| Drawing E1- Frames |
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1. Buffer Beams |
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Usually, one machines the frames first but I have started
with the buffer beams. Whilst passing the local blacksmith's the other day,
I stopped by and purchased a couple of feet of 40 x 40 x 6mm black angle
for the princely sum of £ 2.00 and he even cut two pieces just overlong
for me as well as handing me the offcut. So the first job was to get them
faced accurately to length in the mill. I used a 16mm end mill for this
and an angle plate to act as a backstop. They were mounted back-to-back
in the mill, raised on parallels, and skimmed with a homemade flycutter.
However, the overhang from the vice caused the material to "sing" so I added
a pair of "G" clamps to the ends to dampen the oscillations. Then the finished
faces were clamped together and the second faces machined. |
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The pair were left clamped together, upended in the vice
and the bottom edges milled to size with a 16mm boring bar mounted in the
collet. Once again, the faces were reversed and the other edges milled to
finished depth. Because the height differs from the depth, I marked the
cutaway on the outer faces to prevent errors, then mounted the front beam
face up in the vice, setting the top edge as Y0 and the centre of the beam
as X0 on the DRO. I also modified all the dimensions on the drawing to reflect
distances from my data points. Not all holes are shown on the drawing, however,
and a hunt through found more details on a completely different drawing.
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The 3/16" dia hole for the front drawhook was drilled
first, followed by the holes for the buffers. However, I'm not happy with
Don Young's method of fixing the buffer stocks and have made some changes.The
drawing shows a separate boss screwed into the beam and the stock fitted
to the boss but this means getting the rotational alignment just right.
I will cover the detail a little later but, for now, I have reamed a 10mm
dia hole at the central position, drilled two clearance holes and tapped
two others for fixing the stocks. The rest of the holes in both beams were
finished off, including the slot in the rear beam, and attention turned
to the shaping at the lower corners of each beam. My largest end mill is
a 20mm diameter and this was used to rough out the shape. |
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To get the radius correct really requires a 1" dia cutter
and, as luck would have it, one of the 20mm dia boring bars I have cuts
a circle a touch under the inch. I calculated the "X" and "Y" co-ordinates,
positioned the tool and plunged downwards to finish the internal shape.The
buffer support angles have been made from the same material as the buffer
beams, cleaning up all the outer faces in a similar manner to the beams
themselves. First, though, I had to skim the inside of the buffer beams
to get flat faces and one of my seldom-used cutting tools was used to perform
the task. This can cut quite close into a corner. |
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I wanted the four support angles to all be the same size
and they were clamped together, on edge, in the vice. I didn't lock this
up too tight because I didn't want to deform the angle and force them out
of true. I already had a 16mm end mill in the collet so this was used to
clean them up. I also wanted them exactly 1.250" in height and a quick and
easy method was used to set the height of the final pass; touch on the Hoffman
roller, zero the "Z" axis DRO, remove roller. |
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I wasn't confident about setting up acurately in three
planes simultaneously so I calculated the position of the holes for fixing
to the front beam then added ten thou to my numbers, hoping to leave five
thou per side to skim off the side faces. However, I managed to get my knickers
in a twist with the first pair and, after dry-assembling, ended up with
rather more to come off than I bargained for. That should be reading about
4.135". I marked the two side faces 53 with a felt tip, readjusted my numbers
and drilled the other pair. These came out as expected at 4.137" so those
faces were marked with a 6. The angles were then returned to the vice and
the faces skimmed by the marked amount. On reassembly, these now sit in
the correct position.A couple of thou over but I'm happy with that. The
angles for the front beam are a little thinner than designed but they are
still plenty strong enough and won't affect anything else. I need to rivet
these together before I continue with the side holes and the machining to
the top of the beams but I am going to phosphate these parts, as well as
the rivets, first. |
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Once the parts had been phosphated, I temporarily assembled
the support angles to the beams with countersunk iron rivets and scribed
