Quartering question

[philsandy]

Have just converted the new Bachmann 2MT Ivatt tank to EM.

 

Is it possible that if the quartering is only very slightly out that a loco can run perfectly smooth in one direction, yet have a very slight tight spot when running in the other direction?

Or is it that if the quartering is out, even by a midges, it would show up in both directions?

 

It could be that this tight spot when running in reverse is caused by binding on the valve gear/con rods, but I can not see any thing that is catching.

[bertiedog]

You must first check the quartering, as it is the only thing you altered, if your are using the original rods, not new ones.

One at least will be out and it needs a gauge of some kind, even made in card, to check each wheel is the same. It does not have to be exactly 90, but it helps to get it as near as practical.

 

Check the parts like the rods are still straight, no bends, or twists in them. They should be free turning, without deflecting due to twisted ends. Lay the rods on a flat surface and check with a steel rule that they are still in line.

Make sure the connecting rods to the pistons are not twisted as well as all the valve gear parts.

 

You do not say if the wheels are original or changed, if changed, check the crankpins are correctly mounted at right angles, and that there is the same clearance on each crankpin in the set.

 

If after all of this there is still a running issue with direction, it may be the teeth of the gears are damaged so that pressure in one direction overcomes the problem, but reverse causes the gears to alter position and bind in some way. It can be burrs on the side of the gears rubbing on the chassis in one direction only.

 

Stephen

[34theletterbetweenB&D]

Don't let the bind in one direction thing worry you. There's a ton of 'slop' in a RTR mechanism, and parts take up slightly different positions forward and reverse (to every action an equal and opposite reaction) so this aspect is completely normal.

...It could be that this tight spot when running in reverse is caused by binding on the valve gear/con rods, but I can not see any thing that is catching.

 There's one thing you cannot see in that department, and that's if a piston rod is hitting the end of the hole in the cylinder that it runs in.

[RexAshton]

One thing that would definitely cause problems would be if the quartering is slightly less than 90 degrees. Slightly over won't cause a problem. The slop in the chassis and rods may be an issue. If the rods are too sloppy you may be able to bush and re-drill the crankpin holes or better still replace them with some from Lanarkshire Models

[DCB]

Quartering is critical but only in as much as it needs to be equal on each axle, Some Full size 3 cylinder locos were quartered at 120 degrees (Thirded?)   What is also critical is that the rod length and wheel spacing match, If not the wheel will be pushed back and forth in the slop if any in the axleboxes and or bind up as the wheels turn.  often a bend in the rod will take up some excess length

[davknigh]

It might be worth checking that the slots for the axles on the Bachmann chassis are parallel to each other and spaced correctly. If these are not true then all efforts may be in vain.

 

Cheers,

 

David

[knitpick]

One thing that would definitely cause problems would be if the quartering is slightly less than 90 degrees. Slightly over won't cause a problem. The slop in the chassis and rods may be an issue. If the rods are too sloppy you may be able to bush and re-drill the crankpin holes or better still replace them with some from Lanarkshire Models

 

I strongly disagree with this assertion.  For model railways, "quartering" ideally needs to be at 90 degrees.  The effect of being slightly over or under (leading by over 90 degrees as opposed to trailing by over 90 degrees)  - provided ALL wheels are identically off 90 degrees is the same as if all were at 90 degrees.  Think logically - if "quartered" at 180 degrees the effect is the same as if there were no quartering; on a six coupled loco the outer wheels could go in opposite directions.

 

As DavidCBroad notes some (all?) 3 cylinder locos were "quartered" at 120 degrees.  This is due to balancing power from the 3 cylinders by having them providing power at 120 degrees to each other.  With the outer 2 cylinders at 120 degrees to each other the con rods and thus the coupling rods need to also be at 120 degrees - a whole 30 degrees off the 90 degrees that is used for all models.

 

This does raise the question as to whether we should expect the model manufacturers to provide 120 degree offset for models of 3 cylinder locos.  But given that we can't see both sides of a loco at once does it matter that they use 90 degree quartering as it is simpler and more reliable?  

[RexAshton]

I strongly disagree with this assertion.  For model railways, "quartering" ideally needs to be at 90 degrees.  The effect of being slightly over or under (leading by over 90 degrees as opposed to trailing by over 90 degrees)  - provided ALL wheels are identically off 90 degrees is the same as if all were at 90 degrees.  Think logically - if "quartered" at 180 degrees the effect is the same as if there were no quartering; on a six coupled loco the outer wheels could go in opposite directions.

 

As DavidCBroad notes some (all?) 3 cylinder locos were "quartered" at 120 degrees.  This is due to balancing power from the 3 cylinders by having them providing power at 120 degrees to each other.  With the outer 2 cylinders at 120 degrees to each other the con rods and thus the coupling rods need to also be at 120 degrees - a whole 30 degrees off the 90 degrees that is used for all models.

