Tuesday, 13 November 2018

November 2018 Meeting

This month we held part 1 of our planned locomotive workshop on converting a Dapol Terrier to 2mm finescale (that is the chassis).

Before we got under way there was time to admire Keith's point work for a fiddle yard. This is constructed with flat bottom track soldered directly onto a PCB board, with the necessary electrical isolation cuts. This method would suit embedded track for an industrial or dockside setting.

Dapol Terrier conversion, Part 1

The replacement chassis etch and items from the parts list were obtained from the 2mmAssociation shop 3, with a few added components suggested by Keith and Alan. A couple of useful supporting documents can be found on the 2mm Association website; Etched replacement chassis for RTR loco bodies, includes parts list and generic illustrated instructions for several locos (including the Terrier). A specific etch diagram and chassis arrangement for the Terrier is here. Both documents are downloadable PDFs.

The Terrier etch and diagram, chassis arrangement and the sacrificial Dapol Terrier

Starting off; Keith was careful to explain the point at which we should begin is the accurate positioning of the axles. At this point we ignored the frame assembly jig as it is possible for this to become distorted, instead using the coupling rods for accuracy.

The etch and a block of 'synthetic resin bonded paper'

First Keith tinned the fold-over coupling rods without removing them from the etch.

(left) Using the block of 'synthetic resin bonded paper' he marked out a line and positioned one end of the coupling rods on the etch onto the line and using a .5 drill to insert a .5 locating pin all three axle positions.

Satisfied the coupling rods were accurately located onto all three pins, both coupling rods were removed from the etch...

...then folded and the three layers sweated together and tested again on the pins (below)...

...resulting in the the completed coupling rods.

The next stage was to build the Frame Assembly Jig, cut from the etch.

The sides and ends were folded up to form the box, checked for square and the tabs were soldered in position (below)

(this picture shows Keith using his own jig to hold the etched frame assembly jig square whilst soldering the tabs, note the axes are also in position)

This picture shows the 1.5mm axle steels in place which have been drilled to take .5 crank pins enabling the coupling rods to be checked again.

End of part1; many thanks to Keith

In case it helps fill in any gaps, included are sketched notes below.

Loco of the month is the Terrier!


  1. A really useful post. The problem I came across when building one of these chassis was that the brake pull rods are to scale for a Terrier, unfortunately the crank throw on 2mm wheels is too great and the coupling rods clout them!!
    I will be interested to see how you get round that.


    1. There is a small etch of replacement brakes on the way. Unfortunately I don't have production quantities yet.


  2. I found the con-rod bosses made the crank pin fixings foul the steps, so I removed the bosses to get just enough clearance.

  3. Not entirely convinced by 'the jig can be distorted' argument TBH. But as its deigner you might expect that.

    The key to its stability is the U channel formed by folding up the two sides from the base. If this is done with a folding tool and the sides end up aquare to the base this should not really distort to any noticeable degree.

    If you are concerned by the parts distorting whilst soldering the tabs of the ends into the slots in the side, I would suggest that filing off the tabs and soldering the corners as butt joints should address that issue in a simple manner.

    Having said all of that, you now have one accurate jig that you can use to assemble all of your Terrier chassis. No need for you all to build one!

    1. Not sure why i am coming up as 'unknown'.

      Chris Higgs

  4. Chris
    You are absolutely right, assembly jig will form up into square unit, it is just possible to twist it slightly and someone will find a way to do so. I was trying highlight the benefit of insuring axles are all parallel in vertical and horizontal planes to reduce the margins of error we can build in. I find that proving that jig and coupling rods work together helps in process of making chassis work.
    Jerry is right, coupling rods do clout brake rods, easiest option was to lower brake rods which just about works on original Dapol gear, yet to try etched version, we shall find out later. Another alternative is to reset crankpin throw to 1.5mm as prototype, but that means plugging existing crankpin hole and drilling new. Not everyone's cup of tea!


    1. If you clever boffins over in Essex come up with a jig which will reliably reset the crankpin throw to 1.5mm I will send you a set of wheels....... :-)) otherwise I will wait for the replacement brake etches.