Carriage ride height and springing

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Daddyman
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Carriage ride height and springing

Postby Daddyman » Sun Oct 11, 2020 3:43 pm

Hello. I'd like some advice on carriage springing and weighting if the membership would be kind enough.

I'm building some D&S NER carriages and have replaced the bogies with fully sprung (primary and secondary) ones from Miscellany/Rumney Models. I've followed the instructions, but am having problems with the ride height. Here is a picture of the bogie (please excuse the 00 wheels I'm using for setting up):
20201011_145148_resized.jpg

You can see that the sprung bolster in the centre sits quite high.

And here is the base-plate mount (henceforth BPM):
20201011_145516_resized.jpg


The BPM pictured has a depth of 1.5mm, but the instructions say this will not be enough, and recommend disregarding most of the BPM and substituting it with a piece of 1.5mm PCB and only one part of the BPM, giving a total depth of the new BPM of 1.8mm. I tried that setup, but found it set the ride height too high. But then so does the lower height of 1.5mm - the buffer height is more than 1mm higher than the coach on the right, which is correct (and is fitted with the bogies I'm replacing):
20201011_145041(0)_resized.jpg


Now, if I compress the bolster springs fully by hand, the gap between the bogie top and the lower edge of the underframe looks right (obviously, because in the photo below I'm pressing down on the carriage by hand, I'm compressing both primary and secondary springs, making the ride height too low - disregard that; my point is that the space between bogie and underframe only looks right under maximum compression of the bolster springs):
20201011_145057_resized.jpg


So here's the problem: the ride height is too high (though lower than it would be if I'd followed the instructions), and I'm wondering about how to fix it. I've cussed it all week but that has led to no discernible reduction in ride height. So it seems I'm left with the options below. (By the way, the current weight of the carriage is 120g, and the springs (secondary and primary) are 9 gauge, as per the instructions).

1. Put 50g of weight over each bogie. This solves the ride height problem but puts the bolster at full compression, and brings the weight of the carriage to 220g or more, making it very heavy (there need to be four-and-a-half of these in the train); this amount of weight also seems to make the carriage run less freely - too much pressure on the bearings?

2. Change the spring gauge from 9 to 8 gauge. I'm guessing (haven't tried this) this would allow the springs to compress more under less weight, bringing the ride height down and allowing me to keep the weight of 120g (or a bit more). However, if it's only possible to get the ride height right when the bolster spring is fully compressed (regardless of the spring gauge), that seems to negate the whole point of having a sprung bolster.

3. My preferred option: remove the BPM altogether, put a bolt through the floor with the head of the bolt on the top side of the floor and a tightened and soldered bolt on the underside of the floor. This would save me the 1.5mm of stack height from the BPM (I could shim if necessary), and allow me to keep the 9 gauge springs and the lighter weight of 120g (or perhaps a little more). However, I'm worried that I'm overlooking something and it will come back to bite me on the bum.

Any thoughts? Grateful for your input!
Last edited by Daddyman on Mon Oct 12, 2020 10:15 am, edited 1 time in total.

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Will L
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Re: Carriage ride height and springing

Postby Will L » Sun Oct 11, 2020 5:03 pm

Given you know full spring compression takes you below the height you want, (i.e. the ride height you want is in the available range) and that the axle ends seem to be below mid travel in the W irons, I think putting in thinner wires is the obvious first choice.

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 11, 2020 6:00 pm

Will L wrote:Given you know full spring compression takes you below the height you want, (i.e. the ride height you want is in the available range) and that the axle ends seem to be below mid travel in the W irons, I think putting in thinner wires is the obvious first choice.


Thanks, Will. You're right of course that I'm still within range. And maybe the carriage is still too light - looking in MRJ 275 I notice that Graham Thompson set out with a target weight of 220g, but actually ended up with 280g. So maybe a combination of lighter springs and slightly more weight might work.

