4mm Lynton & Lynmouth - 4mm scale, 8mm gauge.

[Tim Watson]

Tom Mallard has turned up trumps with original works drawings of the valve gear which make it clear how it all fits together: this really is an excellent forum.

The coupling rods were made from 1mm thick steel strip, two sweated together and then drilled 0.8mm on the mill drill.
They were then roughly milled to shape. Sighting rods through the holes ensures that they are sitting level in the machine vice and also helps to stabilise them in the vertical plane.


The two rods were removed from the mill looking quite chunky.


These were draw filed to shape together, again using the sighting rods to keep them in register.


This photo shows one rod as filed roughly to shape and another completed with the inter-boss rod suitably reduced in thickness and the oiler corks filed into place. The screw is 16BA for reference. That is the size of the bearing currently, but these will be running in brass bushes when complete.


Final picture shows a rod sitting in front of the frames.


The Heljan rods are quite close to scale dimensions, but don’t have the oil corks, and boy are they sloppy!

Tim

 

[-missy-]

I'm so glad I have a CNC mill so I don't have to bother with all that faff anymore!

J.

 

[Tim Watson]

Each to their own. I like to keep up the hand skills.

Tim

 

[Tim Watson]

One trick I forgot to show on the first rod was to sweat it to a lump of brass to work on in the vice. The second was to file in the roots of the bosses with a round file, before thinning the middle bits.

A finger nail protects the boss as the safe-edged file works away from it, also draw filing, as the rod begins to get to the correct thickness. The other end is dealt with by turning it round. Always easier to file away from you in this case.

Final result, 90 minutes later.

Tim

 

[Scale7JB]

90 mins, that's pretty good going!

These rods for a 7mm J39 took me a good few hours each and that was only beefing up and detailing the bosses and gradient pins. I may have treated the lubricator crank to a scale hardware bolt.



JB.

 

[Brian McKenzie]

I'm so glad I have a CNC mill so I don't have to bother with all that faff anymore! J.

But can it, and you, produce rods at least as well as Tim's - with the correct shape and radii etc around bosses?
Kudos to you, if you can.

 

[Tim Watson]

90 mins, that's pretty good going!

These rods for a 7mm J39 took me a good few hours each and that was only beefing up and detailing the bosses and gradient pins. I may have treated the lubricator crank to a scale hardware bolt.

View attachment 124416 View attachment 124417

JB.

I have spent a very long time trying to work out how to re-engineer the Heljan mechanism, JB. It sometimes takes longer to fudge something better from an inadequate start than from starting from scratch: over the years I have filed up lots of valve gear so it doesn’t take long. When I made the valve gear for Valour, I used the kit etch: it wasn’t quite right and I ended up taking longer to put it right than if I had started from a lump of steel.

Tim

 

[Tim Watson]

I started to mate the new chassis to the body substructure of the Heljan loco this evening. The design of this engine is really quite complex and it took a lot of head scratching to work out how to reverse engineer a new chassis into it.

The back end of the plastic frames were cut off and the cast fixing narrowed so that it fitted between the brass frames, with the plastic rearward extension on the outside.

The cast internal engine weights have been on the milling machine having space made internally.

This little gadget is very useful for measuring casting thicknesses DENTAL WAX TYPE IWANSON CROWN CALIPER TENTH DIAMOND GAUGE ORTHODONTIC MEASURING 7437328019040 | eBay

The roughly put-together castings gives a clue as to why there is need for a bit more internal space.


Tim

 

[Tim Watson]

With the outside cranks and the somewhat complicated valve gear I thought it would be advisable to be able to drop the wheel sets. To that end, the frames were dismantled and slots milled downwards. The small vertical holes in the frames had been drilled already to take 16BA fixing bolts.


The bottom half of the bearing and keeper was milled from two pieces of 1.5mm thick brass sweated together, with corresponding holes drilled for the fixing bolts. As ever, working on both together saves a lot of time and is easier to file true.


After adjustments the keepers can be seen trial fitted, but before the bearings were properly adjusted.


The Heljan model has no representation of the brake gear and so the keeper was always intended to represent these. However, in reality the rods are set back behind the frames. To achieve this effect, a rebate was milled down the outer and lower edges of each side of the keep.


The bulk of the keep was then filed away close to the frames, but keeping representations of the brake hangers and, of course the bottom halves of the bearings. It’s just roughly placed in this photo and will require further refinement and fitting for the axles.


Quite a heavy evening’s work - the last time I made a chassis like this was for the Baldwin 2-6-0, started back in 1982! Soon be time to get the chassis and wheels all assembled.

Tim

 

[Tim Watson]

The chassis has now been erected and wheels dropped in, at least for the front pair, as the rear axle is awaiting a gearbox and wheels: it is currently running as a little known MW jack shaft driven mechanism...


