Best way to pin Stephenson eccentrics

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jlakes85
Posts: 228
Joined: Thu Feb 23, 2012 6:07 am

Best way to pin Stephenson eccentrics

Post by jlakes85 »

I've finally accepted the fact that the eccentrics will keep slipping until I pin them to the crank shaft. Is a roll pin sufficient to keep everything in place?

-jlakes85
Marty_Knox
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Joined: Thu Jan 09, 2003 6:50 pm
Location: Michigan, USA

Re: Best way to pin Stephenson eccentrics

Post by Marty_Knox »

Tapered pins are far superior to roll pins.
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John_S
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Location: Cumming, GA

Re: Best way to pin Stephenson eccentrics

Post by John_S »

I learned from Fred_V a long time ago a really, really good way to do it. Once you have them set, use a drill through the eccentric to put a V dimple into the axle and then put a pointed set screw in backed up by a flat set screw. I did this on my Allen mogul and they have not moved whatsoever in 6+ years of running.
hoppercar
Posts: 616
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Re: Best way to pin Stephenson eccentrics

Post by hoppercar »

Once I had the valve gear set correctly, I drilled two dimples into the axle, at 90degrees from each other , thru all the eccentrics, and used a pointed setscrew to secure them....in 25 years, they have never slipped
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NP317
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Location: Northern Oregon, USA

Re: Best way to pin Stephenson eccentrics

Post by NP317 »

I used the dual set screw technique described by John S.
No slipping in 15 years of service, so far.
~RN
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10KPete
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Location: Nordland, WA, USA

Re: Best way to pin Stephenson eccentrics

Post by 10KPete »

I'm always a bit leary of pins through shafts. It's too easy to take too much strength away drilling through, and if the pin is small enough to not impact the shaft strength it's too small to do any good. Serious connections are keys and the dimple. The set screw lock screw, which I first saw in a Bridgeport head, works extremely well.

Pete
Just tryin'
jlakes85
Posts: 228
Joined: Thu Feb 23, 2012 6:07 am

Re: Best way to pin Stephenson eccentrics

Post by jlakes85 »

Hi All,

Thanks for the responses. I'm leaning towards the dimple and two setscrew method. This is on a Shay loco, so I have better access than usual. I already have one setscrew per eccentric. I'm guessing I drill a new hole with a marked drill bit, tap using a spiral point to get rid of the chips and then use the two set screws? My biggest concern is losing the sweet spot while I drill the additional holes.

-jlakes85
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NP317
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Location: Northern Oregon, USA

Re: Best way to pin Stephenson eccentrics

Post by NP317 »

Yes: Use the first set screw to hold position while you drill, tap, dimple, and insert the second set of set screws.
Then remove the first set screw and repeat dimple operation +.
Drink a beer.

Better and easier method (requires pre-planning...):
Pre-drill and tap the eccentrics for two set screws, and THEN install and adjust position before securing in place.
~RN
Soot n' Cinders
Posts: 983
Joined: Wed Jun 27, 2012 5:24 pm
Location: Marietta, Georgia

Re: Best way to pin Stephenson eccentrics

Post by Soot n' Cinders »

The eccentrics on my shay are done with dog point set screws set into dimples with flat set screws behind and haven’t moved a bit with it on steam. One eccentric strap started to work loose but the eccentric itself it tight.
-Tristan

Projects
-2.5" scale Class A 20 Ton Shay

Steam Siphon: https://www.shapeways.com/shops/leavitt ... tive-works
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