Guide to Fitting by DT
MOUNTING ACCUCRAFT Z2 CHOPPER COUPLINGS
Envisaging having to fit a good quantity of Accucraftcouplings to existing and new rolling stock the requirement for a simple drilling jig and some accessories was recognised. The rolling stock could be a variety of types being built from kits or from scratch. The decision to make the main jig was prompted by the desire to achieve consistent coupling heights without a lot of individual measurements and calculations.
The jig described is one method which has worked but could no doubt be refined further to suit individual tastes and requirements. The main jig allows holes to be drilled for directly mounting the Accucraft couplings to the outer face of the headstocks.
The main jig shown in pictures 1 and 2 was made from a piece of 50 mm x 50 mm aluminium angle sawn square to 70 mm long. Each leg is 4 mm thick. One leg was shortened to 38 mm height.
The longer leg forms the base of the jig which sits directly on the railhead. In this leg are drilled 4 holes 5,0 mm diameter. These holes were spaced so the jig locates snugly between therails of a piece of LGB track by the heads of four M5 capscrews. If track of more scale dimensions is being used M4 or M3 capscrews might have to be used to ensure the jig seats on the railhead.
The five holes in the short leg of the jig are positioned on the same centreline 33,75 mm from the railhead for a scale 2’ 3”. The size of these holes can be varied to suit individual needs.
The outer face of the short leg contacts the headstock of the vehicle.
The single 3,2 mm diameter hole is central to the track gauge. This hole is used to sight the centreline of vehicle headstock and can be used to drill the hole for a central cast buffer if required.
The two holes for mounting the Accucraft couplings are spaced 20 mm apart. These are 2,2 mm diameter to suit 8 BA screws.
The two outermost holes for mounting the side chains are spaced 53 mm apart for a nominal scale 3’ 6”. The size of these holes is determined by the type of side chains being used.
The jig shown has had the short leg reduced in height locally to clear the end framing of some existing rolling stock.
The mounting socket of the Accucraft coupling is quite large. Some adjustments to the design of the model might be required for fitting and appearance if the socket is to be mounted on the inside face of the headstock. Sometimes the floor needs relieving locally to clear the flange of the socket and/or the lower edge of headstock needs to be closer to the railhead for appearance.
The wooden gauge shown in pictures 3 and 4 can help in determining if modifications are required.
Filing the top edge of the mounting flange flush with the socket body can sometimes eliminate the need to modify the vehicle floor. 39,5 mm is the closest the floor can be to the railhead without modifying the floor. If a completed vehicle or a “dry assembly” of the solebars, floor and wheels is placed on the rails and then lifted so the floor is directly above the longer narrow leg of the gauge when lowered the vehicle’s wheels will be in full contact with the rails if no alteration to the floor is required. If the wheels are clear of the rails floor modifications will be required.
The top edge of the shorter broad leg of the gauge is 28 mm above the railhead. If there is a gap between the top of the gauge and the lower edge of the headstock the socket of the Accucraft coupling will protrude below the headstock.
In use the main jig is fitted to a straight section of track as shown in picture 5. If used on a portable workbench the jig can be held in place with a relatively small “G” clamp.
Before loading the vehicle to the track measure the width of the headstock and draw a short vertical pencil line at the centre of the headstock.
Load the vehicle to the track against the short face of the jig as picture 6. If required clamp a stop block to the track at the rear of the vehicle.
Visually align the pencil line in the middle of the jig centre hole. There will a fair amount of play in the vehicle present but once aligned the visual setting will be quite accurate.
Keep the vehicle in place and drill the first coupling mounting hole through the headstock.
Before drilling the second mounting hole fit a spare drill or mounting screw through the jig and the initial hole to maintain alignment.
Drill the second mounting hole followed, if required, by the side chain holes.
Reverse the vehicle and repeat the drilling on the opposite end.
No further drilling is required if the coupling is to be mounted on the outside face of the headstock.
To aid creating the rectangular hole or slot for mounting the coupling socket behind the headstock a steel local drill jig was made. Picture 7 shows the jig fitted in position. The holes in the local jig are for use with the same size drill as the two mounting bolt holes.
The holes are spaced to provide a witness to aid filing the slot or rectangular hole to final size.
Picture 8 shows the initial pencil alignment line as well as the holes produced by the local drill jig.
The rectangular hole in picture 9 was produced by joining the drilled holes with a piercing saw then filing until the witness from the drill diameters just disappeared. Some limited final filing using the socket as a gauge was required. For the wagon shown in the picture a slot open at the bottom would have worked equally well.
Although the coupling socket is of necessity large some resemblance of the prototype mounting has been included by way of a brass surround fitted to the outside face of the headstock.
8 BA x 3/8” long brass countersunk screws were soldered to the rear of the surround plate as picture 10. The holes in the headstock require countersinking for the screws. This was a personal preference to allow future easier dismantling if required. In practice securing the coupling first with separate countersunk screws then gluing the surround plate in place would be a far simpler option.
The surround plates are prototypes from Worsley Works and are shown with the couplings in place in pictures 11 and 12.