Methods for Removable Loco Wheelsets.

davebradwell
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Re: Methods for Removable Loco Wheelsets.

Postby davebradwell » Fri Jul 05, 2019 1:01 pm

To design a kit chassis that has removable wheelsets it's just a matter of not etching the springs on the bottom of the frames but including them on a keeper plate which also holds the axleboxes in their hornguides......or hold your bearings in their slots if you really must have a fixed axle. Not difficult at all and all my kits have been done this way although I'll confess to dumping the fixed axle and 00 in order to avoid further compromise. Yes Bill, folk still hack it all away and do their own thing. You can only do your best!

Just to keep the record straight and despite the impression this forum gives, csbs are only one type of spring and there are many others - it isn't csbs OR compensation, full stop. There are also more robust axlebox/hornguide systems than the common types where the guiding slot is formed in just one thickness of metal.

I would always advise against rigid axles for the simple reason that they transmit noise to the baseboard. Sprung stock (that sits on its springs) is quieter, assuming, of course, that it can go fast enough to make a noise in the first place.

DaveB

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Noel
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Re: Methods for Removable Loco Wheelsets.

Postby Noel » Fri Jul 05, 2019 3:22 pm

billbedford wrote:
Guy Rixon wrote: I often wonder about the economics of getting better components. Bearings for coupled axles are a good example: the cuboid kind that slide in hornguides. If the bearing blocks were accurately machined, then they could just slide in slots etched in the frames, without the hornguides, and it would be very easy.

That is not a good idea, as the thin edge of the frames cuts into the bearing after a modicum of running


It also assumes that every kit manufacturer uses the same thickness material for the frames...
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Noel

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Paul Townsend
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Re: Methods for Removable Loco Wheelsets.

Postby Paul Townsend » Sat Jul 06, 2019 5:24 am

davebradwell wrote:
Just to keep the record straight and despite the impression this forum gives, csbs are only one type of spring and there are many others - it isn't csbs OR compensation, full stop.

DaveB


Pedant alert:

There are plenty of threads in this forum that discuss other springing systems.
You are right that this THREAD only mentions CSBs. That is because it is the latest idea, best and easiest to install and setup of all that I know of.

davebradwell wrote: There are also more robust axlebox/hornguide systems than the common types where the guiding slot is formed in just one thickness of metal.

DaveB

I totally agree.
My very first P4 kit chassis around 1975 had skinny "hornguides". It ran well as new but the wear soon meant bearings moved longtitudinally and no longer dynamically matched the coupling rods....result, atrocious running.
davebradwell wrote:
I would always advise against rigid axles for the simple reason that they transmit noise to the baseboard. Sprung stock (that sits on its springs) is quieter, assuming, of course, that it can go fast enough to make a noise in the first place.

DaveB

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Jol Wilkinson
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Re: Methods for Removable Loco Wheelsets.

Postby Jol Wilkinson » Sat Jul 06, 2019 7:32 am

billbedford wrote:There is nothing to stop a kit designer taking a holistic approach to their work and provide the modeller with a kit that 'just goes together' The fact that they don't, seems to me, a lot to do with a 'this is the way we have always done it' attitude together with the economics of sourcing wheels etc.


Isn't that what GEM and some other kit manufacturers provided with their cast w/m chassis with pressed in brass bearings and mountings for Romford or similar motors. K's went the whole hog with complete kits including screw retained driving wheels, etc.

While 'this is the way we have always done it' may have some bearing, the economics of a Small Supplier stocking all the parts to provide a "complete kit solution", given the options needed to meet all customer requirements would make it impractical. Customer preferences for particular products also complicate matters, DJH used to supply Romford/Markit 00 wheels with their kits but stopped doing so some years ago, apparently because some buyers wanted alternatives.

billbedford
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Re: Methods for Removable Loco Wheelsets.

Postby billbedford » Sat Jul 06, 2019 9:47 am

Guy Rixon wrote:I often wonder about the economics of getting better components. Bearings for coupled axles are a good example: the cuboid kind that slide in hornguides. If the bearing blocks were accurately machined, then they could just slide in slots etched in the frames, without the hornguides, and it would be very easy.


I forgot about the Brassmaster's bearings which work in exactly the way you suggest. The downside of using them is that they use a 6mm cutout in the frames, which for small moderately wheeled locos the cutout can be close to the top of the frame if.
Bill Bedford
Mousa Models
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High Level Kits
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Re: Methods for Removable Loco Wheelsets.

Postby High Level Kits » Sat Jul 06, 2019 10:17 am

Interesting thread. Over the years, requests for removable wheelsets on High Level products have been second only to grubs screws on all gearboxes (now largely addressed).

I think I pretty much echo Jol’s comments, probably because he’s looking at this from the perspective of a manufacturer trying to sell kits. Working in three gauges, we need to cater for as many preferences as possible (in each gauge) but with as few compromises as possible, and in a way that gives a quality product that’s not so complicated as to put people off . Quite often, one particular approach can be at the expense of another. Compromise isn’t the answer either, or you may end up pleasing no one. If it was just treading a fine line it would be so much more simple!

When I branched into chassis kits a good few years ago, I weighed up the costs Vs benefits and made a conscious decision not to design in removable wheelsets. This was for three main reasons:

One – many customers in OO and EM use Romfords, so they’re not as bothered. Some are, but many are happy to build the chassis without taking it apart again.

