SimonD’s workbench

[simond]

Chassis with CSBs fitted
Clearance for rear pickups is exquisitely tight!

 

[Ian@StEnochs]

“As expected, the loco is a bit nose heavy. Not much but it does look like the wheel rim on the front axle is slightly more hidden behind the hanging bar than the rear. Maybe a bit less than 0.5mm. It’s within the range of ballast anyway.”

Simon,

That is where I have a problem with CSBs. On an 0-6-0, especially tender engines, with motor and gears in the firebox driving rear axle, an open cab so just how do you even up the load on each axle?

Ian,

 

[DavidB]

It’s down to the positioning of the spring supports. The CLAG website has more guidance. See CLAG – the Central London Area Group

 

[Pencarrow]

High-tech being of the essence, waxing spatulae have been pressed into service to make a soldering jig.

It’s stuck to the Unimat T-slot table with double sided tape, and it’s heavy enough to stay put. The piano wire spring presses the “leg” into the slot in the axlebox and the parts can be soldered whilst pressing the axlebox down into the recess - otherwise it tends to “sit up” at an angle which is not ideal.

View attachment 205431

And the first result - Chris’ pannier sitting on its springs for the first time. I’m delighted with the smooth running through my pointwork, CSB really does seem to work.

View attachment 205432

As expected, the loco is a bit nose heavy. Not much but it does look like the wheel rim on the front axle is slightly more hidden behind the hanging bar than the rear. Maybe a bit less than 0.5mm. It’s within the range of ballast anyway.

Next step will be pickups so I can actually run it.

That’s a load of repetitive, simple lathe work, and I don’t (yet) have a CNC lathe at home…

And then we’ll get to the tricky bit. Crossheads and front axle crankpin…

Excellent, I didn't get round to adding weight in the bunker, so yes nose heavy.

 

[Paul Tomlinson]

On Simon's build, isn't there scope to fill the bunker with ballast? ( just seen Pencarrow's post ) BTW, I prefer rectangular brass bar from Macc Models to lead sheet, etc. for purposes of adding weight. Looking at Simon's photo above, the beam is quite a distance from the top of the axlebox - I wonder if it is preferable to position the beam as close as possible to the axlebox top? The hornblocks/cheeks/guides from Invertrain don't have the obstruction that Slaters' do. If it works smoothly, then no problem!

 

[Ian@StEnochs]

On Simon's build, isn't there scope to fill the bunker with ballast? ( just seen Pencarrow's post ) BTW, I prefer rectangular brass bar from Macc Models to lead sheet, etc. for purposes of adding weight. Looking at Simon's photo above, the beam is quite a distance from the top of the axlebox - I wonder if it is preferable to position the beam as close as possible to the axlebox top? The hornblocks/cheeks/guides from Invertrain don't have the obstruction that Slaters' do. If it works smoothly, then no problem!

Paul,

Yes, I understand that Simon has scope to fill the bunker. However my problem is with tender engines with virtually no space at the cab end to add weight.

Ian.

 

[simond]

It's definitely not an issue with the location of the spring supports, it is, I suspect, because the smokebox is filled with depleted uranium, or titanium, or frozen mercury, or something similarly and ludicrously dense. I'll forgive Chris, he's a civil engineer (I'm a "rude mechanical") and weight is not generally something civvies are scared of

I do have a self-seal bag of lead shot which fills the bunker. This will undoubtedly sort out the "concorde coming into land" look but it will probably sort out the baseboards too... Suffice it to say that traction is unlikely to be an issue.

It was all described way back on page 48 or so. SimonD’s workbench

Joking aside, there is a fairly good argument for not over-weighting locos. Ideally, you want the wheels to spin if it gets stuck, rather than cook the windings of the motor. The current through a DC permanent magnet motor is highest when it is not turning, ie, stalled. Some DCC decoders offer some kind of overcurrent protection, but a DC controller and less sophisticated decoders might well provide sufficient current to wreck a stalled motor.

And the reason the CSB wires are as high as they are is to clear the pickups on the rear wheels, which are tucked up high so they are not visible from behind. The clearance between the CSB wires and the pickups will be pretty minimal.

