Biting Off More Than You Can Chew

Well, this saga started simply enough. I started to build a 7mm scale NGG16 from a Backwoods Miniatures kit. It didn’t take long before it started to annoy me and before I started modifying it.

The things that annoyed me were that it wasn’t a particular NGG16, it was trying to be all of them whilst being none of them. It also suffered big time from having been designed for 009 with hand drawn artwork to 8mm scale reduced to 4mm. When hand drawn artwork was still a thing the idea was that you drew it to something like 6 times full size and then photo reduced this to the size you wanted. The idea of this was that it reduced down your wiggly lines to the point where you can’t see the wiggles. Also a pencil doesn’t do cut and paste which is a bit of a bummer where there’s lots of repetition. Reduction from 8mm scale to 7mm scale doesn’t do it. Also details that look OK in 009 don’t cut it in 0-16.5.

Valve gear is an interest of mine, dodgy model valve gear a pet hate. The result was that I designed all new cast valve gear for the loco, posted some picture before it was fitted and then got sidetracked and the project didn’t really progress.

Enter Nick Dunhill, he was building one for a customer and had I got a set of the castings to spare?

I had. He wrote up his NGG16 build on RM Web, Western Thunder and The Gauge O Guild Forum. Then came the “can I have a set” enquires.

Well, I suppose so, thinking that I might sell half a dozen, There aren’t that many Garratt kits out there are there?  Wrong, 25 sets in production and I have never placed an order that large with Shapeways.

What resulted was a redesign at Shapeways suggestion. All the parts for one end of the loco are now on a single sprue so two sprues do one loco.

The redesign resulted in a test print/casting and then 52 castings being made with a seriously large bill from Shapeways. To some extent this was the easy bit as the CAD was done and we just had to wait for them to do their stuff which takes about a month.

When the bits arrived then the fun started and I began to realise this was going to take awhile.

The first job was to drill and ream the holes for the valve spindle in the cast valve guides. These were drilled and then reamed with a 2.1mm drill. This took a long while as hand reaming was slow. A machine reamer might have helped but would have just added cost. It doesn’t matter how much you ask them not to Shapeways coat their castings with a shiny lacquer. It makes them look like bling, it highlights any layering from the print that’s visible and it stops them being soldered. So they were abrasive blasted.

On cue the next part of the saga arrived in two parts. First thing was to discover that my blast cabinet had a perspex window and I couldn’t see through it. Dismantling it and taking the perspex window to the glass merchant got it a shiny new hard glass window and I could see what I was blasting instead of doing it by braille.

Excellent but three days went by between realising I couldn’t see what I was doing and getting the new window in place.

Next part in the blaster saga was the realisation that the filtration of the exhaust  air wasn’t good enough as everything around was getting covered in a fine layer of abrasive. What I really needed was a flanged elbow fitting that also was a reducer.

Where am I going to get one of them? The 3D printer came in handy (once I’d cleaned the abrasive film off it)

That elbow led into an experimental development filter carefully engineered from a cardboard box (aka bodged together). The box contains a bunch of inner partitions so the air has to go round a number of bends whilst slowing down and dropping any particles.  The posh name is a labyrinth seal and whilst it does look like a bodged up cardboard box it does work with most of the particles being stopped at the first turn.

Next job is to make another elbow and a posh version that fits out of the way along the back of the cabinet (pertinent to where its new home will be).

After all the blasting the castings all went for a swim in the ultrasonic cleaner to get all the abrasive off. The before and after photos of the parts explain why I did the abrasive lark.


With that done it was onto the valve spindle parts.

These are made from 2mm outside diameter tube.

This comes in 300mm lengths and then had to be cut into a lot of 25mm length, four per set. 25mm is longer than needed but it leaves something to get hold off whilst working on the parts.

Next issue is that the hole up the middle isn’t big enough so its out with the lathe.

The first job was centre drill into each end of the tube and run a file over the outside to clean off any burrs and to centre the ends ready for a drill.  After that one end of each tube was counter-bored with a 1.45mm drill for a depth of around 4mm

Centre drilled end

Counter Boring one end

Same image but with a fast shutter to freeze the action

By this stage I was questioning my sanity.  At this point I decided any thoughts I had of assembling the valve spindles was crazy so I have done a set (for me) and photographed it to explain the plan.

The aim is to make the brass look like shiny steel and fit an end to it.

This is done by tinning it with solder, wiping off to a smooth finish and soldering a 7mm scale handrail knob in the end. To finish the job off the handrail knob is blackened.


The finished thing held in a pin vice

How it should look assembled.


I think its fair to say I have had enough of these for now! I just hope these builders send me some pictures of their NGG16’s when they’re done



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