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G.W.R Metro Tank in 5" Gauge - Part 1
by James Holden
An engineers account of the pursuit of the Southern Region rebuilt Merchant Navy Class 8.P. Pacific in 5" gauge considering the average person with no knowledge of the basics of engineering in miniature I have discided to start with my first project to construct G.W.R Metro tank in 5" gauge I am writing this with the beginner in mind and hoping to show with sketches and drawings different ways of overcoming engineering problems on lathes, millers, fitting, marking out, rolling, folding and boiler making as well as using high temperture gases.
So lets get too it. At the very start it is allways the main frame material 1/8 x 21/2 wide x 271/2Lg B.M.S. 2 off square up 2 edges using 12" large flat file and 6" engineers square ideally a marking off table is needed at least the length of the frames but at a pinch a plate of glass will do the job. Use engineering blue to locate the high spots, try to keep the file flat so not to rock while filing over the length of the frames when within ' 005 (5 thousandths of an inch) and the marking or spaced very close together using feeler guages between frame and datum surface try to work to ' 002 draw filing to finish.
Using filed edge, lift to light this will show gaps under square. The same principle as before once two faces are filed square we can proceed to the next stage. Tools needed:
We can now mark off the main frames. It is important that both datums are used for vertical and horzontal lines. A horzontal line cutting through the centre line of the cylinder block is one, the other is a vertical line cutting through the driving axle. [bisection] using dividers to split the line into equal sections i.e. 90° degrees all holes can now be taken off these two lines.
Mark out radiuses and general shape then mark out all holes utilising four of the larger size to bolt both frames together using pinch clamps alter when moving job.
Milling machine tools vice parrallels jacks m/c through slots for hornblocks using side and face cutter 5/8dia m/c to slip pile.
3/32 x 31/4 x 271/2 lg B.M.S. for outside frames basically the same as before two datum lines mark off all holes m/c through for front bogie another way of cutting out the hornslots is to chain drill the holes then hacksaw through and file.
Buffer beam 3/16 x11/2 x8"lg B.M.S. same as before square up two sides mark out for hole centres for buffers and angles which hold inner and outer frames to buffer beam also rectangular hole for hook using pinch clamps to hold angle to beam drill 3/32dia for iron rivets [snap head] fasten with 3/32" dollies using one punch and one as die this completes first chapter in the pusuit of G.W.R. Metro tank in 5"gauge.
This article was kindly written and prepared by: James Holden