Crank Pin Alignment

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dampfmann
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Crank Pin Alignment

Post by dampfmann » Tue Nov 19, 2019 9:15 am

Hello,

I have a question regarding the alignment of the crank pin hole on locomotive drivers for Kozo's A3 0-4-0. The construction method does not use keyed drivers. I understand it is critical for the center of the crank pin hole to be 5/8" from the center of the driver hole. Is it also critical for the driver and crank pin holes to be aligned "square" to one another? (See attached photo from Kozo's book.) If that is the case, how does one make the holes on all four drivers in the exact alignment? I am also wondering if quartering the drivers may take care of the crank pin "squareness" issue - as long as the crank pin holes are all exactly the same distance from the center of the driver.

Thanks,

Marty
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gwrdriver
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Re: Crank Pin Alignment

Post by gwrdriver » Tue Nov 19, 2019 9:45 am

There are several ways of doing this job depending upon your equipment. All methods (which come to mind) involve making a jig to locate the crankpin bore an exact distance from the axle bore. You'll notice I used the term "bore" instead of hole, because it's always best to bore these holes to be in true size, spacing, and alignment.

On my most recent project I bored my drivers in my mill. After turning and boring (the axle hole) in my lathe I transferred them to the mill where I had set a locating "jig." The jig was actually only a metal stub, the diameter a tight fit to the axle bore, which was offset the distance of the crank throw. The drivers were then set on the stub, clamped to the mill table, pilot-drilled then bored to size.

If your lathe has enough swing, and the drivers will fit the faceplate, the same type of jig could be used on a lathe, where a stub is put on the faceplate, set over the length of the throw, the driver clamped to the faceplate, and the crankpin holes bored. The "stub" needn't be some long honking length of bar, only a small pippin or button is sufficient to locate the wheel bore.

The "old" way for many live steamers was to make a jig out of a piece of flat plate. You'd put a stub (a thumb-press fit the axle bore) on one end, and a nominal size "drill bushing" (a hardened sleeve) on the other end. The jig was inserted in the axle bore, the crankpin hole was aligned to the crank boss, the jig then clamped to the driver face, and the crankpin hole was drilled and reamed in whatever drilling/boring machine you had available. This wasn't exactly "precision" by any means, but that technique built 1000s of good running live steam locomotives.

I hope this answers some of your question, and perhaps opens the door for other techniques and discussion.
GWRdriver
Nashville TN

dampfmann
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Re: Crank Pin Alignment

Post by dampfmann » Tue Nov 19, 2019 10:46 am

QUOTE:

"There are several ways of doing this job depending upon your equipment. All methods (which come to mind) involve making a jig to locate the crankpin bore an exact distance from the axle bore. You'll notice I used the term "bore" instead of hole, because it's always best to bore these holes to be in true size, spacing, and alignment."

On my most recent project I bored my drivers in my mill. After turning and boring (the axle hole) in my lathe I transferred them to the mill where I had set a locating "jig." The jig was actually only a metal stub, the diameter a tight fit to the axle bore, which was offset the distance of the crank throw. The drivers were then set on the stub, clamped to the mill table, pilot-drilled then bored to size."

RESPONSE:

Thank you. I am using a reamer to bring the holes (bores) to the correct size. Kozo also uses a simple jig as the one you mentioned. Using this jig, is only the distance between axle and crank pin centers the critical measurement? Using the picture above as reference, does it matter if the hole is placed a bit "above" or "below" the pictured center line as long as the center of the crank pin still is on the arc that is 5/8" from the center of the driver?

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gwrdriver
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Re: Crank Pin Alignment

Post by gwrdriver » Tue Nov 19, 2019 12:12 pm

For a driver casting which hasn't been broached for quartering, no (to question #2), but naturally one would try to shoot for the visual center of the crank boss.
GWRdriver
Nashville TN

rkcarguy
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Re: Crank Pin Alignment

Post by rkcarguy » Tue Nov 19, 2019 12:33 pm

dampfmann wrote:
Tue Nov 19, 2019 10:46 am
QUOTE:
Using the picture above as reference, does it matter if the hole is placed a bit "above" or "below" the pictured center line as long as the center of the crank pin still is on the arc that is 5/8" from the center of the driver?
Obviously center it the best you can, but any distance off would just be the appearance of the hole not being centered in the boss on the casting. If you're careful you should be able to eyeball it pretty close ~.010". The important part will come when installing the wheels on to the axles, ensuring the crank pins are exactly 90* from each other.
Last edited by rkcarguy on Tue Nov 19, 2019 2:14 pm, edited 1 time in total.

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cbrew
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Re: Crank Pin Alignment

Post by cbrew » Tue Nov 19, 2019 12:53 pm

rkcarguy wrote:
Tue Nov 19, 2019 12:33 pm
The important part will come when installing the wheels on to the axles, ensuring the crank pins are exactly 180* from each other.
180 degrees? wait what? :D
If it is not live steam. its not worth it.

rkcarguy
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Re: Crank Pin Alignment

Post by rkcarguy » Tue Nov 19, 2019 1:34 pm

cbrew wrote:
Tue Nov 19, 2019 12:53 pm
rkcarguy wrote:
Tue Nov 19, 2019 12:33 pm
The important part will come when installing the wheels on to the axles, ensuring the crank pins are exactly 180* from each other.
180 degrees? wait what? :D
I'm off my coffee for medical reasons and therefore dumb lol, correct to 90*.

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cbrew
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Re: Crank Pin Alignment

Post by cbrew » Tue Nov 19, 2019 1:42 pm

rkcarguy wrote:
Tue Nov 19, 2019 1:34 pm
cbrew wrote:
Tue Nov 19, 2019 12:53 pm
rkcarguy wrote:
Tue Nov 19, 2019 12:33 pm
The important part will come when installing the wheels on to the axles, ensuring the crank pins are exactly 180* from each other.
180 degrees? wait what? :D
I'm off my coffee for medical reasons and therefore dumb lol, correct to 90*.
i figured something like that :) :D :D :o
If it is not live steam. its not worth it.

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gwrdriver
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Re: Crank Pin Alignment

Post by gwrdriver » Tue Nov 19, 2019 2:24 pm

Actually, it doesn't matter if the wheeled axles aren't quartered at precisely 90°, as long as each side is over/under by the same amount.
GWRdriver
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Glenn Brooks
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Re: Crank Pin Alignment

Post by Glenn Brooks » Tue Nov 19, 2019 2:31 pm

What I’ve never understood is how to press, or heat n drop, two drivers onto the same axle such that they are exactly 90* to each other?

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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hoppercar
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Re: Crank Pin Alignment

Post by hoppercar » Tue Nov 19, 2019 3:02 pm

You are always better off to have wheels keyed to the axles at 90 degrees. ..over time, without keys, any slip in the press fit between wheel and axle will result in a lame engine

Glenn Brooks
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Re: Crank Pin Alignment

Post by Glenn Brooks » Tue Nov 19, 2019 3:15 pm

Makes sense. Thanks!
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

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