Member postings for julian atkins

dennis,

thanks for your post! i had found your youtube clip sometime ago and it's great! you have built a cracking loco!

as mentioned in a few other posts on this subject here and elsewhere the drawing errors seem to be as follows:-

the axlebox and horncheeck drawings are awful.

the boiler is nothing like a fullsize TERRIER and neither are the cab controls (which is such a shame as Stroudley was an artist down to the very last detail). so far as the boiler is concerned, it goes for overkill with the grate area and ends up with quite a low free gas ratio through the tubes. it doesnt have the sort of rectangular firehole that the fullsize has nor the large radius on the backhead flange, and it is extended and slopes down over the rear axle. this is quite unnecessary IMHO, and mine has a full depth firebox sitting within the rear horns as per fullsize. the 1/16" inner wrapper i think is suspect as is the lack of proper girder stays. i dont think the palm stays are up to modern standards either. the lower water gauge bush is too low (there should be 2 water gauges anyway as per prototype). my boiler design has a 5/16" foundation ring all round and a 3/32" inner wrapper and a flat topped inner firebox with girder stays. dont forget the boiler is working pressure 90 psi. my own boiler is 4" dia which fits easily between the frames and the front of the rear horns losing only 1" on the grate area of martin evans' boiler design despite the wider foundation ring, and thicker inner wrapper. i have had to use some quite thin boiler insulation material to just about keep to the correct outside diameter. the dome is moved forward to be in line with the driving wheel centre line for the later Marsh boiler.

although the side elevation is pretty accurate in martin evans' drawing, the front elevation is NOT! for some inexplicable reason he widened the buffer beams and side tanks and cab. the GA side elevation is correct for the shape of the cab roof but as you have noted on sheet 8 the detail of the cab roof is not and is wrong.

depending on how particular you want to be, there are lots of differences from the prototype that add nothing to the miniature ie tank extending into the cab on the r-h side, cab windows too large and in the wrong place, tanks slightly too low etc..

for an original A class TERRIER the smokebox should NOT be circular, and in any event martin evans shows the diameter of the smokebox and smokebox door too small by quite a lot.

unfortunately martin evans also completely cocked up the valvegear which has far too large a throw on the eccentrics. this can be accomodated but only with a longer length expansion link to correct this fault. no suspension offset is shown whereas there should be one for good valve events.

apparently the balance pipe requires additional holes in the frame not shown, though personally i dont see a problem with making the balance pipe as per prototype. i dont like the well tank idea, so mine will have a wagon to go behind for extra water and coal.

i have heard horror stories of the press fit valve spindle glands coming adrift so best to silver solder these in place.

the balance weights on the wheels shouldnt be proud of the wheel tread and should be slightly less. the works diameter of the wheels is 4', so martin evans' 4 3/16" is slightly less than fullsize.

shame about the lack of room for 4 lifting links to the expansion links and the cut away required on the slidebars as this precludes the use of channel section slidebars as per prototype. my TERRIER has the cylinder block moved forward by 1/4" to give a longer conn rod length nearer to prototype. if i hadnt already machined the cylinders and crankaxle to drawing i would make the outer crank webs 1/4" thick and gain a bit more space for the port passages and a larger exhaust passage. i would also make the cylinders as long as the castings would allow to get a bit more piston width as there is ample room at the front for longer cylinders.

the front frame cut out should be the same height as the rear freame cut out and it doesnt take much to fabricate a crosshead pump body to fit the larger cut out. the crosshead pumps are in line with the motion centre line on fullsize, and again it doesnt require much to achieve this in miniature.

the reverser arrangement is nothing like Stroudley's, and can easily be made to be the same in miniature.

as mentioned above Stroudley was an artist when it came to details, and there is no reason whatsoever why the correct arrangement and design of cab controls should not be incorporated in miniature.

one advantage of modelling STEPNEY though is that she hasnt had a westinghouse pump fitted since the 1930's! on mine, the brake cylinder (vacuum on the fullsize STEPNEY) is a steam brake cylinder, and the large reservoir contains a filter and supply from the wagon and acts as a sump to feed the injectors which are rather small but are tried and tested!

martin evans' frame stretchers and motion plate are nothing like the prototype, and in fact the prototype had more frame stretchers that can be with advantage be reproduced in miniature.

Stroudley's design is so beautiful and perfect that it seems such a pity to depart from it in any way! generally, a very successful design in fullsize can be reproduced successfully in miniature without any departure from the original apart from the internals of the boiler, and the salter safety valves etc.

otherwise a lovely design and it is remarkable how so many successful working locos have been built to the BOXHILL drawings!