a line on each of them with the height gauge to match the dimension given
on the main frames drawing. These were then loaded to the mill vice and
the frame-fixing holes drilled and tapped 4BA. The fixed jaw of the vice
controlled the distance from the inside of the buffer beam face and the
scribed line the height from the top of the frames. I find that I can see
the position accurately to a couple of thou like this so don't bother with
a wobbler. |
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That left a couple of jobs to do on the buffer beams,
one of them forming the 1/8" wide slot that locates the frames. These were
made using a 1/8" slot drill taking 25 thou depth of cut and winding till
the DRO read 0.250" on the "Y" axis. To set the "X" positions, I just touch
the cutter on one end of the work, zero the DRO, touch the cutter on the
other end and hit the 1/2 button with the "X" axis. Then the two cutter
centrelines are plus and minus 2.125". The top surfaces show a cutaway to
the sides but I don't know what they're for yet, no doubt all will come
to light further down the drawing chain. I touched the cutter on, moved
along a further 90 thou and wound across until I reached the inner edge
of the front face. Left-hand side one way up and right-hand side the other. |
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At this point, I could have filed the square shoulders
shown on the drawing but got lazy and set up a cutter instead. I could have
formed the complete cutaway like this but felt the risk of a dig-in too
great at this stage of the job. The parts were riveted together and the
front faces lightly skimmed to lose the rivet heads, followed by another
dip in the phosphate tub. There is some work to do on the top of the front
beam and the rivet detail to add to the rear beam but this can all be done
later. They've gone even darker with the extra soak. |
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2. Frame Stretchers |
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There are four frame stretchers shown, two the same and
two different. Three are fabricated and the fourth, although being drawn
as bent metal, was milled from solid. I started by making the support angles
for the first three, cleaning up some 12mm black bar to finish at 3/8" square,
making them in pairs and bringing the finished faces together ready for
the next cut. Next, I milled out the insides, again in pairs and roughing
out with a 12mm dia end mill and a finishing pass with a 1/2" dia end mill.
This leaves the sides 1/8" thick which is enough to stop them popping out
of the vice but I wouldn't try this method with anything thinner. |
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The plates were sawn from a piece of 3mm steel sheet and
the widths milled to size but leaving the length up about thirty thou. These
are the parts for the first three stretchers although I still need to cut
the angles in half for the lower pair. To ensure all the stretchers were
the same length, I set up a backstop on the mill vice, then milled each
of the plates to 4.125". |
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The end of the plates was set to "X0" on the DRO. We all
have our favourite way of using a wobbler; mine is to run the wobbler at
about 300-400 rpm, light up a piece of white paper and slowly watch the
gap disappear as it's wound closer to the work. With my deteriorating eyesight,
the contrast works well for me and I can easily see the moment when there
is no flicker of white remaining. The DRO gets 50 thou added or subtracted
to compensate for the width of the wobbler head. With the back of the vice
set to "Y0", the holes were drilled using a 2.4mm PCB drill for 3/32" iron
rivets. The plate was flipped over left-to-right but not back-to-front and
the other end drilled at the same settings. |
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The angles were drilled in similar fashion to the bogie
bolster in a previous post and the angles riveted to the plates. I moved
the holes ten thou nearer to the edges to allow me to face the ends of each
stretcher once they were riveted together. I haven't bothered making these
look pretty, they are inside the frames and out of sight. The stretchers
were loaded back into the mill with the backstop adjusted to leave about
1/16" poking out the right-hand end. This requires a sharp cutter, because
of the width of the cut, and the bigger the better for rigidity. The stretchers
are handed so each was marked with felt-tip pen to reduce the chance of
errors, then drilled and tapped 6BA, using the top and centreline as the
zero references. The top of each stretcher was always loaded to the inside
of the vice and the top ("X0") found each time with a point in the chuck.
The "Y" axis stayed the same for all of them. |
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The remaining stretcher was made from 20 x 12 black bar,
milled all round to finish at 3/4" x 3/8" and the ends dressed to 4.125".