It all turns over nice and evenly by thumb power, even though it’s a bit stiff, as there is no slack anywhere. The chunky 3D nature of the rods and the fly cranks just missing the frames shows up better in a 3/4 view. There is very limited side play on the front axle, steadily increasing to the rear, which is how it should be.


It will be interesting to see if the loco runs more steadily for using the outside bearings, compared to the more normal inside frames and bearings. Last time I made an engine with fly cranks was 1980.

Tim

 

[Tim Watson]

The chassis has turned over under its own power today. The drive system is a Maxon 6V 6mm diameter motor with a 1:4 planetary gear box coupled to an 18:1 transfer box made originally by C & L. It is very narrow but needed some modification to the lower bearings and fixing bolts to make it narrower still.



Setting up the chassis, drive system and coupling rods was a bit tricky, but it has the major advantage of being small and tucked out of the way between the wheels. The motor and transfer gear box will need a torque arm across the top which will also unify them and close up the gear box: this may well fix to the nearby cross member and give some stability to the set up.



It all runs OK, but the frames need to be stiffened up and the axles need spacer washers to keep side play under control. iPhones are really good at picking up gear & motor noise!

The back wheel (bottom left in the video) is due for replacement as it is eccentric, probably due to a small crack in the hub.

Tim

 

[Tim Watson]

I have bent up the torque arm and motor - gear box unifying strap from a piece of 30 thou brass. This had a bit of silver solder run in at the junction between the curved and flat bits to strengthen it.

This was then glued to the motor and gearbox with 5 minute epoxy. If the joint needs to be separated at any time a smidgeon of heat will degrade it. The clip on the end rotates over the chassis cross member and holds the assembly nice and steady; as can be seen, the axle is not dropping out of the frames and the motor is held horizontally.

I think I have worked out how to arrange the battery, receiver, switch and charging socket. At the moment, it all looks like a snakes wedding, but is has dragged its encumbrances across the work bench, looking rather comical in the process.


Tim

 

[AdeMoore]

Brilliant workmanship here Tim, in awe of what you are achieving.
Following with real interest.
Cheers
Ade

 

[Tim Watson]

Yeo made its first trip to Lynton today. The radio control with battery power works well in the engine with good slow running and an appropriate top speed for a terminus. Probably need some track to do the job properly.

There was quite a lot of fiddling to get it all in. The charging plug is in one bunker and the isolation switch is in the other. The whole unit can be taken out after removing two screws with, eventually, a plug and socket for the motor to allow testing on a conventional controller.



The controller is very neat.

Once the motor plug & socket is installed, I will reassemble the body and pony trucks and make a bit of track for it to run on.
Tim

 

[Dave Holt]

I think that's the first time I've seen a steam loco running along without any track since the Titfield Thunderbolt!
Marvelous modelling, though.
Dave.

 

[NHY 581]

Like doesn't do this justice.

We need a 'bloody hell fire!" button instead.

Top stuff indeed.

Rob.

 

[Tim Watson]

I think that's the first time I've seen a steam loco running along without any track since the Titfield Thunderbolt!
Dave.

It had occurred to me. Just needs a model of Chippenham to go with it...
The great thing is that is does away with a lot of wiring and also track wing & check rails can stay rusty.

Tim

 

[Tim Watson]

Today was a track making day for my trial diorama; the engine shed line. Alan Smith has made some beautiful CNC-machined track making jigs for me (it ain’t what you know, it’s who you know...) with correct spacing for either L&B or SR timbers.
Sleepers were simply loaded into the jig and cut to length with Xuron cutters. Then the rail simply soldered in place with lots of flux.



The second rail was then laid, again using lovely gauges from Alan.


Once made, I took a riffler file to the sleeper tops to take away the excess solder and also to put in the electrical gap. Whilst I intend to use battery power on Lynton, it would be a bit silly to not have the option of conventional control and normal slotted gaps can be quite obtrusive. This filing also gives a nice degree of irregularity: PCB sleepers often look too ‘sterile’ and sharp edged in the larger scales.


The track has been given a first coat of paint, bringing out a wood grain and rusty rail. The rail head was chemically blacked, which effectively dulls it a bit. The track will get further weathering - probably some light dry brushing, once it is fully laid and ballasted.

So at least Yeo now has some proper track to go up and down.



Tim

 

[ullypug]

This is some seriously impressive stuff Tim. I have to keep reminding myself it's only 8mm gauge. I'm still shaking my head about you getting RC control in something that small.

 

[Phil O]

Hi Tim,

Where I use copper clad sleepers and timbering, I gap and test before soldering the rails on, it makes testing a doddle. I also find it a lot easier doing it first.