N7 Chassis Question

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Proto87Stores

N7 Chassis Question

Postby Proto87Stores » Thu Jul 11, 2019 4:25 pm

Found a little time to continue working on the N7 chassis. Can someone please advise on the normal chassis outside widths over the side frames that iareused for P4 and also for 00 steam locomotives. I'd like to make sure it would work with both.

TIA Andy

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Horsetan
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Re: N7 Chassis Question

Postby Horsetan » Thu Jul 11, 2019 11:21 pm

Proto87Stores wrote:Found a little time to continue working on the N7 chassis. Can someone please advise on the normal chassis outside widths over the side frames that iareused for P4 and also for 00 steam locomotives. I'd like to make sure it would work with both.


16.5 for P4, I think.

OO: not sure - there seem to be a few.
That would be an ecumenical matter.

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steamraiser
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Re: N7 Chassis Question

Postby steamraiser » Fri Jul 12, 2019 8:12 am

I do not understand why you would want a chassis to work for both P4 and 00 standards given the large difference in gauge.
To meet you objectives you will have to build the chassis with 00 spacers and use a fair few washers on your P4 wheel sets.

Gordon A

Philip Hall
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Re: N7 Chassis Question

Postby Philip Hall » Fri Jul 12, 2019 8:52 am

There are, unfortunately for a manufacturer, differing opinions on frame widths. It depends entirely on the radii you wish to negotiate. For me, 16.5mm is far too tight; once bearings are in (or hornblocks) and depending on the thickness of the boss on the back of your chosen driving wheels, there will be little sideplay left. I usually go for 16mm, leaving me 1.67mm between that and the minimum back to back for some adjustment. This is not cast in stone, however, and I should say that if I find some frame spacers a bit less or a bit more, or the kit ones are about right, I will use them.

In 00, with a 14.5mm back to back and thicker wheels and flanges, I would go for 12.5mm.

Philip

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Noel
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Re: N7 Chassis Question

Postby Noel » Fri Jul 12, 2019 9:08 am

In UK kits intended for all three gauges it seems to be common practice to provide separate OO, EM and P4 frame spacers.
Regards
Noel

Proto87stores

Re: N7 Chassis Question

Postby Proto87stores » Fri Jul 12, 2019 2:32 pm

Thanks for the answers so far.

steamraiser wrote:I do not understand why you would want a chassis to work for both P4 and 00 standards given the large difference in gauge.
To meet you objectives you will have to build the chassis with 00 spacers and use a fair few washers on your P4 wheel sets.

Gordon A


I'm designing this chassis (and subsequently all my others) to incorporate working 4 point equalization and rapid and problem free assembly. To me this is especially important in the case of wanting multiple copies of the same prototype. ( I have 5 N7's to build so I can model a small part of the "Jazz" operations). For my own use, I wish to run my moderate number of UK model kits with P4 wheels on my various existing 3.5 mm proto:scale tracks. However, given the many advantages of such a design for the very close 4mm Proto:scales, I wish to make sure the implementation works (and fits) equally well in either chassis width envelope, in case it is of interest to P4 modellers.

My philosophy is that no design is complete until it is both theoretically sound and has passed worst case testing in all its intended applications. That a lot easier to do if you get the requirements sorted out before you get heavily into the detailed design.

Andy

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ArthurK
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Re: N7 Chassis Question

Postby ArthurK » Sat Jul 13, 2019 7:25 pm

I adhere to the following over-frame standards for my kits:
P4 16mm
EM 15mm
OO 12.5mm

I always supply three separate sets of spacers, one for each gauge.

ArthurK

Julian Roberts
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Re: N7 Chassis Question

Postby Julian Roberts » Sun Jul 14, 2019 4:43 am

Just to corroborate Philip's reply really but with my own perspective.

I don't take anything on trust after my first P4 loco wouldn't go round a 4' bend having used P4 spacers. I work out the sideplay required for that radius with the versine, and the EM spacers are normally what I use now. ( For a 4 wheel chassis no sideplay is needed so I'd use the P4 spacers.) AG wheels have a 0.5mm boss. I don't know if other wheels do. I've got a P4 kit instructing me to remove that boss which makes me wonder why the boss is there and whether removing it will increase the likelihood of wheel wobble...but that's another subject.

FWIW my approach is perhaps over cautious as it doesn't include allowing for the slop in P4, gauge widening which can't be guaranteed, and my Back to Back that may be a tad less than the minimum as I would prefer to err on the safe side. My High Level Barclay Tank made this way turned out to be able to go easily round a 2' curve made using the standard triangular track gauge!

