P2 Locomotive Company and related matters

A perfect symbol of the point where engineering excellence and aesthetics meet.

 

Wow...impressive from any viewpoint.

 

Nah, Cannot be a V4 must be a V3 as its a Tank.

 

Isn't it just..... and think how good a two throw crank to those impressive standards will look if the folks at SP ever get their paws on SECR D class No.737!

 

On the subject of built-up crank axles on locomotives . . .
Are the axle components held in place only by interference fit after the metal cools, or is there anything additional to secure them, such as a dowel through each joint? Can anyone enlighten a non-engineer please?

 

Apart from a key to ensure alignment, there is no fastening otherthan shrinkage and the force of the hydraulic press.

 

Can I "like" post #1465 in the light of response #1466, which I also "like"?

 

Usually you have keys to align and quarter the components shrunk onto an axle. But groves for these keys also significantly weakens the axle parts. As the P2:s had problems with fatigue cracks in the original design, I think the new company tries to make the new design as strong as possible, thus avoiding the key grooves. But I am not sure about this.
From the (unfortunately too small) pictures of assembling the axle, I can't see any keys. Instead they use a laser beam to align the cranks.
https://www.p2steam.com/2017/06/08/cranking-it-up/

 

Seeing engineering pictures like these beats the hell out of arguing about livery. Keep the pictures coming. Skilled men doing a highly skilled job.

 

Best post is ages....

 

Pardon, that should be:
Best post IN ages!

 

The P2s crank design was shared with the A1s and A3s. Andrew Hardy did an excellent analysis in his book on the P2s. The problem was starting the trains, not running them. The mikado design put more weight and pressure on the crank axle, designed nominally for a Pacific.

This was one of several problems the P2s had during the second world war, and was one of the reasons given for their rebuilding.

 

Bulleid must have been involved with P2 crank and did otherwise going south

 

You dont NEED a keyway, it just makes life easier for assembly.

Eliminating it, parred with thickening and smoothing geometry, is the de rigeur way to improve the stress profile.

Is the crank axle diameter the same as the old one? And the big end diameter?

 

Yes, but this P2 is fitted with roller bearings. Is the design the same as that on A1s 60153-57?

 

Check the 'Design Study'page on the P2 WS for answers, the crank axle is at the bottom of the page https://www.p2steam.com/design-study/ - the crank axle has been increased in diameter and has a stress relief groove rolled into it, hopefully to avoid this:



Foxy

 

Seem to remember that the part of the axle into the roller bearing on 2007 (is that a journal)is a larger diameter than on Tornado ( which was presumably the same as the original A1) and is as large as the roller bearing company could allow without increasing the dimensions of the axlebox itself ( which would have required a change to frames, horns keeps etc).

 

If I remember correctly, David Elliott told me the stubs of the redesigned crank axle are 3/8" thicker where they pass through the roller bearings, compared to the original P2. As stated above, this is as large as they could go within the existing frame design.

An extra 3/8" diameter must build in a lot more strength in this part of the axle. Can anybody calculate this?

I also wanted to ask David the following question but never got the chance . . .

Is a stronger crank axle likely to mean that a different component, such as little or big ends, will become the weakest link in the power train and therefore more prone to failure under high torque loads when starting?

I'm sure A1SLT will have considered this, but I don't know if they've felt the need to upgrade other components. Any ideas?

 

I can calculate it if you know the original diameter. But basically, for a given allowed peak stress the load capacity of an axle in bending or in torsion is proportional to the diameter cubed.

 

I understand that the original diameter was 9 5/8" and the new design is 10".