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

[Dog Star]

is the thing in the centre of the following photo what you are referring to?

Yes Richard. The end of the piston rod which goes into the crosshead is generally on a taper and the cotter draws the rod home... hence why the cotter is such a b****er to remove. The Finney A3/A4 crosshead has the head of a cotter cast in... on both sides so that the casting can be either a LH or a RH fitting.

regards, Graham

 

[Dikitriki]

Thanks Graham. One day I'll know what I'm doing.

OK, I might as well finish off the return crank story. Graham asked earlier what was the procedure for fitting the rods, and at the time I didn't know! Well, I do now....



The crank pin is a 12BA bolt. From the wheel, it's top hat bearing, coupling rod, top hat bearing, connecting rod, washer over the bearing to keep the connecting rod away from the back of the return crank, then the return crank screwed on. The 12 BA rod protruding through the last bearing must be entirely contained within the bearing and thicker laminate of the return crank.



All screwed up, and you can see that there is plenty of clearance between the rods, and more particularly between the back of the return crank and the front of the connecting rod.

And side on to show where I am up to at the moment.



The crosshead cotter is noticeable I'm pleased to say. The return crank is screwed on to that position against the bearings, and does not need any Threadlock or similar. There is a few degrees movement either way before it becomes too tight or too loose. I have also tidied up the previously painted wheels and removed, cleaned up and refixed the balance weights, 2 of which were incorrectly positioned.

I'm sort of dotting around from area to area, but that's typical of my modelling. Back to the valve crossheads and making the slides next....probably.

Richard

 

[Dog Star]

Thank you for the photos and explanation of how the rods and return crank "fit" on the driving axle. I do like the appearance of the crank. The cotter is visible on the Good Lady's steed.... you may wish to compare the photo of the model with the photo of a real thing (earlier in the thread).

 

[Dikitriki]

Hi

Graham is concerned that I may have dropped a clanger in that I have inserted my crosshead cotter from below the piston rod, rather than from above as on the Jubilee picture. However, I spotted this anomaly at an early stage, and after studying all my photos came to the inescapable conclusion that the original Patriots had them inserted from below as I have modelled it. It's very difficult finding decent photos, but this one seems pretty clear.

http://www.davidheyscollection.com/userimages/00000-a-ja-coltas-5536-crewe.jpg

Phew!

Richard

 

[Dog Star]

Graham is concerned that I may have dropped a clanger in that I have inserted my crosshead cotter from below the piston rod, rather than from above as on the Jubilee picture. However, I spotted this anomaly at an early stage, and after studying all my photos came to the inescapable conclusion that the original Patriots had them inserted from below as I have modelled it. It's very difficult finding decent photos, but this one seems pretty clear.
http://www.davidheyscollection.com/userimages/00000-a-ja-coltas-5536-crewe.jpg

Quite.
Well done Richard for finding a photo to demonstrate what is "unexpected". Given that driving the cotter home would have been difficult in the situation as shown in the photo I would be quite interested to know how the crosshead was fitted and fitted tightly. Anyone got a drawing of the crosshead assembly?

regards, Graham

 

[Dikitriki]

Hi

Found a better photo...

http://railway-photography.smugmug....90932_s2t2bj#!i=1441141284&k=87Lg7v8&lb=1&s=O

 

[Dog Star]

"I am amazed at the depth of research to which some people will go.... ". My apologies that I am (mis-)quoting from one of Richard's posts of yonks ago, just pleased to return the compliment - .

 

[Dikitriki]

Hi

Today it's the valve crossheads and guides.

I like to put my larger tender locos in forward gear - I like the movement imparted to the radius rod, and just dumping it in mid-gear feels like cheating. Something like the Fairburn I made fully reversible and that will be servo controlled in due course. The Patriot will 99.9% of the time be running forward, and will not engage in shunting, so I am happy to lock it in forward gear.

As with most kits, the designer assumes you will not want to go to this sort of trouble, so the valve guide has no actual guides - it's just a flat inside face, giving no support to the valve crosshead. So that's the first thing to do.

I used 1mm square brass bar, annealed and bent round to give parallel guides.



These are adjusted so that they can be gently sprung and retained inside the kit 'guides' so....



The position is adjusted until correct, and they are then soldered into place and trimmed off flush either end.



The gap in the middle is enlarged until the combination lever is free to move within it, leaving the valve crosshead to sit nicely on the guides. Note also from the last picture that the gap for the combination lever is outside the slidebars which means there is no need to kink the combination lever.

Something I note that Sette Models had to do on their Patriot - and they got the crosshead cotter in the wrong place too (I now know!).

Richard

 

[Dog Star]

Something I note that Sette Models had to do on their Patriot - and they got the crosshead cotter in the wrong place too (I now know!).

Enjoy the feeling that your model is correct.

 

[mickoo]

Fowler Crosshead cotters are below, Stanier crosshead cotters are above

Photo from my collection, author unknown


Crop from drawing D42-16418 copyright Wild swan publications, LMS Derby.


Note crosshead drawing is Stanier variant fitted on refurbishment to Royal Scots and one presumes likewise to rebuilt Patriots and maywell be a modified Fowler original as it differs from pure Stanier designed and built locos.

 

[Dikitriki]

Lovely photo Mick.

You don't happen to have any of Lady Godiva or of the backhead do you?

Richard

 

[mickoo]

Lady Godiva yes, backhead, you'll be lucky but I'll skim through all my books and mags, can't recall seeing one off the top of my head though.

Will sort this afternoon after F1 GP for you.

