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2mm Coal Tank test build


Branwell
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I have no knowledge of the design of the chassis, but, assuming you are using split frame pick-up and the frames are isolated from each other, I would suggest that you solder a piece of PCB across the top part of the pony truck (underneath it if there is room) and then cut through the pony truck top and the copper cladding on the pcb.  That way the two sides of the pony truck will be isolated from one another and there will be no issues if it touches the frames, providing there is enough room for it to swing on your minimum radius.

 

Jim

David,

I agree with Jim's suggestion. Gap the underside of the PCB first - perhaps wider than usual - sweat it on to the top of the frame, then cut the frame in half from beneath. That way, you won't have to re-gauge the frame.

Good luck,

John

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I've attached a photo of the LRM pony truck - in the 4mm version of the kit it's attached to one of the frame spacers by a nut and bolt.

 

IMG_2262_1024_zpswmni9hx2.jpg

 

I think Jim and John's suggestion is going to be the easiest in terms of isolating the truck but that still leaves the question of how to affix it and keep it isolated. Initial thought is to drill through the PCB attached to the top of the truck using the hole in the truck as a guide and then cut away the tail of the truck having already gapped the PCB and attach the whole to a double gapped PCB frame spacer with an appropriately sized nut and bolt.

 

The outside width of the 2mm pony truck is 6mm by the way.

Edited by Branwell
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I'm hoping to pick up the remaining etches from LRM at York this weekend, subject to the etchers having got the etches to them in time. Failing that they'll hopefully be ready shortly after Easter.

 

Chris Higgs is till working on his chassis etch I think, but I'm now having a go at building the LRM chassis. Am doing some serious head scratching at the moment though as to how to isolate the rear pony truck. I think I should be able to isolate it from the frames ok by using cigarette paper but I'm struggling when it comes to isolating it from the wheels - the truck's one piece and sits inside the frames but the wheels are going to come into contact with it and it seems to me that's going to bridge any gap between the frames.

 

Would be grateful for any suggestions as to how to go about resolving this - thought about using cigarette paper on the stub axles but can't see that working in terms of free running plus the clearances are very tight and I can't really open up the axle holes in the pony truck any further. is it a case of cutting the pony truck in half and narrowing it slightly and then attaching it to some thin PCB?

 

All suggestions welcome ...

 

Regards,

 

David

 

As to pony trucks (or I suspect you mean radial trucks here), to be honest I am coming round to the view that building them with PCB strip is just using a sub-optimal approach because we always have, and am looking at 3D printed versions with etched overlays on each side.

 

I don't believe that the LRM frames which make no allowance for frame narrowing at the rear are going to work anyway (unless your loco is only going to travel only in striaght lines) as your wheels are not going to have any sideplay, regardless of whether they have an inner frame truck.

 

Chris

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...........Initial thought is to drill through the PCB attached to the top of the truck using the hole in the truck as a guide and then cut away the tail of the truck having already gapped the PCB and attach the whole to a double gapped PCB frame spacer with an appropriately sized nut and bolt.

Sounds like a plan to me!  An alternative would be to carry the pcb a wee bit along the arm and then isolate that from the sideframes in the same way as isolating the sideframes from one another.

 

Jim 

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What radius do you want to operate the loco on? My 4mm version will readily go around B6 points (I am not sure what radius that equates to, I have seen both 48" and 69" quoted), but struggles on an A5 or tighter. As I said in post #51, it tends to be the cab steps that limit the carrying axle sideplay in 4mm.

 

Might one answer be to use the "pivoted frames" approach. The rear frames, together with carrying wheels/axle are pivoted behind the rear coupled axle. Brassmasters used this approach on their earlier kits of LNWR 4-6-0 and 4-4-0s for the front frames/bogie. If you hung the cab steps on an outrigger from the pivoted frames, you could overcome the restriction they impose.

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Might one answer be to use the "pivoted frames" approach. The rear frames, together with carrying wheels/axle are pivoted behind the rear coupled axle. Brassmasters used this approach on their earlier kits of LNWR 4-6-0 and 4-4-0s for the front frames/bogie. If you hung the cab steps on an outrigger from the pivoted frames, you could overcome the restriction they impose.

