Starting out in loco kit building

[Metropolitan]

I should have added that a rigid chassis must also by definition have trouble over a transition over a hump or the transition from the flat to an incline.This does not cause any derailment risk, but means only the centre wheel touch on a hump and outer on the start of an incline momentarily reducing traction, and may cause a slight stall.over a hump. Why does this not show much?, it is the play in axle holes and slots on RTR, which cover it up. ......but traction will be reduced with a heavy train. If the traction tyre is on an outer axle it may even come away from the track, and you will have a dramatic lurch. under load.

 

A sprung chassis has none of these issues at all, and saying P4 requires it is a tail over from early statements about P4, whose proponents were biased towards P4 in a rather excessive way on suspension.as a cure all. Humps and transitions do not turn up on P4 scale track to any degree that will affect the loco.

 

Repeating that suspension is complex and also unneeded, only puts people off seeking higher standards, and the improvement difference is bigger than a few decimal points.

 

 

 

However, taking your earlier point about the inertia effect of the motion being a factor even in 4mm models then surely a compensated or sprung chassis is more likely to react and be affected by these forces than a rigid one? The reciprocating force is trying to bounce the wheel up and down, which it can indeed do when compensated whilst it cannot when rigid as the force will act on the track. If the loco has enough weight and the track is well laid then these forces are not strong enough to have any effect on a rigid chassis whilst they could well wobble a sprung or compensated one?

 

 

I do not agree that compensation has anything to do with achieving a higher 'standard'. I have no doubt that the highest of standards can be achieved with a rigid chassis kit loco quite as well or better than with a compensated one. Who is to set and judge the 'standard'?

 

I have still no read a coherent answer to my point about the running quality of a modern Hornby or Bachmann loco? What exactly is wrong with the way they run. On my layout they are as perfect as can be and I can't see any way or any reason where an improvement could be made?? They run for hours on end without derailment or faltering in any way. The will crawl and go fast. I can shunt and pull long loads all in near silence. In what way are they lacking?? None that I can see. They meet the very highest standards of running quality. And, if I might say so, so do many of my kit built loco's! I can understand how compensation could help with electrical pickup but the point is irrelevant as my loco's (RTR or kit) do not suffer in this way anyway. I doubt if it is a common problem nowadays unless ones track is absolutely appalling! With live tender and chassis wheels it impossible for contact to be completely lost with the track all without the need for pickups rubbing on the wheels!

 

If anything is bad engineering it is to add complication to something that works fine in the first place! All you are doing is adding more room for error.

 

 

 

 

 

 

 

 

 

[Horsetan]

.....I do not agree that compensation has anything to do with achieving a higher 'standard'. I have no doubt that the highest of standards can be achieved with a rigid chassis kit loco quite as well or better than with a compensated one. Who is to set and judge the 'standard'?

 

You, presumably?

 

If you really want to demonstrate that your way is the right one, and the only one, please build us a demonstration loco in 18.83mm gauge, to your usual standards (in record-breaking time if you want!), and with a rigid chassis. Then let it be tested by the leading lights of Scalefour.

 

I think the results will be highly interesting. After all, if a rigid chassis works for EM, surely it will work for P4/S4?

 

I have still no read a coherent answer to my point about the running quality of a modern Hornby or Bachmann loco?

 

But you've widened the goalposts. This topic was about kitbuilt engines, not RTR.

 

What exactly is wrong with the way they run. On my layout they are as perfect as can be and I can't see any way or any reason where an improvement could be made?? They run for hours on end without derailment or faltering in any way. The will crawl and go fast. I can shunt and pull long loads all in near silence. In what way are they lacking?? None that I can see. They meet the very highest standards of running quality....

 

They benefit from standard assembly procedure and computer control. Your own builds, even though you may adopt the same approach with every one, cannot ever be turned out exactly the same, day-in, day-out, because you are a human individual, not a factory line.

[Metropolitan]

Hi Horsetan

 

 

"You, presumably?

