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MikeTrice

6 Wheel Chassis for GNR Coaches: OO

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Ever since experimenting with the Diagram 3D kits of GNR 6 wheel coaches I have been mulling over how to provide a suitable 6 wheel chassis.

 

GNR 6 wheel coaches are odd beasts, they are very narrow and the centre wheelset comprises an external w-iron mounted to the external face of the solebar with the spring behind the w-iron.

 

There are a number of options to satisfy the above and it is my intent to cover each option and report back any experiences.

 

Options identified are:

 

  1. Brassmasters' Cleminson Chassis MC001
  2. Outer non-swivelling w-irons with centre axle going along for the ride
  3. Outer non-swivelling w-irons with centre axle sprung and able to slide across the vehicle.

I will start with the Brassmasters' Cleminson and follow up at later dates with the other options. I should stress at this point that during experimental mode I will use wheelsets that are not necessarily prototypical and bodge builds until a satisfactory solution is established. I am also only concentrating here on OO although some of my conclusion would also apply to the other gauges. I am also working initially on a 24' 6" wheelbase. Other wheelbases may have different results.

 

This is what you get:

post-3717-0-03818900-1466249179_thumb.jpg

 

The basic elements partially assembled and mounted on my simple testbed:

post-3717-0-63100200-1466249179_thumb.jpg

 

And mounted on the baseplate:

post-3717-0-17972900-1466249180_thumb.jpg

 

As a vehicle enters a curve the centre wheelset move over and the outer w-irons swivel thus:

post-3717-0-63854300-1466249180_thumb.jpg

 

To get maximum displacement of the centre wheelsets the outer w-irons can rotate a considerable amount:

post-3717-0-27493900-1466249181_thumb.jpg

 

More to come.

 

 

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I picked up one of the Brassmasters Cleminson chassis to try under the 3D coaches, as you made a decent job of the body I knew that was possible but thought I ought to make sure I could build a reasonable chassis for them first.

 

but as you know it's wiring I should really be doing....

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Get on with it Dave.

 

I've a Diagram3D kit and Brassmasters kit too. Will you be actually putting the 3 types chassis under the kit to rest on some curved track? It would be interesting to see how tight the curves can be before the coach can't get around them.

Edited by JCL

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Past experience suggests to me that you will find the Cleminson arrangement the easy winner. Much better on curves than the alternatives, and the vehicle will visibly ride  more like a bogie coach, and since there are quite likely going to be bogie coaches nearby...

 

But don't let that prejudice you in any way.

 

The imminent arrival of a RTR model of the single is making me have thoughts of some GNR stock to replace that which I foolishly sold forty years ago. Even though it probably was a good move, as I don't think they were that good in appearance or accuracy.

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Here is the crude testbed. Dummy solebars have been made that clip to the false floor using the parallel marks as a guide. By varying the width the performance tof the chassis can be tested around curves:

post-3717-0-55258900-1466264131_thumb.jpg

 

Fitting the retention wires to retain the centre wheelset actually limits the amount of sideplay in OO as they brush up against the vertical axle suports:

post-3717-0-31713700-1466264132_thumb.jpg

 

So based on the above results have been determined as follows:

post-3717-0-75721900-1466264349.jpg

 

With the solebars at their minimum spacing the end w-irons can no longer rotate so I trimmed back the wires connecting the outer w-irons to the centre unit. With the restriction on the centre axle sideplay the radius is still very limited hower it will now achieve Radius 4:

post-3717-0-98000700-1466264132_thumb.jpg

 

As a final experiment I rerouted the centre retaining wire to maximise the side play of the centre axle (which is effectively just going along for the ride):

post-3717-0-68250000-1466264120_thumb.jpg

 

The result was unexpected:

post-3717-0-02839900-1466264350.jpg

 

I mentioned earlier that GNR coaches are quite narrow. Most drawings of the 7'9" stock shows a dimension across the base of the coach body of 7'4" (29.33mm). If prototype solebar spacings - 6'1.25" is adopted (rounded up to accept the 24.5mm of the fold up units) with 1.5mm solebars a unit fixed at the ends but with floating centre wheelset shows more promise than the Brassmasters' Cleminson which needs greater clearance to work effectively. I have not checked all my Diagram 3D bodies but the one to hand shows a dimension across the base of the coach body of 28.5mm so tighter than the 7'4" prototype mentioned above. It would be possible to thin the solebars where the moving parts of the Cleminson components rotate giving clearance however care would be needed that any axlebox/springs do not catch.

 

More to follow.

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Revised design with the solebars being thinner where the moving parts of the Cleminson fit (giving 26mm clearance). Base plate fitted:

post-3717-0-02103400-1466278328_thumb.jpg

 

Remaining parts with re-instated keeper wires and the axles of the centre wheelset ground down flush:

post-3717-0-51733000-1466278374_thumb.jpg

 

Rolling chassis will now negotiate Radius 2 curves.

Edited by MikeTrice
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Looks good. It'll be interesting to see what happens when you put your cosmetic sides on.

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We had issues with retrofitting these units to 6 wheel LSWR carriages in that the other underframe fittings fouled the chassis and prevented it pivoting as much as it needed to. Of course, if you're building these with that in mind you can adapt the fittings to suit, but it's another factor which needs to be thrown in.

 

I've never yet had a problem with the chassis built as a 4 wheeler and the centre axle just along for the ride, but will be following this with interest.