Philip Hall
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Re: Carriage ride height and springing

Postby Philip Hall » Sun Oct 11, 2020 6:19 pm

I can’t comment on the springing side of things, but my preference is for a carriage that weighs about 180-190g. That seems to make it possible for the buffers and any sprung gangways to do their proper work without any tendency for forces to push vehicles off the track. I should perhaps explain that I like my passenger trains, including the engines, to run coupled buffer to buffer. With pin point bearings (even plastic sideframes on RTR stock) things seem to be quite free running.

Philip

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 11, 2020 6:26 pm

Philip Hall wrote:I can’t comment on the springing side of things, but my preference is for a carriage that weighs about 180-190g. That seems to make it possible for the buffers and any sprung gangways to do their proper work without any tendency for forces to push vehicles off the track. I should perhaps explain that I like my passenger trains, including the engines, to run coupled buffer to buffer. With pin point bearings (even plastic sideframes on RTR stock) things seem to be quite free running.

Philip


Very useful, Philip, thank you. It's good to know an in-service weight that works.

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Sun Oct 11, 2020 9:14 pm

Well I submitted a post which seemed to go but it's not there.

Are the primary springs too high? You can check against the drawing. You have to set both primary and secondary springs separately and it helps if the primary springs are stiffer than the secondaries. First check the bogie frame is the correct height above rail when the body is in place, possibly by putting a reference mark on the hornguide. After that you can worry about the secondary springs and getting the buffer height correct while achieving the correct gap between bogie frame and solebar. It's a bit of hassle for the first coach but you can just copy the settings for any others.

A Bachmann Mk1 body weighs around 130gms and with proper sprung bogies like these, great strings of them can be propelled with safety (ref MRJ200) so I can see no point in adding weight beyond this level. Excess weight becomes a nuisance when gradients are involved. All metal coaches will be much heavier, of course but there's not much you can do about that.

DaveB

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Mark Tatlow
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Re: Carriage ride height and springing

Postby Mark Tatlow » Sun Oct 11, 2020 9:48 pm

Hi David,

What gauge of wire did you use on your primary (axlebox springs). They are designed to take (or rather I use) 9 gauge but in practise as different weights of coach give rise to different compressions, you do have a choice. The wires can also get bent slightly as they are soldered in place, i think it is acceptable to bend them back or simply to bend them a touch more or less to adjust the ride height if you wish.

In the third view down, the primary springs are set to be a touch low; the pin point should be central in the hornblock and I would say it is a fraction below this.

Then I would also say that the bogie is mounted a bit to far below the underframe; the gap between the top of the bogie and the base of the solebar is wider on the one with my bogies in comparison to the D&S kit by a fair amount?

I appreciate you are seeking to reuse some of the D&S mounts but I suspect if you reduced these (potentially by replacement) this is where the main issue is. I use one layer of double sided copper clad, 1.4/1.5mm thick) and then the single layer of etch as per these photographs.

Bogie bearing.png
Bogie bearing.png (68.56 KiB) Viewed 888 times


IMG_7740.JPG


Personally I am not an advocate of adding weight to a vehicle to compress its springs unless it is very light (like a plastic wagon kit). Even the layouts that are designed to be flat rarely achieve it perfectly and the moment you have a gradient, you want stock to be light.
Mark Tatlow

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Mon Oct 12, 2020 7:02 am

davebradwell wrote:Well I submitted a post which seemed to go but it's not there.

Are the primary springs too high? You can check against the drawing. You have to set both primary and secondary springs separately and it helps if the primary springs are stiffer than the secondaries. First check the bogie frame is the correct height above rail when the body is in place, possibly by putting a reference mark on the hornguide. After that you can worry about the secondary springs and getting the buffer height correct while achieving the correct gap between bogie frame and solebar. It's a bit of hassle for the first coach but you can just copy the settings for any others.

