Building Turnouts using Assembly Jigs
by Bill Blackburn
Drawing by author. Photographs Mark Fielder
Web master's editorial note: This article illustrates the use of 2mm Scale Association components and jigs to construct a turnout. The special jigs and components described are available to members of the 2mm Scale Association.
There is no doubt that the introduction of the new Turnout Construction Jigs is another big step forward for the Association. The jigs and templates are designed to speed up the building of simple standard turnouts to a high degree of accuracy giving every chance of them working properly "first time". If the instructions provided are followed it is impossible to get the dimensions wrong so all we have to worry about is producing neatly soldered joints. The system goes a long way in helping beginners and those who have never been able to quite master point construction and this article is written with these people in mind.
Photo 1. Turnouts under construction (click to enlarge)
Photo2. Various turnout lengths and crossing angles (click to enlarge)
At the moment we can construct left and right hand versions of four plain turnouts based on A5, B6, B7 and B8 geometry. This means 1 in 5, 1 in 6, 1 in 7 and 1 in 8 crossing 'V' angles, i.e.11.3, 9.5, 8.1 and 7.1 degrees respectively. We have chosen to relate the turnouts to their crossing angles (as with the prototypes) rather than calling them for example, 2ft radius. They do in fact very roughly equate to 18", 24", 36" and 48" radius as a guide. The A or B only relates to the length of the planed taper on the point blades of the prototypes.
The system comprises a base plate assembly on which the turnout is constructed and templates which are used as guides to position the rails while they are being soldered to the sleepers. A straight template is provided with the base plate kit while templates specific to the four turnout types are available separately. Instruction sheets are supplied giving lots of information to make things as straightforward as possible.
Base plate preparation.
The base plate assembly comes as a kit of parts. The main component is a block of SRBF which has 2mm wide slots machined into it's face to position the sleepers. It also has a row of M2 tapped holes towards one side. Two holes are provided at the ends to allow it to be screwed down to a larger base if desired.
To prepare the base for use a stop strip which is supplied in the pack has to be attached to the side closest to the row of tapped holes. This is to form an end stop for the sleepers along the straight side of plain turnouts. It can be glued on with Araldite taking great care not to allow the glue to squeeze out into the ends of the slots. Alternatively it can be screwed on by drilling and tapping three or four holes along the edge of the block. When we come to make other types of pointwork it may be useful to be able to temporally remove the strip again. The instructions supplied clearly illustrate the assembly.
So let us work through the construction of a B7 turnout using the template Code 1-265 and following the sheet of instructions supplied with it.
Fig 1. (Click to view full size)
Fig. 1 is taken from the first part of the instructions and tells us that we need a total of 33 sleepers ranging in length from 17 to 29mm. We need five at 17, five at 18 etc. up to just one at 29mm. These can all be cut to length first and the copper surface cleaned thoroughly with a fibre glass scratch brush. The sleepers are then laid in the appropriate slots in the base. The diagram tells us that for a B7 one slot is left empty at the blade end and two are unused at the 'V' end. The picture shows a right hand turnout but of course for a left hand point the shortest sleepers will be on the right.
Either before loading in the sleepers or at this stage the insulation gaps must be cut through the copper surface of each sleeper. These can be cut with a fine triangular Swiss file. Fig 5. indicates where the gaps should have been cut but a full description of turnout insulation, switching and wiring appears in the "Beginners Guide" published by the Association. In fact, the whole section in the "Guide" covering points is well worth reading as turnout anatomy is well illustrated and it becomes clear what these new jigs set out to achieve.
The straight stock rail.
The B7 template is now attached in the position shown in Fig.1 using two of the screws provided in the kit. The straight template (again in the kit) is also screwed on and the straight edges of the two carefully aligned before the all four screws are tightened.
The first rail to attach is the straight stock rail labelled 1 on the diagram. This piece of rail, either plain or bullhead, must be prepared by straightening it if necessary and cleaning it thoroughly with a scratch brush. (This applies to all the rail that we will use). It can now be positioned and held against the straight edges of the templates for soldering.
A useful device for holding the rail can be cut and bent from a paper clip as Fig. 2. Three or four of these will secure the rail and hopefully ensure that it remains upright. You will now have both hands free to manage the soldering iron and some resin cored solder. I use quite fine solder, 24 or 26 SWG as the quantity fed into the joint can be more easily controlled. You can put more on more easily than you can take too much off! I also use a 45 watt iron at 350 degrees C, i.e. plenty of heat to melt the solder and make the joint as rapidly as possible. The idea is to make a blob simulating the outside jaw of a chair and the skill is in getting all the blobs all the same size. It only comes with practise. Some people like to apply a small quantity of liquid flux (e.g. resin) along the outside of the rail. Others find the flux in the solder is quite sufficient.