As a punter I'd quite appreciate the kit producer saying what minimum radius his kit is designed to take - with Arthur's fixed dimensions it will depend on the wheelbase (apart from 4 wheel locos).
Last edited by Julian Roberts on Mon Jul 15, 2019 7:27 am, edited 1 time in total.

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ArthurK
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Re: N7 Chassis Question

Postby ArthurK » Sun Jul 14, 2019 11:38 am

Julian Roberts wrote:Just to corroborate Philip's reply really but with my own perspective.

I don't take anything on trust after my first P4 loco wouldn't go round a 4' bend having used P4 spacers. I work out the sideplay required for that radius with the versine, and the EM spacers are normally what I use now. For a 4 coupled chassis I'd use the P4 spacers. AG wheels have a 0.5mm boss. I don't know if other wheels do. I've got a P4 kit instructing me to remove that boss which makes me wonder why the boss is there and whether removing it will increase the likelihood of wheel wobble...but that's another subject.

FWIW my approach is perhaps over cautious as it doesn't include allowing for the slop in P4, gauge widening which can't be guaranteed, and my Back to Back that may be a tad less than the minimum as I would prefer to err on the safe side. My High Level Barclay Tank made this way turned out to be able to go easily round a 2' curve made using the standard triangular track gauge!

As a punter I'd quite appreciate the kit producer saying what minimum radius his kit is designed to take - with Arthur's fixed dimensions it will depend on the wheelbase (apart from 4 coupled locos).



The dimensions I quoted will get my P4 models around a curve of about three feet (900mm) using Gibson wheels and HighLevel hornblocks. Care needs to be taken with eight-coupled locos (e.g. the Q5) zero play on the leading and driving (3rd) axle with as much sideplay as you can get on the remaining two. It works!

ArthurK

billbedford
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Re: N7 Chassis Question

Postby billbedford » Mon Jul 15, 2019 8:45 am

Proto87stores wrote:
I'm designing this chassis (and subsequently all my others) to incorporate working 4 point equalization and rapid and problem free assembly. To me this is especially important in the case of wanting multiple copies of the same prototype. ( I have 5 N7's to build so I can model a small part of the "Jazz" operations). For my own use, I wish to run my moderate number of UK model kits with P4 wheels on my various existing 3.5 mm proto:scale tracks. However, given the many advantages of such a design for the very close 4mm Proto:scales, I wish to make sure the implementation works (and fits) equally well in either chassis width envelope, in case it is of interest to P4 modellers.


So you are not intending to model any between frame details? Not that there's much visible on an N7.
Bill Bedford
Mousa Models
http://www.mousa.biz

Proto87stores

Re: N7 Chassis Question

Postby Proto87stores » Mon Jul 15, 2019 2:14 pm

Proto87stores wrote:

I'm designing this chassis (and subsequently all my others) to incorporate working 4 point equalization and rapid and problem free assembly. To me this is especially important in the case of wanting multiple copies of the same prototype. ( I have 5 N7's to build so I can model a small part of the "Jazz" operations). For my own use, I wish to run my moderate number of UK model kits with P4 wheels on my various existing 3.5 mm proto:scale tracks. However, given the many advantages of such a design for the very close 4mm Proto:scales, I wish to make sure the implementation works (and fits) equally well in either chassis width envelope, in case it is of interest to P4 modellers.



So you are not intending to model any between frame details? Not that there's much visible on an N7.


Apart from my frame spacers, I'm not adding anything between the frames, with the obvious model exceptions of a gearbox and any inter-frame mountings for that and the motor. I'd personally leave adding super-detailing to those that want to do it.

It appears the prototype has 4 ft, 1.5" between frames with a taper at the rear, varying between versions. I obviously will not be able to maintain that full width for a 16.5 mm gauge model. I'm also not planning to use the exact prototype size/shape hornblock slide cutouts. But then I don't think P4 modellers do that either.

Andy

Alan Turner
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Re: N7 Chassis Question

Postby Alan Turner » Tue Jul 16, 2019 7:36 am

I think the point is that the spacing of the "Prototype" frame is immaterial. The model frame/chassis has to work as a 1ft to 304.8mm mechanism in its own right. Its representation to something 1:76.2 bigger is coincidental.

In order to operate as a mechanism it must have appropriate tolerances, clearances and side play to do so a a typical P4 layout with its sharper than prototype curves and the non-scalable dynamics.

The spacing of the frame comes out of those considerations not by reference to some "prototype" chassis.

regards

Alan

Proto87stores

Re: N7 Chassis Question

Postby Proto87stores » Tue Jul 16, 2019 6:02 pm

Alan Turner wrote:I think the point is that the spacing of the "Prototype" frame is immaterial. The model frame/chassis has to work as a 1ft to 304.8mm mechanism in its own right. Its representation to something 1:76.2 bigger is coincidental.