A Bachmann Mk1 body weighs around 130gms and with proper sprung bogies like these, great strings of them can be propelled with safety (ref MRJ200) so I can see no point in adding weight beyond this level. Excess weight becomes a nuisance when gradients are involved. All metal coaches will be much heavier, of course but there's not much you can do about that.

DaveB

Thanks, Dave - that makes sense. I'd been focusing on the secondary springs, but as you say, the primary ones are wrong, the pinpoint not being in the centre of the hornway. As far as I can see (the instructions only have a very low-resolution photo of the GA) the height from rail to the top of the bogie should be 3'0", whereas mine is currently sitting at just under 13mm.

So my options seem to be:
1. 8 gauge wire and as little more weight as I can get away with
- or
2. bend the springs?

Mark Tatlow wrote: What gauge of wire did you use on your primary (axlebox springs).

As said, Mark, and as instructed, 9 gauge.

Mark Tatlow wrote: In the third view down, the primary springs are set to be a touch low; the pin point should be central in the hornblock and I would say it is a fraction below this.


As said, that photo shows the springs compressed by hand and is therefore not indicative of the current setup of the springs.

Mark Tatlow wrote: Then I would also say that the bogie is mounted a bit to far below the underframe; the gap between the top of the bogie and the base of the solebar is wider on the one with my bogies in comparison to the D&S kit by a fair amount.

The whole reason for my post, Mark!

Mark Tatlow wrote: I appreciate you are seeking to reuse some of the D&S mounts but I suspect if you reduced these (potentially by replacement) this is where the main issue is. I use one layer of double sided copper clad, 1.4/1.5mm thick) and then the single layer of etch as per these photographs.


There is nothing from the D&S kits in the set up shown in my photos above. As said above, I first used the copper clad as instructed and as you advocate here, but when combined with part 13 as instructed this gave a mount height of 1.8mm, meaning that it gave me an unnecessary extra 0.3mm stack height over the stack height of 1.5mm I get by using parts 13 and 14 instead; extra stack height is the last thing I need, so I reverted to parts 13 and 14, which is what is shown in the photo - there is nothing D&S there, only your parts.

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 7:09 am

I've now fitted the 8-gauge springs and the carriage still sits too high: both the bogie upper edge and the buffer centres are too high, meaning that both primary and secondary springs are too hard. Putting 20g of weight over each bogie does get the springs to compress enough to give me the correct ride height, but brings the total weight up to more than 160g; I'd rather keep it to 120g.

So the only option seems to be to use 7 gauge wire. Is that advisable?

Dave, what spring gauge do you use in your Bachmann MK1s with proper bogies?



EDIT: Strings Direct don't keep the Ernie Ball "plain steel" strings that I've been buying in .007; the only option is "high carbon plain steel" by D'addario. Is that likely to cause any problems?

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Sun Oct 18, 2020 7:47 am

My springs are longer than yours so a direct comparison isn't possible. Just remember that deflection is inversely proprtional to the 4th power of the spring diameter. You might try phos bronze which is a little more than half as stiff as steel so this will almost double deflection for same gauge. Problem here is stuff I've had from Eileen's deforms very easily - except the 30g which they didn't have last time. Remember Justin's suggestion to bend the primary springs to let them settle a bit lower - this sort of tweaking is necessary to cover a wide range of possible coach weights.

You'll find all steels have very similar stiffness whether hard or soft.

DaveB

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 8:03 am

Thanks, Dave. I was trying to avoid bending the springs, as I would need to get 64 bends consistent across the train (8 bogies, 4 springs per bogie, 2 bends per spring). But anyway, bending only solves the primary problem - there's no way to bend the secondary springs because of how they are held in the bolster.

From your recommendation of PB I infer a wire with more deflection would be acceptable, and if Eileen's can't supply, and all steel is the same, I understand that trying .007 wire would be OK?
Last edited by Daddyman on Sun Oct 18, 2020 9:20 am, edited 2 times in total.

