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All new RTR PGA wagon in 4mm scale


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Looks great in every respect except for the NEM pockets being very close to the outer end of the wagon forcing a huge gap between vehicles. With the pockets so far out, it doesn't even leave the option of swapping for shorter couplings. It may seem like a minor thing but I've always questioned the logic in pursuing accuracy to the nth degree but having a scale 2ft gap between buffers when running on a layout.

I know that Bachmann have some of theirs pushed outwards due to interference between axles and the huge mounting assembly they use for their couplings. I would have thought that, with a clean sheet, this could have been avoided.

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Thanks for your comments Chris. However, there isn't a huge gap between wagons. It's designed to be as close as possible and still allow the wagon to be used on 1st radius reverse curves. The actual hook and loop is to the exact dimensions as a Hornby coupler and the NEM box positioned exactly to NEM standards based on distance from the face of the buffers. The finalised CADs do include a cammed coulper though which we didn't bother with on the initial CAD with the wagon being a 4 wheeler so could pull it in perhaps as this will extend on curves.

 

We could in theory provide a shorter loop and hook or maybe move the pocket further back a touch, I will have a look at the CAD and see how much I can squeeze but we have to think commercially allowing for train set curves. Buffer clashing or locking when propelling are simply not acceptable in this respect. We have to take into account that this wagon may be coupled to a class 60 with its buffers swinging about all over the place in contrast to the wagon which will barely swing at all on 1st rad curves.

 

As we are keen to hear any feedback I will of course take on board your comments and have a look what can be achieved.

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The pockets are at the correct height. As for drooping I too feel that this needs to be addressed and if any droop exists in the current set up we will sort it at the design stage prior to manufacture. I do question the need for cammed couplers on such a short wagon though so will be discussing this with the manufacturer prior to approving any wagon fabrication. The last thing that you want on a rake of wagons that you will potentially be pushing along as a full rake is couplings giving up and causing issues.

Edited by RBE
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This is only my own opinion but some thoughts on the couplings do occur to me. First, most models these days are specified to run on minimum second radius curves. Forgive the pun but would this cut you some slack? Second, there isn’t much to chose between them but I prefer Bachmann tension locks to Hornby ones. The hooks are shorter so there’s less slack. They also look a little less clumsy. Third, I should imagine that cams would add to the cost of the wagon. I think you have decided, quite reasonably, that a shortish four-wheel wagon doesn’t need them.

 

From my point of view, it’s a little academic because I swap Kadees for the tension locks on block trains of modern wagons. My layout has gentle curves and I try the shortest first and then move up until I find the closest coupling which works. It’s why I like sprung buffers but in the case of these wagons, I accept that I shall have to lump it.

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Yes, sprung buffers would be a nice luxury really for a wagon, the cost of these isn't really worth it on the return. I used to only ever run 3 links in 4mm scale and even then sprung buffers were a nice thing to have rather than a requirement I found.

 

Anyway I have taken the CADs and reverted to a fixed NEM and set it 2mm further back to see what effect that has. It of course brings the buffers in and seems to still work with a 1st radius. As you have said though No Decorum, most stock nowadays is aimed at 2nd radius so perhaps we specify that as a minimum radius?

 

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Just for reference this is the NEM standards for the coupler socket. The original position shown above on the coloured 3D CADs is set to this. The revised ones I did on the 1st Radius curve is now set with the buffer face to NEM box distance at 9.5mm rather than the specified 7.5mm.

 

post-6894-0-79845100-1477130914_thumb.png

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Ok I have revised the CAD's which now have a fixed NEM socket (which is also removable to aid our fine scale brethren who wish to use 3 links etc). I have also set the face of the box 1.5mm further back than standard to bring the wagons 3mm closer together when coupled. I was tempted to go 2mm to give a 4mm reduction but I think we need to air on the side of caution when it comes to standard couplers for a RTR wagon.

 

Anyway here are the CAD's revised to show what they look like, as ever feedback is welcome.

 

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post-6894-0-78221300-1477425393_thumb.jpg

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Yes, I like. Bachmann and Hornby NEM pockets have a thin, flexible neck which permits sideways movement of the pocket without the use of cams. (It may for all I know be part of the NEM specification.) Will yours be the same? If so, will they foul the pipes?

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It's not part of the spec. I personally doubt that there is any need to pivot the box on such a short wheelbase wagon, especially now that we aren't really supporting curves below 2nd radius (although I can't see any issue on a 1st tbh). The etched metal hook has enough sideways play to allow movement there to keep the NEM box rigid.