In order to operate as a mechanism it must have appropriate tolerances, clearances and side play to do so a a typical P4 layout with its sharper than prototype curves and the non-scalable dynamics.

The spacing of the frame comes out of those considerations not by reference to some "prototype" chassis.

regards

Alan


Thanks,

I'm in full agreement. For the convenience of keeping hidden track return loops relatively compact, I'd like to have a min. radius using proto scale wheels as close to 24" as possible. How well I do in that regard will have to be seen. But I'm going to have to be very careful and creative to even try.

Andy.

Philip Hall
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Re: N7 Chassis Question

Postby Philip Hall » Tue Jul 16, 2019 11:42 pm

I have, in the long distant past, built engines to go around a 24” radius curve in P4. This is far from suggesting it was desirable, but it was only a light railway.

The thought of trying to get anything of any size and associated coaching stock around such a bend as a means of space saving strikes me as unwise, 36 - 42” would be better.

Philip

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Re: N7 Chassis Question

Postby Armchair Modeller » Wed Jul 17, 2019 8:25 am

Stock with buffers have to be a disproportionate distance apart to get around very tight curves. It just wouldn't look realistic in my opinion to have wide gaps between wagons and coaches in a train.

proto87stores

Re: N7 Chassis Question

Postby proto87stores » Wed Jul 17, 2019 3:05 pm

Armchair Modeller wrote:Stock with buffers have to be a disproportionate distance apart to get around very tight curves. It just wouldn't look realistic in my opinion to have wide gaps between wagons and coaches in a train.


That's also true. My goal was to explore otherwise realistic designs to allow long wheelbase locomotives to go around much tighter hidden track curves and turnouts, rather than stick to space consuming more prototypical ones used on the visible portion of a layout. That doesn't mean a particular modeller must use those tighter curves, or have to incorporate wider inter coach gaps. But I was impressed with the gap controlling mechanism Bachmann use on their MK1 coaches. My Quint-Arts and 305's only have buffers on the end cars, so I have more of a special case.

Image

See above. I did check the wheel sideways movement needed for the N7 to round 24" radius. If I fixed the end axle movement to keep the loco ends/buffer, etc., most centered on curves, then the inner axles would have to move sideways +/- 1.82 mm. And that would stretch the outer coupling rod 0.05 mm, or need a 0.025 mm slop on the coupling rod bearings. No pivot of the rear axle necessary.

Given that only the front wheel on an N7 is restricted by a splasher, that might actually be feasible with no other creative mechanical aids. But clearly, it wouldn't work for a scale model loco with splashers on all drivers. Unless y'all go 00-P ;)

Andy

Julian Roberts
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Re: N7 Chassis Question

Postby Julian Roberts » Wed Jul 17, 2019 5:13 pm

Without meaning to contradict the sound advice given above



SWB wagons, 16 ton and 21 ton types, even with fixed buffers, go perfectly well round 2' reverse curves pulled and propelled at the separation distance of AJ couplings mounted in the standard way. Some other videos there show a longer van too. This was a test for P4 colliery type working.

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Re: N7 Chassis Question

Postby Armchair Modeller » Wed Jul 17, 2019 6:03 pm

Perhaps I should have qualified my comment by mentioning that it is far more of a problem with longer vehicles ;)

(and fixed buffers more than sprung buffers)

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Re: N7 Chassis Question

Postby grovenor-2685 » Wed Jul 17, 2019 6:37 pm


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Noel
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Re: N7 Chassis Question

Postby Noel » Wed Jul 17, 2019 7:54 pm

proto87stores wrote:My goal was to explore otherwise realistic designs to allow long wheelbase locomotives to go around much tighter hidden track curves and turnouts, rather than stick to space consuming more prototypical ones used on the visible portion of a layout.


The classic stock behind N7s from 1924/5 to electrification was one or two Quint-Art sets. Because of the use of articulation, the vehicle bodies within the set were only 13 inches apart [if I've read the drawings correctly]. Getting the loco round 2 ft curves may not be your only problem...
Regards
Noel

proto87stores

Re: N7 Chassis Question

Postby proto87stores » Thu Jul 18, 2019 3:12 pm

Image

Not wishing to get too far away from loco chassis design, a quick check of the Quint-Art outline of two articulated cars shows that the prototype's 13.5" gap would have to increase only 20% to 16.1" in order to just round a 24" radius curve. Which increase may not be apparent to most observers.

I suspect the fact of articulation functionality itself could even provide a basis for a simple means of progressively increasing the gap as the radius increases, using just pegs and shaped slots.

On the meantime I'm off away for the weekend, then back to working on those chassis spacers next week.

Andy


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