 

If you really want to demonstrate that your way is the right one, and the only one, please build us a demonstration loco in 18.83mm gauge, to your usual standards (in record-breaking time if you want!), and with a rigid chassis. Then let it be tested by the leading lights of Scalefour.

 

 

 

I think the results will be highly interesting. After all, if a rigid chassis works for EM, surely it will work for P4/S4? "

 

 

 

Ahh!! Now we come down to it at last. I don't think the OP ever mentioned P4 which is utterly irrelevant to this discussion as it is to the generality of railway modelling in this country. What has P4 got to do with it? My guess is that 99.99% of the 4mm model railways in the UK and the trade sales that go with it are not P4! I have nothing but admiration for those who model in P4 and enjoy my membership of the Scalefour Society. But it seems to me that those who go to extremes of P4 track laying must expect problems with their stock which simply do not occur in 00/EM and therefore the faults inherent to P4 do not need to be considered. If I were to build a loco to P4 gauge I'd use EM wheels!!

 

If they despairingly need to experiment with various forms of suspension in order to keep their trains on the rails so be it. That is their need and their choice. But for 99.99999 percent of modellers their efforts to reduce the constant derailments are meaningless.

 

You still have not answered the question: What, exactly, is wrong with the running quality of my Hornby Black 5 on my 00 gauge layout?

 

 

 

 

 

"But you've widened the goalposts. This topic was about kitbuilt engines, not RTR."

 

 

 

No, not at all. I am using a Hornby Black 5 as an example of a very simple rigid chassis and making the point that it's virtues apply equally to kit builds.

[bertiedog]

However, taking your earlier point about the inertia effect of the motion being a factor even in 4mm models then surely a compensated or sprung chassis is more likely to react and be affected by these forces than a rigid one? The reciprocating force is trying to bounce the wheel up and down, which it can indeed do when compensated whilst it cannot when rigid as the force will act on the track. If the loco has enough weight and the track is well laid then these forces are not strong enough to have any effect on a rigid chassis whilst they could well wobble a sprung or compensated one?

 

 

Therein lies the miss understanding, the compensated chassis will be the one in firm contact with the track, and forces from the drag, gearbox or reciprocating weigh of the piston rods and motion, may on a rigid chassis bearing on a wheel that is out of contact with the track. causing a monetary bind as the wheel rotates, it is impossible with springing where the wheel is in firm contact with the rail.. Motion effects for the rods and piton rods are very slight, on a RTR chassis they will never be noticed.

 

It seems people confuse springing with parts flopping about, it is not true, at any instant the system is rock solid, incapable of binding as it is in a dynamic system that adapts to the conditions.

 

I think it is best this discussion is moved to a suitable posting in motors and gears etc., and I will post on springing properly, and compensation, don't expect science, I have never worked any figures for CSB systems etc., absolutely no need in practical terms., it is straight forward very simple home mechanics, any modeller can build a kit, the work has been done for you all ready. or with a little experience, and help, you can improve, or simplify the springing to taste, you will get better running.

Stephen.

[micklner]

I think I have finally got on Metropolitans wavelength only on "some" of his points .

I also model OO at my level/interest of 4mm modelling if it works and well !! = Job done move onto something else, and normally a big sigh of relief too !! Hence I have a mixture of rtr and kit builds.

I have attempted one compensated chassis I could never get it work . I swopped for a "normal" kit chassis from another maker worked first time.

The comments re Hornby above are incorrect. I presume they refer to old locos? .

I seen nothing wrong with the current Hornby can motors and indeed use Mashimas or similar on kit locos. Yes they have diecast chassis , but the axles run in Brass bearings/sleeves in said chassis. The valve gear whilst not perfect is reasonable at normal viewing distances. The Driving Wheels and Bogies are Plastic centres not Mazak albeit a bit chunky and not perfectly true , but again they run on my Code 75 with no problems.

