Railway Preservation News • View topic

bobyar2001 · **Posted:** Mon Mar 12, 2007 9:28 pm

The ghost of Tommy Davis (master mechanic at Loveland) is smiling at that work on No. 90. What is that new driving wheel for?

Stephen Hussar · **Posted:** Mon Mar 12, 2007 9:28 pm

Kelly, great posting -- excellent pictures. Thanks for taking the time to put it together!

Stephen

johnacraft · **Joined:** Thu Aug 26, 2004 2:53 pm **Posts:** 660

Kelly Anderson wrote:

Here’s a question for you mechanical engineering types: What is the reasoning behind having the round crank discs with the dog bone shaped slots in them? Why not use the more standard rectangular shaped crank throws? They went to an awful lot of trouble machining those slots into place. If you picture it with the crank at 12 o’clock, it seems like they wanted to make the discs very rigid and resistant to twisting side to side, while not too rigid up and down. Any one have a good explanation?

Looking at the position of the cranks, and the size and position of the counterweight, my guess is that part of the answer relates to balancing as much of the rotating weight as possible without adding to the driver counterweights.

The "dog bone" in the middle is interesting. It appears they hollowed it out to the extent they could, limited by the lateral elements. Other than weight reduction, I don't see much point in doing that.

All in all, it appears to be designed to have minimum negative impact on lightweight track.

Great photo of Jeff.

S. Weaver · **Posted:** Tue Mar 13, 2007 11:03 am

bobyar2001 wrote:

... What is that new driving wheel for?

Our new railcar specialty: Yet another non-powered Thomas replica.

Ted Miles · **Posted:** Tue Mar 13, 2007 11:33 am

kelly,

Can you give us narrow gauge folks something in the way of news or pictures on the RGS 20?

Have you started the inspection process yet?

Ted Miles

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

PCook · **Joined:** Sat Jul 02, 2005 7:16 am **Posts:** 2127

The "dog bone" cutout appears to be centered in what would normally be an area of highest risk of fatigue cracking in the throw web. The fillet radius between the main shaft (the axle) and the web is the point at which you are most likely to generate a slip band and a low stress high cycle fatigue crack. By machining the cutout at that point, it looks like they tried to restrict bending forces caused in the axle by the ride dynamics from being applied at what is normally a very critical structural intersection in most crankpin systems. The cutout would also tend to cause the force from the rod to be transmitted to the web as tension on one side of the dog bone and compression on the other, during the portion of the engine stroke where the greatest force is being applied to the throw. These are just guesses on my part, but the point right in the center of the dog bone cutout is exactly where slip bands usually develop in low stress high cycle fatigue. Looks like the designers knew a lot about the torsional performance of the component and neatly designed their way around potential problems.

Kelly Anderson · **Joined:** Tue Sep 14, 2004 7:52 am **Posts:** 2477

PCook · **Joined:** Sat Jul 02, 2005 7:16 am **Posts:** 2127

Nice detective work and some very useful information!

jasonsobczynski · **Posted:** Fri Jun 15, 2007 5:10 pm

Link no worky anymore, do you have another? I have GREAT interest in this rebuild.

Brian Norden · **Posted:** Sat Jun 16, 2007 2:10 am

The narrow gauge discussion forum had its host boot it without notice a week ago. It is back up running! From the ng discussion forum moderator:

Quote:

If you haven't heard, we had a problem with our old host company deciding that we were using too much of their server's resources so they abruptly, and without warning, pulled the plug on us. And, yes, I'm a little P.O.'d about it. BUT it can't be helped; they decided they wanted me to either move the site to a dedicated server (fiscally not an option) or move it elsewhere. We're elsewhere.

When asked about old posts (archives) the response was:

Quote:

They're coming, they're coming, one thing at a time (like trying not to get fired.....).

So, probably some time in the future ....