Coupling Rods

Got home on Friday after 2 weeks in Thailand, and promptly did nothing in the workshop for a few days because I was too tired, and it was too damn cold anyway.

I wanted to get the coupling rods sorted, which also meant figuring out the crossheads & piston rods. I had vague notions of making up some nickle-silver items, but the nylon bits from the same N-gauge chassis which provided the slidebars proved to be pretty close to exact scale, so I went with those.

Here's the relevant bits - the idea is that I'll glue the nylon T-shaped bit to the metal rod. The shape of the rod end holds the crosshead in place once it's on the slidebars.


Here's the completed rods. I tried using 2 types of Araldite to stick the bits together - the 15 minute version & the full strength version. They both failed miserably despite being placed in a warm hot water cylinder cupboard to dry. The nylon part fell off when attempting to fit the rod onto the loco. What did work was superglue - the gel version. This is something of a worry, as I'd always thought of Araldite as the adhesive to use when high strength was needed, or when nothing else would work.


I added a styrene valance to the footplate, then clipped the rods onto the crossheads & put the crankpins back in.


Seems to work O.K. The piston rod diameter is probably a bit skinny, but I can live with that.

Assembly Lines

Having removed the wheels in order to paint the frames, it was a good time to add the counter-weights. A bit of styrene & 15 minute Araldite, and they were ready for a paint job:



The wheels were then refitted & gauged. The next step after painting the wheels was to try & "heavy up" the front bogie to keep it from bouncing off the rails every time it hit a bit of grit or dodgy track. I drilled out the holes in the PC board frames & used full-width lengths of brass tubing to act as bearings, soldered the radius bar to the main body of the bogie and finally glued a piece of lead between the axles. Here's the whole assembly as it looks now:


Note the springing between the bogie wheels. I had to thin down the sides of the bogie frames to get those in.
The little coiled spring you can see at the front of the chassis just touches the top of the bogie. This is further insurance against it bouncing around too much. It's .008 phos-bronze wire.

So with everything assembled again, here's the almost-complete chassis:


Still needs headstocks & a few other odds & ends, but you get the idea.

With the main chassis done it was time to start on the footplate & boiler. The footplate was a fairly straightforward affair made from a single piece of brass sheet. The necessary huge hole in the middle was done by drilling a series of 2mm holes around the outside of the marked area, and using a pair of cutters to nip out the webs between the holes. Once the waste was gone, I cleaned up the cut-out using a Dremel rotary file.

The smokebox is a piece of brass tubing, suitably cut & bent at the base where it joins the footplate, and the (very skeletal) boiler is another piece of tubing soldered into the smokebox & cut to fit around the motor. The lump behind the boiler representing the firebox is an old piece of cast lead weight from inside one of the TT locos from TradeMe and it's held in place with Araldite. All the white dribbly bits will be hidden by the bodywork .... hopefully. The weight was needed to bring the CG back between the driving wheels.




Looks ugly in the close-ups, don't it? Here it is fitted onto the chassis:


So at this point I'll be taking a break for a wee while. We have visitors coming next weekend, and then we're out of town for a couple of weeks. Hopefully there'll be more to report the weekend of July 18th.

Current Events

On Wednesday the phos-bronze wire arrived from Tichy Trains. Very fast shipping, and very inexpensive compared with other U.S. vendors I've bought from in the past. I'll be using them again.

So - first off, the chassis was stripped down to allow easy fitting of the current collector PC board, and to have the outer surfaces of the frames painted black.
The collector wires were soldered to the copper tracks of the PC board, then the motor wires inserted from behind. The pictures do a better job of explaining it:




Above: Here's the bottom view. The brass plate immediately in front of the collector PC board is to hold the bogie radius bar in place



Above: The top view. The motor will hide all this when it's re-installed.


While the chassis was bare, I decided to figure out how to build & mount the cylinders & slidebars. This took a bit of headscratching, as all of the ideas I had up till now involved making up nickel-silver slidebars & soldering or gluing them into minute holes in the rear of the cylinders. I have a copy of "Making Model Locomotives in 4mm scale" by Guy Williams, and that's the method he recommends.
In the end, I did what I should have done in the first place, and that was to pillage my stock of TradeMe bits for ideas.
Some of the ways in which commercial manufacturers made slidebars are crude - to say the least, but on an N-gauge chassis I found what I was looking for. The slidebars are cast from nylon rather than plastic, and are in the form of a simple "L" shape with a pin to plug into a hole beside the cylinders. And they were exact scale size for the loco, too. Brilliant!

Rather than tax my patience by trying to make 2 identical cylinders, I decided to cast them. You can see the results below:



On the left is a tentative Westinghouse pump I've made to try & improve on the rather primitive ones I've done previously. The first cylinder casting is in the middle, and the master is on the right. The slidebars are at the back. Sorry about the slightly fuzzy picture, but lighting wasn't good on this one.



