Welcome to
Steve's Britannia
5" gauge Adams O2 - Calbourne
Drawing E1(a). Drawing E1(b). Drawing E2(a). Drawing E2(b).
Drawing E3. Drawing E4. Drawing B1. Drawing B2.
Drawings S1 and S2 Boiler Assembly Assembly and Alignment Errors and Ommissions
Drawing E3- Eccentrics, Expansion Link etc
  1. Eccentric Sheaves and Straps  
The sheaves were made by turning complete from 1.1/2" dia mild steel bar and parting off a little overlength. After turning the o/d to 1.15/32" and facing the front, the groove was formed with a 2mm carbide grooving tool by touching the front of the workpiece, then winding the compound slide along a measured amount and making the first plunge. Two further plunge-cuts were made followed by sliding the tool along the bottom of the groove. The same tool was used to start a parting groove, leaving the work ten thou overlong. In reality, a hacksaw was used to cut off each billet using the groove as a guide although I polished the bottom of the grooves with a thin strip of emery cloth first. The sheaves were reloaded to soft jaws and the backs faced off to leave the sheaves 0.250" thick
The straps were made from 1/2" bronze plate. A 2" wide slab was able to provide eight billets, each cut off at 7/8" long. Unfortunately, there was quite a lot of swarf as I had to thin them down to 1/4" but was unable to get two pieces from a single billet. The billets were machined all round to give me eight pieces 1.15/16" x 13/16" x 0.240" thick. This is ten thou less than the sheaves to ensure they dont rub together. This was followed by machining the bolting lugs to each end of the billets.
The step-down is 5/32" so the opposite end was done by resting on a 5/32" drill. Slightly out-of-square won't matter in this instance. The next thing I did was to drill the bolt holes and fix them together with 8BA screws, in pairs, marking each set with a letter to keep them matched. Then they were returned to the mill vice and centre-drilled for setting up on the lathe.
A long centering-rod was held in the tailstock and each set clocked true in the independent 4-jaw chuck. Flatness was handled by loading each assembly proud of the jaws, then pressing back with a flat plate until level with the jaw faces. However, I found this wasn't going to work very well when the first one moved whilst drilling the pilot hole through. I should have put a large-diameter, hollow backstop behind the work for support. Time for "Plan B", which was to return to the mill and remove the centre by using different sized slot drills to move up in stages, finishing off with a 20mm boring bar that made a 1" diameter bore. Plenty of support and a much better set-up.
The exercise was then repeated using a boring head, adjusting upwards about fifty thou per pass, until I could finish all four sets with a 1.312" diameter bore. Then it was back to the lathe and the clearance for the rims of the sheaves machined in. A packing ring was set behind the work and a 45 thou deep reccess machined on each side, out to 1.1/2" diameter. The first set disassembled and fitted around a sheave but was found to be a bit too tight so it was reassembled, using the mill vice to ensure flatness, and rechucked on the lathe. Run-out is unimportant here, just flatness, and an extra two thou per side removed by winding the compound slide along the required amount. With the width correct to fit the grooves, a tiny amount of easement was needed to get the sheaves turning nicely in the straps. This was done with fine sanding drums in the dremel, slow and steady being the order of the day. These are the assembled sets showing each sheave lettered to match it's respective strap. The next stage is to drill and ream the axle hole, followed by broaching a keyway in them. As them late Don Ashton and many others have said in the past, there is only one correct position for the eccentrics and mine will be fixed to the axle with keys.
  2. Eccentric Rods  
I decided to mill these from solid and silver-solder the fixing bracket to the arms so started by milling some 12mm black bar down to 3/8" square. Although I had enough 3/8" square BMS in stock, I was concerned about the possibility of them going banana-shaped after machining. The forks are offset from the main arm and the top and bottom arms have different offsets. The fork also finishes at 3/8" wide by 5/16" thick. I milled the channel in each of the forks first using a 3/16" slot drill, finishing at 9/32" deep to prevent the sides collapsing. The shanks were machined next, two milled to the first size and two to the second. All four were then milled to 5/16" thick, removing the support web in the process, and the arms were thinned to 1/4" wide. Four mounting feet were cut from 1/4" x 1/8" flat steel and a 1/4" wide slot milled by 1/8" deep to fit the arms. The 6BA clear mounting holes were also drilled at this stage.