 

This does raise the question as to whether we should expect the model manufacturers to provide 120 degree offset for models of 3 cylinder locos.  But given that we can't see both sides of a loco at once does it matter that they use 90 degree quartering as it is simpler and more reliable?  

If it's good enough for Ian Rice it's good enough for me - and as I've built a lot of locos over the years - I'm satisfied it works. Also if you quarter a loco at 120 degrees without gear coupling the axles it'll never run. I did state that  a slight increase on 90 degrees would work. Accuracy as always is important but unless you have a quartering jig - and they don't always work - you'll be lucky to get them at exactly 90 degrees. Anything less than 90 will bind badly so I still stand by my original statement.

[pete55]

Have just converted the new Bachmann 2MT Ivatt tank to EM.

 

 

 

That's interesting.....in a previous thread you said it couldn't be converted to EM because of lack of clearance behind the slidebars. So how did you achieve the conversion out of interest?

 

In answer to your quartering question, yes, a slight "mis-quarter" can cause the symptoms you describe in my experience.

[philsandy]

That's interesting.....in a previous thread you said it couldn't be converted to EM because of lack of clearance behind the slidebars. So how did you achieve the conversion out of interest?

 

 

In answer to your quartering question, yes, a slight "mis-quarter" can cause the symptoms you describe in my experience.

 

 

 

Hi Pete,

 

Yes, I thought it couldn't, but Dunsignalling suggested moving the cylinders further apart, which is what I ended up doing. 

Moved each cylinder 0.7 mm.

Used Alan Gibson wheels on the front axle, and did away with the crank nuts by fitting the 1 mm crank pins tother way round, ie. the screw head up against the coupling rod.

 

 

"In answer to your quartering question, yes, a slight "mis-quarter" can cause the symptoms you describe in my experience".

 

Yes agree, after a tiny adjustment of one wheel I eliminated the slight tight spot when running in reverse.

Job done, and running very well.

[knitpick]

If it's good enough for Ian Rice it's good enough for me - and as I've built a lot of locos over the years - I'm satisfied it works. Also if you quarter a loco at 120 degrees without gear coupling the axles it'll never run. I did state that  a slight increase on 90 degrees would work. Accuracy as always is important but unless you have a quartering jig - and they don't always work - you'll be lucky to get them at exactly 90 degrees. Anything less than 90 will bind badly so I still stand by my original statement.

 

Sorry Rex(?) but I guess we must agree to differ.  I still maintain that a loco with wheels all quartered at 89 degrees will work as well as one with all wheels quartered at 91 degrees.  If you were correct and the 89 degree quartering runs badly, then surely the 91 degree quartered loco must run equally badly in the opposite direction?  Indeed I believe that PROVIDED ALL WHEELS ARE QUARTERED THE SAME then an error of up to 5 degrees will have a negligible effect on running.

 

I note that quartering at 120 degrees is liable to cause problems with models and I state quite clearly that 90 degree quartering is the ideal.

 

Agreed that I "Cheat" in that I prefer to use Romfords where the design provides the necessary quartering.  Also With the K's kits I've built, they come with a "D" shaped axle and corresponding hole in the wheel again making quartering somewhat simple.  However I have on occasion had to quarter by eye - Ultrascale (I think) wheels on an old Tri-Ang Nellie; requartering a Mainline BR Standard Class 4 spring to mind.  Done by eye as I don't have a jig.

 

Sorry I can't quote an expert, I rely upon a mix of experience and logic.

[billbedford]

I note that quartering at 120 degrees is liable to cause problems with models and I state quite clearly that 90 degree quartering is the ideal.

 

 

In what way? Have to tried it?

[stewartingram]

I've tried 180 degrees with an 0-4-0 and it didn't work. As I was using Romfords, it was easy to change that to 90 degrees.

 

Stewart

[DCB]

90 degrees is the best as one rod is at 90 degrees as the other is at a dead centre.    Not sure if 120 is practical in 00 without independent drive to more than one axle.     I used to think the 120 degrees made Gresley pacifics poor starters but after watching Sir Nigel Gresley start from Goathland on about 7 bogies on a wet day I revised my opinions as I don't think she slipped at all and it must be about 1 in 100.

 

Having axles square across the chassis and rod lengths the same as the axle spacing (which can vary from side to side) gear wheels concentric with axles and rods which don't rub on the wheels are all considerations which can give the appearance of duff quartering.  In extreme cases it can break the side rods (My Dean goods) or have the wheels work loose ( My Hornby  9F converted to loco drive )

[t-b-g]

90 degrees is the best as one rod is at 90 degrees as the other is at a dead centre.    Not sure if 120 is practical in 00 without independent drive to more than one axle.     I used to think the 120 degrees made Gresley pacifics poor starters but after watching Sir Nigel Gresley start from Goathland on about 7 bogies on a wet day I revised my opinions as I don't think she slipped at all and it must be about 1 in 100.

