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G.W.R Metro Tank in 5" Gauge - Part 3
by James Holden
Engineering Gibberish. [Adventures of Jammy the Journeyman]
A word relating to the prevous chapters I will always show what I consider to be the easyist option open, Milling the hornblocks by engineering means, The set up is for easyier. But with limited tools it can be machined on a lathe.
Axleboxes these are made from phosphor bronze and are solid, Best way a stick of cast bronze enough to make 4 axleboxes will do nicely allowing for machining, Set up in milling m/c clock vice to *000 +*005 using D.T.I.megnetized to m/c column. Support bar with jacks m/c to size 1"x 5/8"Using end mill cutter or fly cut surface, m/c one surface using parellels for support turn over and m/c opposite side next turn one good edge against backside of vice m/c then turn, When all surfaces or to size and square. Cut to length of 1 3/16" + 1/8 face up. Set up for marking out useing angle plate, veeblocks, square 6" vernier height gauge. Scribe a line 11/16" from datum edge[bottom] turn through 90*and another line 1/2"up to datum centre,where line bisects centre punch, lightly drill and tap for engineers button. Set by using slip pile from base to under side of button both ways, when locked in place. Remove to lathe.
Place m/cd block in lathe fasten in 4 jaw chuck bring D.T.I. onto base of machine and clock button to *002 tranfer to face and clock as above remove button and centre drill, then pilot 3/16"opening the size of 39/64" reaming out 5/8"complete the process on the rest, `Remove the burrs` Clock vice on milling m/c. Parrellels jest less than width of axle m/c slot 15/32"or nearest down side,this slotdrill leaves *008 either side to take off by moving table cross feeds both ways, Finish to a depth of 1/16"micrometer or vernier across the slot must be less then 7/8 =*002 to =*004." Mark out holes for coil springs and oil lubrication drills 3/32 and *098" respectively for 5BA tapping all holes taken from datum centre line. Ways in which all of the operations are completed Solutions @ Steammania.
Axle boxes complete we can now move on to the trailing axle, first obtain a piece of 5/8"dia silver steel this will come in a length of 13"inches and will do nicely for the two axles, both journals have to be concentric to each other. First cut the length to its various sizes leave aroundabout 1/8"plus on the finished product. By using lathe with 4 jaw chuck,clock bar to a tolerance of *000 to *002 and centre drill the end extend bar leaving 1/2"remaining in the chuck reclock along length.
Using tailstock rotating centre or dead centre support rear of shaft end. Using knife tool turn length to 21/32"+000 to+010"and to a diameter of 1/2"=000"to 002"turn round and do exactly the same at the other end making sure that between wheel centres of 4*687"a tolerance of no than +002"to=002" `use vernier celiper`!
Chank axle this is made of individual parts in all 10 pieces be careful all journals or concentric start by cutting all, bar and flat pieces with a little extra for ending up.
The chank can either be done in a lathe or on a milling m/c for the lathe, Solutions @ Steammania Journal ends these are straight forward working from the lathe clock up and centre drill, turn as above remove then m/c opposite side to suit chank webs, 9/16"=001"to +0015"for press fit finish remaining shafts. A start can now be made of the chank webs obtain a length of 7/8 x 5/16 x 8"lg if possible mark off using ruler, square, scriber, centre punch, vee blocks, 1/2 pound hammer[ball pain] also vernier heigth gauge. Mark off and allow a bit for ending up, cut off 4 pieces, m/c one bottom face for datum face scribe centre line through, mark first line 1/2"up from m/cd face then moving to 1"centres [chank throw] using indexing on milling table ' don't forget set index at zero'!
Milling m/c clock vice then using parrellels, jacks, and jacobs chuck set in arbor of miller a centre drill is now used number 3 'will do'!insert into chuck working cross &horizontal feeds position on centre punch mark and drill build up sizes to 1/64" less than 9/16"reaming diameter, finally finish with reamer, set table indexes to zoro and move over 1" and complete same operation again till all 4 chanks are finished.Rotary table is now set up m/c spigot for centre of table to locate chank bore clamp down job and then using side & face cutter m/c round to 7/16"radius. another way is to mark off radius using dividers, hacksaw and blend in with file.
Mark out for 1/8"silver/steel pins to be attached to each shaft mark off as before on 1"centres 'do not assemble chank axle yet'!.
The eccentrics are next B.M.S.is now used 1 5/8"dia or + is needed and around 12"lg clamp in 4 jaw clock up and m/c top dia to 1 9/16"knife tool is used. Change over to recess tool 1/4"wide this as got to be micrometered to =000"to+002"for strap Set cross slide index to zero and m/c in 1/32"to a diameter of 1*500"=000"=002" 'vernier caliper recess depth'! Now bring back D.T.I. set against toolpost outside edge bring index to zero touch job with tool using 002"feeler gauge between both bar and tool undo one jaw and move workpiece over *375"after this centre drill then pilot 3/16"stepping up in drill sizes to 1/64" less for 5/8"ream lathe must be geared down for the reamer, tapered shank for tailstock insert, 'make sure there is enough for four'!
Bring back to concentricity, and part off using correct tool.
Move to face of job touching with side of tool then using toolpost cross slide index at zero turn to *312" plus width of parting tool, slow speed & feed, allow *010" for facing up after, chack with vernier caliper.
Mark off for 2 grub screws opposite one another into the bore on datum centre line drill & tap 4BA the drill size is *118"this concludes the eccentrics.
Driving & Coupled wheels are cast iron with machining allowance 'be careful and even it out'!
working from a 4 jaw chuck grip on the rim holding on to no more then 3/32"using scribing block point on wheel tyre true up as near as possible then change to face,using knife tool face up inner land area 'chank' then m/c tyre face this should be 3/32"less then chank area this can be chacked by the use of parrellels and slips. Next m/c top diameter to 5*500 on tread 'length here is important 15/32"lg'! leave a step in the root for slight radius a former is needed for shape over rim. This can be made out of 1/16" gauge plate. Using tool steel 2 pieces grind radiuses internal and external to suit template with faces m/cd chamfer using rougher tool at 45*degrees bring in tail stock using jacobs chuck, centre drill and build up drill sizes to reamer 1/2"diameter.
Turn round and clock bore using spindle silver steel will do, when satisfactory m/c down face with knife tool using surfacing traverse to width. m/c top diameter to 5*812" then using radius tool blend in form finish with smooth file. Make jig to locate in axle centre, using milling m/c table indexes plot centres at 1*000 =001" to +001" a drill 15/64"is needed for 1/4"reamed hole for coupling pin.
This concludes chapter Three