thoughts. The best part about making this stuff is figuring how to, and not necessarily actually making the parts ... which just confirms that the method works.
I have been struggling with workholding on another pair of parts and should the umpeenth attempt be successful it will be documented in this build.
Regards,
Andy

[Harold_V]

Andy,
I've faced those exact problems over the years. Doesn't seem to matter the size of the machine, there's often a job that is a little larger than the machine can accommodate.

Continued success with your project!

H

[Bill Shields]

first law of purchasing a machine tool:

"10 minutes after you have commissioned a new machine that will handle the largest job that you have ever done...."

[Andy R]

Still having fun with the rods.

I purchased a 0.6255 reamer, but failed to check the shaft diameter - which is larger than the nominal capacity of my chucks. The light bulb went on, and I mounted it as if it was a boring bar, at maximum extension, and all worked out well. Next will be the driver (main) rods, although the cylinders would make more sense first.

[JBodenmann]

Beautiful! Nice work Andy
Jack

[Andy R]

Contrary to what Mr. Coventry's 1928 and 1958 drawings show, and what is not shown in the photos, is that the rods were milled on both sides.
The original plans show the [ shape but milling both sides results in an I shape, which is much more structurally stable. In this size it might not matter. But during a conversation with Jack Bodenmann he said that somebody would feel the other side of the rods and say: "OOOOH, You fluted both sides!" So that was enough encouragement. Actually, it was not much more effort, and I did all 6 of the rods that way.

[Odyknuck]

Milling the same material off both sides keeps them straight. Nice work.

[Andy R]

I purchased twelve cast-iron wheel castings from John Kurdzionak at Friends Models:

Then a bit of time was spent machining them.
The 12-wheel tender of the P7d has the same diameter wheels as the pilot truck and the "Standard" 8-wheel tender used under the P7, P7a, etc., so the availability of castings was fortuitous.

[Pontiacguy1]

That's a whole lot of work, right there.

[Greg_Lewis]

Andy,
I've faced those exact problems over the years. Doesn't seem to matter the size of the machine, there's often a job that is a little larger than the machine can accommodate.

Continued success with your project!

H

I remember being in Chama many years ago and seeing a couple of guys attach a machine to the crankpin of one of the drivers of an engine they were working on to clean up the worn pin bearing surface. It was sort of like an outside boring machine. It dawned on me then that while we take parts to our machines, it is also possible to take the machine to the part. I used that lesson a couple of times, one hanging the boiler shell off the side of my mill table to cut the holes in the tube sheet, and another opening the window so a long workpiece could stick out into the side yard and still fit on the table. I should have already known this as long before that I had taken my Model A Ford to have the cylinders bored and the shop bolted a boring machine to the top of the block and did the job without taking the engine out of the car.

[Bill Shields]

General Electric field services has been doing a good job worldwide doing just what you describe.

Ever tried to move a steam turbine to the machine when the turbine is in xxxx and the mill in Schenectady?

Sometimes the lash-up looks tube Goldberg, but if it works...

Ever seen the rigs where they turn the flanges on locos while still under the loco?

[Andy R]

If memory serves me right there were portable milling machines available - not in the sizes to machine a full-size turbine shaft, driver tire, or locomotive cylinder (I have seen photos of those) but in the size that would have made any home machinist envious. Maybe someday i will remember the name.

Thanks Pontiacguy1, Greg and Bill, for your comments and interest in this thread. I have been working on some of the motion work and will follow this with some related posts.

And yes, that dozen of wheels was a lot of work. Especially after i accidentally bumped the compound's handwheel and had to take a few more thousandths off the OD of the rest in order to make them all the same.