Taking care to get them the right way round, each of the feet were silver-soldered to the arms. They are numbered 3 and 4 to match the drawing numbers, it's easy to get them mixed up. I had deliberately made the arms 1/32" overlength and they were now trued up and brought to length as a single operation.
It seemed important that the four eccentic rods were all the same length but, because the arms get bolted to the eccentric straps, there was the possibilty of getting cumulative errors. Therefore, the arms were bolted to the straps first and the pivot holes in the forks machined next. I used the base and pillar from my tapping fixture to act as a back-stop. Using the vice to grip the lower arm of the fork, the upper arm of the fork also needs support and a piece of 3/4" x 3/16" gauge plate was used between the arms. Loading to the vice with this in place sets them square in the both planes plane. The packer was then be moved back to the end to allow the drilling to proceed. They were centre-drilled, drilled and reamed 5/32" diameter.
The forks needed to be thinned to 3/16" wide at the back and a fixture was made to support the eccentric rods. A 3/16" wide spacer was made to fit between the arms of the fork and an M4 cap screw used to bolt this end down. The other end was supported on packing and clamped over the top. An equal amount was milled from each side. After this, it was all hand-work. All the fancy shapes were filed or linished, then finished off with sanding drums in the dremel. The four rods were temporarily assembled with the expansion links on the bench to check that all would go together correctly and to get an overview of the arrangement. To get the 7/16" spacing needed for the valve guide, there is only 1/16" spacing between the forks.
DY seems to favour tight-fitting, flush pins in the forks to carry the expansion links but I'm not in favour of this. I decided to make shouldered pins with a 1/32" thick head and to create a recess in the arm of the affected forks to set the head into. "E" clips were used on the outer ends to retain the pins because they are in fresh air. In the next picure, I'm setting up to cut the groove for the clips using a slitting saw mounted on a steel shank. The last photo shows one of the pins assembled and the recess on one of the other arms. I've just noticed that I also need to file the titty off the loose pin in the picture.
  3. Keying the Eccentrics  
Before I start on this, a note to prospective builders of this locomotive. As far as I can see, Don Young failed to record anywhere on the drawings what angle to set the eccentrics at. He probably hadn't got a clue and expected the builder to tinker around with the angle until something worked. The only drawing that offers any insight scales out at about 245 degrees to the centreline but that isn't much help to a builder. Nor is it very accurate. I asked Nigel Bennet what angle he had used for his "Ashey" and he very kindly sent me a drawing of his one-piece design for the whole eccentric assembly. This was a little too complex for my poor old lathe, better suited to CNC turning, but it showed that he had chosen an angle of about 260 degrees. I then spoke to my colleague, Wilf ,and asked for some help and he drew out the valve gear in his CAD program. We decided to aim for 10 thou lead steam in mid gear and this produced an angle of 261 degrees, so pretty close to what Nigel had done. This was the angle chosen and later references to 9 degrees are three-quarters of the way round (270 degrees), then back 9 degrees.
I'm probably missing a trick here but, as I see it, the hardest part about putting keyways into the eccentrics is an alignment issue as it's very difficult to accurately true up the offset bore. To get round this problem, I decided to drill a pair of accurate locating holes in the eccentrics and fashion a simple fixture to load them to. The first job was to put the locating holes in so the eccentrics were loaded to a 3-jaw chuck on the mill and a pair of 2.4mm dia holes drilled on the centreline. With that job out of the way, attention turned to the fixture. This was made from some 1.1/2" x 3/8" flat material, loading to the 4-jaw chuck and boring a recess at one end to be a snug fit to the eccentrics. The fixture was then taken to the mill, clocked up square in the vice and the centre of the recess found. I needed this to be particularly accurate so took my time and double-checked everything. A pair of 2.3mm holes were drilled at the same co-ordinates as the eccentrics and a 3/4" diameter clearance hole drilled and bored 5/16" from the centreline. An M10 tapped hole was also made for a clamping point.