 

[Dog Star]

Thank you for the extract from a LMS drawing - my reading of the drawing is that the cotter is inserted from the outside and above the centre line... just as I would expect given the need to pull the taper of the piston rod home when the cotter is driven into the crosshead.

There appears to be a bolt fitted just below the piston rod... is this a filler plug for an oil reservoir in the bottom of the crosshead?

regards, Graham

 

[Dikitriki]

Hi

Before I can go too much further on the valve gear, I have to look at what I am going to hang it from. The kit design assumes that you solder the slidebars to the slidebar brackets, and have one unit - cylinders, slidebar support bracket and valve gear support bracket - that you can screw in place. That immediately causes a problem as the valve crosshead and spindle are forever locked in place as on the original Patriots, the valve crosshead guides are not attached to the back of the cylinders, but to the front of the slidebar support brackets.

Ist step then is to make this 2 separate units, the cylinders and slidebars as one, and the slidebar support brackets, valve crosshead guides and valve gear support brackets as the second. This means adding a bracket to the front of the slidebar support brackets and a mounting on the chassis so this latter unit can be screwed in with 4 bolts.



You can also see in the following picture how I am going to mount the expansion link. I soldered a 12 BA nut on the inside, and then trimmed a 12 BA bolt such that when it is screwed home against the nut, it does not contact the bearing cover plate soldered to the outside of the supports.





Once this unit and the cylinder unit are screwed in place, I can look at the fitting of the valve crosshead and combination lever...... and run into a problem......

Richard

 

[Dog Star]

What is the benefit to you of separating the cylinders from the motion brackets?

To take advantage of such a separation there must be a removable joint between the piston valve spindle and the return crank.... where will you make such a joint?

regards, Graham

 

[Dikitriki]

What is the benefit to you of separating the cylinders from the motion brackets?

To enable me to remove the valve cross head and spindle, and thence the rest of the valve gear. As a bonus, it will make painting easier

To take advantage of such a separation there must be a removable joint between the piston valve spindle and the return crank.... where will you make such a joint?

You are correct. The joint will be between the radius rod and the combination lever. The valve gear will be in 2 parts - the crosshead, drop link, union link, combination lever and valve crosshead and spindle; and the radius rod, reversing arms, expansion link, eccentric rod and return crank. It will be removed from the model by separating the cylinder unit and the support bracket unit, separating the combination lever/radius rod joint and unscrewing the expansion link and reversing arms bearings.

 

[Dog Star]

Thank you for the explanation Richard.

I asked because the Finney A4 kit provides a screwed attachment between the motion plate and the slidebar bracket. I could not see any benefit of a screwed joint between the two pieces when there is no removable joint between the radius rod and combination lever. OK, I could try to incorporate a removable joint....

So with the design as is, removal of the two pieces as one unit exposes the radius rods to damage since the single point of attachment can rotate left/right and hence bend the rods. Yes, I could insert a fooling pin in the platework.

So in best WT "bodge style" I have replaced the single strip of metal between the motion plate and the slidebar support bracket by two vertical strips, adjacent to the frame plates, and soldered the pieces into one unit.

regards, Graham

 

[Dikitriki]

OK, well the problem alluded to in my earlier post......

You assume when building a kit, or at least one by one of the better designers, that it is correct, buildable, and that the parts look like the real thing. It's perhaps only when something doesn't quite work that you start investigating fully, and if you're doing a mix and match from different suppliers as I am here, this happens more often than not.

Ist problem... The valve crosshead guide was too far from the bottom of the valance, and too close to the top slidebar. Solution, remove, drill new locating holes, and relocate about 1mm higher. No real problem.

2nd problem... The hole for the valve cover on the cylinders was about 2mm too low. No way would the valve spindle have located well. This may be because I had used proper slides, so the alignment was more critical, but the previous builder had enlarged the hole in the valve cover to an unacceptable degree, and left it in the wrong place. Valve cover replaced and relocated.

3rd problem... Having sorted this lot out, the gap between cylinder cover and valve cover on the cylinders was too great, but that between the valve crosshead support and the slidebars was too little. Solution.....buy an MOK 9F kit. The reason (I suspect) is that the kit included a Jubilee or Black 5 slidebar/crosshead set, and that a smaller set specific to a Patriot had not been mastered. I'm leaving this as is on this rebuild, but when I come to build a proper Patriot, I shall replace the slidebars and crossheads too.

4th problem. Having made all the adjustments above, the combination lever centre from the union link bearing to the valve crosshead bearing was too short. Solution - move a couple of holes. How can you move a hole?



On the left is the completed combination lever/valve spindle assembly. On the right you can see that the combination lever has had an additional (middle) hole drilled, and the topmost hole (which needed to be bigger) was enlarged by filing upwards rather than kept in place. The valve crosshead was thinned down at the top so that there would be room for the radius rod to be attached. The redundant hole was plugged with some tapered nickel silver rod soldered in and cleaned up, and the thickening of the combination lever round the bearing holes was filed off...



I was also able to work on the radius rod, and the last 2 pictures show the rescued one from the original build and the final version with forked ends, thinned down slides and relocated oiler, and reinforced bearing holes where it fits to the expansion link.





Richard

 

[Len Cattley]

Hi Richard really enjoying your build Where do you get your valve gear or do you make them?

Len

 

[Dikitriki]

Hi Len

Glad you're enjoying my ramblings

The valve gear is from one of three sources, and I have tried to indicate which when I have described the components.

But to pull it all together:

Original kit: crosshead, radius rod

Scratchbuilt: reversing arms, eccentric rod, return crank

Cast: gudgeon pin (DJB) drop link, union link, combination lever, valve crosshead and spindle, expansion link (all MOK from Sanspareil)

Cheers

Richard