 

Having axles square across the chassis and rod lengths the same as the axle spacing (which can vary from side to side) gear wheels concentric with axles and rods which don't rub on the wheels are all considerations which can give the appearance of duff quartering.  In extreme cases it can break the side rods (My Dean goods) or have the wheels work loose ( My Hornby  9F converted to loco drive )

 

One of the reasons why Gresley adopted three cylinders was because of a more even application of power to the driving wheels when starting up. 3 lots of power at 120 degrees each wheel revolution is more even than one at 90 degrees followed by another at 270 degrees.

[Grovenor]

I've tried 180 degrees with an 0-4-0 and it didn't work. As I was using Romfords, it was easy to change that to 90 degrees.

 

Stewart

!80 degrees is not 120 degrees !

 

One of the reasons why Gresley adopted three cylinders was because of a more even application of power to the driving wheels when starting up. 3 lots of power at 120 degrees each wheel revolution is more even than one at 90 degrees followed by another at 270 degrees.

Don't forget steam engine cylinders are double acting, so a 3 cylinder machine gives 6 thrusts per revolution at 60 degree intervals, a 2 cylinder machine 4 thrusts per revolution at 90 degree intervals.

Regards

[bertiedog]

I think you must return to basics, 90 degree is the correct quartering for wheels, it is geometrically correct, and phases the cylinders movements correctly.

 

However you can allow about 10 degrees max each way as long as the same figure is applied exactly to each wheel.

Most jigs will put the wheels within tight tolerances, less than 1/10 the degree.

 

The reason 180 deg work, or appear to work, is we forget there are another set of coupling rods in action, the rails themselves, so that any dead centre tends to be covered up as it runs.

 

You may say that when you test a 180 deg in the hand but still turns, yes, because there is no load on it to show the dead centres.

 

The whole thing is clouded by the massive tolerances used in model trains, these both mask problems and cure them, look at the vast number of modellers who cure quartering issues by simply opening up the rod holes..........

 

Experience,...... I manufactured 00 wheels, and out of curiosity made a precision standard chassis, with ball races, and a matched set of rods to precision standards, again with races. I then assembled many sets of wheels at various settings and tried them out.

 

It completely confirmed that only 90 will work smoothly, but a few degrees out as long as even, still work, but not as smoothly. At about 10 degree dead centres began to cause jerky rotation when off the track, but not on the track.

 

The same precision rods were then used to drill out brass frames with typical bearings with a few thou slop, and then you could get away with about 20 degrees out.

 

So it comes down to theory against the real world, aim at 90 deg with a sound straight chassis and matching rods, and believe me the vital thing is matching rods, they are the bain of bad running models, and need far more care in drilling and fitting than most modellers ever realise.

They must also be dead straight, and have absolutely no twist to them.

 

Also there is a long forgotten problem with all 90 degree quartering, it is out of static balance, there is no cure, even with wheel weights.

The rods have a weight and it is out of balance, and as the speed increases the effect causes vibration and noise, and with O gauge models actually cause trouble at low revs due to the heavier rods.

 

In 00 the rods are relatively light, so the effect is smaller. In case you are wondering, the real things wheels weights are there to balance the piston thrust, as well as helping balance the rods.

 

Stephen

[bertiedog]

On 120 degree on models, don't!........ it can work, as the rail top provides another connection to the rotative movement, and with a bit of general slop in the bearings and rods, the loco will run, but in theory it runs though dead centres, covered up by the play etc.

 

You cannot compare the real three cylinder engines with models, the three cylinders give six power strokes around the circle, and they overlap enough to get away with using it, as Gresley discovered.

Each of the full power strokes acts over 60 degrees, then another starts, but it does cross in theory a dead spot. In practice the steam is cut off, and the circle would be six bursts of power each rotation. Inertia etc carries the wheels forward steadily, and at speed the Gresley system works well to smooth out the power impulses. It did leave the theoretical dead centre spots when about to pull away, but it usually worked!!!

 

On some other three cylinder locos, the driver, if he got no response as the regulator first opened, he just moved the gear to reverse for a moment to shift the position.

 

The only three cylinder locos in the UK that had starting problems were Mr Webbs Compounds on the LNWR, where the slip eccentric middle driver could stop in mid gear, or reverse position, causing the loco to move off with one set of wheels in reverse. However this only happened if the driver forgot to open a bypass valve to the big cylinder, which allowed it to rotate to engage the slip eccentric as the other two cylinders provided the power.

 

Stephen