The centre was cleared away with a boring bar in the mill, working back
and forth at twenty five thou DOC each time and leaving end shoulders of
about 3/16". To finish, the stretcher was held on end and the three holes
also drilled and tapped 6BA. This should be a little more rigid than what
was drawn but, at the moment, I'm a little concerned that the chassis is
not going to be stiff enough. If there is room, I may try and incorporate
a longitudinal stretcher somewhere on the model. At present, there is nothing
to stop the frames assuming a banana-shape and the frame plates, as supplied,
have a slight bow to them but both in the same direction. I might try and
put a slight set in the opposite direction of one of the plates to compensate.
Anyway, with the stretchers finished, I can now drill the frames and get
the basic chassis assembled. |
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3. Main Frames |
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This is my first experience with laser-cut
parts and I didn't know what to expect regarding quality or price. The frames
have arrived and I'm very impressed with them. Accuracy is spot-on and the
cut edges are very crisp and clean but not razor-sharp. I was also pleasantly
suprised with the cost. They are advertised as "spotted" and I was a little
concerned that there would be largish dimples where each hole should be
but it's just a small cross at each point similar in depth to an etching.
I won't be using these, all holes will be positioned using the DRO on the
mill, but they would be a godsend for someone without one. |
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There is not much to say about the mainframes. They all
have to marked out and drilled, whether by hand, with a DRO or laser-etched
/ laser-cut. I'm using laser-cut frames from MEL and DRO positioning to
drill the holes. However, the etched position of the holes is a good reminder
to do the right number of holes in the right places. I set mine up as a
pair and used a Hoffman roller in the horn guides as a means of pinning
them in line. The size of the cutout is extremely precise. I'm not drilling
all of the holes at present, just the ones for the buffer beams, the various
stretchers and the main horns. Once I have a lot more photos of the full-size
loco, I will see what I need to drill to replicate the full-size features.
I've levelled the frames against tee-slot packers and have clamped them
onto a strip of 9mm MDF. On most things, I would use PCB drills but I'm
using a centre drill and HSS drills on these. The material is quite tough
and HSS drills are more forgiving than solid carbide. |
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Each group of holes was referenced from their own datum
point to suit what was going there. Buffer beam holes were referenced from
the top and respective end, stretchers from the top and their centre-line,
horns from the base and centre of the first horn guide. The second horn
was positioned with respect to the first one, winding along 6.7/8" from
the centre of the first and resetting the "X0" before drilling the second
set. The beams and stretchers have been assembled with a few screws to get
the basic chassis together. Now that the really mundane work is done, it's
time to start on some of the more interesting parts. |
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4. Main Horns |
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There are castings available for the main horns but I'm
fabricating as much as possible and four billets were cut from some 13mm
bronze plate. The first job was to clean up all the edges and bring the
height and width of each to finish size. Then they were laid flat in the
vice and the faces skimmed to clean up. I'm leaving these oversize at present
because I wanted to recover the four inner sections for another job. |
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To remove the centre section, I have stitch-drilled a
series of 2.9mm dia holes on a 3mm pitch but left the two holes at the bottom
spotted but undrilled at present. This section can be sawn and chiselled
out later but is being retained for strength at the moment. The centre and
bottom of the horns have been chosen as the reference points and will remain
so throughout all the following operations. My top corners were at X41.5mm
and +/- Y10.5mm. The frame location faces were next, roughing out all four
to 175 thou deep and leaving 15 thou on each side and the top. Once again,
twenty-five thou DOC and full width going round anti-clockwise. I needed
two passes across the top because my cutter was only 12mm dia. With all
four done, I replaced the end mill with a new one and made a final pass
round each in turn, taking ten thou more from the base and bringing the
top and sides to size. |
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The parallels were replaced with a taller set, the work
flipped over and cutaways machined to leave the bracing webs on the back
of the horns. For this, I used a 4mm dia solid carbide end mill at 1200
rpm, cutting full depth. The cutter was set to the top of the packer, lifted
0.156" and locked tight. The tool path for each pocket was worked out and
the waste removed with a perimeter cut 10 thou inboard all round, the island
nibbled away and a final pass round at finish size. The other side used
the same numbers, just negative on the "Y" axis. The end pockets were formed
in a similar fashion but with sharp corners left at the top. It was a slow
job that required concentration to avoid working to the wrong set of numbers.
