Rob Roy 3 1/2" gauge tank locomotive - anybody built one?

I have decided to continue with the construction of Rob Roy and will be seeking advice and tips from people who have built one.

Oh - one tip that is probably a bit too late is the cylinder machining/ drawing error. I machined the cylinder blocks about 25 years ago to the wrong port face dimension!!

My first question relates to the firing of the boiler. Has anybody got one running on gas?

I am building one as a first loco, runs on air !

If that is the error that means the valve rods don't line uo with the gear then snap - cranked adapters on the end of the valve rods solved mine.

There is a thread covering a working gas fired Rob Roy here

Phil

I see you've decided to complete your Rob Roy. As it happens I can probably help you with your question on gas firing here.

My thread on gas firing a Rob Roy

**LINK**

And the full story here

**LINK**

Near the end YouTube videos of it running, on gas.

I'll admit it probably isn't as good as being coal fired, but I've never tried coal firing it. Its quick to get get running and quick to get packed up at the end of the day.

Happy to help with any questions but please post them over on the HMEM site to keep the info in one place

Pete

Edited By Doubletop on 27/05/2012 02:31:54

Hi

Built a Rob Roy but eventually listed over 2 pages of errors in the drawings. Nice little loco when finished.

Bob

Yes Andy, the cranked cross heads might be required and yes Bob - I'll keep a look out for the corrections. Ive seen various lists posted on the net so I will proceed with caution.

Pete - the pictures look excellent and the thread on gas firing looks very helpful. I notice that I should be ok regarding traction. I didn't realise that this engine was so capable.

I will take some pictures of the parts that I have completed so far but there won't be many of them. My first job is to put some protective film over the drawings and I will order some steel.

Phil H

Some pictures - as promised. The frames have been very badly attacked by evil rust so I will need to start again. One of them will at least serve as a good drilling jig.

The wheels, axles and axle boxes have a little bit of surface rust that can be cleaned off.

The real thing. I copied this from a book called 'The McIntosh Locomotives of the Caledonian Railway 1895 - 1914'. I would like to find more pictures to use as a guide for the finished article. I noticed a superb front view in Pete's posts.

I understand that this is a simple model but there are a couple of details that are probably quite easy to copy. For example, the coupling rods have a pivot joint to the trailing wheels and the buffer heads look a little bit larger than the model drawing dimensions that I have.

One of the cylinder sets partially finished. I machined these 25 years ago.

One of the wheels and a set of axle bxes made from BMS with brass bushes.

Yep - I was sad enough to scoop out the back of each wheel and file the spokes to an oval cross section.

I know it is cheating but
**LINK**
have lots of laser cut bits for it.

Bob

Phil

Thanks for the picture I searched and searched the internet for a picture and came up with nothing like your picture from the book. The best I've seen. All I could come up with was

(image on original site)

And here

**LINK**

and here

**LINK**

Looks like you've made a good start there, abeit a while back

Pete

Edited By Doubletop on 28/05/2012 08:38:02

Edited By Doubletop on 28/05/2012 08:42:41

Excellent shots Pete. They confirm the larger - what looks like modified buffer heads, the 8 fixings for each buffer stock and position of the engine number on the smokebox door.. These should'nt be too difficult to copy.

I have the saddle casting and I had wondered how it should connect up to the smokebox tube. The pictures clearly show an all in one, riveted saddle/ smokebox assembly so I can now machine the casting correctly.

An interesting question for you. What temperature does the smokebox of the model reach? For example, if I carefully machine the saddle and join it to the brass tube using a combination of screws and solder - would soft solder survive?

Phil H.

Phil

In one word NO soft solder is a no go anywhere near a boiler. screws should be more than adequate for fixing the smokebox to the saddle.

Bob

Phil

Like Bob I'd suggest screws you'll be taking it apart a few times to get it set up. The valve chests aren't that easy to get to and the inlet and exhaust pipework has to come out to get the covers off.

And no soft solder it does get hot.

Pete

Bob/ Pete,

Great help guys this is exactly the sort of tips and advice that I'm looking for.

Ive just ordered the plain BMS for the frames. I had considered the new fangled laser cut versions but I couldn't bring myself round to placing the order. As you said Bob its sort of cheating isn't it?

Phil H

Guys,

Any tips on painting before I assemble the buffer beams and main horns? I read an article a few years ago that proposed the use of primer during the riveting stage. A rather messy process but it was suggested that the primer prevents oil and grease from staining and ruining the paintwork that is applied at a later stage.

