Monthly Archives: April 2015

S7 Stanier 8F Part 11 “Obtain a running chassis”

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The instructions are a little terse at times, such as this: “Obtain a running chassis” !

Small Obtain a running chassis 01

After a struggle, this is where I am now at:

 

Motion bracket, etc., in position on the frames.

Motion bracket, etc., in position on the frames.

However it will take a little while to describe how I reached this point!

 

This is what I had constructed so far:

I had bought the special ScaleSeven wheels, but it turned out that  the wheels rims/tyres had been made to S7 standards, but the central boss part of the wheels was far too thick.  I was lucky once again to be able to enlist Richard Davidson’s help, and he used his lathe to thin down the wheel centres by about 0.5mm each.  This extra space on each side would be crucial to allow the wheels and coupling rods to turn behind the slidebars and crossheads without catching.  Even with the wheels thinned down, it is a very tight fit.  It was simply not going to be possible to fit the manufacturer’s crankpins, washers and nuts.

Wheel BoltOnce again, Richard has been the saviour.  He manufactured four specials crankpins – bolts to go through the coupling rods from the outside.

I decided that on the first axle the special crankpin could be used without a washer inside, as the coupling rod was slightly thicker around the crankpin, giving clearance over the wheel centre.  For the second axle, though, a washer would be needed between the special crankpin and the wheel boss, as the articulation in the coupling rod would foul the wheel centre otherwise.  For the third and fourth axles the Slater’s crankpins could be used.

Small Annotated Obtain a running chassis 02Shown here are the different crankpins in place.

When I first put the axles in the frames, bolted the retaining plates to keep them there, attached the coupling rods loosely and turned the chassis over: JOY – the chassis could be pushed forward and the wheels all rotated with minimal binding.  Too easy, as they say here in Aus.

“Too easy” in fact ….  Once I tightened down the crankpins the binding started.  I am not sure what the correct way to sort this out is, but Richard had once shown me how to push the frames along, and when the wheels stopped rotating, move each segment of coupling rod sideways with a pair of forceps to see if it moves: even a little movement shows that this is not the part which has stuck.  When a crankpin with no movement is found, the hole in the coupling rod probably needs to be enlarged (with a small tapered reamer).  I slowly opened out the holes in the coupling rods where the binding was occurring.  At least with the articulated coupling rods this is made easier.  However it also became obvious that on one wheel the countersunk central bolt holding the centre of the wheel to the axle stood out too far and was scraping against the coupling rod – the bolt had to be filed back just a little.

This all seemed to take ages, and the special crankpins were difficult to take out each time – I had to buy a “pin chuck” (like a very small drill chuck) to hold the circular heads of the crankpins.  However in the end I did “obtain a running chassis”, although one without the connecting rods, etc in place.  I couldn’t then resist a trial fitting of my Portescap motor and ABC gearbox, to see it all turn for the first time!

Using the Slaters crankpins and their “top hat” bushes made the coupling rods stand out an unrealistic distance from the wheels, so next action was to thin down the flange of the top hat bushes (almost removing the “rim” of the “top hat”!), and shorten them so that they are only slightly longer than the thickness of the rods.

Small Obtain a running chassis 03After all of this, fitting the cylinder/slidebars/motion bracket assembly revealed that all the work was being rewarded, with a small but definite clearance between the front crankpin and the crosshead on the slidebars.

The connecting rods were still not fitted, so next was to attach these to the crossheads.  There was nothing in the instructions about how to do this.  There is a post coming out of the recess in which the small end of the connecting rod fits, about which the rod will move.  I cut this off flat with the crosshead rear (the was no way it could be allowed to protrude!).  After some thought I measured the post: 2mm diameter, and made two tiny circles of flattened nickel silver wire (curled around a 1.9mm drill, then flatted between a steel ruler and a granite benchtop with a hammer (lucky the household manager was out again).  I could then solder the wire circle around the post to hold the connecting rod in place.

Small Obtain a running chassis 05Connecting the connecting rod then allowed me to see the next difficulty – the expansion links have to be made very carefully so as to hang just wide of the connecting rod.  I had not done that (it’s not easy to see this difficulty before this latest part of the construction), so some reconstruction is going to be needed now.

 

S7 Stanier 8F part 10. Curving the tender sides.

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I have started on some of the bodywork for the tender. For someone like me, this threw up some significant difficulties due to my lack of expertise: how to bend the top edge of the tender sides? I have bent sheet metal before, to make the Belpaire firebox of my industrial Garratt, but this was brass, and not a particularly wide sheet of metal, either. The nickel-silver sheet for the tender side requires an even bend along a length of about 11cm. Dave Sharp from MOK has instruction about how to do it, but they are sketchy. The bend covers a height of about 3.5mm in the side, so I worked out that as the bend was through about 45 degrees, a bend of about 8mm diameter would be about right [8×3.5=28mm, divided by Pi = approx. 8mm diameter].
Small Bending the tender sides 01The instructions show how to draw lines on drafting tape inside the bend, to position it accurately. This is good, but how to make the bend? My first try was to place a slightly smaller diameter drill to bend around, and clamp the tender side in my big vice.

However I simply couldn’t bend the nickel silver!
In any case, the drill wasn’t really long enough, and the ends might not bend properly. I was talking/e-mailing Richard at the time, and he suggested I buy a longer rod, of slightly smaller diameter than the bend I wanted to make, and then either roll the sheet over the rod using a rigid metal plate to transmit even pressure, or clamp the top edge of the tender side in the vice and bend the body over the bar. I suppose it was a little foolish of me to try to do it the other way around, but somehow it seemed right to bend the bit that is supposed to be bent, rather than bending the body down whilst holding the part which is supposed to be bent, upright in the vice!
I started to try to bend the sheet over a piece of 1/4 inch (6.3mm) aluminium rod which I found, on our granite kitchen benchtop (the household manager was out), but it was very difficult to bend, and also I thought that this technique might not produce a discrete bend in the flat sheet of the tender side (if you see what I mean), but rather make it a nice continuous curve in the metal sheet. It was impossible to hold the rod still relative to the sheet metal whilst trying to make the bend.
Small Bending the tender sides 03So, back to the vice. The trouble now was to hold everything at once, to allow the rod and the tender side to be exactly positioned. So I used masking tape to hold the rod against the aluminium angle used to make smooth jaws in my big bench vice, as shown on the left.

Small Bending the tender sides 04

Then I put the tender sides into the vice and could adjust the position so that the start of the curve was held in between the rod and the vice, the other end of the curve being above this (in the picture one can just make out the second line):

This finally allowed me enough leverage, using a thick rigid steel rule, to make the bend in the tender sides.
Small Bending the tender sides 06

Small Bending the tender sides 05It also allowed me, using the same technique, to form the vertical curves at the front of the tender sides (a bit out-of-focus in the picture, sorry).

HAPPINESS !

David