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Second testbed, this time with the solebars set at 24.5mm and fitted with Bill Bedford sprung w-irons:

post-3717-0-82081800-1466419527_thumb.jpg

 

An MJT internal rocking unit was filed down elongating the axle holes to provide a centre cradle:

post-3717-0-27257800-1466419528_thumb.jpg

 

Then soldered to a length of 0.6mm ns wire and a brass plate at the end:

post-3717-0-09839900-1466419529_thumb.jpg

 

Now the centre unit has been fixed to the chassis:

post-3717-0-08078200-1466419575_thumb.jpg

 

This unit will just go around a Radius 2 curve but would be improved if I thinned the solebar to provide greater sideplay to the central axle. Thinning the solebar would probably also permit it to negotiate a Radius 1 curve.

 

The downside to this arrangement is that the central axle does not remain parallel to the track on displacement although it does not appear to make any difference to the running:

post-3717-0-58006100-1466419529_thumb.jpg

 

I should add that in all these experiments I am using reasonably heavy cast metal wheels like the Markits ones.

post-3717-0-82081800-1466419527_thumb.jpg

post-3717-0-27257800-1466419528_thumb.jpg

post-3717-0-09839900-1466419529_thumb.jpg

post-3717-0-58006100-1466419529_thumb.jpg

post-3717-0-08078200-1466419575_thumb.jpg

Edited by MikeTrice
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post-2173-0-60282100-1466422117_thumb.jpgHi Mike

When the LB&SCR used Cleminson trucks on their saloons, the solebars were spaced out to the width of the body/solebar join. Very easy to spot in photos, even this rather poor example, all I can find quickly!

So do your solebars need to be at normal spacing anyway?

Cheers

Ian

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post-2173-0-30375100-1466423544_thumb.jpgAlso, Dave Hammersley at Roxey devised a very simple version, sliding centre connected by a wire to pivoting outer w-irons. This being my copy of that but now with springing as per Bill Bedford's method. This has worked very well in P4 at 3' radius.

Edited by ianmaccormac

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So do your solebars need to be at normal spacing anyway?

It depends what you mean by "normal spacing". The overall width has to fit within the narrow width of the body which is 7'4". The inner dimension can certainly be greater than prototypical, which is what I have done with the first testbed with recessed solebars to increase clearance.

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Dave Hammersley at Roxey devised a very simple version, sliding centre connected by a wire to pivoting outer w-irons. This being my copy of that but now with springing as per Bill Bedford's method. This has worked very well in P4 at 3' radius.

Isn't that what I have done in my second option? And I agree, it works very well.

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Slight variation. The central wire has been extended and threaded through a hole in the buffer beam to see if the central axle remains parallel on displacement. I would not expect to use the buffer beam in this respect going forward but have a small projection down from the floor.

post-3717-0-72291100-1466442116_thumb.jpg

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Looks good. It'll be interesting to see what happens when you put your cosmetic sides on.

Like this?

post-3717-0-88818400-1466442242_thumb.jpg

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ooh. Now that's nice. Go on, if it's the right length, go the whole hog and balance the Diagram 3D body on top! You know it makes sense. :)

Edited by JCL
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I have to agree with Jason, that is a very fine looking underframe, it almost makes one want to convert to GNR......

 

Andy G

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ooh. Now that's nice. Go on, if it's the right length, go the whole hog and balance the Diagram 3D body on top! You know it makes sense. :)

Not as easy as that. The Diagram 3D body is too narrow at 27.8mm across the bottom. I will have a go and build one specially for the Diagram 3D body.

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Slight variation. The central wire has been extended and threaded through a hole in the buffer beam to see if the central axle remains parallel on displacement. I would not expect to use the buffer beam in this respect going forward but have a small projection down from the floor.

attachicon.gifIMG_8335.JPG

I like the look of your "slight variation" which appears to address many of the Cleminson problems in 4mm scale in a simple and inexpensive way.

Note to self: must build some of my 6 wheel coaches and try it!

Thanks

Jim P

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With regards to the central axle, what if you glued some square rod or similar either side to give it a channel to slide within? I did this with that 6 wheel coach I tested the Silhouette on way back. Or would this create too much friction in this case? Also, what is the wire size?

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Ouch, sorry, didn't go back...

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Managed to shoehorn some form of chassis into the Diagram 3D bodyshell. The recesses across the faces are 24.5mm so the Brassmaster's Cleminson is not practical:

post-3717-0-44590200-1466606849_thumb.jpg

 

I wanted to use this as a testbed for a third variant based on Bill's sliding centre axle. Unfortunately none of Bill's w-irons are characteristic of the GNR coach w-irons. With this in mind I have used some pedestal units with a view to adding my own cosmetic w-irons later. For those unfamiliar with Bill's units the main components are as shown:

post-3717-0-29822500-1466606848_thumb.jpg

 

Although they will accept 14mm OO wheels they are not really designed for them and there is little clearance between the flange and the brass base. Being brass makes it liable to short if the wheel rises in its slot:

post-3717-0-80873400-1466606848_thumb.jpg

 

So I need to do some head scratching and come up with a way of improving the wheel clearance in the pedestal units before I continue. I could simply cut the centres out and epoxy the individual w-irons to the chassis but I would have to ensure they maintain alignment while I do that.

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Why not cut a wee slot each side of the base to allow a bit more vertical clearance for the wheel tread?

This could, relatively simply, be done using a cutting disc

Jim P

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