A small G3 loco

[jamiepage]

www.gouldstudios.com

Select 'products', then 'Trains' then 'GG1'

The website says his rather excellent colour illustrations are not currently available but the line drawings (set of three in the case of the GG1) are.
Jolly interesting website.

 

[jamiepage]

Sorry, start at the 'store'.

 

[mickoo]

Chi Ching, sold!

 

[jamiepage]

A little progress. Brake hanger brackets and a large, very visible running board bracket have been fitted. The items were temporarily glued in place with Loctite 480 (wonderful stuff), then drilled through for rivets. All holes were countersunk on the inside and the rivets peened over and filed flush as a precaution in case the valve gear or Slomo end up needing all the available width later.
The opportunity was taken to reposition the rear guard irons (must learn to check properly), and the front axle bearings have been modified to allow the axle to escape downwards, which will be necessary once cylinders and slidebars are in place.
Talking of cylinders, a large lump of brass has arrived so I can start hacking away. Brass will be quite adequate; with graphite impregnated PTFE piston rings, there should be little mechanical wear.

 

[JimG]

Talking of cylinders, a large lump of brass has arrived so I can start hacking away. Brass will be quite adequate; with graphite impregnated PTFE piston rings, there should be little mechanical wear.
View attachment 42915

Jamie,

From your sketch next to your brass chunk, do I take it that the valve face is horizontal?

Jim

 

[jamiepage]

Hello Jim,
Yes that's right. It follows a G1 design from Paul Forsyth. The port face is on top of the half height bit that goes through the frame gap. A separate steamchest with valve glands sits on top of that face, than a cover on top of that, all screwed down from above.
Not sure yet whether to use a large single steamchest to mechanically link the two cylinders across the frames or leave them separate. That may depend on how well they line up with each other!
Jamie

 

[JimG]

Hello Jim,
Yes that's right. It follows a G1 design from Paul Forsyth. The port face is on top of the half height bit that goes through the frame gap. A separate steamchest with valve glands sits on top of that face, than a cover on top of that, all screwed down from above.

It will make valve setting a bit easier as well - certainly before the smokebox is fitted. Maybe the idea could be inverted, with the valve faces pointing downwards then the valves would be accessible with the loco fully assembled. I've read of slide valve designs with the faces pointing downwards where the theory is that the steam pressure holds the valves on the face when the regulator is open. It has also been suggested that the valves can be held on the face with light spring pressure.

Not sure yet whether to use a large single steamchest to mechanically link the two cylinders across the frames or leave them separate. That may depend on how well they line up with each other!

Why not make the cylinders and valve chest assembly be the frame spacer, then there are no line up problems.

Jim.

 

[jamiepage]

Jim,
Yes indeed, the main advantage of this set up is the fact that valve setting will be easier. And it is a significant advantage because it's quite difficult to peer down between vertical faces to see where the valves are- even with the opposing cylinder stripped out. Having said that, some people are skilled enough to set valves without eyeball access, but that's far, far beyond my abilities.
It is quite feasible to have the valves sit inverted underneath the cylinders, and steam pressure does seal them without needing springs- a few thou float is all that's needed and the valves get pushed onto the portface as soon as steam is introduced. It's helpful to have valve rods supported at the front end in blind glands. The advantage as you say is ready access without dismantling smokebox etc. Once the valves are set however, access shouldn't be needed very often. Hopefully. And if it is, the smokebox can lift off fairly easily.
The original cylinder design did indeed have the two halves bolted together through a couple of lugs to form one fabrication, which then slotted into cutouts from above (or below), and was the main source of strength and alignment to the frames. Those properties are supplied by the substantial bufferbeams on this model so it's not essential the cylinders supply them, but it doesn't hurt to build in more strength if it's there for the taking I agree.
Having just said all that, please don't think I know what I'm talking about particularly. As you'll see as this loco progresses.
Jamie

 

[jamiepage]

Main cylinder hacking complete. What will be the port faces meet pretty well across the frames so a one piece steam chest to bridge the two is probably the best option, as discussed above.
Fiddly bits to do now though; ports, steam ways and covers. After that, I should carve away at them in neutral areas to reduce the overall mass of brass. Less brass to warm up probably reduces a tendency for steam to condense on its way to do some work, especially with the rather long passages with this layout. A thin cladding sheet will restore the external appearance eventually.