 

[Richard Gawler]

It's definitely not an issue with the location of the spring supports, it is, I suspect, because the smokebox is filled with depleted uranium, or titanium, or frozen mercury, or something similarly and ludicrously dense.

Just passing through, but titanium is chosen for its high strength to weight ratio. It is quite a lightweight metal.

 

[simond]

Just passing through, but titanium is chosen for its high strength to weight ratio. It is quite a lightweight metal.

Thanks Richard, you’re right of course, Homer moment, I meant tungsten.

 

[Brian McKenzie]

I'll forgive Chris, he's a civil engineer (I'm a "rude mechanical") and weight is not generally something civvies are scared of

But weren't the civils the bane of CMEs etc when it came to weight restrictions imposed on new loco designs etc?

 

[Richard Gawler]

I have a packet of Slater's hornblocks but I am yet to try them. I am finding it really helpful to see what they look like installed on a chassis. Thanks

But I am pondering, if the front-most supports for the CSBs were closer to the front hornblocks, would this pick the nose up a bit?

Or even, remove the front supports for the CSBs and install new ones with a hole a little further down, i.e. closer to the bottom of the frames, to lift the nose?

 

[Pencarrow]

It's definitely not an issue with the location of the spring supports, it is, I suspect, because the smokebox is filled with depleted uranium, or titanium, or frozen mercury, or something similarly and ludicrously dense. I'll forgive Chris, he's a civil engineer (I'm a "rude mechanical") and weight is not generally something civvies are scared of

I do have a self-seal bag of lead shot which fills the bunker. This will undoubtedly sort out the "concorde coming into land" look but it will probably sort out the baseboards too... Suffice it to say that traction is unlikely to be an issue.

It was all described way back on page 48 or so. SimonD’s workbench

Joking aside, there is a fairly good argument for not over-weighting locos. Ideally, you want the wheels to spin if it gets stuck, rather than cook the windings of the motor. The current through a DC permanent magnet motor is highest when it is not turning, ie, stalled. Some DCC decoders offer some kind of overcurrent protection, but a DC controller and less sophisticated decoders might well provide sufficient current to wreck a stalled motor.

And the reason the CSB wires are as high as they are is to clear the pickups on the rear wheels, which are tucked up high so they are not visible from behind. The clearance between the CSB wires and the pickups will be pretty minimal.

Guilty as charged. The 1366 was my attempted first ever loco build and the kit was sold to me as ideal for a beginner... At some point about 10yrs ago, having just transitioned to 7mm, and being somewhat impressionable, I was advised on an "ideal weight" for an 0-6-0 tank. I suspect it might have been a little towards the side of overkill.

At the time, based on the compensation I was using, some careful thought went into where the weight should go, keeping the CoG in the 'triangle'. This included the 25kg due to be added in the bunker....

I suspect we're now on Exhibit F on why I should stick to doing scenic stuff and buildings.

 

[simond]

I have a packet of Slater's hornblocks but I am yet to try them. I am finding it really helpful to see what they look like installed on a chassis. Thanks

But I am pondering, if the front-most supports for the CSBs were closer to the front hornblocks, would this pick the nose up a bit?

Or even, remove the front supports for the CSBs and install new ones with a hole a little further down, i.e. closer to the bottom of the frames, to lift the nose?

Richard,

yes, sort of. Your first suggestion increases the spring stiffness, your second addresses preload.

if you flick back to my 45xx build, the opposite problem existed, the cab, being whitemetal, made it tail-heavy, and not really much option to try to move the CoG forwards (might have been possible to put some weight in the smokebox) so using the CLAG website, I calculated the longitudinal spacings of the spring supports to get the loco level, which worked.

But, there is never a free lunch. To increase the support for the offset weight, the effective stiffness of the rear axle springs needs to be higher, so the loco body reacts more to a disturbance on that axle than on either of the other two. Ideally, you might set the axle loads so you have ~35% on the leading and trailing axles, and the remaining 30% on the middle one, which is probably about ideal, and would give smooth running. I think my 45xx is more like 35/20/45. Flicking back further, @adrian & I were discussing “fixed axle” compensation which is disappointing as any track disturbance leads immediately to the loco body lurching unprototypically, and clearly the whole point of doing this is to improve the illusion, which such lurching destroys. An even weight distribution, with the CoG central in the coupled wheelbase is the ideal.