Number two, on top of removable brakegear, details etc, this would further complicate the construction. This would be unwelcome by customers who wish to build chassis rigid.

There may also be an impact on appearance and limit space for pick-ups. In three gauges, it would also bump the fret area and nut/bolt count right up and thus the costs/box size.

Third - and this was a major consideration – on small chassis, where the frames are not deep, sometimes no more than a few millimetres of material above the cut-outs, the lack of any bracing at the underside would seriously compromise strength. Compare a chassis to a saloon car turned upside down – the springs running under the wheel being the roof. A soft-top car requires a strengthened floopan as there is no roof to stiffen the overall structure and so an ‘open bottomed’ chassis would require reinforcement above the wheels. This would, to some extent, be provided by the hornblock etches, but the thing would be very flimsy until that were soldered solidly in place.

Tolerances on components are a separate issue...

Julian Roberts
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Re: Methods for Removable Loco Wheelsets.

Postby Julian Roberts » Tue Jul 09, 2019 6:54 am

High Level Kits wrote:
Third - and this was a major consideration – on small chassis, where the frames are not deep, sometimes no more than a few millimetres of material above the cut-outs, the lack of any bracing at the underside would seriously compromise strength. Compare a chassis to a saloon car turned upside down – the springs running under the wheel being the roof. A soft-top car requires a strengthened floopan as there is no roof to stiffen the overall structure and so an ‘open bottomed’ chassis would require reinforcement above the wheels. This would, to some extent, be provided by the hornblock etches, but the thing would be very flimsy until that were soldered solidly in place.



I had exactly that problem on my Crab chassis, a Comet kit, and Mark had also found the same thing. IIRC the necessary strengthening was made with a horizontal spacer above the hornblock slot which complicates sliding the gearbox and motor out.

If the axle has no suspension however there's no reason I can see why the hornblock slots can't go upwards. The springs etched as part of the frame below the axle can give the necessary stiffening. Wheel plus motor and gearbox removal much simplified and no need for widths to be less than frame width. (I'm assuming the "fixed" axle mounted in hornblock bearings that are fixed in place in the slots with wire or whatever.)

That wouldn't be relevant to the commercial kit maker unless a fixed axle was part of the design but might interest Brian with your OP question?

polybear
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Re: Methods for Removable Loco Wheelsets.

Postby polybear » Tue Jul 09, 2019 11:50 am

Many thanks to all who've taken the trouble to respond to my OP, and apologies for bringing the Forum (slightly) into disrepute at times...
The posts have raised some important points I'd overlooked/were unaware of, as well as raising alternative options and opinions, I'm currently reading thru' Will L's excellent post on CSB's here:
viewtopic.php?f=19&t=947
May thanks also to those involved in the design of chassis (Dave B, Jol, Bill, Gordon and Chris - in no particular order) for giving us an insight into the complexities of design and trying to please everyone, all of the time, no matter what the Gauge...
Decisions, decisions....

Kind Regards,
Brian

Philip Hall
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Re: Methods for Removable Loco Wheelsets.

Postby Philip Hall » Tue Jul 09, 2019 2:15 pm

Seeing all these discussions have led me to think about the two contradictory attitudes I have in these respects!

The first is that when building a chassis (whether ‘flexible’ or not) and got it running smoothly, I never want to take it apart again. I think Guy Williams wrote once that if it was properly built, apart from bushes in coupling rods and a drop of oil now and then it should not need attention for many years. I make sure the wheels are properly round and true, and everything rolls along nicely. Once this desirable state of affairs is reached the last thing I want is to disturb it all to paint it. So I make up the frames and most of the detail, paint where I cannot get a brush later, then put in the wheels (already painted and cleaned) and go on from there. So far this has (usually) worked. Where it hasn’t I have been reduced to much work and having to touch up the paint.

However, when I convert a RTR engine I love the fact that I can assemble the wheelsets and drop them into the chassis, screw the keeper plate back in and away I go with the bits and pieces. Once again I always paint the frames and the difficult to reach bits, so that essentially I am just putting in prepainted wheels and details onto a finished chassis. In most cases I have even cleaned the tyres of the wheels and never touch them again. It is undeniably easier to trundle a wheelset up and down on the bench to make sure it runs true, put in the right number of sideplay washers etc. But here again I never want to take the thing apart, not least because on a RTR chassis a number of details and brake gear are clipped on and secured by superglue. I only want to get it running smoothly once, not take it apart and change all the parameters.

One thing, however, is that I can see no virtue in actually building a rigid chassis in P4; it’s quite difficult (for me at least) to do, with our fine flanges. It’s much easier to build in some form of suspension. I know I quite happily convert lots of rigid RTR chassis, but the reality is that these actually aren’t that rigid at all. They have enormous amounts of slop in them so the wheels can quite happily move up and down, and some of them even have a sprung axle here and there. Taking out too much of the slop can actually cause problems, and you will understand how I came to find that out. But building a rigid chassis, with the normal clearances that a hand built job entails, means that it really is rigid with very little play, so if it’s not absolutely dead true (and the wheels ditto) means all sorts of problems in P4. You can get away with it in EM and 00 because of the greater depth of flange. I would do it in EM and 00, but not P4.

Philip


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