Dave Holt
Western Thunderer
I have currently put aside my own model projects in order to complete some work for a friend. The project started off as completion of a part built chassis for a LNWR Special Tank. The model had, I believe, originally been built in EM gauge from a London Road Models kit. However, on close inspection there appeared to be rather too much play in the axleboxes/horns which, together with the narrow frame spacing resulted in about +/- 0.3 to 0.5 mm waggle at the ends of the axles. The coupling rod holes were also over size and a loose fit on my jig axles. Also not to my liking, though not fatal, was the compensation arrangement, with a fixed rear axle and a single pivoted beam spanning the front two axles. Although this does work as a compensation arrangement, it results in very poor weight distribution if instability is to be avoided.
Fortunately, my friend has been able to obtain a new chassis kit from LRM, so a fresh start has been made.
The choice of suspension was between full floating compensation, with twin rear beams and a central pivot for the front, or CSB. I have built a few tender chassis with CSB but never a loco, so this seemed to be the chance to try it. I found a few worked examples for locos with the same wheelbase but in every case the front spring anchor point was off the front of the frames. It might be possible to calculate a suitable arrangement, but I don't have the ability to use Excel on my computer, so that wasn't an option. So, full floating compensation it is.
I have set up my Avonside Chassis Jig to match the etched holes in the frames and the coupling rods which, thankfully, all matched. The twin rear beams have been cut and the rear two horn slots cur out. I'm leaving the front as is for now, so that I can set the front rocker to bear on the axle at the correct ride height. Once the frames are assembled, the filler plates, already partly cut, can be removed and the front horns fitted using the jig.
A couple of view of the frame plates on the jig using the axle hole bushes fro location but with the horn guides and compensating beam loosely placed.
The LHS frame back on the jig with the centre and rear horns over the frame slots and the front end located by the bush. You can see that I've pre-cut most of the way for the front horn slot.
Dave.
Fortunately, my friend has been able to obtain a new chassis kit from LRM, so a fresh start has been made.
The choice of suspension was between full floating compensation, with twin rear beams and a central pivot for the front, or CSB. I have built a few tender chassis with CSB but never a loco, so this seemed to be the chance to try it. I found a few worked examples for locos with the same wheelbase but in every case the front spring anchor point was off the front of the frames. It might be possible to calculate a suitable arrangement, but I don't have the ability to use Excel on my computer, so that wasn't an option. So, full floating compensation it is.
I have set up my Avonside Chassis Jig to match the etched holes in the frames and the coupling rods which, thankfully, all matched. The twin rear beams have been cut and the rear two horn slots cur out. I'm leaving the front as is for now, so that I can set the front rocker to bear on the axle at the correct ride height. Once the frames are assembled, the filler plates, already partly cut, can be removed and the front horns fitted using the jig.
A couple of view of the frame plates on the jig using the axle hole bushes fro location but with the horn guides and compensating beam loosely placed.
The LHS frame back on the jig with the centre and rear horns over the frame slots and the front end located by the bush. You can see that I've pre-cut most of the way for the front horn slot.
Dave.
