LNERJP, on 09 June 2010 - 21:01 , said:
I belive you and I may be a bad influence on each other
Probably! You'll have to help me when I get stuck.
Anyway a few more details on progress. For the Scale7 version of the kit the instructions recommend the first thing to do is remove all the narrow gauge etchings from the sheets and putting them to one side to prevent you accidentally using the wrong piece in the build. I prefer to cut out etchings using a piercing saw to minimise damage but I didn't fancy cutting out all those pieces for no immediate gain, plus taking out various etchings makes the remaining sheet more fragile. So instead I went through the etchings with black marker pen putting crosses on all those components that have a Scale7 replacement.
To make sure that I got every component I ticked off the equivalent item on the Scale7 etched sheet. Note: on the Scale7 sheet I think there is a small mistake as there is one component marked 305 which I believe should be marked 320. It's only a minor thing as it's all part of the rear bogie suspension and it's quite obvious which piece fits when you put it together.
The instructions then move onto cutting out the frames and making up the hornguides and suspension. The kit is designed for the gearbox to be mounted on the rear driving axle, probably fixed. Then there is a pivot bush to solder in as the centre and front driving axles have beam compensation. My own preference is for sprung suspension so I haven't progressed this any further while I work out the options.
In the meantime I looked at the feasibility of fitting miniature ball races to the axleboxes. It's not something I've tried before but I thought if it's good enough for Tony Reynalds then it's good enough for me! Also I'd like to see if it really does offer a marked improvement in running. So I bought a set of FR156zz ball races from
rcbearings (excellent service and very competitive prices). The outside diameter of the bearing is 5/16", same as the supplied brass bearings. I wondered if I could bore out the supplied bearing to accept these ball races. The boring tool I have for my lathe wouldn't do anything this small but the mini-lathe handbook by Dave Fenner had a few details about making various D-bit tools. I'd seen various articles about this but it's not something I've tried before so I thought I'd give it a go and see how it worked. So this is what I ended up trying.
I got a short length (2") of 5/32" silver steel round bar. At one end I filed a flat on the bar down half way to the centre and a depth of just over 1/8", this was because the bearings are 1/8" deep. The silver steel was then hardened by heating to a cherry red and then quenching in water. It was then cleaned up and tempered to a light straw colour. Although by the time I'd quenched it the colour ended up being a pale blue - a lesson to learn for next time! I then got a bit of rectangular steel bar out of the scrap box, drilled and reamed a 5/32" hole in the end, from the side a couple of holes drilled and tapped 6BA for clamping screws. This was then mounted in a tool holder and set at centre height.
I have an independent 4 jaw chuck so to locate the axlebox I mounted a 3/16" silver steel bar in the tailstock and used this to hold the axlebox in place whilst I tightened up the jaws, a couple of attempts and I got it running fairly true.
The bearings were then carefully bored out for the ball races using the D-bit. The depth of the flat providing a useful depth indicator. On one test piece I bored it out to exactly 1/8" depth, unfortunately when I inserted the bearing the inner race was touching the brass bearing and it was apparent that it was adding a bit of friction. So you do need a whisker over 1/8" on the depth. Once the housing was bored out the remaining 3/16" brass bearing was opened up slightly by running the D-bit through the last bit as I didn't want the axle to catch on the brass bearing.
So this is the final result. From left to right, the ball race, the original brass bearing, a bored out brass bearing[1] and finally a ball race fitted to the bearing.
[1] You can see on the bored out bearing that the brass has spread out a bit on the centre of the flats. The brass bearing is 5/16" across the flats and the ball race is 5/16" in diameter so I half expected to break through slightly whilst boring out, instead the brass being soft just spread out a bit. Once I'd fitted the bearing adding a bit of loctite then a quick fettle with the file returned it to 5/16" across the flats.
So that's as far as I've got - 2 practice pieces followed by 2 bearings from the kit, still another 4 bearings to complete, I've still to see how it works out in the chassis. I just hope I can tell the difference in the running after all this effort!
Adrian
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