Your second suggestion is also possible, however the CLAG calculators for CSB start with the assumption that the beam is horizontal, ie preload on all axles is equal. It would be relatively easy in 7mm to put in threaded, adjustable spring trunnions, but clearly more work. It appears that the etch kits provide “multi hole” beam location points. My approach of soldering the trunnions to the inside of the frames also allows for some flexibility if I find I need to increase the preload at one end or the other.

And the third option is simply to add some ballast at the stern….

Certainly I shall be building my saddle tank so that I can ballast it to a useful weight, with the CoG central

atb
Simon

 

[simond]

Postscript to previous post.

Calculations would be rather more difficult if the wire is not assumed to be straight In the unloaded condition. I’m sure I was taught such things at University, and I’m equally sure I’d need to consult one of my kids to attempt to solve it now.

 

[Richard Gawler]

I wonder if you can drill out or otherwise reduce the ballast weight in the smokebox. If its static loading is making the nose dip, I suggest the dynamic loading is going to make the nose drop even more during deceleration. Logically, if you try to balance things out with a weight in the bunker, the nose will rise during acceleration.

Out on the driveway this morning, the MX-5 carries all of its engine behind the front axle and indeed most of the heavy parts of the car are are within the wheelbase. So when those brake calipers engage, the car stays fairly flat (though the much smaller rear brakes don't do much work).

If we are going to have springing on every axle of a loco, maybe we should have as much of the the weight as we possibly can within the wheelbase?

 

[Pencarrow]

It may be worth adding that the 1366 will be used for shunting and harassing clay wagons on a branch layout. I'm not envisaging much need for high speed runs, rapid acceleration and emergency brake applications.

The original weight application was not completed and the intention was to add more in the bunker. It shouldn't end up nose heavy when completed. As such I'm not overly concerned about the current nose heavy trim.

 

[Paul Tomlinson]

Simon, going back to post #954 in your link above, you said that with the added ballast in the bunker, the weight came to 850g? I've looked online and the RTR Ex-Lionheart 54xx is 933g - so yours doesn't appear to be at all overloaded(?).

 

[simond]

Thanks Paul

there's a bag of shot, and it fills the bunker (and finds the holes therein...) and I recall that it put the CoG somewhere in the middle. I suspect I would go for a bit less weight than Chris has, but I don't see it as a problem.

Richard's observation is relevant to all things, particularly things that roll, having the CoG somewhere in the middle is definitely a bonus. Dr Porsche was sufficiently brave that the 911 engine is behind the rear axle, and I believe the same layout is used for the old VW bug. Mr Issigonis too - the engine of a "proper" Mini is ahead of the front axle. They seem to have "got away with it", but of course, the CoG is somewhere between the wheels - I can be confident in saying this - if it were not, they would tip up...

It doesn't concern us in model railways, but pushing heavy bits to the ends does increase the polar moment of inertia, which means that more steering effort will be required to generate a given rate of turn. If you want to see that taken to a glorious conclusion, there's some youtube footage of a Lancia Stratos strutting its stuff in the forests. A car so short and compact that it was almost the same width as length - and that V6 sound...

I'm not unduly concerned about "wheelies" and "stoppies", as Chris says, it's a wagon-worrying loco. But actually, the "nodding dog" syndrome is a real issue with sprung model locos, and my own 1366 was a bit of a PITA in that respect when it was newly built. It is coil sprung. I stiffened the end axle springing and softened the middle axle and it is ok. I'm hopeful that Chris' pannier and my 1361 saddle tank will be better.

In any case, I'm confident we can make it work

 

[John57sharp]

I've nothing to add concerning springing but thankyou so much for the Stratos video. Flippin’ gorgeous.

John

 

[SimonT]

My thanks for the video too. We had planned to go and see it on the Roger Albert Clarke but we both had the Lurghi on the day. The second stage was very close to us.
Talking about square footprints, don't forget the lovely little Renault Alpines or the Deltas.
Simon
Ps. If your track makes locos knock and bounce possibly the track needs a good looking at.