 

[Steve Cook]

Cracking on Jamie, it looks good already. Are you tempted to add draincocks to the cylinders, given the scale of the loco and its intended use? I think they would prove beneficial in service, especially given the mass of brass as you have alluded to. The other question I have is are you going to run an open smokebox as opposed to a sealed one? One advantage with gas firing (as I'm sure you know) will be the option to run an open smoke box and a chuff pipe to direct the condensate down towards the track rather than over the engine...got to keep that paintwork clean and tidy
Thanks
Steve

 

[jamiepage]

Steve,
Thank you. I had started to think about draincocks and would like to, but not sure how at the moment. I fitted DJB automatic drain cocks to the 4-4-4T, where they are hidden inside the frames and front bogie but they would be a bit too prominent on this one. Options I guess include piping from the cylinder ends to inboard drain cocks, or have a go at making some smaller external ones, or just fitting cocks to the steam chest and doing without on the cylinders. It would be nice to incorporate them though, not just for the condensation issue but R/C controlled manual cocks would be something else to play with during a shunting session. And a whistle maybe. ( I suppose DCC and a sound chip would miss the point?)

Yes, I will build this one using the open smoke box principle, gas poker burner etc. Haven't done it before so it will make a change, and the idea anyway is to incorporate as much 'Roundhouse type' principles in the thing as possible, plus chuff pipe and Slomo to see how it all turns out.

I'm still trying to understand the reversible inside valve gear that was visible in your recent photos of your green loco. Basically, can I ask how it reverses what seems like a single eccentric? I'm only interested in pottering at slow speeds so it doesn't need to notch up in any efficient way; but I do need to be able to reverse with R/C.
Any help appreciated, thank you
Jamie

 

[JimG]

I'm still trying to understand the reversible inside valve gear that was visible in your recent photos of your green loco. Basically, can I ask how it reverses what seems like a single eccentric? I'm only interested in pottering at slow speeds so it doesn't need to notch up in any efficient way; but I do need to be able to reverse with R/C.
Any help appreciated, thank you

Jamie,

I was wondering about that as well. The reversing lever seems to operate into a box between the cylinders with pipes to/from the cylinders - maybe some form of switching steam in/exhaust out to reverse the operation.

Jim.

 

[Steve Cook]

Hi Jamie
I hadn't thought about draincocks to the steam chest, thats an interesting approach. The Steam Trains In Your Garden book provides another option to consider too.

As for the green chassis - its a 'simulated Stephenson' set up where the axle eccentrics control the piston valves in the steam chests - that motion is translated via the rockershafts from inside the frames to outside the frames and once set up, the piston valve timing relative to the cylinder piston remains the same. The reversing comes from the cab operated lever which moves another(!) piston in the steam distribution block which sits between the pairs of steam pipes feeding each cylinder. I can't see a way to strip down that block, but it must simply swap the direction of the steam feed (which comes in via the top) and thus reverse the engine direction.
You'll have to forgive me for not stripping my engine down to explain it better but I have found this document which details setting up the valvegear on the Accucraft Ruby - it is exactly the same and shows what I am talking about. I'd like to know how the passages are arranged within the reverser block too, but I haven't found a photo yet. If I do, I'll post it up as I'm interested in how it works too.

Hope that helps
Steve

 

[jamiepage]

Steve,
They don't deal with the real issue of water that has got in the way at each end of the cylinder of course but they probably give a bit of general relief. As I understand it anyway. So cylinder drain cocks are much preferred and the design in Steam Trains in your Garden looks promising. Thanks for that, a copy has been ordered. What a good idea the book corner was.
As to the reversing, thanks for the document; I'm intrigued to know what's going on in that central distribution box, but I suppose the clue may be in the use of piston valves? The arrangement of pipes leading to both cylinders could suggest alternative inside or outside admissions maybe? Or either side of the bobbin? Hmm, way past the point where I've any idea what I'm talking about now but it is interesting.
On this loco I've already committed to slide valves really, so may well have to bite the bullet and do the full Stephenson's thing. All good fun though.
Thanks again
Jamie

 

[JimG]

On this loco I've already committed to slide valves really, so may well have to bite the bullet and do the full Stephenson's thing. All good fun though.

