7 1/4" gauge wheel profile

[ettingtonliam]

Before I machine 'Locomotion's wheels to the profile shown on the Piddington/Reeves drawings I'd just like to see if there is a nationally agreed profile, just in case things have changed in the 20 odd years since these drawings were done. Can anyone point me in the right direction for this information?

[cplmickey]

Here's a link to the relevant page on the 7 1/4 website. Ian

www.sevenandaquarter.org/about-us/?/Services+%26amp%3B+Track+standards/69/

[ettingtonliam]

Thanks Ian, thats what I wanted, but it has rather opened a can of worms. The drawings show wheel width of 3/4" but the standard is 13/16". Flange height is 5/32 on the drawing and 3/16" in the standard. I can meet the standard on the loco wheels, but the tender ones have already been faced off to a gnats over 3/4", so that will have to do for them.
The worst thing, and I know its critical, is the back to back dimension, which the standard gives as 6 13/16". The drawings don't give this dimension clearly. You have to start with the axle length, subtract twice the wheel seat length, then add back on the length of the bosses projecting from the back of the wheel. Doing this gives 6 7/8" for the tender wheel set, and 6 11/16" for the loco wheel sets! I'll try the calcs again in the morning, in case I'm miscalculating somewhere.

Oh well, I'll just have to work to the standard, and make the necessary changes, though it does seem to mean that the outer faces of the loco wheels will be 1/4" further apart than the drawing suggests (plus 1/8" on back to back dimension plus 2x 1/16" for the wheel width increase.) Seems quite a lot, but given Locomotion's unique configuration it probably just means increasing the length of the overhead cross head arms by 1/4", it doesn't affect cylinder centres at all.

Apparently the original Locomotion was built to suit 4' 8" gauge, and never altered, so gave rise to some nervous moments when it was displayed running occasionally on 'modern' track, transiting check rails being an issue, - the last time being in 1925, I think, when motive power was an IC engine concealed in the tender.

[cplmickey]

Hopefully if you can meet the critical dimensions she won't give you any trouble.
I've only worked on the tender frame for my locomotion so something to remember when I eventually get round to doing the wheels.

[ettingtonliam]

I don't know if you've bought the wheel castings yet, but something to watch out for is that at some point, the small boss on the back of the pattern for the tender wheels fell off, and my wheels, bought about a year ago, don't have a boss projecting from the back of the hub. Reeves are aware of this, and in fairness to them, offered to get me a new set of wheels after they had repaired the pattern.

I'd already made a start on the wheels, so turned down their offer, as its easy enough to add a 1/4" long boss spigotted into the back of the wheels.

I've pretty much done the tender woodwork and the tank (which really stiffens the chassis) but the planking is held on with temporary brass woodscrews until such time as I can summon the enthusiasm to make about 70 square headed coach screws, and all the square headed nuts. I've made a start, but somehow there always seems to be something more interesting to do, such as the boiler at present.

[cplmickey]

I know the feeling - made a load of square nuts then left them out and they all went rusty.

Thanks for the heads up on the wheels - not started on them yet as other projects taking priority at the moment. I only started the wooden chassis as it was something I could do in the house in the winter months.

[ettingtonliam]

Yes, thats what I've done over winter. I don't think boiler making in the house is going to go down well, so that will have to wait until the warmer weather till I can work on that outside.