Another newcomer's question re wagon suspension

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Daddyman
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Another newcomer's question re wagon suspension

Postby Daddyman » Tue Jan 14, 2020 3:18 pm

Hello
I've recently finished my first P4 wagon, and am having a problem that isn't really addressed in the numerous other problems-with-my-first-wagon threads!
The wagon is a D&S van, whitemetal, so quite heavy. I've replaced all the underframe detail with MT etches and, crucially, BB suspension units. While I've had 00 wagons run perfectly smoothly with BB suspension units and Wizard wheels (many have passed the roll-off-the-workbench-on-to-the-floor "test"), I can't get it to work with the same combination of suspension and wheels in P4. Specifically, what's happening is that there's a lot of play in both wheelsets. I've located this play to the interface between the wheel and the bearing; at this point the wheel is free to move somewhere in the region of a millimetre (along the long axis of the wagon), which is obviously having a major impact on the clearance between the wheels and the brake shoes (i.e. the brakes are rubbing); the wheels barely spin by hand. The W-irons being vertical, the only possible cause I can see is that the pinpoints are either machined too deep, the wheel axle is too short, or the bearing needs packing inwards with a washer (another of these threads alludes to washers). Does my diagnosis sound plausible? What fixes would people suggest? Dave Bradwell cautions against the use of waisted bearings for his application, as they are machined shallower than other bearings, but I wonder if in this instance they would solve the problem? Incidentally, I have used standard top hat bearings (from Wizard, I think), whereas in my 00 models I've used waisted (same source).
Many thanks in advance for any help!
David Addyman.

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Tim V
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Re: Another newcomer's question re wagon suspension

Postby Tim V » Tue Jan 14, 2020 3:55 pm

Where to start?

What length are the axles? A lot of axles are under the recommended 26mm. Most I measured were 25.8mm. This can lead to slop.

Only 'some' of the pinpoint bearings are actually accurate and within tolerances. Mike Clark (Masokits) used to do a little etch to help you decide what depth of coning was appropriate. Me? I ended up specifying Exactoscale bearings - as only they met my needs.

What is the width between the faces of the W irons? It should be 24mm, but a lot are not - some can be considerably more.

A combination of some or all of these factors give rise to the slop you mention.
Tim V
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DaveHarris
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Re: Another newcomer's question re wagon suspension

Postby DaveHarris » Tue Jan 14, 2020 4:14 pm

Tim,

Something in the back of my dusty mind says someone was/is producing small brass washers of varying thicknesses, presumably to help with the variations you describe?

Dave H

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Le Corbusier
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Re: Another newcomer's question re wagon suspension

Postby Le Corbusier » Tue Jan 14, 2020 4:46 pm

I have to admit I have always used waisted bearings with my BB W Irons ... I find that it vastly simplifies/minimises the creation of the recess within the axle boxes to allow the suspension to move up and down. My experience to date is that I have no problems with back to front slop. It might be worth trying some waisted bearings ... mine are Gibson ones.

Having set the wheel back to back I do make sure that there is next to no side to side movement by pinching them together - My Wheels were also from Wizard. I have also on occasion taken a file to the axle pinpoint effectively sharpening it to ensure the point properly bottoms out in the bearing, but generally I have not had to do this.

The caveat is that I am only onto my 10th wagon to date. ;)
Tim Lee

Martin M
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Re: Another newcomer's question re wagon suspension

Postby Martin M » Tue Jan 14, 2020 4:58 pm

I agree with Tim just squeeze the w irons together to remove slop... keep it simple?

Martin ;)

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Tim V
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Re: Another newcomer's question re wagon suspension

Postby Tim V » Tue Jan 14, 2020 5:05 pm

DaveHarris wrote:Tim,

Something in the back of my dusty mind says someone was/is producing small brass washers of varying thicknesses, presumably to help with the variations you describe?

Dave H

I think it was Masokits again.

Trouble is it's a workaround for poor quality components.

Also squeezing the W irons in just puts them at an angle. It they are vertical, the coning should match the pinpoint on the axle. Off vertical? Well you do the maths.
Tim V
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Jol Wilkinson
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Re: Another newcomer's question re wagon suspension

Postby Jol Wilkinson » Tue Jan 14, 2020 5:09 pm

As Tim says, the w-irons need to be vertical and parallel for the sprung bearing carriers to move freely.

I find that I usually have to go through my collection of pin-point bearings to find some that will provide that with whichever axles I am using. Using "deep" bearings with packing washers as already referred to is another way of getting the geometry right.

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Le Corbusier
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Re: Another newcomer's question re wagon suspension

Postby Le Corbusier » Tue Jan 14, 2020 5:09 pm

Tim V wrote:[

Also squeezing the W irons in just puts them at an angle. It they are vertical, the coning should match the pinpoint on the axle. Off vertical? Well you do the maths.


With me the pinching is very minor and causes no discernible movement out of vertical, it just tightens things up a bit ... anyway it seems to work as the wagons are very free running with next to no slop. :thumb
Tim Lee

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David Thorpe
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Re: Another newcomer's question re wagon suspension

Postby David Thorpe » Tue Jan 14, 2020 6:25 pm

On the other hand, when dealing with wagons with a wheelbase of less than, say, 10', many here would say that there's no need for any compensation or springing. Mind you, having said that, if you're building a kit it's maybe as easy to fit some form of springing as it is to ensure that the rigid underframe is completely square so that the wheels are all resting on the rails at the same time. I do think, however, that some forms of springing/compensation now on offer can be a bit over-engineered and over complicated. Nor are they always reliable.

