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G.W.R Metro Tank in 5" Gauge - Part 4
by James Holden
Engineering Gibberish. [Adventures of Jammy the Journeyman]
The coupling rods. These are made out of b.m.s. 1" x 1/4" x 9* 562" plus 1/8" to clean up 'they are little trickees'?
We can start off by marking the rod out, first put the datum centre line around the job 7/16"from vee block base using vernier heigth gauge 'this will do the trick'! then mark off the centres this will be whatever the horns are on the main frames in this case 8*875" +002" to =002" a steel ruler good quality, scriber, centre punch,and 1/2" ballpain hammer. Punch hole positions,after this a milling m/c is setup clock vice,clamp job while using jacks underneath rod now put spirit level rested on top and jack till level.
Set table indexes to zero and centre drill first hole opening up to 25/64"for reaming size of 13/32"dia finish off move over correct distanence and complete second reamed hole,with both holes now reamed take out and deburr.
Set ends on vee blocks using vernier height gauge,mark off width of rod at centre then scribe line 3/16" either side of datum centre, only scribe lines at the middle which is the wider part of the rod. Stand rod on end and scribe line 3/4" from base of vee block 'same other side'. Turn back with holes facing forward utilising this line for narrowest part of rod 5/32" either side of datum centre connect the two lines up giving the rod a taper. Using spigot located in holes for chank pins find centre and punch lightly, using dividers scribe line on radius of 11/32" both sides, blend radius with file [ half round] into narrow part of rod doing the same at the other end.
Next taking the centre between the holes bring the line up vertical for oilways then split the differance 1/8" a side, on the flat a round piece of brass with a small hole for the oil is inserted in,drilling through into the bore. We now can begin to m/c both sides working from the miller clock up vice gripping the rod just below its datum centre line we can now begin by using a 5/8" slot drill chop away at the metal leaving just enough at middle of rod +010" is quite sufficient.
Turn the rod over and m/c doing exactly the same,once accomplished. Using the line showing the taper m/c across leaving +010"approximately,do this on all four sides dropping just short to blend in with a hacksaw, and file. Setup rotery table making spigote for centre, position hole of rod locating on m/cd dia and clamp.With the aid of a end mill m/c to 11/32" radius. Blend in with file top side of rod and bottom,clean up with enmery paper. Ideally the use of a horizonal miller with a side&face cutter which will give you run out at either end of the rod, start by clamping the rod down flat using 3 clamps one each end and the other in the middle to be moved as cutter traverses forward. Using table Indexes, scallop out to a depth of *048 both sides leaving 5/32" thickness on plus side,run out to finish roughly 3/8" from centre of hole Solutions Steammania.
Once the m/c operation is complete turn over and do exactly the same again but pack up underneath to *048 using shims, the rod should now be 5/32"+010" then take to size by draw filing to finish clean up with glass paper removing all marks and blemishes.
Make phosphor bronze bushes to suit 15/32"x 9/32"lg shouldered to 13/32"dia operation 4 jaw chuck in lathe clock bar turn top dia to 15/32" reduce down to 13/32"leaving step then centre drill build drill sizes up to 5/16 ream dia.Part off 9/32"lg by touching face and indexing across with toolpost cross slide, 'make 4 one for each rod end'! Check hole centres of rods with axles, axleboxes, in position in horns if alls well the rods should be a snug fit.This completes the coupling rods.
Crank pins, these can be made out of silver steel 5/16"dia a length of 13"is required, straight forward turning excise, 4 jaw chuck, clock up m/c to a shoulder *250" -001" +001"and to a length of 5/8" turn job round in chuck and reclock m/c top dia to 3/16" x 1/8"lg making sure that their is a full 5/16" surface area left. If necessary bring workpiece further out to screw cut 3/16"x 32 m.e.taps or 2 b.a.which ever the choice. If quick change gearbox is on lathe, set to 32 t.p.i.english form find piece of tool steel using thread form template grind toolsteel to suit angle of 55*degrees, when satisfied with shape fasten in toolpost slow down m/c.Using screwcutting lever engage, tool is now in play touch job lightly and bring tool out in undercut, runout for area for tool reverse direction of chuck and return to starting point,set cross slide index to zero and find depth of thread in zeus book it will be around *020" to *026" indexing in at *005" at a time, when near root dia die nut the remaining waste metal away giving this the Ideal form.