 

That sounds similar to the approach Mick Simpson took with his NER N10 loco. Details are here (and in other posts on the same blog). The position of the cab steps would mask the split in the frames.

 

Andy

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As I said in post #51, it tends to be the cab steps that limit the carrying axle sideplay in 4mm.

 

This may well be an issue. The overall width of both 2FS and N wheelsets is greater than the prototype. Whereas in 4mm, P4 matches the prototype, and both EM and OO are under.

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That sounds similar to the approach Mick Simpson took with his NER N10 loco. Details are here (and in other posts on the same blog). The position of the cab steps would mask the split in the frames.

 

Andy

 

I'm still pondering how best to do the pony truck and have a couple of ideas that I want to try out, but I had a chat with Mick at York show on Saturday and his advice, having had a look at the etches, was to concentrate on getting the chassis running as an 0-6-0 first and then worry about the pony truck later - depending on the weight of the loco and how well it's balanced it might be that the pony truck won't need to act as a pick up and can be built in a such a way that it's entirely isolated from the rest of the chassis.

 

Whichever way I go though, I'm not going to get anywhere by simply sitting and pontificating, so I've soldered the frame bushes in place and loosely fitted the wheels so as to work out the best motor and gear combination. When I first started talking to London Road Models about this project in May last year, I was also picking Nigel Hunt's brains, and his initial suggestion was a Nigel Lawton 8mm motor with a 30:1 worm wheel on the rear driven axle and it looks like that may well work but the proof of the pudding is, as they say, in the eating.

 

May get a bit more done tonight but if not I've got another long weekend coming up next weekend.

 

One thing that's becoming clear though is that clearances are tight, both for the motor and for the wheels, so may have to be a bit of fettling here and there.

 

The other thing for now is that unfortunately John Redrup hasn't received the additional etches yet so for those still waiting to get there hands on set if you can bear with me a little longer please and I'll be in touch as soon as I hear any more from John ... and in the meantime here's a few more pictures of the build as it stands:

 

IMG_2263_1024_zps22nxxxeo.jpg

 

IMG_2266_1024_zpsivfcek8q.jpg

 

IMG_2264_1024_zpspqklkxjv.jpg

 

IMG_2268_1024_zps83munvka.jpg

 

IMG_2267_1024_zpsf60ant4q.jpg

 

IMG_2265_1024_zpsi4g2ljy9.jpg

 

IMG_2269_1024_zpsittvmuy6.jpg

 

IMG_2271_1024_zpsch7tsyz1.jpg

 

IMG_2270_1024_zpsj3nsx4on.jpg

 

Regards,

 

David V.

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As I mentioned in my last post, I've started playing around with motors and gears and whilst it's a snug fit, the preferred combination of a Nigel Lawton 8mm x 16mm midi motor and a 30:1 worm gear on the rear axle is looking like it's going to work, albeit with some surgery to the body to make room for the worm and the gear - part of the footplate needs cutting away as does part of the cab floor and the lower half of the front of the cab.

 

Whilst it's possible to do the cutting after you've built the body, for anybody using the London Road Models chassis it's probably easier to do it beforehand and I suspect the same will apply with Chris Higgs' chassis as well, though it will make locating the cab front trickier  - if you wait until after you've assembled the body, there is, I think, a danger of breaking the back of the body when making the cuts.

 

Anyway, I've taken a few more photos to show the alterations that I've made. The motor isn't quite in it's final position and will have to be inclined to clear the frames but there appears to be enough room in the boiler to lift it, though it's becoming apparent as the build progresses that there's going to need to be some weight in the smokebox to keep the loco balanced.

 

As for the pony/radial truck, I'm still playing around with ideas and will post further on that in due course.