Lastly re P4 how many layouts exist which are not end to end or have the luxury of curves of a very large radius to get them around without derailing? Everybody for their own tastes

[Metropolitan]

I think it is best this discussion is moved to a suitable posting in motors and gears etc., and I will post on springing properly, and compensation, don't expect science, I have never worked any figures for CSB systems etc., absolutely no need in practical terms., it is straight forward very simple home mechanics, any modeller can build a kit, the work has been done for you all ready. or with a little experience, and help, you can improve, or simplify the springing to taste, you will get better running.

Stephen.

 

Agreed!

 

 

There is another area you have not dealt with which you might like to consider when you post on springing which is relevant to the discussion:

 

TILT!

 

When a sprung wheel is moved up and the wheel on the other end of the axle does not the axle and wheels have to tilt.

 

Apart from the undesirable effect on the self centering properties of profiled wheels this has a number of consequences.

 

1) If the axle cannot tilt the other wheel must lift as well.

 

2) So to allow the axle to tilt there must be sufficient play in the hornguides or bearings (assuming the frames cannot be curved!) ? ie: mechanical slop!

 

3) The same applies to the coupling rods.

 

But we are told that play and slop are very very bad things!? How is this good engineering practice as the need for slop is absent in a rigid chassis?

 

 

 

 

 

 

[bertiedog]

On compensation, what's the complexity? The drawing shows an 040,( 060 and 080 arrangements are derived from this basis), each box bearing, or sleeve bearing (as shown) on un-driven axles, has the compensation beam (in red) touching it.

 

 

 

 

All coil springs would be the same size and rate, and would be supplied in a kit, the correct pivot points will have been worked out, hornblocks and springs supplied to some established system, and all should go together,and work, otherwise it might just be a badly designed kit of course.

 

If your particular Kit is more complex , then it may be a bit overdone, but I suspect that the instructions are the problem, as usual they do not often explain, but tend to direct you, and only in an over simplistic manner.

I repeat it s not complex, and it works, same as the real thing.

 

Mention of Hornby design or exact details is fraught with difficulties, they have had so many designs and changes in 50 odd years, and any comment is generic, not to a specific model, unless the example is identified precisely. Currently most do have brass bearings on axles, but rely on play to maintain contact, in fact earlier designs may have been better, with more generous play. But the fact is these are not precision models, they are made for the toy based RTR trade, very different to a custom made kit or scratchbuilt model.

I fully understand that the mention on the word toy in connection with model railways is contentious to a lot of enthusiasts, it is not derogatory, or denigrating in any way, just the correct definition of the products the trade supplies.

Stephen.

[bertiedog]

Agreed!

 

There is another area you have not dealt with which you might like to consider when you post on springing which is relevant to the discussion:

 

TILT!

 

When a sprung wheel is moved up and the wheel on the other end of the axle does not the axle and wheels have to tilt.

 

Apart from the undesirable effect on the self centering properties of profiled wheels this has a number of consequences.

 

1) If the axle cannot tilt the other wheel must lift as well.

 

2) So to allow the axle to tilt there must be sufficient play in the hornguides or bearings (assuming the frames cannot be curved!) ? ie: mechanical slop!

 

3) The same applies to the coupling rods.

 

But we are told that play and slop are very very bad things!? How is this good engineering practice as the need for slop is absent in a rigid chassis?

 

 

Basically forget it!, tilt has no practical effect on models, the axle is always near parallel with the point contact the tyres are resting on, on the rail surface, but the chassis may be twisted slightly out of parallel, by trying to connect another axle that is also in contact with the rail, but may not be to the same plane as the other. due to track out of alinement, but springing covers this situation, it allows for it.

Your still thinking in terms of the axe and wheels "floating" up and down, they do not, they are firmly on the track, and the chassis is the floating item, isolated from the wheels. The chassis can bounce, twist or move about to adopt the mean position of the system at any one point.

 

It is the chassis that we are suspending from stable, firmly in contact with the track wheels,on a sprung chassis.

