7mm The Old Man's Workbench - a new 7mm show beckons

Discussion in 'Area 51' started by Dog Star, 17 August 2012.

  1. Dog Star

    Dog Star Western Thunderer

    For those few who know about life not too far north of the A303, where the first road sign says Exeter "this way", there is no such thing as a normal day or a typical workbench, actually there is no workbench here, just a space of variable size.... and most of the tasks going on seem to be too big to consider as Shelf Queens. This cultivated confusion has given me much trouble in deciding how to provide an insight into railway modelling Shay-Nue... and then I realised that the best way of contributing something to WT was just to write about jobs / tasks / projects which have been completed recently or presented a problem with an interesting solution.

    At this time there are three 7mm layouts under construction:- the permanent way for Hartley Hill is being laid, the baseboards for the Basingstoke Club layout are being constructed and the scenery for Scrufts Junction is making a mess on the floor. Which gets done when often depends upon the weather or who else is in the house.

    Apart from the layouts, there are several S7 projects on the go, from a GER Tram engine through to a GCR 9K and from a Class 37 to a Class 66... with the GWR represented by a Ransome and Rapier 36T Steam Crane. All of those are being built by my son Peter whose modelling projects are more interesting than my focussed ideas.

    What did I achieve today? After reading about Adrian B's fun with CPL crank pin nuts for AGH wheels I have been modifying the CPL version for "Slater's wheels" to fit AGH crank pins. The CPL castings have been tapped at 10BA and some 10BA Nickel Silver studding soldered into the casting. Hey presto - a crank pin nut where a clean and full-form thread runs the length of the screw.

    Too dark for photos now, I shall take some pikkies in the morning and edit this thread to include the images.

    regards, Graham
  2. Dog Star

    Dog Star Western Thunderer

    As promised yesterday here are some photos of the new crank pin nuts for some AGH wheels. CPL can supply cast nickel silver crank pin nuts for Slater's wheels, (hole tapped at 12BA) and for AGH wheels (10BA screw). Adrian B started with the AGH version and found difficulty with getting a good thread form just under the cast "nut". I started with the Slater's version and soldered each nut to a piece of sacrificial brass strip, then the nuts were drilled 1.3mm for tapping 10BA.


    The nuts were removed from the scrap strip and soldered to a 10BA tapping jig to get the new thread at right-angles to the thrust face of the casting. A piece of 1.6mm Nickel Silver rod was threaded 10BA with minimal stock removal, by opening the die as far as possible, to ensure a good fit in the casting. The nut and studding were soldered and finished.


    First crank pin nut in place.


    And from a different angle to show how the result enhances the appearance.


    Finally, the next problem... this crank pin nut is about 20 th thick at the head.... with about the same for clearance to the coupling rod. This fastening is an AGH retainer with a thinned head and being round is a devil to tighten. Somehow I shall have to devise a fastening method which fits within the real estate and is not likely to come undone easily.


    And in case anyone thinks that the method described here is a "neat idea", I am happy to acknowledge that the whole shee-bang was started by Adrian B's comment on a similar task... and helped along in the correct direction by workshop advice from Paul Penn-Sayers.

    regards, Graham
  3. Dikitriki

    Dikitriki Flying Squad

    Hi Graham

    That's a useful addition to the fixing armoury.

    I had even less clearance with my Standard 5 (Shelf Queen no. ......not a clue). I required a totally flush fixing.


    The front retainer is a reversed top hat bearing, tapped 10BA, but the outer coupling rod laminate is filed to only just clear the bearing flange. 2 holes were drilled 0.5mm and a home-made peg spanner tightens it all up. I wish I'd thought of this years ago!


  4. Steph Dale

    Steph Dale Western Thunderer

    Well that's cleared that up then....

    I've long wondered what the difference is between the two types of CPL crankpin nuts. I also know that my technique to re-thread the 'Slater's' ones for 10BA is the way to go for the home-brewed 10BA crankpin system I use normally.

    Incidentally Graham, I don't feel the need for a sacrificial holder, but drill and tap them while they're still on the sprue.

  5. Dog Star

    Dog Star Western Thunderer

    Whilst that would be the ideal, there are a couple of concerns with that approach. I wanted the thread in the nut to run at right angles to the inner face of the nut so that the complete unit presents a thrust face which is parallel to the connecting rod.... I doubt that I could do that if tapping a casting on the sprue. More to the point, the cast nuts are attached to the sprue by a metal section that is probably no more than 15-20th square... the castings fall off of the sprue as soon as any tool gets near the metal.

    regards, Graham
  6. Dog Star

    Dog Star Western Thunderer

    Never mind the front crank pin retainer... how did you produce what has an appearance of a castle nut on the crosshead?
  7. Dikitriki

    Dikitriki Flying Squad

    The gudgeon pin and castle nut is a rather tasty casting from Sanspareil - from my extensive goody bag store.

  8. Dog Star

    Dog Star Western Thunderer

  9. Dog Star

    Dog Star Western Thunderer

    Four out of six done.... leading crank pin nuts still to be sorted. The CPL sprue for GWR crank pin nuts to fit Slater's wheels contains ten castings:-

    (a) two for driving crank pin on outside cylinder engines;
    (b) six for all crank pins of inside cylinder engines and for non-driving crank pins of outside cylinder engines;
    (c) two "top hats" to use as described by Richard above.