After pressing a pair of 3/32" iron rivets into the 2.3mm diameter holes, the fixture was taken back to the lathe and loaded to the 4-jaw chuck, clocking out on the 3/4" diameter clearance hole (which was the reason why it was bored rather than just drilled). The eccentrics were loaded in turn and the offset hole drilled and bored to size. I could have done this on the mill but it's easier on the lathe; too many tools to keep swapping out on the mill. It would have been easy to make a mistake with orientation when cutting the keyways so I printed off a screenshot of the Dockstader arrangement that I have been using and marked the crank webs and the slots with a felt-tip pen. With the con rod journal to the back, the eccentrics lean forward by 9 degrees. I've chosen to offset the keyway by 45 degrees because, otherwise, one of the keyways would be in the thinnest part of the eccentric and probably break out.
To cut the keyways in the correct position, I needed to be able to align the broach at 45-9=36 degrees to the perpendicular for two of the eccentrics and at 45+9=54 degrees for the other two. The fixture was modified with a pair of fences bolted to one of the sides and the front to become guideways. It was then clamped to my rotary table on the mill and the longest side clocked true. I don't need to bother about any other reference at this point. The scale marker was zeroed and the table wound round 36 degrees. Now it was trued up on the 3/4" clearance hole so that I could mill a 3/16" slot in the first fence for the alignment peg. Then I had to repeat the operation at 54 degrees for the other one. I've wedged a piece of 3/16" thick ground flat stock in one of the slots for clarity.
With the fixture complete, I moved on to putting in the keyways. I had to make a collar for the broach guide to lift it from 14mm to 5/8" diameter, then cut away the slot area. I also made a couple more shims for the back of the broach. Here is the setup for the second pair of the keyways showing how the guide bush is supported. The front fence/guide has been removed as those ones are finished. After all four were made, they were cleaned up and assembled to the eccentric journal. It took a few tries to get them lined up in the correct order and the right way round but I got there in the end. The inset shows an end view of the arrangement. I've recorded the arrangement because I need to dismantle this again. The eccentrics need a locking screw to stop them moving sideways on the shaft and it will be easier to get the journal pressed into one of the webs first, then build up the journal again.
  4. Expansion Link  
I had some 3/16" thick gauge plate in stock so this was used to make the expansion links. After working out the missing dimensions, the two pieces were cleaned up at 1.5/8" x 5/8". Then the two holes for the link bracket were drilled and the two holes for the eccentric pins were drilled and reamed 7/32". There are two different radii on these and a special carrier plate was made to hold them whilst on the rotary table. A pair of holes were reamed to take some locating pins, another hole tapped M8 to take the clamping finger and two reamed holes for dropping over a locating pin.
The rotary table was fixed on the mill and the DRO zeroed on the centre of the pivot pin. The locating pegs for the link were pressed into place on the plate, which was loaded using the hole for 3.5/8" radius and clamped parallel to the table. Ididn't bother clocking the plate square because the extremities of the slot will be set by eye. The first link was loaded to the pegs and clamped down, using the other one as packing. Winding the table along until the DRO read 3.500" set the radius for the slot and a 4mm hole was drilled in two places where I guessed the ends to be.
A 4mm end mill was used to rough out the slot, eight passes at 25 thou depth of cut, stopping when I hit the back of the drilled hole each time. The slot was then opened out using a brand-new 3/16" slot drill.
The outer radius of the expansion link is 2" so the carrier plate was remounted on the table on the second pivot point. This reamed hole was set at 5mm less than two inches to compensate for using a 10mm cutter to form the shape. The back end was machined next and I pulled the pins from the carrier plate and used them to support the work in the vice, thus ensuring everything stayed square.
The ends were linished around a filing button to give the final shape. A pair of phosphor bronze bushes were made and pressed into place with a drop of Loctite. Once dry, they were reamed 4mm and the ends of the slots were filed square with needle files. The link brackets were made from 1/2" x 1/4" flat mild steel, milled down to 3/16" and drilled to match the expansion link. The hole for the pivot pin was also drilled at 1/8" diameter. The only variation from the drawing that I have made was to move the pivot pin back fifteen thou so that the forward offset becomes 0.047". There will be a few other modifications that will be detailed at he appropriate time.
The pivot pins were turned to size and parted off, reversing to put a 1/8" dia x 1/8" long tail on them to set in the link bracket pivot hole. These were then silver-soldered into place. I've screwed them into a bar so that I can heat from below and gravity will drop them tight together. The clearance for the valve spindle fork was milled away next, using a 4-jaw chuck to support the work.
