Compensated Chassis Binding

[SWTDriver]

Can anyone offer a solution to the problem I have with this chassis binding in the zone shown on the photos and how I can remedy it.

I can confirm the following:

 

1. The chassis is square.

2. The height is level.

3. The compensation beam is in the right place.

4. Previous attempts to run the chassis have resulted in the crank pins in the middle wheel either unscrewing or shearing.

5. I will never go near a compensated chassis again as long as I live!

[PhilMortimer]

Sounds like the rods are slightly different length to the wheelbase. Check the rod crankpin holes match the wheel base exactly. Did you use a jig to set up the chassis?

 

This can happen on rigid chassis as well.

 

Easiest way to check is to use some rods that are the axle diameter which have tapers machined on the end. They can be purchased from various suppliers. Remove wheels and gearbox and place dummy rods through the chassis bearings. Now offer up the rods and check the match between the crankpin apertures on the rods and the wheel base. They should match exactly. if they don't, there is the likely cause of the problem. Some people remedy the situation by opening up the crankpin holes, but IMHO, that can make things worse. More work, but better to adjust the bearings of the wheelbase to match the rods. This might involve removing the bearings and opening up the holes a touch, before resoldering in position. Use the dummy axles and rods to hold the bearings in the exact correct position whilst soldering.

 

Good Luck!

 

PM

[Ton van Mastrigt]

4. Previous attempts to run the chassis have resulted in the crank pins in the middle wheel either unscrewing or shearing.

 

 

Have you checked if there is a proper fit of these crankpins in the holes?

Of course you must heed Phil's warning that the holes must not be too wide, but the crankpins should thurn in the holes without friction.

 

You may check this by turning the rods around, i.e. with the hole of the middle crankpin over the rear one. If the crankpin of the rear wheel will be unscrewing or shearing, then the hole is too narrow.

 

Good luck,

Ton

 

PS: Make sure your chassis is running freely without the motor, to make sure that the problem has nothing to do with the gears.

[Siberian Snooper]

With the motor removed and one pair of coupling rods removed, check to see if it runs as an 0-4-0 if this is good, then repeat the process with the other pair. As has been noted above not all coupling rods have the holes at exactly the correct spacings, for the chassis, especially with older designs which were drawn by hand rather than on a computer. to check that the spacings in the rods are the same, draw a straight line on a piece of wood and using a drills which will just fit through the hole in the coupling rod drill into the block of wood, making sure that the drill is vertical. leave the drills in place and see if the other rod will slip over the drills. If not you will need to fill the hole in one with solder and redrill using the other coupling rod as a guide. You will then need to ensure that the bearing holes conform to the rods using one of the methods described above.

[Sandy Harper]

Can anyone offer a solution to the problem I have with this chassis binding in the zone shown on the photos and how I can remedy it.

I can confirm the following:

 

1. The chassis is square.

2. The height is level.

3. The compensation beam is in the right place.

4. Previous attempts to run the chassis have resulted in the crank pins in the middle wheel either unscrewing or shearing.

5. I will never go near a compensated chassis again as long as I live!

You appear to be using rigid rods and compensated axles? Mmmm,I don't think that is how they are supposed to work? If you expect the axles to move up and down then the rods need articulation too! However, the points already mentioned are very valid and should be checked first before proceeding.

Regards

Sandy

[MikeTrice]

You appear to be using rigid rods and compensated axles?

The photo suggests otherwise. They are articulated on the centre crankpin.

[Izzy]

 It might be of help if you could say which chassis you are constructing as someone may have experience/knowledge of problems or issues with it. I guess from the shots that it is an outside cylinder OO gauge 2-6-0 of some kind, 43xx perhaps?

 

Anyway, the position you show the binding to occur immediately suggests to me that it is an issue to do with quartering/discrepancy between the various parts, rods/crankpins etc and is not basically because the chassis is compensated. It might be an issue associated with it, but not the root cause.

 

The only real way of solving problems such as this is in my experience is to return to the start and check all parts to ensure they match. The crankpin throw on the wheels is the same - they appear to be Romfords so I would expect them to, but you never know, and they appear slightly different. Is this because they are insulated/non-insulated? Are the crank throws the same? Are all the wheels seated on the square ended axles at 90 degress and run fairly true. Do the rods match the wheelbase? Slop of the rods on the crankpins will not normally be an issue, you have to have a lot before it can become problematic - just look at how much many RTR locos have, BUT, a small mis-match between the coupling rod and crankpin/wheel centres will be. Just making the rods a loose fit won't cure this either. Are the axle bearings square and true in the chassis ( I presume that is what is fitted) i.e. the bore is actually in the middle? I've had them where they weren't. If this is the case turnng them a quarter can sometimes make the difference.

