Thanks for your thoughts. They're are considered and interesting, as always.
If you read my post, you will note that I made no comment on whether machining a wheel in a lathe is easy or difficult. That distinction is best left to bjviper, as I have no idea about him or his modelling friend’s access to, or ability/confidence with a mini lathe.
I read you post with interest because you imply that machining down a RP25/110 steam locomotive wheel cannot be done. In fact, it can be done and has been done. You speak of ‘problems’ as though they are insurmountable, which is a pity, because they are not. Perhaps on man’s problems are another’s challenge?
In short; I too used to share you scepticism. But having now been involved with the process, it is my opinion that it is easy and relatively quick. Or, as my gay friend, Paul, once said to me; “Don’t knock it ‘til you’ve tried it...” Ahem...quite.
You raise a good point. Typically (always?) the tire width must be reduced from the front face (to preserve the flange), while the wheel centre must be reduced from the back face (to preserve the spoke and crank boss detail). Therefore, the wheel centre must be removed from the tire. Remove Wheel Centre from Tire
A good modelling mate and I have achieved this by turning down a piece of brass rod, which is slightly smaller in diameter than the wheel centre. With the axel removed and tire sitting on a flat, stable edge (such as an open vice jaw or second turned piece of brass tube), the centre is then gently knocked out from the front. It should be noted that if the wheel was fixed in with glue etc, then you may be in some trouble. As TheBlackSmith has suggested, you may run the risk of damaging the wheel components (most likely the weaker wheel centre). Happily, I have not had this trouble.Machining the Tire
The tire needs to be mounted on another tool, so as to keep it true while being machined. The first attempt was to turn down a piece of brass rod, such that one end had a recess diameter that was equal to the original wheel centre diameter. The tire was then slipped over the top and machining was commenced. While the fit was very snug, the tire began to slip while being machined. Back to the drawing board. The second, and successful option, was to turn down a mandrel to a diameter that is slightly larger than the original wheel centre. The tire is then pushed on, with the ‘spring’ of the mandrel deflecting in and then pushing out against the inside of the tire, holding it firm.
The tire was then reduced to the desired width by use of vernier callipers and a ‘stop’ on the lathe bed. The wheel profile was finished with a lathe tool, cut to the correct specifications (in this case P87). The tool was borrowed from another good modelling mate - thank God for every last one of them.
The wheel centre was pushed back on, using a small jig to ensure that the face was recessed at the correct depth. The protruding wheel centre was then cleaned up from behind using some fine emery paper that was stuck to a flat surface. With the desired wheel back-to-back spacer, the wheels were pushed on to the axel, using Loctite to secure. The resulting driver wheels are very stable – I have exerted significant force on them (far
more than the force generated by the mass of the model) and they have stayed true and square.
Unfortunately, I do not have any photos of the driving wheels, as they are still at my mate’s workshop. However, I do have pictures of the finished tender and pony truck wheels.
Compare the machined pony wheels:http://vrdays.blogspot.com/2011/08/so-long-and-thanks-for-all-fish.html
With the prototype:http://www.victorianrailways.net/motive%20power/jsteam/jsteam.html
Please note that the wheel face-to-face effectivly stayed 'put', while the flanges were effectively spread (to answer your question).
As previously stated, I think that this is a relatively easy process. While, one could manufacture the wheels from scratch (see the most recent copy of Model Railway Journal for an example), this was not my approach. In fact, I think that the more time consuming aspect will be to modify the frames, connecting rods, and cylinders etc. Again, I see this as a challenge, and can’t wait to get back into it.
I’ve just relocated with my work to Vancouver, Canada. Consequently, all my modelling gear is floating somewhere in the Pacific Ocean. Once it arrives, I will get back into work. The intention is to have two modified VR steam locomotives completed by Christmas. One will remain here, while the other will be shipped back to Victoria and its owner. I’d suggest that these two will be the first of several. I will update my blog as I make progress.
PS: Anyone considering fooling around with steam loco kits could do worse than get their hands on a copy of Iain Rice's book 'Locomotive kit Chassis Construction in 4mm': http://www.amazon.co.uk/Locomotive-kit-Chassis-Construction-4mm/dp/1874103100
Ignore the reference to 4mm scale - the methods described are readily transferable.