3/4-inch scale B&O P7d Cincinnatian

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

Post by wewilliams »

A silly question from one that does not know..

The Eccentric Rods & Combination Levers are shown with square bottom notches but you did a radius (which is stronger & stress resistant) Will that cause clearance issues down the road?
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

Occasionally it can cause interference at full travel.

Stress concentration as you have described is generally not a problem with our models
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Andy R
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square bottom notches

Post by Andy R »

WEWilliams,
I can use a file to square the notches if needed upon fit-up.
But as you mentioned, the curved bottoms (drilled) are stronger and as an added bonus, much easier to make.
Bill is correct, the forces involved at this scale are too small to worry about.
Regards,
Andy
Andy R
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Starting on the cylinders

Post by Andy R »

When I purchased this project the cylinder castings were not included.

About a dozen years ago I was describing the project to Robert Morris who said something like "Dad may have cylinders for that!"
So shortly in the mail arrived a very nicely machined pair of cylinders, Gratis. THANKS Robert!
The only thing noticed at that time was the mounting to the frame would eventually need modification, so the cylinders were packed away to continue to age.

This past December It was time to start on that, but alas, I discovered that the vertical distance between spool valve and cylinders was about 3/8-inches too short. That is something that could not be accommodated within the P7 design. Perhaps the cylinders are or were intended for a Hudson or a different Pacific. There were no marks to indicate any relevant design.

So the cylinders were returned to Robert, (Thanks again!) and enquiry to John Kurdzionak at Friends Yankee Shops was made.
John indicated that he had cored castings available, so $ was mailed, and this past Friday these showed up:
IMG_4479s.jpg
IMG_4479s.jpg (103.23 KiB) Viewed 7550 times
They are very nice castings.

And as an added surprise, the coring included the recesses around the spool valve sleeves for steam distribution.
I was concerned prior to receipt that I would have to mount these on the face-plate of the lathe to cut the recesses. :D

I plan to follow the steps described by Jack Bodenmann for his 0-6-0 in this old thread:
http://www.chaski.org/homemachinist/vie ... =8&t=83490
and of course the articles that Mr. Coventry wrote in the ModelMaker magazine about 90 years ago for the 2.5-inch gauge version as well as the 3.5-inch gauge version. These will keep me busy for a while.
Andy R
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Union LInks Part # 8128

Post by Andy R »

This is the only part lately machined that I had the presence of mind to photograph the work in progress:
IMG_4480.jpg
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There were so many different setups that it was a holding challenge. In restrospect it would have been better to (a) use a larger piece of steel because the bits remaining afterward were way too thin, and (b) affix with 3 screws into the steel angle instead of holding with machinist parallels.

Here is the finished result:
IMG_4483.jpg
IMG_4483.jpg (112.49 KiB) Viewed 7431 times
It is interesting to see the parts enlarged on the screen. What looks good with the un-magnified eye looks quite rough. I will likely make a new pair.
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

Separate the two pieces by another .3".

Put a through bolt horizontal thru the part into your fixture.
Too many things going on to bother listing them.
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Harold_V
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Re: Union LInks Part # 8128

Post by Harold_V »

Andy R wrote: Thu Feb 16, 2023 6:14 pm instead of holding with machinist parallels.
In the interest of not perpetuating improper terminology, those are not parallels, but parallel clamps. Please understand I am not trying to diminish your contribution to the board. Just trying to help the new guys in gain proper terminology.
Here is the finished result: <snip>
What looks good with the un-magnified eye looks quite rough. I will likely make a new pair.
There's a couple things you could do to improve the finish. One of them is to take a very light climb mill cut for the last pass (anywhere from .002" to .005" is usually adequate, assuming the torn surface isn't horrible and your end mill isn't dull). Also, the use of a little lubrication for the cut can go a long way towards improving finish, especially if the end mill used is not pristine. It can be applied with a small brush (acid brushes are a great choice). Sulfur based cutting oil is quite helpful, but if you have some tapping compound suited for ferrous materials it, too, would be quite satisfactory. Lastly, carbide end mills are really superior for producing a nice finish. Not only will they tolerate a greater surface speed, they tend to have a much keener edge, thanks to the use of fine grained diamond wheels and modern production machines.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

And carbide mills hate to recut chips, so you need a way to keep chips out of the pockets while you are cutting
Too many things going on to bother listing them.
Andy R
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Re: Third Try for Union Links Part #8128

Post by Andy R »

Bill and Harold,

I followed your advice, and still made plenty mistakes, but ended up trying several approaches to making these little parts.
This picture shows the third pair attempted in process of separating from the larger chunk-o-steel:
IMG_4490s.jpg
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What is not shown is the milling which was done on the opposite side; that allowed leaving 3 little tabs to keep the part still during milling. I cut the tabs with a jewelers file and cut too close to the little oiler on one end of one part, visible in the next photo.

This is the final result.
IMG_4491s.jpg
IMG_4491s.jpg (133.73 KiB) Viewed 6806 times
It is not perfect, but i enjoyed trying to make them using the milling machine rather than using a 1/4-inch square piece of steel and a file with a couple of hardened buttons. That was what Mr. Coventry recommended and would probably have been a lot easier. On the way i managed to break 3 milling cutters and a center drill. Learning is oftentimes a function of making mistakes (such as the spectacular SpaceX rocket failure yesterday). So I suppose that I learned a lot.

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 loco parts had a rapid, unscheduled disassembly?
Too many things going on to bother listing them.
Andy R
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Andy R »

"... a rapid, unscheduled disassembly?"
YES.
Guilty as charged.
On the first two tries.
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

no matter how you are getting there, the results are appealing.

John K does have nice castings....

since you are not a 'production shop attempting to make $$$' -> efficiency is not important (except for cost of cutters).

a very good friend, whom I considered to be an excellent photographer told me the secret to his success (on Kodachrome) -> DO NOT SHOW ANYONE YOUR BAD SHOTS - THROW THEM AWAY).

building a steamer is similar -> very few 'outsiders' care about the fullness of your scrap bucket.

All they want to see is a running steamer...especially since very few of them have actually ever seen a full size steamer, museum piece or out on the rails.
Too many things going on to bother listing them.
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