Here's a better shot of the resin cast cylinder with the slidebars in position. The castings still have to be properly cleaned up, and look a bit rough as yet.

I soldered a bit of threaded rod through the frame holes where the cylinders are to be mounted, and left it at that for the day.

Gearing Up

The problem with making a gearbox for this particular chassis is that the motor has its mounting screw-holes on the rear of the case rather than the more usual front. Which meant that the motor mount was going to have to be in 2 parts - one to actually hold the motor in place and the other to correctly locate it relative to the idler gear.

I made the idler gearbox first from a piece of C-section brass channel, leaving a brass tongue long enough to slip down between the chassis rails & be soldered in place once I'd set up the working clearances between idler & final drive gear. The front bearing of the motor fits perfectly into a 4mm hole drilled in the channel, and is sufficiently flexible to allow the motor to be moved up & down to adjust optimum backlash between the worm & idler. 'Optimum backlash' is a technical term for "feed it voltage & adjust for sweetest running". The rear mounting plate is just a piece of shallow channel section drilled to match the motor mounting screws & soldered to the frames after adjusting as noted above. So here we have it - motor secured firmly, and running very freely:


The above shot illustrates maximum travel allowed from centre on the driven axle


Side view showing rear mounting plate. Motor angle is actually shallower than I allowed for originally, giving an additional 2mm working clearance between the top of the motor & the underside of the saddle tank.

The little piece of wire you can see soldered to the side of the gearbox just above the rear wheel is to stop the idler axle from making unscheduled appearances. The idler gear isn't fixed to the axle, but I will need to remove it if I should want to take out the gear at any time in future. Using a wire restraint seemed better than gluing the axle in place.

Looking good, and runs really smoothly. Now - when will that phos-bronze wire get here so I can make the current pickups?

Bogies I have known

The bogie itself is a fairly simple construction as shown here:



The front bogie, or pony truck for those of you who prefer American terminology, is mostly just there for show in 1:87 scale. Even so, there are a couple of things to watch out for when making them. First, we need to prevent the situation where two wheels of the bogie on opposing sides touch the side of the bogie frame when going around a corner & cause a short circuit. I chose to avoid this by making the frames from a piece of printed circuit board. The second is to check what clearance is needed to allow for the bogie to clear the frames when rounding a corner. The problem is illustrated below:



This shot shows the clearance necessary to allow the bogie to clear the chassis on curves. It's about 0.7mm.



I'll make a radius bar to connect the bogie to a pivot point somewhere between the front drivers. A block of lead will be cast to fit into the channel section which holds the PC board frames apart, and maybe a piece of 0.008" (8 thou.) phosphor bronze wire as a loading spring once I receive it from Tichy Trains. Now to figure out how I'm going to keep the motor in place ...

Chassis-bashing

As it's a long weekend and the Domestic Authorities hightailed it out of town for the day, I spent an unusually uninterrupted few hours in the workshop & managed to get the chassis aligned & on its wheels.

This involved:

• Seperate the 2 frames & tack the axle bearings into place
• Install frame spacers using temporary screws
• Solder one side of both frame spacers to chassis frame. This leaves one frame able to be adjusted for best fit.
  
• Put axles through both frames & fit wheels temporarily
• Adjust loose frame until axles turn freely, then tighten spacer screws
• Place chassis on glass & test for any diagonal rocking between wheel pairs
• Use soldering iron to adjust bearings until all 4 driving wheels are resting on the glass
• Test that both pairs of driving wheels still rotate freely
• Solder loose frame to spacers. Chassis is now rigid
• Test again on glass
• Fit siderods & adjust until wheels run freely. This involved opening the siderod holes slightly larger than the 1.4mm crankpins required, but wasn't too much of a problem.
  

After all that, this is what the chassis looks like:



The top view showing top-hat style axle bearings in place:




And a trial setup with the bogie wheels I intend to use, showing why I had to open up the originally scale wheel-arches.



Next major tasks are the bogie frame & its pivot along with the motor/idler gearbox.

Getting Framed

First stage in chassis construction is to figure out what the main frames actually look like from the diagram, and transfer the drawings onto brass. I measured the length of the frames, and cut 2 pieces of 0.6mm brass to that length, joining them with double-sided tape.
I used to solder frame pairs together, but found that the tape works just as well & is a lot less messy to clean up.

Then, I cut the frame shape from the photocopy of the plans, and stuck it to the brass blanks with another piece of double sided tape like this:



Then, a pleasant 20 minutes or so with a piercing saw and a couple of files resulted in the basic frames taking shape:



The pop marks you can see are for the frame spacers - which are the next task in the process. At this point I'll 'fess up to making the driving wheels 1.5mm closer together than they are on the plan. This is because I have a nice set of etched siderods from an old loco kit which I'm using on this project, and they are not quite 100% scale between centres. I figure the time & aggravation saved is worth the trade-off.