Wayne Rite Posted April 15, 2014 Share Posted April 15, 2014 I've just picked up on this topic and have to say that the Comet product has always exceeded my expectations and I have built (and rebuilt!)several over the years. The mention of all axles being in the same plane causing poor pick up and running is a valid one, for many years I rewheeled Tri-ang and Hornby Dublo chassis with either turned down original wheelsets or more commonly Romford wheels, and in order to make them run well it was my practice to reduce the tyre diameter of the centre wheelset in the Unimat to prevent the chassis 'rocking' on point work and track joints. I don't where the idea came from but I strongly suspect it may have come from Ian Rice in the old Model Railway News many, many moons ago. Before the advent of the later Romford /Markits wheels the standard Insulated Romford Wheel would be far from concentric and always required some fettling of the spokes and attention to the wheel centre square hole, in fact I bought a Broach from Buck and Hickman when they were 'the' tool suppliers in London to use with a jig to ensure the hole was correct. The axles too often needed attention to ends to ensure the milled square was square to the axle. Yes, I've seen some doozies with 3 flats instead of four! In common with accepted practice I would finish the tyres in the lathe with the wheels in the orientation that they would be in the chassis,ie with the right quartering, I know it sounds a bit OTT but every little bit helps. The tyres would be finished with the headstock set over to allow a coning of 3 degrees on the finished wheel. Note, all outer wheelets would be turned to the same dimension (easily set up the cross slide) and the middle wheelset having a quarter of a millimeter or so turned off the tyre but leaving the flange untouched so the eye would be fooled into seeing the wheels were the same (outside) diameter. Seemed to work OK, I only had one chassis returned for rework, and I just increased the amount turned off to a millimetre (20 thou in the old money)and my client was very pleased. It's just a variation on what Geoff has been doing on his chassis, and it works! Regards Link to post Share on other sites More sharing options...
artisan100 Posted April 15, 2014 Share Posted April 15, 2014 Thankyou Geoff, I'm not questioning your design policy, it just surprised me as I've never heard mention of it before and a lot of people build and like Comet chassis. I'd also much rather have a loco with all it's wheels on the ground, like the real thing, so will be popping in an order to you for some hornblocks later this week. I will however pull you on one thing - the EM spacers I have here are not 13.25mm, but closer to 13mm. The jigs are spot on but when assembled the spacers just fall through the frames with plenty of sideways movement available. Looks to me like t Ooh, the suspense. What was the rest of the sentence? Seriously, sorry about any discrepancy between the turned width of the aluminium spacer in the EM loco chassis assembly jig, and the etched width of the nickel silver spacers. The chemical milling / photo etching process is excellent at locating points accurately in two dimensions, but it is not so good at producing items at a specified width. There are many factors affecting the end result including the variability of the metal itself, the newness (and hence strength) of the etchant, the temperature of the etchant bath, etc. It is for this reason that etched chassis, for example, need to have the axle bearing holes reamed out a touch because if they had been drawn 'right' size then any overetching would mean that the bearings would be a sloppy fit and could be misaligned when soldered in place. Once the metal has been etched it is inspected at the factory and any obvious overetching or blemishes mean that the sheet is etched again, and once the metal arrives here it is again inspected for obvious problems and rejected if necessary. You can appreciate though that we can't put a micrometer across every fret of spacers but if you have any product that isn't up to scratch then please return it for replacement. Regards, Geoff Brewin Comet Models Link to post Share on other sites More sharing options...
Horsetan Posted April 15, 2014 Share Posted April 15, 2014 When did you changeover to aluminium for the spacer jigs, Geoff? The ones I've got are all brass! Link to post Share on other sites More sharing options...
artisan100 Posted April 15, 2014 Share Posted April 15, 2014 The spacers in just the EM jig are aluminium. They are machined to 13.25 to match the EM spacers etched on the separate nickel silver frets that we can offer as a substitute for the included fret of 00 spacers in the chassis which have been updated to nickel silver. The earlier version of the EM spacers were brass, and the turned spacer was also in brass. The change took place about 5 or 6 years ago, maybe more. The spacers in the 00 and P4 jigs are brass. Geoff Brewin Comet Models Link to post Share on other sites More sharing options...
Quarryscapes Posted April 16, 2014 Author Share Posted April 16, 2014 Ooh, the suspense. What was the rest of the sentence? Oops, you've already guessed correct anyway - was about tolerance of etched parts, 0.2mm being about right on 0.5mm ish material. I have an ever increasing shopping list of Comet kits, having just acquired another Collett Goods, a 14xx and a Manor - all of which are going to need chassis building. The 14xx is also going to be built split frame, so a challenge! Link to post Share on other sites More sharing options...
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