Entry posted by buffalo
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Although the main focus of my Camerton layout will be in the Edwardian era, I do hope to run a variety of stock from later Victorian years through to nationalisation. For this, like all good GWR branchline layouts, I'll need some pannier tanks. At some point I would like to include an early pannier conversion from an early saddle tank, for example, a representative of the 1813, 1854 or 2721 classes. I'm going to start, however, where everyone else does, with a 57XX or 8750. As I already have a couple of Bachmann bodies, the obvious way forward is to add High Level chassis to these, a task that has been keeping me busy over the last couple of weeks. Let's begin with the obligatory shot of the etch:
Apart from the etch, there are various bags containing gears, hornblocks and other bits and pieces. Like other High Level kits, this one comes with a gearbox and includes frame spacers for 00, EM and P4. It is designed to be built either rigid or using the supplied compensation beams on the centre and rear axles, with a rocking front axle. However, as the title suggests, I decided to go for a CSB arrangement rather than compensation. Recently, there's been much muttering over on the main forum area about springs and compensation with all the usual cries about them being difficult, time-consuming, etc. Hopefully what follows might pursuade one or two folk that they are not really the work of the devil.
Before getting stuck in, another warning is in order. This is a luxury build with all mod cons when it comes to jigs and other tools (though I don't have a quartering jig or a hold and fold, and don't feel the need for them). Those of a more spartan pursuasion may chastise me for this so it's worth saying that none of these are necessary. I've done it all before and could have done it all again with simple hand tools and three lengths of 1/8" silver steel rod but I simply chose not to.
So, let's start with the frames and rods. The frames were removed from the etch, cleaned up and the holes for rigid axle bearings reamed out to take the supplied bushes. The rods are a three layer lamination jointed together with a supplied rivet. The result is a substantial 0.85mm thick:
So why did I bother with the rigid axle holes and bushes? Firstly, so that I could use a High Level CSB jig to help mark out the fulcrum positions for the beam:
I was going to spend some time with the well-known spreadsheet working out the positions but I discovered that the job had already been done for me. The 57XX is just one of many examples illustrated on one of the clag.org.uk CSB pages.
The High Level jig is intended to be used with their CSB tags that are attached to the bearings in their horn guides. The jig has three rows of holes corresponding to the holes for the spring wire in the tags and, together, these allow some flexibility of choice in placing the wire. In this case, the highest of the three holes promised the least interference with frame spacers and other parts. Once this was decided, holes were marked out and drilled. Some small cutouts were needed in the front spacer, motion plate and firebox front. In the latter case, this only needed a slight extension of the slots provided for the normal compensation beams. The cutouts are circled in yellow below, and the intact EM spacers are also shown for comparison:
Remember that I said there were two reasons for using the rigid chassis axle bearings? The second was to aid setting up my Avonside jig using both frames and rods to give a double check on the axle spacing:
Once the jig was ready, the area around the rigid bushes was removed and the sides of the resulting slots cleaned up ready to accept High Level hornguides. At this point, I also removed the representation of the underhung axle springs so that later the wheels and axles could be dropped out without removing the wheels from the axles. I will be using Gibson wheels and I think it is essential to minimise the number of times they are removed from and replaced on the axle.
