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G.W.R Metro Tank in 5" Gauge - Part 2
by James Holden
The inner and outer frames are now cut and shaped with all holes drilled buffer beams shaped with angle brackets fitted and riveted on. The frames should be checked for square using a ruler across the frames left to right bolted using 4 B.A. hexagon x1/2 Lg setscrews.
Once established that the frames are pulling straight and square to buffer beams remove the bolts used as temporaries and clamp the two inside frames together utilising four holes with the help of two pinch clamps. Tools milling m/c two parallels and toggle clamps with tees into slots of milling m/c table clamp the plates to the table using parallels and clamps set square to table by using spacially fitted ground flat bar into m/c slots knock up too this will bring the frames in line with the m/c table.
Machine slots for horn blocks using 1/2 diameter end mill do not go into the corners change cutters to1/4 diameter for radii mill slots to 1 9/16 x 1" wide for horn block flanges. First finish slot which carries drive chank axle this will be the datum to work the other slot off remove and deburr.
Do exactly the same for the outer frames front bogie m/c to 3/4 wide x1 9/16 lg remove and deburr now the frames are ready for the stretchers only two are required with a cover plate to rear horn these can be cast iron or gunmetal also can be fabricated important width 41/4" open dimension but work as close as possible to plus +002 or -002 best way fit vice to milling machine clock vice with D.T.I.to within *002"than m/c a datum edge top turn over and finish to 2 1/2" wide using parallels in vice m/c sides to 4*250" +002 to --002" using end mill.
The second stretcher exactly the same except 1*750 +002 to --002 finish.
Cover plate straight forward 1/16" plate m/s cut and file square leave an allowance for forming radii of 5/16" diameter this can be done by using 5/8 dia bar clamped with material in a 4" to 6" vice using brass or aluminium draft with 2lb ball pain hammer belt over till plate is at right angles to each other.
Next the horn blocks 4off cast iron or gunmetal casting skim up front and back side [ using milling m/c ] clamp machine surfaces in vice and lightly machine top then turn over and machine bottom side to 2 1/16" lg using parallels of given height allowing enough to m/c flange out to depth of 1/8" inch leaving wall thickness of 1/16" a width of 1" x 1 9/16" using inner frames drill back through for 3/32" rivets fasten horn blocks to frames in four places when complete clamp frames back together again and m/c through to width of *875 --000" to +002" and a depth of 1 1/4" once this operation is over the frames can be split for the last time and stretchers buffer beams and cover plate for rear horn can now be fitted the box his complete.
The horn block keep plates can now be made these are of m/steel a strip of 3/8" x 3/16 x 8 1/2 lg can be used tools milling m/c parallels 15/32" slot drill D.T.I. fit vice clock up to *002" insert parallels in vice making sure that more than 1/16" is sticking out of the vice m/c through using 15/32" slot drill to depth of *062" leaving 3/32" from edge using table. Indexing move over 1 11/32" m/c through mark out and drill counter bore for rods to hold compression springs on axle centres 7/16" fit and bolt to bottom of horn block this concludes second chapter.