For no better reason than it felt right I decided to make some 7.2mm dia. wheels. I started with a length of 10mm dia. CZ121 grade brass. To make a blank for the tyre I drilled and parted off a ring with a 6.5mm bore 3mm wide. From the same material I turned one end down to 5.7mm dia. 5mm long, with a groove near the end (for glue, perhaps not neccessary but I didn't think it would do any harm);
Using quite a lot of epoxy (Evo-Stik Epoxy Rapid, all I could find locally) I glued the tyre to the centre making sure that the gap between the two parts was fully filled, and left the tyre and blank in a V block to set for a week or so. Note the gap between the tyre and centre;
I left a gap of .4mm, I'm unsure if this is about right or whether I could get away with less. Once the glue had set the job was faced off then the top turned down to 8.9mm (finished flange dia. plus .1mm). With a parting off tool the width was reduced to 2.2mm, then a step turned to 7.3mm dia. (tread dia. plus .1mm) leaving a .8mm wide width for the flange;
With a NEM 310 'N' gauge profile tool the lathe was set to 150rpm and the wheel profile formed;
I parted each wheel off overlength, then held them in a step chuck to finish to length;
Here's one faced to 2mm wide;
Each wheel then had its face profiled, again held in the step chuck;
In the photo above are the two insulated wheels (lower) plus 2 solid brass uninsulated wheels.
As the tread is only glued in place I played safe by only taking light cuts and working very gently! In hindsight it might have been wise to do a destructive test by taking bigger and heavier cuts to see if the glue would fail.
This technique so far seems to work ok on smaller wheels but I'm not sure that it would work on larger wheels where the turning forces are greater, or harder materials than free machining brass. More experimentation required!
Of course the next job will be to build a working chassis to test these, then of course I'll need to build a body to sit on that chassis...
Paul.
Paul, there was an article in Railway Modeller in the 70's about insulating Hornby Dublo 3 rail wheels.
ReplyDeleteTheir method was to drill two small holes opposite each other just under the wheel tread.
Using a jewellers saw cut between the two holes on one side of the wheel only, fill the saw cut with "Full Strength Araldite", leave for at least 24 hrs then repeat on the side of the wheel. The wheel is then 'two railed and is still concentric.
That sounds like a lot of work! Interesting method though. Thanks for the comment.
DeleteInteresting. When you mentioned you were doing insulated wheels this isn't quite what I'd expected. I'd assumed you'd turn all the wheels the same and then add an insulating bush to the wheels on one side. I'm guessing this approach has the advantage of the wheel surface looking identical on both sides which is nice, but it seems such a slow process (waiting a week for the epoxy to cure) that I think I'd go mad waiting.
ReplyDeleteIs there an obvious benefit of doing it this way that I've missed?
Patience is the most important thing a modeller can have!
DeleteI have made a wheel with a bush (acetal), although being a test piece it has never been used. It would work well enough but care needs to be taken to make sure that the wheel remains concentric once the bush has been added.
There could well be several benefits, if this idea works well in the long term. Firstly, as mentioned above, the entire wheel is turned as one piece so concentricity, or lack of, will not be an issue. Secondly, bushed wheel centres can look a bit unsightly (but thats probably just me). Thirdly, if the loco has valve gear then the cylinder/slide bar assembly doesn't need to be electrically insulated from the chassis, which it would need to be if only the wheel centres were bushed (obviously not an issue with plastic centred wheels). And lastly, there would I feel be an added benefit when building an outside framed loco, that is that outside cranks could be soldered to the axles without fear of melting the plastic insulating bush/plastic wheel centre. Obviously car would still need to be taken.
However, I have yet to test these wheels so I do need to build a loco using them to prove that the basic concept is sound.
And I should also add that I just like experimenting!
DeleteYes I need more patience. I hadn't thought about benefits of isolated valve gear, or the fact that it's much more likely to be concentric than fitting a bushed wheel centre. All very good reasons for going this route.
DeleteAnd yes, experimenting is a good enough reason on it's own!
Try also MRJ no 1, where Roy Link undertook such an exercise.
ReplyDelete