I nearly did once but caught myself just in time. In the photo, the two
lower ones have had the corners dressed with a rotary burr although the
feature doesn't stand out very well. |
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The endmill was replaced with a 2.5mm PCB drill and all
the holes drilled. I am using M3 countersunk socket screws rather than the
specified 6BA. The dimensions I had entered onto the frame drawing were
transferred to the horns drawing, adding 0.125" to the verticals because
the horns sit 1/8" below the bottom of the frames. The horns were held firmly
in the vice and the parallels removed from beneath before drilling. This
is why I've kept the middle intact for the time being. After deburring the
holes, they were tapped freehand in my small tapping fixture - all seventy
of them. I wasn't sorry to see that operation completed. |
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Six of the supporting ribs are machined at an angle and
the two outer top ones are at about fifteen degrees. It was easy to just
rest them on an angled packer and mill these by eye. The centre rib is left
square for an oil hole. I tried the same arrangement for the side ribs but
they weren't loading as nicely as before, the result of milling away some
of the clamping face at the top. Instead, I set up a small vice an an adjustable
angle table and milled away the four upper ribs, the lower ones left untouched.
I had a bit of a dig-in on the first one with the work lifting in the vice
so added a top clamp for safety. |
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Now that I no longer needed the support of the centre
piece, it was cut through with a hacksaw and then attacked with a small
chisel. Holding on edge in the vice, the four horn stay holes were drilled.
Care had to be taken here because the drill would have broken out into a
half-and-half void, risking drill breakage. Using the vertical DRO, I drilled
to precisely 170 thou, leaving a blind hole. They were tapped 6BA freehand,
held in the bench vice. To complete this stage of the work, the horns were
upended in the vice and the oil hole drilled. I used a pilot drill of 2.4
mm dia to a depth of 3/16", then followed through with a 1.9mm drill. I
don't know what the oiling arrangements are at this stage but that will
allow me to set a piece of 3/32" dia copper tube into the hole. Finally,
a filing button was clamped to each in turn and the corners linished away.
I will mill the internal horn faces once these are assembled into the frames. |
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5. Horn Keeps |
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A rummage around in the scrap box unearthed some embryonic
horn keeps, bits of 1/2" x 1/2" x 1/8" mild steel angle. The holes in one
side of the angle will be milled away and not be a problem. The outside
faces were linished clean and didn't require any machining, there will be
very little to see by the time these are completed. The wider leg was milled
to size first and, because I particularly wanted this edge square to the
side, I used a packer to clamp the angle against the back jaw of the vice.
They were all finished to the width of the horns, 0.406". Next, they were
reloaded and the other edge milled to 0.250" high. Then the inside faces
were cleaned up with a single pass of a 12mm dia cutter. Removing the cutaway
was next and an end-stop was set up to get them all in the same place. After
setting the centre of the component at "X0", one cut through the centre
plus one either side leaving ten thou on each of the inner edges saw them
roughed out. Then they were returned to the vice and the width of the cutaway
completed to size, a nice fit to the base of the horns. The advantage of
doing all these operations in this order was that, once the depth was set,
the cutter didn't get moved until completion. |
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The final job on these was to drill the holes and, once
set down on the packer, this was removed and the six holes centre-drilled
and drilled to their respective sizes. I re-dimensioned my drawing so that
it more accurately reflects the important sizes. I've also made a few of
the related items including the spring pins and retaining plates, items
which don't require any description. These have been phosphated along with
the horn keeps. |
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6. Next Item... |
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