7mm Dikitriki's Dark side: A WD 2-8-0

[mickoo]

Graham, I think that taper pin goes right through the crank and I think there will be a groove on the square shaft to accept this and stop the crank from coming off the shaft, much as the pinch bolt does the same, IE there being two methods of making sure the crank does not fall off the crank. Bolts fail, mainly through constant stretching and tightening, the pin does not suffer the same stretching, so I suspect that the pin is the failsafe fitting in case the bolt shears off.
I would expect the pin to have some sort of retention on its narrow taper end, a split pin or something but that photo does not seem to show anything of the sort, I'd hate to rely on the taper friction alone to hold that pin in place.

A photo of the crank pin minus the return crank will explain all, I'll see if I have a photo of that part somewhere later this evening, and yes Richard does need to start his A4...to give me some inspiration to get 'one' of my ever expanding list of projects going LOL.

Kindest

 

[Dog Star]

Mick, your thoughts on the reason for the taper pin as an additional retention device makes sense.

 

[alcazar]

I dreamed about return cranks last night.........I made one with a square shaft in it and a scale pinch bolt!

 

[Dog Star]

I made one with a square shaft in it and a scale pinch bolt!

OOoohh, aaahh. Photo please!

 

[mickoo]

Just for closure, found these of an A3 return crank shaft, clearly seen are the two grooves in the square shaft for the pin and pinch bolt.




Originals and authors pages found here
http://www.flickr.com/photos/jwright/4598627225/sizes/o/in/photostream/
http://www.flickr.com/photos/the_jon_m/7433772184/sizes/o/in/photostream/

 

[Dikitriki]

Wow, what a fantastic mine of information

 

[Simon Dunkley]

Wow, what a fantastic mine of information

It's even got your initials on it...

 

[mickoo]

Wow, what a fantastic mine of information

I'm glad you think so, didn't want to dilute your thread too much. I'm looking for some decent drawings of LNER 6' 8" wheels as I may CAD them and 3D print one for casting a large scale static model, little point paying £4-500+ for wheels on a loco that will never move.

Kindest

 

[alcazar]

I didn't ACTUALLY make one, but I had the idea of taking a small piece of SQUARE steel bar, drilling and tapping it , say 10/12BA, and using the threaded crankpin to screw into it. It could be fixed in place with loctite? And then you'd have a prototypical looking fixing which pointed the right way too, and wouldn't slip......

 

[Dog Star]

If you think that your idea might work, how about a sketch of the design?

 

[alcazar]

I'll see what I can do. It would need a piece of plain bearing beneath it for the coupling and connecting rods to turn on.

Got to take the eldest to uni at Loughborough in half an hours, maybe later.

 

[mickoo]

Just for Richard as I can see he likes his details , A4 return crank in detail.



Original here and copyright to said owner http://www.flickr.com/photos/jimoftheday/7833559444/sizes/k/in/pool-363419@N24/

I see 60009 was on the TT at NRM at the weekend <bang head> bet they don't put it on a road where you can photo walkaround! But Mallard is now out of the paint shop, resplendent in a new coat of paint.

 

[Dikitriki]

Right, onwards with Lady Godiva....

Tiny step back this week. I discovered that the bespoke crank pin bearings that I had been forced to work with (I say forced because the holes in the rods are sized for them) had been fabricated and not machined. I was tapping the leading one 10BA when the flange came off. A close inspection then showed that they had all been made from thick walled brass tube with a washer soldered on the end.

I wasn't prepared to trust my model to that so I made up another bespoke set on the lathe. I don't often get to do any lathe work, but it was really satisfying to make something up from raw materials. I feel a scratchbuild coming on when I get the pantograph miller working!

I then turned my attention to the crossheads. The basic crosshead is, well, basic, but useable and just needs tidying up. I did file off the gudgeon pin which seemed to be a cast in nut and washer, to replace it with a DJB castle nut pin (Laurie Griffin has just released his own casting for these, describing them as coupling rod pins). The drop link is an MOK 80000 spare I think.

The pic is self-explanatory...



Richard

 

[Dog Star]

Come on Richard, where is the cotter for the piston rod? You know you can.... and the split cotter on the reverse side... of course you can!

 

[Dog Star]

I did file off the gudgeon pin... to replace it with a DJB castle nut pin.... . The drop link is an MOK 80000 spare I think.

Sometimes I do wonder about the size of your spares box .

 

[Dikitriki]

 

[dibateg]

I've spotted something missing Richard - representations of all the big hammer marks on the prototype components!

 

[Dog Star]

I've spotted something missing Richard - representations of all the big hammer marks on the prototype components!

Now then, now then.... you cannot have the hammer marks on the crosshead until Richard has installed the cotter for the hammer to hit - or, more appropriately, to miss! .

In passing, I am not surprised that the crossheads got some much of a battering given how tight those cotters could be. In the past I have removed slidebars to rotate a crosshead just so that I could get a decent hammer swing onto the end of the cotter... and then had to draw file to cotter for my sins.

regards, Graham.

 

[Dikitriki]

Graham

Using one of Mick's Jubilee photos, is the thing in the centre of the following photo what you are referring to?



Richard

 

[Dikitriki]

Come on Richard, where is the cotter for the piston rod? You know you can.... and the split cotter on the reverse side... of course you can!

'Course I can........



and no, only on this side!

Richard