Rob Roy boiler test

[AndrewP]

I borrowed the club test pump today to see if my ebay purchase was a bargain after all and, deep joy, not a leak in sight.
My input to date is confined to boiler fittings, regulator and some motion work but you never know, I could be steaming next year!

Proof!


I simply couldn't resist popping it on the chassis, starting to look less like a pile of bits now.


Note my confidence - big sheet of plastic on the bench.

Next milestone will be air chassis so much filing is on the cards, unless of course I finish the cnc conversion of the mill, but then I'll get distracted again

[baggo]

Hi Andy,

Looks very well made so far - you got a good buy there. When you get around to the cylinders note that there were errors on the original drawings which placed the valve rods too close to the frames so they did not line up with the valve gear! The errors section on Alan's site gives details of this and a few other corrections as well.

John

[AndrewP]

Cheers John, yes I was pleased to say the least, especially since I've been quoted over £900 for a commercially built boiler - not that it was ever an option but it's nice to know how much you are saving whilst sweating over big blowlamp!

The reason for me making an inner dome was partly because the previous builder had fallen foul of that drawing error and partly because it was brass, so I turned one from the solid in gunmetal.

My drawings seem to be correct for the valve rod positions but unfortunately the previous builder also managed to get that wrong too, not sure how since the drawings came with it.

First thoughts were to silver solder a spacer to the port face but a stepped valve crosshead sounds plausible, wouldn't that put an eccentric load on the valve rod and it's gland though?

It might be easiest for me to cast a new taller valve chest since casting is sort of 'my thing' - ooh decisions, decisions.

[baggo]

Hi Andy,

you could put a spacer in between the port face and the valve chest and then make a deeper valve nut and use the original valves or make new deeper valves. My brother's Rob Roy (another Ebay purchase) suffered from this problem but in the end the original cylinders were so badly machined that I machined him a new pair to the correct dimensions after getting a pair of castings cheap. Incidentally, I made new valves from a block of PTFE.

John

[AndrewP]

John

I see, a spacer like a big rectangular washer, I was just going to make one like the cover but with ports in it - use the original valve and nut etc.

I've been pleased with the vast majority of my ebay finds, especially now I've sussed what's wrong with the Baker valve gear on my Juliet 2 - air chassis my a***.

[chris vine]

Hi Andy,

You may not need to worry too much about an offset load on the valve or crosshead. I made a Bridget by Ken Swann some years ago, 7.25" Gauge. The valve is driven from one corner by a buckle. He had missunderstood the original engine.

It has worked fine for a long time now.

Otherwise his drawings are absolutely excellent.
Chris.

[AndrewP]

Thanks for that Chris, offset valve crosshead seems the easiest way to go - I'll mock it up first, I'm a great believer in cardboard and plastic mock ups - a lot quicker than cutting metal and finding it doesn't fit!

Great book btw, dipping into it occasionally since I'm a while away from painting yet!

Official boiler test last night so I now have an hydraulic certificate and test book ;D ;D ;D and so on as infinitum.

Cheers, Andy

[chris vine]

Hi Andy,

Sorry did not see your reply earlier, Thanks for the comments on the book.

I look forward to seeing the painted, finished locomotive....

Don't forget to keep painting in mind while you are making bits, especially if they are going to be different colours on one part. Best to keep one colour to one part if you possibly can.

Chris.