Building the MOK "King Arthur"

oldravendale

oldravendale

Western Thunderer
In true Dave Sharp fashion he was on the phone last night to discuss the valve rod. If only all businesses were as customer-centric, and I don't mean just in the model railway business!

He's advised that the valve rod should be 3/32" steel. Interestingly the piston rods are 2mm steel which makes the valve rods a bigger section, as I suspected. Anyway, the valve rod guides are certainly oversize for the 2mm rod and pretty well an interference fit for 3/32" so that's the road we'll follow for now. If it starts to irritate me I'll consider sleeving the guides and fitting a smaller diameter rod.

Dave also advised that there is a cast rod in the brass fittings. He's substituted steel rod in the kit as it looks better, which it does, and also because the dimensions in terms of roundness (if that's a word) are less accurate in a casting. However the cast rod will give me the opportunity to check the dimensions as designed.

I'm hoping to get in to the workshop again today. If so there'll be more to follow.

Brian
 
oldravendale

oldravendale

Western Thunderer
Simon - I can assure you that at a certain time of day GD&T can certainly be confused with G&T.....:))

Keeping well and spending time in the man cave, and thanks for asking. Please do the same.

B
 
Dave Holt

Dave Holt

Western Thunderer
I'm not surprised that the valve rod is a larger diameter than the piston rod. These (and some other Southern locos) did not have separate valve spindle cross head guides, as used on LMS, LNER and BR Standard locos to support the outer end of the spindle and take the weight of the valve gear, so needed large diameter rods to give an adequate bearing area to prevent excess wear on the stuffing boxes.
Dave.
 
oldravendale

oldravendale

Western Thunderer
Aah yes, Dave. Thank you. I knew someone would have the answer, and Dave Sharp's research is usually so good that I doubted he had it wrong.

It's good to know the reason, though. I've been working on the 3/32" steel rod this afternoon and have a fair representation now of the ends as demonstrated in Dave's casting. It's required a fair amount of metal carving but is close to getting there now.

One supplementary - which I should have anticipated. As I've worked the steel everything - bench vice,and various files - now have a beard of iron filings which are very difficult to remove. They wipe off and immediately jump back on again. (If we could harness the power we could have perpetual motion...... or not). Any ideas how to demagnetise them??

B
 
mickoo

mickoo

Western Thunderer
oldravendale said:
Aah yes, Dave. Thank you. I knew someone would have the answer, and Dave Sharp's research is usually so good that I doubted he had it wrong.

It's good to know the reason, though. I've been working on the 3/32" steel rod this afternoon and have a fair representation now of the ends as demonstrated in Dave's casting. It's required a fair amount of metal carving but is close to getting there now.

One supplementary - which I should have anticipated. As I've worked the steel everything - bench vice,and various files - now have a beard of iron filings which are very difficult to remove. They wipe off and immediately jump back on again. (If we could harness the power we could have perpetual motion...... or not). Any ideas how to demagnetise them??

B
Click to expand...
Get a 'bigger' magnet :p

Or....... you could get a de-magnitiser tool, or smack them with a hammer, or best yet, just buy new ones :thumbs:
 
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Yorkshire Dave

Yorkshire Dave

Western Thunderer
oldravendale said:
One supplementary - which I should have anticipated. As I've worked the steel everything - bench vice,and various files - now have a beard of iron filings which are very difficult to remove. They wipe off and immediately jump back on again.
Click to expand...

Try wiping them with a damp rag.
 
Peter Cross

Peter Cross

Western Thunderer
I have somewhere in the UK a demagnetiser. It's a coil of shellac coated wire, that when energised is move away from the object.
 
oldravendale

oldravendale

Western Thunderer
So, this is where I am now - or was early this afternoon. Dry run only - the valve rod is clearly far too long, because there's a similar finish at the other end and both parts will have to be cut to length.

IMG_20200322_134746161_HDR.jpg
Here's where I could do with a bit of advice. All those large brass castings have to be fixed to the cylinders. I always prefer solder. The problem with that is that the use of sufficient heat will probably cause the cylinder wrappers to pop. My thought, therefore, is to attach them with 5 minute epoxy. The advantage is that, if I get anything wrong I'll be able to separate them by immersion in hot water.

That access hole in the cylinder side looks promising, but it may just about be possible to reach the rear piston cover. The internal baffles prevent reaching the other components from the inside. I considered the use of a torch but the heat generated will probably pop the wrappers.

You can see the valve rod here with the completed ends, ready to be cut. Note also that the cylinder relief valves are in place.

Suggestions on a postcard regarding the fitting of the castings, please.....

IMG_20200322_134945160_HDR.jpg
This is close of play today - again a dry run. Expansion link bracket made up - cladding yet to fit and the associated motion bracket in place with the units for the other side on the bench in front. These are really satisfying chunky castings and the expansion link bracket is a masterpiece of etch design.

IMG_20200322_171908823_HDR.jpg

Brian
 
mickoo

mickoo

Western Thunderer
I'd go with epoxy personally, you're right any decent heat in there will just undo what's been previously done.

I have had epoxy bits fail, probably because one surface or another was not correctly cleaned, what I do now is try to add some on the inside as well, especially if there is some sort of spigot. The resin rends to bond together with that on the outside and gives it a bit more of a fighting chance of not coming adrift later.

Others mileage may vary.
 
oldravendale

oldravendale

Western Thunderer
Thanks Mick. That is the direction in which I was already travelling. Good advice to get some on the inside too which I should be able to do through the aperture in the rear of the cylinders. I may have sufficient bits prepared this afternoon to give it a try.

I too have had epoxy joints fail and agree, it's probably down to poor preparation - or perhaps the epoxy itself is too old. I've used epoxy in split axle construction for quite a few years now and only ever had one of those joints fail so it can clearly be very strong. (I now keep a spare axle in case it happens again). The benefit for me in using the 5 minute version here is that I've been able to get joints apart previously by immersion in hot water. This is comforting for me as I'm never entirely confident that I have everything in the right place!

Brian
 
oldravendale

oldravendale

Western Thunderer
Thanks Mike. Another good point. I buy the 256 gram bottles of the Devcon product and always mix more - usually a lot more - than I need as any slight inaccuracy in the mix is of less importance than when trying to mix a small amount. I then end up throwing a huge amount of the mix away, but better that than a failed joint. (It's rather like Colman's Mustard. It's reckoned that the fortune made by the original company was created because of the amount people threw away!) I bought the twin syringes for a while but usually found that they blocked after a while, and one tube would always be more willing to release its content than the other, so proportions couldn't be guaranteed anyway.

The large bottles last well and are freely available on the Bay of E and other such suppliers. They'd probably last even better in the fridge.

Brian
 
mickoo

mickoo

Western Thunderer
Interesting, I use the two syringe method and not has many issues, I do tend to mix quite large blobs and they're often not exactly equal but seem okay. It just seems to extend or shorten the cure time.

I tend to hold back until I have quite a lot to do and hit it all in one go to save on wastage, but you do have to get a shift on mind lol

Didn't know about the hot water trick, good job I didn't put any models in the dishwasher to clean them up:eek:
 
oldravendale

oldravendale

Western Thunderer
The hot water seems to soften the adhesive so that the parts can gradually be pried apart. A friend fitted a back head with 5 minute epoxy rather too low on the boiler back and was able to separate the parts with a blunt knife. The adhesive then seems to go rubbery and can be peeled off.

Having said which, this is only a single experience of the hot water treatment and other experience is quite possible!

Above all, don't use boiling water if white metal components have been fixed with low temp solder. I wonder how I know that.......

B
 
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