9F why does not having a flange on the centre wheels stop it being mainlined

Highly unlikely in the case of a 9F with 10 coupled wheels although I have personal experience of an 0-6-0 (underground) diesel with centre flangeless wheels doing just that on a sharp curve. Yes, it did re-rail itself. In fact, the first I knew was a loud bang and a jolt. When I stopped the loco, I couldn't see anything wrong. After it had happened three times on this curve I stopped the loco before the point where the bang occurred and found the cause was the centre wheels were completely off the railhead. The actual derailment itself was not noticeable, only the re-railing.

 

I have just extracted this page from an Eastern Region working timetable dated 1959.

It would appear that raised check rails were a problem in BR days for 9Fs.

 

Interesting indeed! Thanks for posting that.

 

Interesting question. I haven't got anything about the Scottish Region. The only nomadic member of the class was 90763. This was allocated to Carlisle Kingmoor. It certainly travelled over the S & C to Leeds. For a year during 1959/60 it was allocated to 6F Bidston, a home for 3 9Fs. During this time it worked over the CLC system and was photographed at 9F Heaton Mersey and 27E Walton sheds.

 

Just had a look at Evening Star in the NRM and my impression of the flangeless third driving axle is that it has a wider tyre than the flanged axles.
Another impression is that the flangeless wheel is cylindrical and not conical in profile and would not therefore self center on the rails as a normal rail axle would.
Additionally the flangeless tyre has a (approx) 1" x 1" 45 degree bevel machined on both inner and outer edges. (Speculation - to facilitate re-railing).
The machining is quite coarse and visible to the naked eye. This seems to make the width of tyre available to ride on the rail less than the flanged wheels.
I hope this further muddies the waters!!!

 

Normal tread wear?

 

In the U.S. flangeless drivers ("blind" in their parlance) had a slightly convex tread which, is assume, helped them to 'centre'.
Ray.

 

I'm no expert, but what value would a coned profile on the centre wheels have?
(Unless the wheels also had sideplay).
Wide treads, no coning and the chamfered edges seems logical to me, but I'm utterly ignorant of the finer points.

 

My thoughts too. Surely a convex profile would introduce a high point loading and cause instability whilst in motion, as the wheel would tend to try to move sideways off the centreline of the rail?

 

A degree of self centering will exist due to the majority of the rails around the country being angled in at approx 1 in 20.
Only areas with level rail will generally be vertical pointwork. Which also hosts the other problem Raised Checks.

 

But flangeless wheel profiles don't exist on the modern railway.

 

But, as @Ploughman has pointed out, the rails are canted towards each other. If you have a perfectly cylindrical tyre, the wheelset is going to sit on the outer edge of each rail, which has a comparatively small radius compared to the convex profile. A convex profile (provided the radius is not excessive) will sit on the main surface of the rail, thus actually leading to a reduced contact stress, and the load will be closer to the centre of the tyre.

Here's a picture of 92203's centre driver. I would suggest that that tyre was originally machined convex, and has since worn flat or even slightly concave in the centre, where most of the running has been done. This leaves the impression of a chamfer on the outer edge.

As for the unworn bits of machining looking slightly rough, if a convex profile was done with a form tool on a wheel lathe (easiest way in times past) I'm not surprised. Holding a good finish with a cutting edge that's the full width of the tyre isn't easy.

I'm now waiting for somebody who really knows about 9Fs to tell me I'm talking complete rubbish...

 

Difficult to machine all wheels the same size if one set has a different profile. Why would it not have the standard 1 in 20 (or whatever) taper?

 

Derby drawing SL/DE 21233 shows the tyre profile for the flangeless centre driving wheels on the 9Fs.
The tyre is 5-11/16" wide. The OD is cylindrical, i.e. flat. On each side of the tyre, 1-3/8" in, an angle of 10 degrees is machined on, with 5/8" x 30 degrees machined on the outer edges.

 

Thank you. Which diameter of the tapered profile coupled wheels does it match?

 

The reference diameter on the coupled wheels is measured at a point 2-11/16" in from the inside face of the tyre.

 

Thank you. I guess one could think of advantages and disadvantages, but it is a compromise anyway with a long wheelbase.

 

When we had 92214 at bury on the east lancs after rileys had carried out the boiler re-tube it managed to get round bury south curve fine & up onto the heywood branch. Plus the curve of heywood station is relatively sharp too & it never seemed to encounter any difficulties with the check rail there.