Try driving a car on solid wheels without suspension....................

All the points you bring up guide us to the answer, springing deals with it!!!

 

Also coupling rods do not require spherical bearings or play for the wheels to go up and down, they don't in relation to the track, they go out of line with other joints on other axles on a different plane, a subtle difference, but important. On most models a few thou clearance deals with this issue.

 

Stephen, (see other thread on springing in motors and gearboxes)..

[Portchullin Tatty]

Guys,

 

I would be inclined to say everybody has said their piece on this thread.

 

You do not agree with each other; it does not matter, it is a hobby and each can do what they wish.

[Metropolitan]

Basically forget it!, tilt has no practical effect on models, the axle is always near parallel with the point contact the tyres are resting on, on the rail surface, but the chassis may be twisted slightly out of parallel, by trying to connect another axle that is also in contact with the rail, but may not be to the same plane as the other. due to track out of alinement, but springing covers this situation, it allows for it.

 

 

 

Only if the chassis can twist as well!! Springing does not cover the stuation at all on its own.

 

On the relatively narrow 00 gauge tilt on ONE axle is significant and can cause the axle to lock up on the bearing unless there is sufficient slop in the bearing or hornblock. A 1mm amount of vertical movement will cause a significant angle of the axle against the chassis and this together with, say, a 6mm total top hat bearing surface will cause a lock up unless there is a good deal of slop or the bearings are thinned right down in which case the life of the chassis will be much reduced.

[bertiedog]

First, .5mm is the MAX movement the axle moves up relative to the chassis, and the resultant angle of the wheel against to frame would be in the order of .5 degree, and this would need about 5 thou slack in the hornblock, which on most OO locos are not a tight groove but only have the slide guide on the outside, and the hornblock , even with a precision ball race in it would freely move with that amount of play..

 

 

This posting is not helping the poster to build his desired kit, according to you advice he should junk the chassis fit a solid block chassis, fitted with Hornby wheels and gears, with a Hornby motor and it would run, well it would run, but it would not be a good example of kit building at it's best, which a well finished 7200 kit with a proper chassis would be.

[Kempenfelt]

I think Metro's suggesting the OP should ditch the 72xx chassis and replace it with that of a Hornby Black 5! May look slightly odd but will be at the pinnacle of running quality. Makes you wonder why the kit market exists at all!

 

I again support the movement of the useful "Rigid vs compensation" debate to a dedicated thread.

 

Best wishes

 

Paul

[bertiedog]

Thanks PMP, I had not got a Hornby 5 to hand to check, but assumed it was un-sprung on all axles. Like newer Bachmann they must be springing one axle to maintain electrical contact, better than no springing. If this is now standard on new Hornby I suspect t is to do with having the middle wheels in contact with the track these days.

 

 

The old need for the smaller or flangeless smaller wheels was the transition Tri-ang Hornby needed to go up the standard Tri-ang Hornby ramp set and over the hump of the gradient pillars and bridges they did,

 

This governing factor lead to them retaining the smaller diameter for many years and also governed the front bogie design, particularly with the Lord of the Isles, which was forced to have small wheels and a low bogie to allow the transition to the slopes, and stay on the track.

 

if the rear is sprung it would allow for the same transitions from flat to slope, although I suspect Hornby do not set such tight changes in slopes these days as standards. .. and Bachmann spring the middle axle for similar reasons..

No scale layout would have such sharp changes in slopes and gradients, and in P4 and EM they are virtually non existent, with slow transitions at nearer scale values.

 

There is a posting in motors and gears on this whole issue to clear out this posting to get back to the GWR 7200 and other kits.

[Andy Y]

Guys,

 

I would be inclined to say everybody has said their piece on this thread.

 

You do not agree with each other; it does not matter, it is a hobby and each can do what they wish.

 

I do agree Tatty. As this is getting increasingly combative rather than productive I'll lock the topic.