Postby Russ Elliott » Wed Sep 29, 2010 12:10 pm
Blimey, those manufacturers are right on our case in this thread... here's what Chris Gibbon offered me as a message for the forum:
The new jig has generated lots of interest and as I had no advanced publicity before the show, I can only assume it's down to the influence of your S4um and CLAG web sites so I think you can feel pleased with yourselves for that. The phone's still ringing...
With reference to comments in the thread, Dave Franks more or less summed it up regarding tolerances. The manufacturing tolerances that you can realistically expect to achieve (at any price) for the various hornblock parts are simply not acceptable for our purpose. The bearing needs to be a smooth, sliding fit, with a gap of almost zero between the sides and the horncheeks, so the actual tolerance is (arguably!) even less than this amount. The way I deal with this is by moving the errors to where they can be dealt with easily and effectively. As you can't add metal, I calculate everything on the tight side, so the last bit of fitting can be done by the customer to achieve a perfect fit. Remember also, that the upper cheek tolerance value must overlap the lower block value (after finishing, which must also be taken into consideration) or you may get sloppy blocks from the word go. The bore on the blocks is slightly tight to allow for variation in axle dia but, again, it gives scope for an absolutely perfect fit. This is standard engineering practice.
Regarding the new tag design, the third bend in the tags allows the small hole to be much nearer the edge of the material (the edge nearest the loco frames) so the carrier wire can run much closer to the frame for extra stability. A standard hole would need to have more material around the outer edge of the hole. This third bend also has the added advantage of providing a nice, flat sliding surface, preferable to a sharp knife-edge, and this limits friction should the tags ever touch on the back of the hornblock etch due to block rolling or sideplay.
As far as inventing the actual tag is concerned, I'm not really bothered who lays claim to the design for a simple L-shaped piece of metal with a hole in it, though I certainly didn't copy this idea from anyone else. I was steered over to the CSB's (and tags) when talking to Dave Franks and if glasses are being raised, as far as I'm concerned I'll be drinking to your good self for doing all those sums, Ted (Scannell) Bill Bedford and a whisky for Dave, who were playing around with this idea long before most of us. For my part, I hope I've provided some useful tools to make the job easier.
