3/4-inch scale B&O P7d Cincinnatian

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

Post by Andypullen »

Looking great Andy!

A
Clausing 10x24, Sheldon 12" shaper, ProtoTrak AGE-2 control cnc on a BP clone, Reed Prentice 14" x 30", Sanford MG 610 surface grinder, Kalamazoo 610 bandsaw, Hardinge HSL speed lathe, Hardinge HC chucker, Kearney and Trecker #2K plain horizontal mill, Haas TL-1 lathe.
Andy R
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Assembled Frame for B&O P7d

Post by Andy R »

Jack and Andy,

Thank you both for your kind words!

Here's a photo showing some recent progress. Most of the frame work is done.
IMG_4219.jpg
My photographic skills are lacking. I put a towel on the bench to reduce the background clutter.

The next things for me to work on will be springs, spring hangers, and yokes - a lot of time-consuming and repetitive work.
FKreider
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by FKreider »

Progress looks great! Good to see another 3/4" builder in the year 2021!
-Frank K.
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NP317
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by NP317 »

"The next things for me to work on will be springs, spring hangers, and yokes - a lot of time-consuming and repetitive work."

And I remember being at that stage during two different locomotive fabricating projects.
Both successfully completed.
So you will get those accomplished for sure.
Looks really good!
RussN
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JBodenmann
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by JBodenmann »

Hello My Friends
Very cool Andy. It's starting to look like a steam locomotive. As you stated, " A lot of time consuming and repetitive work". Spring and brake rigging especially. An example, Commonwealth six wheel tender truck brake rigging with its clasp brakes has over a hundred bolts with castellated nuts. Best to just dive in, and Get R" Done.
Jack
Andy R
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Spring Saddles #4170

Post by Andy R »

IMG_4226.jpg
Mr. Coventry's plans show these to be bent from 1/16-in thick steel sheet.
Not having either a shear or brake, and my good friend who does lives a good 2.5 hour drive away, so I opted to machine these out of solid.
The time would have been more effectively spent making the drive. These took a lot more time than originally estimated.
Oh well. 6 needed and 6 are now done. Now on to more spring assembly parts.
Andy R
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Lead truck is finally sprung

Post by Andy R »

The lead truck is finally sprung.

I followed Print No 146, dated 8-8-1930.
IMG_4247.JPG
Mr. Coventry's design for the spring pack (Part/Assembly No. 7137) shows 20 leaves, 0.015-in. thick, and 20 spacers, 0.015-inch thick.
I cut the leaves from 0.015 spring steel, made a jig to hold the spring steel in the milling vise, then drilled holes and milled slots, and did the same for 0.015-in Delrin AF spacers.
The Delrin AF was obtained in a 1-inch wide strip from McMaster-Carr, and I found that it spits easily when scored.
Each of these were a real "fiddle" trying to make sure that all the lengths were correct and matched the spring steel strips.

Only the top two steel springs are long enough to be secured to the equalizer hangers (part no. 5137) and they are the source of almost all of the spring flexibility. The remainder of the stack principally supplies support for the top leafs. The spring force is additive, and I realized that the same force and deflection properties could be obtained by making only 20 steel leaves that are 0.030-in. thick. Because this will all eventually have to be painted, this assembly is temporary. Considering that I will eventually remove the spring stacks, I may just go ahead and make new ones and omit the Delrin AF spacers.

I have already cut and drilled all of the other springs for the drivers and trailing trucks - per plans - but not yet all of the Delrin spacers. I am seriously considering making all of the springs double the thickness shown by Mr. Coventry and not use spacers at all.
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Bill Shields
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Bill Shields »

So you will may end up with springs that are not springs at all...but are so stiff as to be rigid...been there done that...did it over
Too many things going on to bother listing them.
Andy R
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springs for 3/4-inch scale B&O P7d Cincinnatian

Post by Andy R »

Bill,
Do you recall any of the specifics of what you did initially and what you did over, and what were the results?
Thanks.
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 »

I doubled the thickness to 'make up height' as you are thinking....and ended up with a solid block of spring material that had no give to it under the loads expected.

I then went with the recommended thickness with a think, non-spring spacer layer in between...like a layer cake, and it worked just fine. I forget what I used for the spacer - polypropylene or PTFE or...whatever...it has been years. You can actually use brass for the spacer material since it contributes nothing to the load bearing of the spring.

My top leaf is a little thicker than the shorter ones...but that is not unusual..i wanted the top to be a bit thicker so that I had something 'to work with'

On some of my models, the 'hanger' for the spring is silver soldered to the top leaf...so it needs to be a bit 'beefier'.

After it was all over with, I went to some engineering handbook that I had and looked up 'leaf spring design'...and there it was...all the info that I had just learned empirically -> someone had been there first and made a chart.

I am sure that today you can google it from some 'engineering toolbox' web site.

Basically ..rule of thumb...if you double the thickness of the spring leaves and do nothing else, you will cut the deflection by half -> so if you put a 50# load on a spring that originally deflected .1" -> it will now deflect .05".
Too many things going on to bother listing them.
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Greg_Lewis
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Re: 3/4-inch scale B&O P7d Cincinnatian

Post by Greg_Lewis »

I have two Excel tables for calculating leaf spring data. I have no memory of where I got them or even how to use them, but if you or anyone else wants them, just send me a p.m. with your email address and I'll forward them on.
Greg Lewis, Prop.
Eyeball Engineering — Home of the dull toolbit.
Our motto: "That looks about right."
Celebrating 35 years of turning perfectly good metal into bits of useless scrap.
Andy R
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Springs for 3/4-inch scale B&O P7d Cincinnatian

Post by Andy R »

Bill,
Thanks for your explanation !

I understand the need/desire to have thickness to work with. The top (as mounted - bottom) leaves for the pilot truck are slotted - not so easy with 0.015-in spring steel. The top leaves for the drivers and trailing truck have holes - easily drilled in a fixture.

My rationale for doubling the thickness of the springs was based upon observing that the top two leaves of each spring stack are much longer than the rest, in order to connect to the hangers. They also are significantly curved, so that all deflection is of those top two leaves until flat, and then and only then do the remainder of the spring leaves apply any resistance.

Greg,
PM Sent.
Thanks !
I'll use your spreadsheets to check the designs.

I also have a copy of Mr. Coventry's articles about spring design from the ModelMaker magazine and will check against his methodology as well.

Regards,
Andy
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