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If you are building a loco kit, getting it to run is the main worry, and it is a valid anxiety because a model that runs badly is very demotivating. An Avonside jig is a something to consider if you decide to build a few locos because, correctly used, it eliminates a number of basic variables in chassis construction. It is quite expensive, about the price of a typical 7mm etched loco kit, but you only need buy one and you are set up for the rest of your hobby life.

The Avonside Jig makes building a successful chassis much easier. A chassis has to be square in all three dimensions, all the wheels should be on the track whether the chassis is rigid, compensated or sprung, and the coupling rod crank pin bearings must be spaced exactly the same as the axle centres. Other things to do with the wheels, the electrical pick up, the motor and gears have also to be right, but essentially the chassis structure must follow the rules above or you’re wasting your time. The Avonside Works Chassis2 Pro addresses all of these requirements and if used with care will result in perfect chassis structures every time.

The core of the device is a platform that contains adjustable sliders into which turned axle alignment pins are screwed so that they pass vertically through a slot in the platform. Short axle alignment pins are supplied for setting up the frames using the rods, and long pins for assembling the frames in the chassis. The sliders are below the platform and are moved by rotating threaded rods from the end of the jig. These are adjusted so that the coupling rods fit over the turned down ends of the shorter spacers and then the sliders are secured with bolts so that the axle pins are at exactly the same spacing as the coupling rods and are exactly in line. The instructions come on a CD that includes a file of photos, some written instructions with clear diagrams of all the component parts of the jig, and a video of the jig in use.

The unit is supplied in a rigid plastic case which stores everything safely together when not in use. The chassis I built is for a Midland Railway Johnson 3130 class 0-6-0 from a former Fourtrack Models kit now marketed by Dragon Models. The first parts of any chassis to be built are the coupling rods because they are used to set up the jig. The rods were laminated together and arranged to flex in the prototype way using a joint next to the centre crank pin hole. During assembly you can potentially make one rod a bit longer than the other. This is not a good thing, but the jig can be used to set up the rods by fitting them over the alignment pins as you work on them.

The jig is useful for setting up a chassis whatever the suspension option you choose. The simplest option is completely rigid axles which have the advantage that the wheels only move round, not up or down and the coupling rods do not need to be jointed or flexible. This is a robust and straightforward system and has been used effectively on many models.

The disadvantage can be if slow running is required and/or the track is not too level, causing electrical pick up problems. There is a whole range of options to make wheels move up and down to ensure that they make maximum contact with the track.

They vary from giving the centre driver some movement up and down - with the other wheels rigid, to compensation where some wheels move but are controlled by pivots and beams, right up to fully sprung chassis. Or you can make a combination of springing, rigid and compensation – the common objective of all of this is to keep the wheels on the track, mainly to ensure good electrical pick up. The Avonside jig enables all of these things to be done or at least avoids some of the inaccuracies that can cause the downfall of good running.

With the jig set up I could move onto locating the bearings in the frames. I first tried out the jig with the original holes in the chassis without any option to move a bearing up or down. If you are using the jig in this way you must first make sure the pins are absolutely in line by pushing the sliding fence (the long silver bit that goes along the jig and has calibrations on it) up to the alignment pins and make sure it touches all of them at the same time.

The jig, alignment pins and clamps

It may seem obvious but first ensure that the bearings fit in the holes in the chassis prior to fitting them on the jig. In other words, are the holes in the chassis big enough? If when in the jig they refuse to fit in the frames even though they did when you tested them, you have to file the holes in the chassis until they will fit. Do not make any adjustments to the alignment pins. To ensure the chassis sits level with the track, its top edge is pushed against the sliding fence, which is then screwed down. To ensure that both sides of the chassis are the same and the axles are not further forward on one side than the other, an end stop is provided to stop the chassis moving along the jig.

The chassis side is then clamped in place using some special clamps provided with the jig. I found them a bit of a fiddle to fit but they stop anything moving about. A slight problem was that the bearings sit on the base of the jig but cause the frames to be lifted by about 1mm offering the potential of the sides not being square to the bearings. However if the clamps are located in line with and close to the bearings, the chassis is forced equally onto the bearing flanges and stays level – but keep an eye out for this. When everything is secure the bearings can be soldered into place, and the other side of the chassis treated in the same way but using the opposite sliding fence.

As I was going to make the chassis flexible I only soldered the rear bearing in place. I removed the frames from the jig and turned my attention to the other four bearings. Sliding horn-guide assemblies are available commercially from a number of sources and the Avonside jig can be used with any of them. I usually simply elongate the holes in the frames at the top and bottom and secure the bearing with a length of wire soldered to the frame at one end and the top of the bearing at the other, this also acts as a light spring. The main consideration is to get the sliding fence in the right place to ensure a level chassis, so once you have set it up the first time mark its position on the end fence using a pencil.

Put the bearings over the two front alignment pins and position the sliding fence by using the pencil marks on the ends of the jig. When everything is set up, with the frames in place, solder the bearings to the wire bearing springs, or if you are using horn-guides attach them to the frame. Then lift the frame out of the jig and do the same to the other side using the opposite side fence. You now have two complete side frames ready for assembly – just check that the bearings move freely up and down.

The Avonside jig makes assembling the chassis easy and I did the whole thing in about forty minutes which is good considering I spent ages checking everything about ten times. First I unscrewed the short alignment pins and replaced them with the long pins that will fit right across the chassis. I then fitted the vertical fence. The vertical fence is a long L section strip that sits on top of the side fence and is fixed by the same bolts. By lining its vertical face with the edge of the side fence, the top of both sides of the chassis are lined up with each other so that they are exactly parallel.

I used the long pins and the vertical fence to locate both sides of the chassis onto their spacers. Make sure that any tab and slots engage fully into each other and that the spacers are in contact with the frames at all points. Check that the frames are parallel in a vertical direction - and you can solder them in place to both sides of the chassis – job done. However I also used the jig to ensure that the fixed compensation beam over the front axle was located in the right place, touching the centre of the axle and holding it at the right height. You have to make suitable holes in the frame spacers and slot the beam in them and hold it onto the alignment pin while you solder the ends into the holes. The vertical fence holds the chassis in the correct position while you do this.

Theoretically the job of the Avonside jig was now over but I left it set up for this chassis while I went to the next stage – getting things running. After all, if in a panic stricken moment I had upset the chassis while tinkering about with it, all I had to do was pop it back in the jig and re-fix the offending component.

I must say that the Avonside jig delivers what it says on the can. It is a luxury item but as with all good tools it removes to some extent the level of uncertainty. You don’t need a jig to build a chassis that runs well, but there is a sort of easy professionalism about using such a sophisticated and accurate tool. So if you have got the loco kit building bug, consider investing in an Avonside Works Chassis2 Pro jig. Alternatively if you are in a club, have a word with the committee about buying one for common use.