Building a Caledonian Pug in S Scale

JimG

Western Thunderer
Here's a blast from the past - almost nine years on and the Beetlecrusher pokes above the parapets again. :)

The Caledonian 498 class tank loco was designed by McIntosh for a specific task. It was to deal with the working of the freight in and out of Braby's Eclipse works near St.Rollox. I suspect that there was a combination of tight radii and gradients which precluded using larger 0-6-0 tanks, and the smaller Neilsen/Drummond 0-4-0 tanks were probably not quite up to the job. So McIntosh produced a very compact 0-6-0 tank with small drivers and a short wheelbase, but with a tractive effort nearly equal to the larger 0-6-0 tanks. He only had two built - one was kept around St. Rollox for the Braby work, and the other went to Grangemouth docks. The pugs were known as the "Braby Pugs". But a few years later, McIntosh's successor, Pickersgill, built another twenty-one for use in dockyards. They all came in to BR ownership and lasted up to 1962. Railway enthusiasts coined the nickname "Beetlecrushers". :)

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This is one of the class in early LMS livery - the picture is from the late Jim MacIntosh's collection.

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...and here's a reminder of all the bits produced nine years ago, top to bottom: slide bars, cylinder parts, coupling rods and wheels. I also got the High Level gearbox with motor to power the loco. So they've had a good few years to mature. :)

I opted to use a scale thickness of frame material - 0.015" nickel silver which is actually a thou under scale.

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The frames being cut out. I actually did them again since I started with a 1mm cutter which had seen better days - you can see the rough edge round the cuts. A second set was cut with a new, sharp cutter. :)

Since I acquired a 3D printer a few years ago, I've thought of one way of using it in loco construction and that is to 3D print frame spacers. In S scale we like to use split axle/frame pickup and resin printed frame spacers are ideal to achieve that end.

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So a couple of spacers were drawn and printed for each end of the frames. No official drawings of the class have survived and the only drawing I could source was a Skinley drawing which has no between frames detailing at all. So no Mick Davies quality prints here. :)

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The frames and their spacers before assemble...

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...and the parts assembled. The spacers have small lips on the tops and ends to provide insulation from the loco body and buffer beams.

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14BA countersunk screws are used to hold things together. Pilot holes for screws were drilled at the CNC stage and these are opened out to 0.8mm tapping size for 14BA to use as guides for drilling the tapping holes in the resin spacers. The spacer holes are then tapped and the screw holes in the frames are opened out to 1mm clearance for the screws and also countersunk. At the moment I've only done one screw on each side of each spacer just to hold things together. The countersunk screws hasn't quite fully bedded since the tapped hole in the resin needs just a whiff of the countersink cutter since the 0.015" frame material is just a bit thin for the 14BA countersink.

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The next use of the 3D printer is to produce hornguides. I am interested to see how well brass bearings work in the resin guides. It could be OK with a small touch of grease to help matters.

The next job is to fit all the screws and see how firm the chassis is. At the moment it can be twisted a bit and the addition of the other screws should firm it up. I also know that there should be a spacer in the middle but I'm waiting to see what space the motor and gearbox takes up driving on to the rear axle before I draw up that spacer.

Jim.
 

JimG

Western Thunderer
The next job was to make up the axles for split insulation. I know there are several ways to make split axles but I still prefer the basic way of making separate axle parts with spigots and bores, held in place with Araldite.

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The first job was to make the gearbox axle, in three parts so that the central section is insulated to keep the gearbox frame insulated. The three parts of the axle are at the top with spigots on the outer parts and a hole bored though the central part. The spigots are 1.5mm diameter and the bore through the central part is 2mm giving 0.25mm clearance for the Araldite. The tool below is a special "V" block which I machined up to hold the axles. I've shown 5 minute Araldite which I chose by accident. I actually prefer the 24 hour version for this work which I changed to. Both types have the same colouring of the tubes which was the cause of my initial wrong choice. :)

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The central axe in the "V" block and clamped in place. There's a strip of paper under the axle in case a stray bit of Araldite gets between the axle and the block. It does get quite liquid, even at room temperatures. After about eight hours, the Araldite starts to harden and I release the axle from the clamp and remove the paper and any excess Araldite with a craft blade, then re-clamp the axle for another sixteen hours until the Araldite is fully hardened.

Next were the other two axles - each made in two parts.

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...with the spigot and bore sizes the same as the three part axle. The turned wooden skewer bottom right is to help push the Araldite into the bores in the axles.

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...and the axles clamped up with paper underneath them. All the axle bores have a clearance hole which allows excess Araldite to escape when the axles are being assembled. These holes also provide keys for the Araldite. The spigots on the other parts have notches filed on them to provide additional keying.

The next job was to machine up some axleboxes. I was looking for 3.5mm thick brass and didn't have any around, so I dug them out of the sheet of 6.3mm brass I had used for the 1:32 scale drivers I made a year or two ago.

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This is part way through the milling process - digging in a brass pit. :)

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...and then result is here in the foreground. The High level gearbox on the right has its axle fitted. Behind are sthree sets of 3D printed hornguides - each to a slightly different width until I got a set to fit the bearings. The first set made were slightly under width, the second set, at +0.1mm were just too loose, and the third set at +0.05mm were just right - a bit of Goldilocks machining. :)

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A closer shot of the gearbox with the insulation just outside the gearbox bearings. I had to turn up a small collar, just to the right of the worm wheel, to take out the 2mm lateral play in the axle.

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A closer shot of bearings. The flat "V" shapings on the inner sides are to provide point contacts for the CSB spring wires. The small holes are to provide sockets for wiring for current collection - the one hangup with using resin hornguides. :)


Jim.
 

michael mott

Western Thunderer
Jim I had to go back to read the beginning of this thread, all I can say is Wow! You are doing an amazing job with the loco.

Michael
 
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