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Sun Oct 18, 2020 8:19 am

Unless there's physical limits to how far springs can deflect - will they hit something - then that would be "yes" a few times. Tweaking springs isn't too bad as once you've made one you can just copy it on the others. Drill a 2mm hole in a piece of anything and scribe a line across at the correct spring height and use it to tweak the others. Yes, it's another job but you can do it before the .007 wire arrives.

One bit of caution - the primary springs should be stiffer than the secondaries otherwise the frame ends up in a sort of no man's land and doesn't have much of a defined position.

Off to the hills!

DaveB

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 8:30 am

davebradwell wrote:Unless there's physical limits to how far springs can deflect - will they hit something - then that would be "yes" a few times. Tweaking springs isn't too bad as once you've made one you can just copy it on the others. Drill a 2mm hole in a piece of anything and scribe a line across at the correct spring height and use it to tweak the others. Yes, it's another job but you can do it before the .007 wire arrives.

One bit of caution - the primary springs should be stiffer than the secondaries otherwise the frame ends up in a sort of no man's land and doesn't have much of a defined position.

Off to the hills!

DaveB

Thanks, Dave. Enjoy the hills - I envy you!

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ianpenberth
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Re: Carriage ride height and springing

Postby ianpenberth » Sun Oct 18, 2020 9:58 am

The D'Addario strings are fine as a substitute for Ernie Ball, e.g. I use PL019 "High Carbon Steel Custom Singles" for 19thou (a size that EB don't make).

(There are some cheaper ones that don't work so well for our purposes - a diagnostic is that they stay coiled up when you take them out of the bag.)

Dave mentioned the fourth power relationship between (D)iameter and (d)eflection - I find this means in practice that too large a D will in essence be rigid, too small and the spring will just collapse, with only two or three 1-thou increments of D in between that give a sensible result (i.e. a static deflection circa 0.5 - 1.0mm). - so it should be evident if the 7thou wire is too thin, but worth a try I would think.
Ian
PenBits Model Railways - Diesel bogie springing and detailing

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 10:25 am

Thanks for that, Ian - and for explaining the fourth power thingy: my PhD is in literature so I need such things explaining in small words...

Just one question: you say "a diagnostic is that they stay coiled up when you take them out of the bag" - that is a diagnostic of cheap or good-quality springs? I'm guessing from the fact that the EB strings straighten out that remaining coiled is a bad thing - is that right?

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ianpenberth
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Re: Carriage ride height and springing

Postby ianpenberth » Sun Oct 18, 2020 12:30 pm

Oops, yes it's the cheap ones which stay coiled up (even when you unwind the ends out of the coil). I tried some as they were half the price - perhaps they're fine for guitars!

You also have (in theory!), for a simple wire spring between two knife edge supports...

(L)ength vs d is a third power relation so a small change in L can have a larger effect on d.

(W)eight vs d is linear, so increasing W increases d in proportion - W = k x d. (k includes the higher powers of D and L as above, but for a given spring they don't change, so k is constant).
Ian
PenBits Model Railways - Diesel bogie springing and detailing

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 1:20 pm

ianpenberth wrote:Oops, yes it's the cheap ones which stay coiled up (even when you unwind the ends out of the coil). I tried some as they were half the price - perhaps they're fine for guitars!

You also have (in theory!), for a simple wire spring between two knife edge supports...

(L)ength vs d is a third power relation so a small change in L can have a larger effect on d.

(W)eight vs d is linear, so increasing W increases d in proportion - W = k x d. (k includes the higher powers of D and L as above, but for a given spring they don't change, so k is constant).

Thanks for explaining, Ian - that's all clear.

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Sun Oct 18, 2020 3:29 pm

Dr. Daddyman then, it would seem.

Well, he's floored me by mixing up lettering conventions, but then I'm working from an old textbook that uses pounds and inches and assumes we're on planet Earth. d was always wire diameter with D reserved for diameter of coil springs. Deflection was anything else.