Next the cross head this is made up from 7/16"x 11/16"x 1" pieces of phospher/ bronze or mild/steel case hardened a rectangular piece is obtained 1/2"x 3/4"x 12"lg more than enough to make the crossheads. Clock vice on milling m/c fly cut or slot drill across the surface area making sure that the flat piece is supported at both ends with jacks and parrellels, m/c down to 7/16"x 11/16"x 2 1/4"lg Once finished remove to lathe and using 4 jaw chuck grip the flat bar with just enough showing to m/c a shoulder, using left hand knife tool this will have to be specially ground to get into the recess, turn back to 1/16" from front face then left and rigth hand form tools round edge as shown, bring tailstock in with jacobs chuck, and centre drill the end open up to tapping size for 3/16"x 40 t.p.i.''tap out this is done by utilising the body of the tap in the drill chuck to centralise its self in the hole, using taper, second, and plug taps. Remove to milling m/c now a 1/4"slot drill is required finish to depth of 3/32" each side, check with vernier celiper to size of 1/2"- 002" -003" transfer to marking off table, scribe line with v.h.g.5/8" up off vee block base, all the way round then lay flat slots facing forward put datum centre line round and where lines bisect centre punch, using slocombe centre locate hole and drill bring up to 3/16" reaming size then finish.
Stand on its end and from datum centre split the differance of 7/32" each way is 7/64"scribe right round turn on end and another line 5/8" of an inch up from vee block base this gives you the slot for the connecting rod stand on parrellels in vice and m/c out in stages of 1/16"to start with, when nearer bottom a heavyier cut can now be taken.
Slide valve. This can be 1"x 5/16" x 21/2"lg m/c same as before to clean up to size 15/16"x 5/16"x2 1/2". When m/cd cut sections of 1 1/16"lg 2off this can be m/cd down to 31/32"provided that the vice is clocked square with parrellels undeneath and leaving no more than *080" in vice m/c out square using end mill with size finishing at 25/32" check with V.C.and to a depth of 7/32" leaving flange thickness of 3/32" turn job over and touch middle of top and m/c out to a depth of 7/32" and a slot width of 11/16"x 17/32" retangular shape start this by squaring out with first a 3/8" slot drill then changing over to a 1/8" slot drill ' So ends this item'!
Valve buckle material ph/ bronze, size 5/16"x 1"x 2 1/2" m/c same as before, fly cut or slotdrill to size of 1"x 9/32"x 2 1/2"lg cut to length with an allowance 1" plus 1/8"for final m/cd finish,start by m/cd away to depth of 5/32" each side leaving 1/4"in the middle using endmill 5/8" dia job in vice on parellels but over hanging edge m/c across to length of 31/32" taking equal amounts of both sides, change over to slotdrill and m/c 1/16" off top of one side leaving lug untouched only m/c the area 31/32"x 1" switch over cutter and m/c out inner section to 25/32"x 25/32"sq using 3/8"slotdrill reducing down to 1/8"cutter for corners finish by squaring out with a file to suit slide valve.
Piston and Piston rod. material rod is st/steel while the piston is ph/br. First the piston a piece of ph/br. roughly 1 1/8"x 12"lg ' the remainer will come useful'! Chuck in 3 jaw face up and top to 1"--001" to --002" using knife tool utilise toolpost with recess tool the width being 1/8"+001" to +002" and finishing at depth of *500" this is done by moving tool over from front face 1/8" width of tool plus 3/32" distance from front face set index at zero working in *250" do exactly the same moving towards the chuck then part off. Check length of piston with V.C. must be a full 5/16" centre drill and build up to 3/16"x 40 t.p.i. tapping for rod. The rod this is st/steel 3 21/32"lg using stock and die 3/16"x 40 m.e.thread, 5/16"each end making sure that the rod is concentric when using die ' work as close to chuck will allow' ! with diestock resting on toolpost and tailstock following up with light pressure on stock.
Queries. Mike Wiles asked about the Hunsett Boiler. In the lower part of the firebox their seems to be a skirt. This is in fact the foundation ring usually in 4 sections material 1/4"thick copper silver soldered between the inner and outer firebox plates level with the base.
This concludes chapter Four