Jamie,

There's always a gear driven valve gear. John van Riemsdijk showed some many years ago in the G1MRA newsletter and I actually built a spur differential one which worked very well, but the case of the differential was too large to go under the loco boiler. With the spur gear differental type, one side of the differential is locked to the axle and the other side carries a single eccentric free to run on the axle. You alter the phase of the eccentric by rotating the cage of the differential. J. v. R's valve gears were very similar but used a train of gears on an arm which, when rotated, varied the phase. I've tried Googling to see if I can find mention on the web, but have had no luck so far. I'll try digging through my old G1MRA stuff to see if I can find any articles. I do remember that an Australian member at the time (1980s) had done work with differential valve gears and he sent me an excellent letter with a lot of detail in it. I might be able to find that letter.

Jim.

 

[JimG]

I'll try digging through my old G1MRA stuff to see if I can find any articles. I do remember that an Australian member at the time (1980s) had done work with differential valve gears and he sent me an excellent letter with a lot of detail in it. I might be able to find that letter.

I found the gearbox.



The eccentric side, with one sheave still there. This rotated freely on the 5/16" axle and it looks as though I've bushed it with a bit of bronze as well.



The driving side of the gearbox which was locked on to the driving axle - the grub screw is still there. To the right are the two shafts of the spur differential.



And an end on view of the gearbox. The large screw was for lubrication of the internal gearing.

The drawback of the gear was that it fouled the underside of the locomotive boiler when rotating the differential cage. It didn't help that the prototype loco was an earlier Caledonian 2-4-0 with the boiler pitched quite low. The length of the gearbox was just under 1 3/8" and that was really governed by the size of the gears I could get at the time - i.e. big enough to fit on a sleeve on a 5/16" axle for the driving and the driven gears and the smallest matching DP gears for the two cage gears of the differential. I dare say I could probably get it smaller nowadays with much better search facilities to search for different gearing. The gears in the box were from Muffett who were about the only source of ready cut gears available for model engineering at the time.

It took ages to weather it.

Jim.
.

 

[jamiepage]

Jim,
I would be extremely grateful, thank you. Sounds fascinating actually
Jamie

 

[Steve Cook]

... So cylinder drain cocks are much preferred and the design in Steam Trains in your Garden looks promising. Thanks for that, a copy has been ordered. What a good idea the book corner was.

Possibly an expensive one I'm pleased it has proved of interest to a variety of people so far.

As to the reversing, thanks for the document; I'm intrigued to know what's going on in that central distribution box, but I suppose the clue may be in the use of piston valves? The arrangement of pipes leading to both cylinders could suggest alternative inside or outside admissions maybe? Or either side of the bobbin? Hmm, way past the point where I've any idea what I'm talking about now but it is interesting.
On this loco I've already committed to slide valves really, so may well have to bite the bullet and do the full Stephenson's thing. All good fun though.
Thanks again
Jamie

No worries Jamie, it has certainly kept my brain entertained working it all out and I didn't have to strip my loco to boot

I think I have figured out how the reversing block works, it is about changing from inside admission in forward gear to outside admission in reverse gear as you suggest. Once I'd realised that there was probably a hole inside the piston in the reverser block in same way that there is in a piston valve it all made sense, I guess the two chambers on the piston are equal size too.

Clever little system but no use on slide valves though.

Jim
Wonderful looking gearbox, the weathering is excellent
I'm agreeing with Jamie, a fascinating idea and great that you got it into metal, such a shame it didn't fit your loco.

Steve

 

[JimG]

Jamie,

I've found the relevant issues of the G! newsletter - 1982!! - and I'll scan them to PDF later on today (got to get some S scale parts out to members this afternoon). The original idea actually came from a small booklet which the G1MRA produced in the 1970s - "Modelling in Gauge 1" - and I wrote my idea using a differential gearbox to the Newsletter in early 1982 and J.v.R responded with a fully detailed letter in the following Newsletter. It could be that the idea better befits Gauge 3 with a bit more room between the frames and under the boiler.

Jim.

 

[jamiepage]

Jim,
Sorry, I think our previous posts must have co-incided. That gearbox is fascinating, and I will look forward to any other info. I'll try to track down those references as well.
You think that's weathering?
How about this smokebox? Actually, just high temp paint which wasn't.
Jamie