The final shaping was done by holding the work on the pivot pin and one more support pin to get the angle, flipping over to do the other side. The packing under the pin lifts it to the correct angle. To finish, the parts were all cleaned up and each expansion link riveted to it's bracket with two 3/32" iron rivets. These should be countersunk but I've chosen to use roundhead ones. Once painted, it will be very difficult to notice this departure from the drawing.
  5. Weighshaft  
The weighshaft is just a length of 5/16" diameter bar with three arms silver-soldered on. Two connect to the lifting links and one to the reach rod. I had a nicely-ground bar that came from a defunct scanner and used this for the shaft. The two inner arms were made on one of my simple milling fixtures but the outer arm has a pair of bends in it which were done first. Then the holes were drilled and reamed followed by profiling the sides. As with all these type of parts, one end was fixed and the other clamped after moving over a calculated amount. The inner arms were soldered on first and, to keep them aligned, a piece of 4mm bar was passed through the eyes and nutted each end. After fluxing up, solder rings were placed on each end and the position of the arms carefully adjusted. Heat was applied to the middle section of the rod and the inside faces of the arms only and the solder drawn through.
The outer arm needed to be placed radially with respect to the inner arms as well as maintaining the 5/16" dimension from the end of the weighshaft. I drilled and tapped an M2 hole in the outer arm and used an M2 grubscrew to hold the arm in place. Once soldered, the protruding screw was linished away. The two trunions seen on the drawing were made from bronze offcuts, they are just simple top-hats .And this is the weghshaft mounted between the frames. The shaping on the trunions can be seen and is to clear the bend in the reach rod arm.
  6. Lift Links  
The lifting links were made from lengths of 5/16" dia rod, drilled 11/64" with a 1/4" dia spigot turned on the end and parted off at the respective lengths. 3/8" x 1/8" flat bar was drilled 1/4" dia at each end and the rods silver-soldered into place. They were then held in the vice propped up on some 1/16" packing, thinned to 3/32", profiled with a 4mm endmill and, finally, reamed 3/16". Reaming after soldering ensures that the two holes are parallel to each other. These are the two lifting links after a bit of cleaning up. Because DY's valvegear dimensions were not optimum, both the links and lifting arms are made to new dimensions.
  7. Reverser Frame  
The reverser frame is a mild-steel fabrication with some interesting shapes to machine. The mounting block had a 1/8" wide channel milled into it to locate the plate and I also milled a pair of 2mm channels at the front to locate the webs. The webs were made from 2mm (0.080") material, rather than 1/16" as drawn, and the plate had a pair of 2mm channels milled for the webs. I also drilled and reamed the 3/16" dia hole for the pivot pin and the cutaway which is on the prototype but not on the drawing. The parts were silver-soldered together, resting on packing pieces so that heat could be applied from below.
The two latch plates were cut from 1/8" material and clamped to the back of the reversing frame. The assembly was then loaded to the milling vice and the two clamp-screw holes drilled for 8BA bolts. The rotary table was used next to enable forming the shape at the top. The webs have been machined parallel with the base for the time being to facilitate clamping and a locating pin was made to fit the pivot point. Twenty-five thou depth-of-cut passes were made until I hit the 2.250" radius.
With the top finished, I set the frame square to the table by clocking along a side face, then roughed out the two cutaways at the top. Multiple plunge cuts with the boring bar took me to 1/2" radius. Then a boring head was set up to 9/16" radius for the last few cuts.
The penultimate job for the rotary table was to cut the inside radius of the latch plates. A 4mm end mill was touched on the outside edge, moved inwards by 410 thou to set the inside radius and the winding process repeated until the waste dropped away. With the frame set square to the table once more, a 1/4" dia endmill was used to reduce the width of the lower section which also formed the radii at the lower corners. The final shaping was done freehand using the linisher, files and sanding drums. The only machining op remaining was to taper the webs towards the top and the frame was mounted on the angle table for this. Trial and error set the angle to about three and a half degrees.
The reverser pole was made by mounting on one of my milling fixtures and adjusting one end or other to get the taper. The other small bits and pieces were quite straightforward comprising of spacers, handle, latch lever, lever handle and pivot pins. This is the frame unit temporarily assembled. I will make the notches once the reach rod is made and distances are worked out.
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