    I have not bought the sprue for AGH wheels so I am not sure if the above holds tru for that sprue.

    Here is a photo showing the two different sizes of castings in use on a non-GWR engine. The casting for the driving crank pin is of a larger diameter than the casting for the non-driving cranks. Seems that this cruel photo shows that I need to do some fettling to finish the job.


    regards, Graham
  10. Dog Star

    Dog Star Western Thunderer

    Now for something slightly different...

    Valve gear...

    Of the Gresley conjugated kind.

    Most kits seem to mount the conjugation levers in the frames (fine) and then connect the levers to the front extension of the piston valve rods (fine).... whilst the rear of the piston valve rod is onnected to the valve crosshead and hence the remainder of the motion through to the return crank on the driving crank pin. And then the instructions provide the simple(s) statement of "join front part of piston valve rod to rear part of piston valve rod".

    Unless I am missing something, the "true" length of the piston valve rod may be critical to ensuring that the conjugation levers do not overtravel or bind as the wheels rotate. So, when joining the front and rear piston valve rods (inside the velve chest) where should the LH / RH crank pins be placed and how would the conjugation levers be set?

    thank you and regards, Graham
  11. Rob Pulham

    Rob Pulham Western Thunderer

    Hi Graham,

    They do look very nice and I like others have stored it up for future reference but I have a question.

    I have done similar for both the A3 (with the supplied DJH castings) and with the CPL ones for the J63 but I have screwed the 10BA threaded nut onto a 10BA CS screw which replaces that standard 12BA Slaters offering along with a threaded crank pin bush. DJH supplied a smaller "bolt" casting that I threaded 16BA to join the connecting rods at the knuckle joint and CPL supply those too

    After all that, my question is what are you screwing your modified nut/bolt into? Would you be able to take a shot of all the components from the modified CPL nut/bolt through to the wheel/crank pin/bush so that I can better understand how it all fits together?
  12. Dog Star

    Dog Star Western Thunderer

    Hi Rob,

    I shall have to take the rods off of the engine to show you how the AGH crank pins are constructed.... although I think that Derek Mundy has a similar format for his product.

    The AGH crank pins are a tube with an internal 10BA thread... and an external collar about halfway along the tube. The tube is pressed into the wheel and thereby produces a crank pin. The AGH product includes a 10BA bolt with a plain, round, head to secure the rod - the problem with this design is that the retainer is just a circular flange and very difficult to hold when fitting... and does not look anything like the prototype.

    Now all of this might be academic given that AGH wheels are no longer available.... we have some more wheels for a couple of Cupboard Queens and that is probably that. I wonder if Richard has any in his goody bag?

    regards, Graham
    Rob Pulham likes this.
  13. Dikitriki

    Dikitriki Flying Squad

    He has indeed:)

    A full set for a 9F, drivers for a Patriot and a full set of S7 wheels for a L&Y Highflier which need re-axleing. No tender wheels for any of them.

    I know, I know, why not build the Highflier to S7. Not going to happen.


    Richard Spoors likes this.
  14. Dog Star

    Dog Star Western Thunderer

    Now I understand why you are interested in the piece on crank pin nuts.
    regards, Graham
  15. Rob Pulham

    Rob Pulham Western Thunderer

    Thanks Graham, I had missed the bit about modifying the Slaters to fit AGH.... it all makes sense now:thumbs:
  16. Dog Star

    Dog Star Western Thunderer

    As I said, rather academic unless you have access to Dikitriki's goody Big-Bag. An interesting exercise in making the jigs and fixtures to hold the parts whilst drilling / tapping / soldering and then cleaning... all without any broken drills or fibreglass in the fingers.

  17. Dog Star

    Dog Star Western Thunderer

    Work on the Gresley knitting conjugation gear is taking a rest whilst waiting for supplies from Eileen's Emporium. In the meantimne I am cleaning a Toby Tram in preparation for a coat of paint.

    For such an esoteric subject there seems to be a fair number of these engines from Big Jim in the hands of WTers and the liking of readers for such engines prompts me to pose a couple of questions about construction of the kit.

    [1] the roof can be soldered to the body... a roof which is fixed to a body which is fixed to the footplate would make painting of the interior a difficult task. Anyone any suggestions as to how to "attach" a removable roof to the body?

    [2] the boiler is loose at this time, rather than soldered to the footplate as per the instructions, so as to make painting of the interior as easy as possible. As with the roof, anyone any suggestions as to how to "attach" a removable boiler to the footplate?

    thank you, Graham
  18. Rob Pulham

    Rob Pulham Western Thunderer

    Hi Graham,

    I soldered the boiler to the foot plate but made both the body and the roof removable. The body I made removable by soldering some short pieces of tube below the side window frames tapping them 10ba and screwing up from the chassis into them. You can see them in some of the photos on my build.

    I will have to double check on the roof for you as I cannot remember how I did that...
  19. Rob Pulham

    Rob Pulham Western Thunderer

    Hi Graham,

    The roof I did by fitting the etched ends as close inside the body ends as possible this was further "tightened" by the paint giving a clip in result that takes a bit of getting apart.
  20. Dog Star

    Dog Star Western Thunderer

    Thank you Robin for providing info on how you did the roof of your tram.

    What a pity that Big Jim's instructions do not suggest making the body as a removable item... so much easier for painting the bolier and the interior of the body.

    Unfortunately our tram has the body secured to the footplate and the roof just dropped into place.

    regards, Graham