7mm The Old Man's Workbench - tales of a rivet side

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 our railway modelling ... 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.

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.

regards, Graham
 
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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 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.

cpin-1.jpg

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.

cpin-2.jpg

First crank pin nut in place.

cpin-3.jpg

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

cpin-4.jpg

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.

cpin-5.jpg


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's comment on a similar task... and helped along by workshop advice from Paul Penn-Sayers.

regards, Graham
 
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Dikitriki

Flying Squad
Somehow I shall have to devise a fastening method which fits within the real estate and is not likely to come undone easily.


regards, Graham

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.

chassis4.jpg

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!

Regards

Richard
 

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.

Steph
 

Dog Star

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

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
 

Dikitriki

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

Richard
 

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 AGH sprue so I am not sure if the above holds true 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.

cpin.jpg

regards, Graham
 
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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
 

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?
 

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
 

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.

Cheers

Richard
 

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.

Graham
 

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
 

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...
 

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.
 

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
 

Rob Pulham

Western Thunderer
That's a shame, but I wonder could you get away with painting the boiler with acrylics and then soldering it in from the underneath before painting the under side of the body.

I ask this, as I had painted the tender (with Halfords acrylic primer and Railmatch Acrylic Doncaster green) on the A4 when I discovered that I had soldered the wrong buffers on and had to remove them. After failing miserably with the soldering iron I heated it up with the microflame and removed one set of buffers and put on the correct ones without marking the paintwork - I was expecting a partial repaint at the very least.
 

Dog Star

Western Thunderer
Earlier in this wandering thread I posed a question (post no.#10) about the arrangement of the outside piston valve spindles in the Finney A4 kit... and I guess that the question is as applicable to the A3 and V2 kits as to the A4 kit. After sleeping on this question for a while I think that a different and related question might be easier to answer.

The Finney instructions do not provide dimensions for the length of the front and back portions of the outside piston valve spindles (including the fork)... similarly there is no dimension for the gap between the front and back portions when joining those parts with the 0.8mm wire "U" shape (as in Fig.9 of the A4 instructions). This lack of dimensions is the root of my concern about setting up of the conjugation gear.

Scaling from drawings, especially from those which are not dimensioned or from those which are photocopies, is not a good thing... generally. In this case placing the assembled cylinder casing / slidebars / slidebar bracket over the appropriate drawing in the kit shows that the drawings are very close to 7mm scale (the discrepancy over the longest length of the assembly quoted is 1mm in 100mm). This closeness to "scale" suggests that I could start by making the front part of the outside piston valve spindle to the same length as the (un-dimensioned) drawing... and similarly for the rear portion.... and then set the parts apart by the gap shown in "Fig.9".

There are several WT-readers who have built models of prototypes with Gresley conjugated gear... and some of those models are built from Finney kits (Richard and Christian with A3s at least). If you have built these sort of models... how did you decide on the length of the 1.4mm wire when making the front / rear parts of the piston valve spindles?

Whilst our model is being made from a Finney kit, it is possible that the DJH kits might have a similar approach in this area.... so what did you do with your A3 Robin?

thank you, Graham
 
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