With the hornguides in place, the frames were erected on the jig and the spacers soldered into place:
CSB fulcrums were created by soldering short handrail knobs into the holes drilled earlier and we were ready for the first test of whether the springy beams lined up and were clear of any obstructions:
All was well, so on to the next stage. The lower part of the boiler was rolled to shape, the gearbox was assembled and tried in position:
At this stage, I couldn't resist a sneak preview of the final result, so three wheels were pressed on to axles and, after removing a few small bits of plastic, one of the bodies was placed over the chassis:
The Gibson 4'71/2" GWR P4 wheel is one of those that comes without the pre-drilled hole for the crankpin, so these needed to be drilled. Consistency in the crank throws is an important factor in obtaining smooth running. To get the holes in the right place, a simple jig made from a piece of brass with a 1/8" and a 0.75mm hole at the right centres would suffice but, again, I took the luxury route. With the milling vice loose on the table I clamped a piece of 1/8" rod in the vertical V groove and inserted the other end in a suitable collet. The vice was then clamped to the table and, after removing the rod, offset the table by 3.17 3.34mm to represent the 91/2 10" crank throw*. Then, the pin holes were drilled in each wheel. The wheels were either already mounted on an axle, or on a dummy slightly undersize axle:
Interestingly, the small depressions molded into the wheels were found to be at a slightly larger pitch, so some care was needed in starting the small drill. Another feature of Gibson wheels that's often commented on is the fact that the crankpin holes align at or near the edge of the inner molded boss. Something has to be done here to ensure that the heads of the crankpin screws do not foul the axle bearings and the screws are not forced off centre. Two common solutions are carving away some of the boss with a scalpel or countersinking the holes. I chose the latter approach and this was aided by my setup in the milling machine. I simply countersunk the inner end of the holes using a 2.5mm drill:
Next, the wheels were fitted and quartered. Again this is often presented as one of the arcana of chassis building but is really very simple. First, I pressed the three loose wheels part way on to their axles and aligned the quartering roughly by eye. The cranks on each side do not need to be exactly 90 degrees apart, but the cranks on each axle must all be at the same angle. I took the rear axle as my datum and fitted crankpin bushes to the pins on this and the centre axle, leaving the plain unbushed pins on the front axle. I then fitted the rods and adjusted the wheels on the centre axle until the chassis would roll freely. If you look carefully at the next photo, you should be able to see that there are no bushes on the front pins:
At this point, the rear and centre axles have exactly the same quartering. Then, I put the bushes on the front axle and replaced the rods, adjusting only the front wheels until the chassis would roll freely. Once everything is aligned correctly, the wheels were then pressed fully on to the axles using a b2b gauge to fix their final positions.
As I had only reamed the holes in the rods to be a sliding fit with no slop on the crankpin bushes and was testing without any lubrication, I wasn't surprised to find there was a very slight binding between the rods and bushes. It is very slight, though and I'm confident that with just a touch of the reamer and some oil it will all smooth out. However, as I was running out of time this evening and wanted to get this post finished, I quickly refitted the motor and went for a quick run on the rolling road. It works 
Now all I need to do are the little fiddly bits like the brakes and pickups, and solve the little problems of how to make the underhung springs removeable and how to mount the vacuum pump without fouling the CSB spring 
Then sometime, I must finish the second one and get back to carving off the topfeed and other modifications to the Bachmann body.
Nick
Update 2012-12-03:
CK asked below about other ways of drilling the Gibson wheels. Here's what I would have done if I didn't have the mill. First take a piece of brass about 3mm thick and mark off two points at the crank throw distance, in this case, 1/8" (91/2" full size) 3.34mm (10" full size)*:
The one in the photo is actually a scrap piece of aluminium, but something like the earth pin of a 13A plug would be ideal.
Drill both points at 0.75mm, then open out one to 1/8". If possible, do this in a drill press to ensure the holes are vertical and parallel, otherwise do what you can by hand. Next, take a piece of 1/8" brass rod, put it in a drill chuck and polish it with some emery cloth. The idea here is to reduce the diameter very slightly so that it will be a good sliding fit in the wheel's axle hole. Use as a jig to drill holes. It's maybe a bit tricky to line up when starting but should ensure that the holes are parallel and all the same pitch:
On the back of the wheel, either trim with a scalpel as below then countersink or, when you finished using the drilling jig for the pin holes, open up the smaller hole to around 2.5mm and use as before to countersing the hole.
Update 2013-03-16
* Diligent work by Miss Prism has found that the crank throw should be 10" so I've updated the above to show the correct measurements. Perhaps the dimple in the Gibson wheel is in the correct place? Mine remains half an inch undersize but, hopefully, no one else will be misled...
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