DT

Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Tue Jan 14, 2020 6:40 pm

Thanks for the replies.

Tim V wrote:Where to start?

What length are the axles? A lot of axles are under the recommended 26mm. Most I measured were 25.8mm. This can lead to slop.

Only 'some' of the pinpoint bearings are actually accurate and within tolerances. Mike Clark (Masokits) used to do a little etch to help you decide what depth of coning was appropriate. Me? I ended up specifying Exactoscale bearings - as only they met my needs.

What is the width between the faces of the W irons? It should be 24mm, but a lot are not - some can be considerably more.

A combination of some or all of these factors give rise to the slop you mention.


Axles are 25.9, W-iron b-to-bs are 23.8 - so it must all be in the bearings. Could the 0.2mm you quote really create the amount of slop I'm getting - or indeed any slop (as opposed to operational tolerance)?

[quote="Le Corbusier"] I have to admit I have always used waisted bearings with my BB W Irons ... I find that it vastly simplifies/minimises the creation of the recess within the axle boxes to allow the suspension to move up and down. My experience to date is that I have no problems with back to front slop. It might be worth trying some waisted bearings ... mine are Gibson ones.

I think you're right - my use of waisted bearings with BB units in 00 explains why they've always worked before.

DaveHarris
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Re: Another newcomer's question re wagon suspension

Postby DaveHarris » Tue Jan 14, 2020 8:51 pm

For information guys. Alan Gibson sells shimming washers in packs of 30 in 1mm, 0.5mm, and 0.25mm thickness in 1/16, 1/8 and 2mm bore, to suit varying axle diameters refs 4M76/1 to 4m67/3 and 4M68 cover the items likely to be needed. Hope this is of some help?

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Guy Rixon
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Re: Another newcomer's question re wagon suspension

Postby Guy Rixon » Tue Jan 14, 2020 10:42 pm

Waisted bearings also vary in depth, between manufacturers and between batches from the same manufacturer. Traditionally, Gibson bearings tend to be shallower and Markits/Romford bearings deeper. The BB axleguards sold through Eileens need the shallow bearings and those in the Mousa kits generally need the deeper kind.

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Will L
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Re: Another newcomer's question re wagon suspension

Postby Will L » Tue Jan 14, 2020 11:40 pm

We've been here before, fairly often, try doing a forum search on "bearing depth". There can be a significant variation in 1, the distance between W irons, 2, axle lengths and 3, effective bearing depth. Particularly the last one. This only becomes a real issue with sprung systems at they do need vertical W irons to work as intended, while compensated or rigid axles are not so choosy. For them just bending the W irons in or out a bit is a viable option. You've just been lucky so far Tim. I think the very last section in the "Bearing and axle interfaces for coaches and wagons" write up on the CLAG website explains it all quite nicely. But then I would.

Despite the fact that people new to building sprung wagons keep on discovering the same issue, some experienced modellers seem not to be aware there is a problem and somehow it all works for them. They could just be lucky (I don't believe that), or maybe they have settled on the products of a small set of manufactures that are reliable compatible, or perhaps because they are just better at building things more consistently than those with less experience. None the less this has come up often enough to accept it is a real issue. It does no harm to know that it is necessary to ensure the effective length over the bearings and axle is just very slightly less than the width between W irons and this can take a little work. So yes, reducing the end float on those axles is the way to go, using which ever bearings or padding washers give the desired effect.

Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Wed Jan 15, 2020 6:39 am

DaveHarris wrote:For information guys. Alan Gibson sells shimming washers in packs of 30 in 1mm, 0.5mm, and 0.25mm thickness in 1/16, 1/8 and 2mm bore, to suit varying axle diameters refs 4M76/1 to 4m67/3 and 4M68 cover the items likely to be needed. Hope this is of some help?

Thanks!

Guy Rixon wrote:Waisted bearings also vary in depth, between manufacturers and between batches from the same manufacturer. Traditionally, Gibson bearings tend to be shallower and Markits/Romford bearings deeper. The BB axleguards sold through Eileens need the shallow bearings and those in the Mousa kits generally need the deeper kind.


Very clear and helpful thanks, and I've now changed the bearings for waisted and the issue is solved.

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Le Corbusier
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Re: Another newcomer's question re wagon suspension

Postby Le Corbusier » Wed Jan 15, 2020 7:58 am

Will L wrote: This only becomes a real issue with sprung systems at they do need vertical W irons to work as intended, while compensated or rigid axles are not so choosy. For them just bending the W irons in or out a bit is a viable option. You've just been lucky so far Tim. I think the very last section in the "Bearing and axle interfaces for coaches and wagons" write up on the CLAG website explains it all quite nicely. But then I would.


Duly noted :thumb Very interesting link.

It would appear that by using the Eileens BB irons and the Gibson waisted bearings I seem to have happened by chance on a good fit with the batch I have. Thanks to David for raising a potential problem I don't seem to have encountered yet but undoubtedly will.
Tim Lee


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