3/4-inch scale B&O P7d Cincinnatian

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Andy R
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Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

Brake shoes for 3/4-inch scale B&O P7d Cincinnatian

Post by Andy R »

Thanks Jack!

The brake shoe casting, pattern No. 537, is just a ring of cast iron.

I mounted it in the lathe as shown here, and machined one face and the OD holding it with the 4-jaw using the inside face, but could not figure out how to hold a tool to cut the slot in the circumference. Oh well; the joys of not having a really big lathe.

The casting was then reversed, holding in the 4-jaw chuck on the OD, and the other face was machined and the ID finished, including the 2-degree taper to accommodate the taper on the drivers.
IMG_4275sL.jpg
A line was scored at the diameter of the mounting holes before dismounting from the 4-jaw.

Next the #50 holes for 8 shoes (allowing for 2 spares) were laid out and drilled. A thin brass template was made, and using a sharp scriber, the shape was transcribed onto the iron ring in 8 places, being mindful that half are opposite hand from the remainder. A new 2-inch diameter slitting saw was used to cut the shoes, with only a bit of curvature needing file work.
IMG_4333s.jpg
The slots while shown on the drawings as radial were milled straight using a 1/8-in end mill.
IMG_4332s.jpg
Finally, one leg of each shoe was drilled #30 and the other tapped 2-56, being mindful that the mounting of the bolts is from inside the frame for the front and main drivers, but outside for the rear drivers.
Test fitting showed that the mounting holes for the hangers should have been drilled #50 instead of #30. Right now the shoes are a bit loose, but will have to be removed anyway to mount the drivers. I may make some tiny sleeves.
Andy R
Posts: 441
Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

Quartering the Drivers for 3/4-inch scale B&O P7d Cincinnatian

Post by Andy R »

IMG_4336s.jpg
Covid was not nice to me so i was unable to make much progress.
I did make 2 pairs of long 60-degree centers to match the OD of the drive pins, then used them to quarter the drivers.
I have used this method in the past, and if a long write-up is needed, i recall that Jack Bodenmann wrote about it for his 0-6-0 build.
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

Welcome to the other side (temporarily) of 19 😀

Assuming they are glued and will be dutch keyed?

Or did you give them a start with the tail and finish in a press?
Too many things going on to bother listing them.
Andy R
Posts: 441
Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

Re: Quartering Drivers

Post by Andy R »

Bill,

Yes.

I aligned them and slightly pushed at the tailstock end, twisting by hand as needed, and finished in my "press" - a 1940-ish Reid vise.
I pressed each assembly a little, put back on the lathe, checked, removed and pressed, etc. Maybe 3 times each. Back-to-back dimensioning was against shoulders on the axles and checked with a gauge that I made for my last locomotive project.

And yes, they are glued with Locktite, but after completing the rods and verifying that everything rolls well, I will split the difference between the cast iron wheel and the steel axles with a 1/8-inch end mill and insert a steel rod of that diameter. It works well on all of my other 3.5-inch gauge locomotives.

Thanks for your comments!
Regards,
Andy
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

Your press is similar to mine.. probably the same vintage.

I have had success with light fits that can be adjusted in place in the lathe (by hand) with all against the shoulders. As soon as the glue starts to set up, can walk away.

The trick I use is to put adjustable parallels across the horzontal pins to center so they do not move while the glue dries. The verticals can be clamped.

After that...off to the races.

Ever seen side rods silver soldered together to get the correct length?
Too many things going on to bother listing them.
Andy R
Posts: 441
Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

It is starting to look like a locomotive

Post by Andy R »

IMG_4423s.jpg
Assembly of the drivers on to the frame was easy without the brake components installed, but really fiddly with the brake hangers because they are captured in 3-axes.

I posted on July 27 of last year, in regard to castings (parts No. 4134 and 8142) that “I have elected to not (yet) finish any surface that does not need finishing. Paint will hide everything anyway.” And in particular in regard to Part No 8142, the brake hangers, I wrote: “I may thin the web to the dimensioned 1/16 inch, but at this time it appears unnecessary."

Boy, was I wrong. Everything related to the brake system had to be re-machined. The clearances on this loco are really small. The thin web in particular is necessary to clear the outside of the drivers, and the outside to clear the inside of the rods.

But after a lot of work, it all rolls nicely.
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JBodenmann
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by JBodenmann »

Hello My Friends
Beautiful! I remember looking at this engine when it was boxes of parts. Great Progress!
Jack
FKreider
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by FKreider »

Beautiful work! Not many of us building in the small scales these days - its nice to see other projects out there!
-Frank K.
Andy R
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Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Andy R »

Jack and Frank,
Your compliments are most appreciated, and encouraging!
Regards,
Andy
Andy R
Posts: 441
Joined: Wed Sep 26, 2007 2:18 pm
Location: So. Calif.

Trailing Rods - Pattern 513, Part of Ass'y 2131

Post by Andy R »

IMG_4445s.jpg
I'm back to work on the P7d, and having fun machining rods.
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JBodenmann
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by JBodenmann »

Hello My Friends
Beautiful side rods Andy. The rods on a locomotive are one of the main aspects that make them so interesting. They are one of the first things checked out when viewing a model. Time spent on making them beautiful is time well spent.
Jack
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Harold_V
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Re: Brake shoes for 3/4-inch scale B&O P7d Cincinnatian

Post by Harold_V »

Andy R wrote: Tue Jun 07, 2022 1:37 pm but could not figure out how to hold a tool to cut the slot in the circumference.
Would it have been possible to turn the compound such that the handle was at the rear, which would then allow the tool to extend towards the operator? That might provide the necessary reach.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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