|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"
||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
||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.
||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.
||8. Next Item...