 

Regards,

 

David V

 

IMG_2278_1024_zpspaxtqjbu.jpg

 

IMG_2279_1024_zpsk6qeuoz1.jpg

 

IMG_2280_1024_zpsg7zpltxy.jpg

 

IMG_2282_1024_zpsp0rudkxv.jpg

 

IMG_2284_1024_zps8vozfupv.jpg

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  • 2 weeks later...

Here is a test of my chassis design using a 3D printed block in the place of the etched parts that will be in the final version. It demonstrates the positioning of the gear train and the mounting holes for the body and motor mount. Sadly it would not be useable as is with the etched sides from the LRM etch (as illustrated) as it is too thin and weak on the side where the secondary spur gears will be located. However it is both quicker and cheaper to prorotype the design this way.

 

post-1605-0-67500700-1460581660_thumb.jpg

 

post-1605-0-22056600-1460581671_thumb.jpg

 

post-1605-0-13848700-1460581692_thumb.jpg

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............ Sadly it would not be useable as is with the etched sides from the LRM etch (as illustrated) as it is too thin and weak on the side where the secondary spur gears will be located. However it is both quicker and cheaper to prototype the design this way.

Could the 3D printed material be tapped 12BA, or even have a threaded hole printed?    If so, could individual spacers be 3D printed and the frames screwed to these via holes etched in the frames?  This would allow spacers with holes for the body mounting screws to be made, providing perfect alignment of both frames and body mounting position.  If the screws are located so that they are behind the rims of the driving wheels they won't be seen.

 

Jim

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Could the 3D printed material be tapped 12BA, or even have a threaded hole printed?    If so, could individual spacers be 3D printed and the frames screwed to these via holes etched in the frames?  This would allow spacers with holes for the body mounting screws to be made, providing perfect alignment of both frames and body mounting position.  If the screws are located so that they are behind the rims of the driving wheels they won't be seen.

 

Jim

 

I have not tried tapping this material so do not know whether it would grab or not. Printing a thread would certainly task my 3D skills to breaking point!

 

You can also just superglue the spacers, especially as here where the axle bearings are providing the alignment.

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I have not tried tapping this material so do not know whether it would grab or not. Printing a thread would certainly task my 3D skills to breaking point!

 

You can also just superglue the spacers, especially as here where the axle bearings are providing the alignment.

Thinking about it further, you could just have a hole through the spacer, solder short stubs of wire/rod into holes in the frames (to provide accurate alignment) and then superglue the frames to the spacers.  The stubs need only be a couple of mm long.

 

As I type this, the idea has come to me of just having a 10thou deep recess in the top of the spacer and a bent in tab on the top of the frame which fits accurately into the recess.  Or, a 10thou projection on the end of the spacer which fits into a rectangular gap/hole in the frames?

 

Or am I thinking too far out the box now!   :dontknow:

 

Jim

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Thanks for your efforts with the chassis Chris. How are you accommodating the pony truck?

 

For those who've ordered the etches, the additional ones I ordered from LRM have now arrived with me and will be posted out at the weekend.

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Thanks for your efforts with the chassis Chris. How are you accommodating the pony truck?

 

For those who've ordered the etches, the additional ones I ordered from LRM have now arrived with me and will be posted out at the weekend.

 

So far I am not. Coal Tanks don't have a pony truck. It's a radial truck and I had planned just to give extra sideplay on the trailing axle by narrowing the frames, but not have it rotate. I have been advised this might not work, so I am trying to work out a way to test this out perhaps by getting a 3D printed block running and test it on a layout.

 

Incidentally, the total wheelbase on a Coal tank is less than the coupled wheelbase on a GWR 42XX, so I am just trying to work out what kind of radius it will go around if simply built rigid.

Edited by Chris Higgs
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The new material from Shapeways, the black HD Acrylate, is supposed to be tougher, and slightly cheaper, than FUD, so might be worth trying.

 

However, looking at my existing stuff, some is failing on wall thickness on this material where it passes on FUD, and is also showing as more expensive. This I think is because there is no cost penalty in FUD when you have multiple items in a print, whereas with other materials there is. I would like to avoid having artificial sprues between items to circumvent this

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