We have digressed on to the subject of soldering so returning to fixing our straight rail, I find it best to first solder the rail to a sleeper at about the centre of the row and then at about every third sleeper working out toward the ends. As each sleeper is soldered we must ensure that the rail is down on the sleeper surface. The gaps are then filled in over the whole 33 sleepers.
The curved stock rail.
The process is now repeated for the curved stock rail labelled 2 on the diagram. Again we must watch that the rail is firmly down on the sleeper surfaces during the soldering. Using the wire clips, nothing could be easier!
The crossing 'V'.
We must now prepare the two pieces of rail that will form the crossing 'V'. Each has to have an end filed to a wedge shape so that they can be spliced together as in Fig. 3. and thus make the 'V' angle of 8.1 degrees as required for a B7 turnout. It is quite easy to get the angle right as the instructions tell us to file chamfers which are 3,5mm long. This is easily measured. A block of brass or aluminium in the vice will form an anvil and support the rail while it is being filed. Make sure that the taper is square i.e. not tapered across the rail as well as towards the end.
The 'V' can now be soldered to the sleepers. The rail for the straight track labelled 3 is slid into the V formed by the templates as far as it will go. On all turnouts the tip of the 'V' coincides with the edge of a sleeper. The rail for the branch labelled 4 slides in to splice on to the side of the first rail. The two rails can be held by wedging a piece of sleeper strip between them as shown. See that the rails are pressed down. A small amount of Carrs 188 solder paste applied at the tip of the 'V' and between the two rails initially anchors them. A fine soldering iron bit gets between the 'V' to complete the soldering job.
The straight point blade etc.
Now we come to the straight point blade, closure rail and wing, labelled 5, (ref. the "Guide") and we make these all in one piece. The instructions tell us to make this piece of rail 136mm long so we can cut it to length and square off the ends. We have standardised the length of the wing for all points at 14mm so the knuckle bend can now be made with a small pair of flat nosed pliers. Take care to get the bend square and as close as possible to the required 8.1 degrees. It makes life very much easier if we get this angle correct right from the start. I have made a template by drawing lines on a piece of white card. I started with a horizontal line, fixed a datum point and have gone across 7" and up 1". By joining this point back to the datum point it forms the 1 in 7 or 8.1 degree angle. The rail can be laid on the card and the angles compared by eye until we are sure we have got the knuckle bend right.
The 1,75mm long lead at the end of the wing can be tweaked out by a couple of degrees. don't overdo this angle as the rail end only needs to go out by about half the thickness of the rail.
Check again that the end of the blade will be 136 minus 14mm i.e. 122mm from the knuckle bend. We can now file the taper to form the blade. Again our block in the vice makes a good anvil and first a medium cut file and then a fine file will be needed to quickly do the job. The planing will be on the outside of the rail, that is, the same side as the wing. The planed length will vary with the type of point and our instructions tell us it should be 25 - 27mm for a B7. It shouldn't be longer than necessary. The ready milled blades presently available from Shop 1 can be used Code 1-012 plain rail or 1-016 bullhead. I polish the blade after filing with a piece of very fine emery (Halfords 'wet and dry') stuck to a small block of wood.
Fig 4. (Click to view full size)
The main template can now be removed from the base and the position of the straight template moved to its new position as in Fig. 4. Our point blade can be slid in position such that the tip of the blade is just before the third sleeper and the knuckle will be approx. over the edge of the sleeper two away from the nose. The rail should again be held against the straight template with the clips. A .020" feeler is placed between the wing and the 'V' to check that the gap is correct but it shouldn't be far out. The blade position can be adjusted along the template to get the .020" just right but the wing must remain parallel to the 'V' rail. Don't be tempted to splay it out a bit in an attempt to shorten the distance between the knuckle bend and the tip of the 'V'.
The feeler is best made from a piece of insulation material such as SRBP if you can get the thickness. This won't conduct the heat away during soldering. I use a piece of card cut from a breakfast cereal packet as I have found a piece that is just the right thickness. Take a micrometer round Sainsbury's to check which brand is suitable! Customer Service might understand the problem!! Alternatively a strip of brass (Eileen's Emporium) or aluminium which won't take solder can be used.