You can predict the deflection your 7 thou' wire will give by just writing down some fourth powers: 6**4 is 1296, 7**4 is 2401, 8 gives 4096 so these are the ratios of the deflections. (**4 is to the power of 4).

A fine day with some distant sun, strands of mist, autumn colours and a nice drive with no camper vans.

DaveB

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 4:28 pm

davebradwell wrote: A fine day with some distant sun, strands of mist, autumn colours and a nice drive with no camper vans.


Sounds nice. I've mostly been cussing bogies...

I think trial and error appeals more than that maths, though.

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Sun Oct 18, 2020 4:53 pm

I only meant you to use an approximation - the ratio between the numbers for 7 thou and 8 thou' is about 5/8 so before you buy your wire you can see it will give 8/5 ths of the deflection - quite promising, but will it be enough? Going to 6 thou' will give 3 times the deflection of the 8 and so comes outside of Ian's useful range.

DaveB

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 4:58 pm

davebradwell wrote:I only meant you to use an approximation - the ratio between the numbers for 7 thou and 8 thou' is about 5/8 so before you buy your wire you can see it will give 8/5 ths of the deflection - quite promising, but will it be enough? Going to 6 thou' will give 3 times the deflection of the 8 and so comes outside of Ian's useful range.

DaveB

Thanks, Dave - I can understand those numbers. 7 thou is ordered, but I may only use it for the secondary springs. In fact, I may only be able to do so, given what you have said about the need for softer springs for the secondaries: make the primaries 7 and I've got nowhere to run for the secondaries...

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Sun Oct 18, 2020 5:16 pm

......but aren't the lengths of primaries and secondaries different? Back to the sums!

DaveB

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Sun Oct 18, 2020 6:00 pm

davebradwell wrote:......but aren't the lengths of primaries and secondaries different? Back to the sums!

DaveB

Rats! 15mm between anchor points for the secondaries, and 17.3 for the primaries. So secondaries stiffer than primaries if the same gauge wire used for both...

davebradwell
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Re: Carriage ride height and springing

Postby davebradwell » Mon Oct 19, 2020 8:32 am

Just reflecting on this setting issue: as you're trying to get the body the right height as well as the bogie frame you'll need to be very lucky if you can find a combination of wire gauges that will do the trick. Surely a bit of wire bending is almost inevitable unless you do an alternative such as re-drilling the spring fixing points with the bearing carrier plates being the easiest.

Remember the secondary springs need to be soft to keep the natural rolling frequency low.

DaveB

Daddyman
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Re: Carriage ride height and springing

Postby Daddyman » Mon Oct 19, 2020 11:08 am

davebradwell wrote:Just reflecting on this setting issue: as you're trying to get the body the right height as well as the bogie frame you'll need to be very lucky if you can find a combination of wire gauges that will do the trick. Surely a bit of wire bending is almost inevitable unless you do an alternative such as re-drilling the spring fixing points with the bearing carrier plates being the easiest.

Remember the secondary springs need to be soft to keep the natural rolling frequency low.

DaveB

Thanks for your continued help, Dave.
I wonder if part of the problem might be that the secondary springs are bend too close round the anchor points, making the spring stiffer? Here's the arrangement I've had until now, with the springs (not trimmed) bent hard up against the anchor points:
20201019_115148.jpg

Whereas I wonder if this arrangement might change things, with the spring not bent so hard up against the anchors, but with a bit of wiggle room to flex its muscles:
20201019_115458.jpg


Part of the problem is setting up things when the springs make everything a moving target. But I've made a jig to indicate the height of the bogie top, and the carriages seem to be sitting right at least where that measurement is concerned. So it's all about the secondaries now. I haven't had chance to test the result of the changes to them described above.

Here are some pretty pictures for anyone who's getting bored. You can see how crucial it is to get the ride height right, as the bogie steps have to line up exactly with the long footboards between the bogies - several days' work even with the rigid bogies fitted here:
10.JPG

20200927_101222.jpg


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