 

I'm a little reluctant to add slop to the box as this then introduces inconsistancies with regard to shunting/propelling etc.

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That sounds good. Bachmann is proud of itself for having introduced the less obtrusive tension lock coupler and everyone has followed suit (except old Hornby wagons). It has brought problems in its wake, though, in that coupler deflection has been introduced. That’s fine when hauling a heavy rake but, as you point out, it doesn’t work so well when propelling. Not to mention interfering with the pipes.

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That sounds good. Bachmann is proud of itself for having introduced the less obtrusive tension lock coupler and everyone has followed suit (except old Hornby wagons). It has brought problems in its wake, though, in that coupler deflection has been introduced. That’s fine when hauling a heavy rake but, as you point out, it doesn’t work so well when propelling. Not to mention interfering with the pipes.

 

However Airfix did it over 30 years ago but the Triang/Hornby style persisted and was abandoned by Mainline when they took over the Airfix range!

 

These shots compare the two!

 

Mark Saunders 

 

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post-3578-0-44296500-1477477581.jpg

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It's not part of the spec. I personally doubt that there is any need to pivot the box on such a short wheelbase wagon, especially now that we aren't really supporting curves below 2nd radius (although I can't see any issue on a 1st tbh). The etched metal hook has enough sideways play to allow movement there to keep the NEM box rigid.

 

I'm a little reluctant to add slop to the box as this then introduces inconsistancies with regard to shunting/propelling etc.

 

I also don't see an issue with a rigid NEM pocket on a short wheelbase wagon and I'd prefer not to see any 'slop' in the pocket dimensions.  The coupling of choice should ideally be held tightly both horizontally and vertically.

 

I don't know how much of your potential market use 1st radius curves (potentially only in hidden sections), but I'd still be tempted to cater for them if possible.  

 

I'm not sure if I'll end up purchasing any of these wagons as I don't think any have made it to Scotland in the post-privatisation period (ie in Lafarge livery), but if I do, the couplings would be replaced with NEM Kadee couplings, so as long as the setback of the pocket from the buffers is in the range 7.11mm (#17 with generous curves) to 11.68mm (#20 with generous curves) there should be a workable solution.  I would favor a set back of around 8.5mm, which should permit a #18 coupling, but I don't know what users of alternative couplings would prefer.

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Thanks for the insight into Kadee requirements. We can't of course make the wagon everything for all men but as it stands the NEM box is positioned 9mm back from the buffer faces. This falls within your requirements and is not far from your ideal.

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Ok so the bad new first. After modelling the couplers as fixed units it seems that there would be issues with trying to use the wagons on a 1st radius S curve. I can see the wide eyes and raised eyebrows now at such a track plan but you just know that someone out there is going to be rocking a fiddle yard with a fan made of setrack point who wants a rake so we have to cater for this.

 

Heres the issue:

 

post-6894-0-97815600-1478026188_thumb.png

 

As you can see it goes around the curve easily but at the S bend, oops.

 

So we have reverted to the original cammed design (the arm looks pretty robust for deflection resistance tbh so I'm ok with it) However due to a lack of space to make it close coupled I have produced a shorter tension lock to fit into it. This brings the coupler albeit not the NEM box further in to the same location as the fixed version above.

 

Heres where its at:

 

post-6894-0-06924200-1478026381_thumb.png

 

Again comments always welcome.

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Cams are not necessary for me but if you feel it’s necessary to design cams in, it’s not going to put me off the wagons. I’d only repeat my point that it would be an advantage to make the holes for the pipes round so that the pipes can be inserted at an angle if necessary to allow for the movement of the pocket.

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  • 2 weeks later...

I have made a start on Part 2 of the Historical Train Formations Guide which will cover the post privitisation period.

 

Beast has kindly started a topic in the Prototype Discussions section covering the Mountsorrel to Trowse workings over the past five years:

 

http://www.rmweb.co.uk/community/index.php?/topic/116677-6l396m436l47-the-mountsorrel-norwich-trowse-pga/

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  • 2 weeks later...

During the mid-1980s when the PG012As were having an overhaul, some examples received full protection panels between the end bracing. We would like to include these end panels on our model.
Cav has kindly produced a couple of renders to show the PGA model with the panels fitted.

 

 

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  • 3 weeks later...

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