Once we are happy that all is OK we can solder the rail to the sleepers. The blade end is left unsoldered over a length of 8 or 9 sleepers to allow it to move.
The curved point blade.
The next stage is to make the curved blade/wing rail, labelled 6, in the same way. We are told to make it 0,5mm longer than the straight one to get the blade tips to match. Form the curve roughly to it's correct shape but this isn't critical.
Fig 5. (Click to view full size)
The straight template is now taken off and the curved rail placed in position and located using two or three Association roller gauges Code 1-250. This is shown in Fig. 5. Again fix the gap with the bit of Cornflakes packet, or whatever, and you should find that the two knuckle bends should align side by side. Solder the rail down just like the straight one and it is best to arrange the curve of the rail so that it naturally lies against the straight stock rail.
Insulation gaps have to be cut in the two closure rails in the places shown in Fig. 5. This is best done by threading a piercing saw through the sleepers. The job must be done very gently so the rails are not accidentally bent.
We haven't mentioned the practise of putting in a small set or joggle in the stock rail just ahead of the tip of the point blade. If the end of the point blade is thicker than it might be or if it doesn't lie tight against the stock rail there is the possibility that a wheel flange that is feeling a bit contrary might hit the blade end and ride up. A small joggle allows the end of the blade to hide behind it and hence there is no opportunity for derailment. I would suggest that a blade that is planed wafer thin at the tip doesn't need a joggle. Bullhead prototypes, contrary to what we might expect, are said to have only had a joggle in the curved stock rail although there are plenty of photographs showing one in the straight rail as well.
Fig 6. (Click to view full size)
In our scale, a joggle doesn't need to be more than about .005" as shown in Fig. 6. Oversize joggles ruin the appearance of an otherwise perfect turnout. If they are going to be put in they are best made with a small pair of flat nosed pliers before the stock rails are soldered on to the sleepers. Fortunately, with our system, we can accurately predict at the start that they will lie half way between the second and third sleepers. Joggled stock clearly rails won't sit close against the template over the third and probably the fourth sleepers when we come to solder but this slight local 'gauge widening' is, after all, the point of the exercise.
The check Rails
The check rails, labelled 7 and 8, can be cut to the standardised 26mm long and the 1,75mm lead tweaked inwards to match the amount on the wing rails. We can sandwich the .020" shim between the check and stock rails while the soldering is going on and providing the gap is really .020" no adjustment will be necessary. A wagon should run through the crossing faultlessly first time. Surely, no-one will be able to get it wrong!!
Fig 7. (Click to view full size)
A useful clip to hold the check rails can be made from plain rail providing the rail is a true .020" thick. Fig 7 shows the idea. You need seven pieces of rail soldered together side by side with the outer ones bent forwards and backwards to allow the device to stand up. You need two of these. They clip over the rails neatly gauging and retaining the check at the same time. Should the rail be a bit undersize as mine was, you just solder the two outer sleepers first and then with the clips removed, one end at a time, we soften the solder again slipping in a correct .020" gauge to make the correction.
The tie bar.
We are now only left with the installation of a tie bar. Much has been written about tie bars and many designs have been put forward. For a beginner, I suggest that a moving sleeper, in our case the third sleeper, will get us 'off the ground'. If the sleeper is to be attached to the blades while the turnout is still in the jig, it should be slimmed down by a few thou' to make it slide easily in the slot. It will probably have been left out at the beginning to prevent it being soldered accidentally to the stock rails. It can now be slipped in under the rails and pushed up to the end stop.
An 'L' shaped shim of aluminium cooking foil is slipped under the straight stock rail and sandwiched behind the curved blade as it (the blade) is held firmly over against the stock rail. The blade can now be soldered to the moving sleeper. Take care to leave the upper half of the blade free from solder to be clear of a passing wheel flange. The foil prevents the solder running to where it isn't wanted and fixing the whole lot solid! Move the sleeper away from it's stop by about .030" and insert a spacer (a sleeper, maybe) behind the now attached blade. The straight blade can now be held against the curved stock rail interposing another piece of aluminium foil and soldered to the sleeper in the same way. Remove the cooking foil and all is finished!
The completed turnout can be removed from the jig by carefully inserting a pointed scalpel under the rail and levering up thus lifting the sleepers from their slots. Work along each side lifting a little at a time.
If it has taken you about half an hour to read this article then read it all over again now. The total time that you will have then spent reading is all it should take you to build a complete turnout from scratch!