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GWR Small Metro Tank (1)


Ian Smith

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A couple of years ago, I made a somewhat abortive start on a 2FS scratch built loco. I had got to the stage of a rolling chassis, and a body that consisted of footplate, valances, buffer beams and a cab bunker. Where I had failed was getting the chassis to actually run happily. In the end, I decided to shelve the project and move onto my 1854 Saddle Tank that has been documented previously that used one of the 2mm Association etched chassis kits.

 

Now that I have proved to myself that I can construct coaches, track work (and most importantly get a loco to run well) in 2FS, I have decided to resurrect my Metro Tank project. A look at what I had already built prompted me to discard the chassis - not because it is unsalvageable, but rather because with such a small 2-4-0 engine I feel that weight will be key to getting a successful outcome - the original chassis was constructed traditionally with 0.25mm phosphor bronze frames held together/apart with PCB.

 

Initially, I had intended to use one of Nigel Lawton's small 6mm diameter motors driving the leading drivers (an earlier iteration of the chassis tried to drive the rear drivers with the compromise that some of the gearing would be visible in the cab), but on this re-work, I have decided to utilise a Nigel Lawton 8mm diameter motor along the boiler into the smokebox (again driving the leading drivers).

 

A diagram was drawn up in Inkscape to verify that everything would fit in this new arrangement :

blogentry-12089-0-73566200-1406576680_thumb.png

 

The first thing to produce was a set of coupling rods, these were fretted and filed out of a sheet of 0.028" nickel silver (the pair soldered together until complete) :

blogentry-12089-0-06529000-1406576938_thumb.jpg

Once finished, the pair were separated giving these :

blogentry-12089-0-42538700-1406576946_thumb.jpg

 

To provide as much weight as possible in this version of the chassis, I have decided to construct a solid brass chassis comprising a 6mm square main block, and a 6mm x 1mm strip alongside. Initially the pair were double-sided taped together while a pair of 1mm holes were drilled outside the finished frame ends which were then tapped 12BA to allow the pair to be kept together for the remaining machining. 3 further 1mm holes were drilled in the chassis proper clear of the wheels and gears to allow the chassis to be held together once the chassis is cut to it's finished size. These holes in the main block were opened out to 2.5mm, then subsequently plugged with milliput which once dry and hard were re-drilled 1mm (using the outer frame as a jig) and tapped 12BA too.

blogentry-12089-0-59547900-1406576910_thumb.jpg

 

A 0.4mm hole was drilled in the chassis block on the centre of the rear drivers (0.4mm because I couldn't find any 0.5mm drills!), which allowed one of the previously made coupling rods to be "pinned" in place so that it could be used as a jig to drill a further 0.4mm hole for the leading drivers.

blogentry-12089-0-18100700-1406576920_thumb.jpg

 

Once the coupling rod jig was removed, the axle holes were opened up to the axle size of 1.5mm (later opened up again to 1.6mm as the stub axles on the wheels I have wouldn't fit in the holes).

The two chassis parts were separated, and the axle holes in the main block milled out to accommodate the "muffs" used in 2FS to hold the 2 stub axles together (leaving a 1mm deep axle hole on the outside edge of the main block). The area where the gears will be was also milled away :

blogentry-12089-0-43621500-1406576927_thumb.jpg

 

A trial fit of the wheels and gears has shown that I need to remove a little more of the main block to accommodate the worm gear, and I also need to remove some from the top of the chassis to house the gear box which will also be milled from solid - the cross shaft of the gear wheel is too close to the top of the block so was never intended to be in the main block (it will also allow easier set up of the quartering,etc if it isn't locked solid be the worm) :O

 

Once the above has been done, the lower part of the chassis ahead of the leading wheels, and behind the trailing drivers will be removed to give a better looking chassis profile (the area between the leading wheels and the leading drivers will also be removed).

 

Hopefully, the brass for the gearbox and the 0.5mm drills will appear in the next few days to allow further progress.

 

Ian

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Looks really good Ian. Looking forward to seeing it in action.

 

Regards, Andy

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I do like this idea. I have a chassis kit for a manor (Nigel Ashton) which uses the same principle. It seems even more sense for a Metro tank. Did you do the cutting out on a mill?

Don

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Looks really good Ian. Looking forward to seeing it in action.

 

Regards, Andy

Andy,

So do I !! :-)

 

 

I do like this idea. I have a chassis kit for a manor (Nigel Ashton) which uses the same principle. It seems even more sense for a Metro tank. Did you do the cutting out on a mill?

Don

Don,

It was Nigel's Manor and his articles in the 2mm magazine on his Cambrian 0-6-0 that gave inspiration for this project - I've pretty well copied his ideas/direction throughout.  The cutting out was on my lathe with the vertical slide for milling in place.  A chuck adapter was fitted in place of the 3-Jaw chuck, and a Jacobs chuck used to hold drills and milling cutters (not best practice using Jacobs chuck for milling but I was only doing fairly light cuts as i wasn't in too much of a hurry).

 

Ian

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  • RMweb Gold

Good stuff Ian!  Glad you've resurrected the Metro, another of my favourite GWR locos :-)

 

Dave

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Nice robust chassis design, food for thought, Ian.

 

How strong is the Milliput for holding threads?  My instinct would be to press in a plastic insulating rod and tap that but if Milliput is up to the job, then seems a lot easier.

 

Mark.

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Nice robust chassis design, food for thought, Ian.

 

How strong is the Milliput for holding threads?  My instinct would be to press in a plastic insulating rod and tap that but if Milliput is up to the job, then seems a lot easier.

 

Mark.

Mark,

I'll let you know!!  It seems to be OK at the minute, but I'm not intending to be assembling and de-assembling regularly.  Obviously so long as it's good enough to hold the two chassis parts together securely then it's probably good enough.  Clearly I need to be sensible when tightening up the bolts so as not to over-tighten and strip the thread in the milliput - I believe that Nigel used 24hr araldite in his Cambrian 0-6-0.  If I decide that it isn't up to the job then a plastic plug will be a sensible replacement.

 

Ian

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  • RMweb Gold

Another great thread posting Ian. I do think this is the way to go for 2mm chassis with all that weight low down, particularly smaller protoypes. I have a significant birthday approaching and have asked for one of the little Proxon mills so will be having a go at one myself - an Ilfracombe goods for Tucking Mill.

 

Jerry

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Another great thread posting Ian. I do think this is the way to go for 2mm chassis with all that weight low down, particularly smaller protoypes. I have a significant birthday approaching and have asked for one of the little Proxon mills so will be having a go at one myself - an Ilfracombe goods for Tucking Mill.

 

Jerry

Jerry,

Having seen how well Andy's Manor runs, I also think that a solid chassis is better than one from 0.010" sheet (OK it won't have the spring detail, etc but I see no reason why if you're desperate for that sort of thing why an overlay couldn't be attached - I won't be although I have ideas about adding brake detail).  That's not to say that an etched chassis is a bad thing - I'm perfectly happy with the way my saddle tank performs and it's haulage is remarkable (at least 6 bogie coaches on St Ruth without slipping).

 

I was looking at those Proxxon Mills at Kidderminster and really surprised how small they are.  If I could have justified one I might have considered it but had already invested in a vertical slide for my Peatol lathe a few months ago primarily so that I could try this method of chassis construction.

 

Ian

 

PS Look forward to seeing how you get on with your Ilfracombe Goods (and Mill) :-)

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I have splashed out and bought a Proxxon MF70 mill but need to get other jobs before setting it up. I also belive low down weight improves road holding..

Don

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