Also, the book suggests normal cellulose paint. Is that ok considering your earlier comments on soft solder on the smokebox. Do the frames get very hot too?

Phil H

Phil

Use an etching primer on your frame and basically anything else that you wish to paint at a future date, Smokebox a good high temp black paint, boiler cleading (not misspelt) once on use a good quality paint. Please look at this site not cheap but good
**LINK**
Also has lots of advice. The frames on the loco will not get to hot. But no matter how good your workshop is RUST will be your enemy so get that primer on as ASAP. Look at Chris Vines "how not to paint a loco" he is a very ameniable chap and happy to give advice.
I could go on but good luck and keep all of us posted

Bob

When I painted my Rob Roy it was the first time I had painted a loco. I used heatproof paint and painted the inner frames red and the outer frames black. Once that was done I baked the frames. It turned out that I hadn't baked them enough and the constant work and copious amounts of oil when getting it going the paint job started to look pretty shoddy. In the end I gave up and left it until I got the loco running properly and then completely stripped it down again , removed all the paint and had the frames powder coated. In order to do that each of the places where components joined were masked off to maintain dimensional integrity. The powder coating company provided the high temp masking tape.

Here's the link to the section of my thread on the powder coating

**LINK**

I’d suggest, the issue of heat isn't a problem the powder coat is baked at about 200degC. Outside of the boiler won't be that, even at 80psi.

The trouble heat proof paint is it doesn't gain its oil and solvent resistance until its been well baked. Until then it will come off at the slightest hint of oil. I now use a hooded gas barbeque with a temp gauge in the hood. It will take a whole frame and the baking can be kept at about 200deg for an hour without SWMBO complaining about the stink in the kitchen and the next Sunday roast tasting distinctly dodgy.

I'd imagine others have painted many more locos than me but from my experience, I'm on my third now, I'd leave it as late as possible. I had my Rob Roy apart about 5 times before I was happy with it; the paint gets decidedly tattier each time.

Pete

Hi Phil

"Oh - one tip that is probably a bit too late is the cylinder machining/ drawing error. I machined the cylinder blocks about 25 years ago to the wrong port face dimension"

I am just about to start cutting the cylinders and valve chests for my Rob Roy so can you point me in the right directioon to moify the above error before I start.

Thanks Bob

One list of errors here and another wordier one here both cover the relevant gotcha.

Andy

Thanks guys,

I agree with Bob that rust is an enemy. My first set of frames (made when I was 16) are heavily rusted and totally useless now (apart from being a good drilling jig for the new ones). I like the idea of high temperature paint from Pete too.

I think I will get the book from Mr Vine but continue to make loose parts until I've read the book. I've machined the horns, polished both sides of the frame steel and cut most of the buffer beam parts (all drenched in oil of course).

Phil H

'I am just about to start cutting the cylinders and valve chests for my Rob Roy so can you point me in the right directioon to moify the above error before I start.

Thanks Bob'

Bob,

I've looked at the list from Andy and there are a few mods mentioned in the book 'Rob Roy & William' by Martin Evans. Some might be repeated but thought they were worth mentioning.

1. Check the height of the horizontal stretcher. The book suggests raising this by 1/16" to give more clearance to the eccentric straps.

2. Cut a 'U' in the upper left vertical stretcher to give clearance to a possible blowdown valve.

3. It suggests using cast bronze for the connecting rod big end bearings instead of drawn bronze to give a longer life.

4. The flange on the valve crosshead is removed and its boss increased by 1/32" giving more support to the valve spindle?

5. The oil check valve is fitted with a plunger instead of the spring bearing directly on the ball.

6. Bushes are used on the backplate and smokebox plate instead of threading the plates themselves.

7. The safety valve vent holes are increased in size from No 55 to No 52. The spring locating pin or spindle is reduced in diameter to accomodate the above mod.

I think I saw a string on this issue somewhere else and these changes are a puzzle to me i.e., I have worked in a design office for 30 years. All the mods would take less than a few hours to correct including a mod record (either electronically drawn or by hand). I wonder why we don't do it?

Phil H

There was another I'm aware of and that’s the lack of a stretcher between the cylinders and the inlet/exhaust in effect become a stretcher. Mine wouldn't go round some of the tighter corners and when I measured the gap between the frames at the cylinders it was too wide at the bottom ( the saddle act as a stretcher at the top). I drilled through a pair of opposing cylinder mounting holes, made a piece of 1/4" silver steel the correct spacing, drilled and tapped the ends and put it between the frames. That ensured the correct spacing at the bottom.

Sorry no picture for some reason

Pete