 

Izzy

[Jol Wilkinson]

Sounds as though the correlation between the coupling rod hole centres and the axle hole centres in not correct. The photo shows that the binding is happening when the alignment is most critical and if a crankpin is shearing then there is some significant force and therefore definite misalignment.

 

I have built twelve compensated loco chassis using firstly Perseverance parallel end and latterly London Road Models taper end axle jigs (bottom of first section - https://traders.scalefour.org/LondonRoadModels/various/components/ )  to set up the horn guides in relation to the fixed, driven axle. I have only occasionally had to slightly ease one or two of the coupling rod crankpin holes.

 

So I would suggest getting a set of axle jigs (if you don't already have them) and check the axle/coupling rod correlation. If these are correct then the chassis should work, although you may need to open out the crankpin holes very slightly. Ensure the rods always go back on in the same place. 

 

As for you last point, I would never build a rigid chassis again. Setting up a compensated or sprung chassis using axle jigs ensures correct alignment between the axles and coupling rods, something you can't always guarantee with a rigid chassis where the parts are used as supplied or where you have to ream  out any bearing or crankpin holes.

[John_Hughes]

I've seen too many cases where both the 'rear 0-4-0' and the 'front 0-4-0' run beautifully when divided as suggested above; turn the chassis into the 0-6-0 it's meant to be and an evil little bind appears that takes for ever to sort out. And this is despite my using a chassis jig and taking meticulous care setting the whole thing up!

 

What causes it? I suspect it's a horrible coming together of errors which are in themselves insignificant; possible culprits are crankpins which aren't quite vertical to the wheel, wheels which aren't absolutely vertical to the axle, slop between crankpins and their bushes, crankpins which aren't exactly the same distance from the wheel centre, burrs in holes in the rods, sloppy rods which aren't retained reasonably snugly to the face of the wheel, rods which snag on balance weights, and probably a load of other factors I haven't thought of.

 

Cures? Check each of the above, taking your time to do it, and sooner or later the bind will disappear and you may never know what caused it. But it takes time, sometimes an awful lot of time - but if you don't get it right, you'll never be happy with the loco!

 

And good luck!

Edited September 1, 2017 by John_Hughes

[hayfield]

You have had some really excellent advice from the posters and I am certain the answers lie within. What surprises me is that when you look at the likes of Hornby locos there is so much slop but all runs OK but when a modeller tries this all locks up

 

I guess someone has already suggested this but I would use a parallel reamer on each set of bearings, then test the chassis without the motor to see that it is very free running. I then use a broach on the coupling rod holes to ensure the holes are round, fit one pair first to check for binding. If there is binding swap sides ( the coupling rods will be upside down) to see if this clears it. It might be that a very slight easing of the hole cures it. Swapping wheel sets may also cure it, or at least identify the problem.

 

If the first coupling rod works well, try the other coupling rod with the centre wheels. just a process of elimination to find where exactly the fault(s) lies

 

Good luck 

[PhilMortimer]

Also check that rods / wheels are not catching on anything sticking out (Brake mounts, sanders etc). I was driven to distraction with one of my garratts where a rod was rubbing on one of the motion brackets. It gave symptoms of bad quartering / rod mismatch and took ages to locate, 1/2 a minute to fix.

[Captain Kernow]

Can't think of much else to add, but (having just finished another compensated chassis myself), I'd advise to check that the Romford wheels are turning true to their axles. Someone else mentioned the need to carefully fettle the wheels, to ensure the machined steel axles fit snugly, but also without being forced. If you do try to force them, I found (this time around), that the wheel won't go onto the axle in a true, 90 degree fashion, if you see what I mean.

 

If you still don't have any joy, is there anyone you know locally, eg. in a club etc., who could offer some practical 'hands-on' advice?

 

Best of luck.

[SWTDriver]

Thank you all for the help and advice, I have finally come to the conclusion that despite setting it up on my Avonside jig in the first place and following the whatever is in Iain Rice's book to the letter it is time to admit defeat and get a paid professional look at it.

Edited September 2, 2017 by SWTDriver

[Jol Wilkinson]

Sorry that you have given up. It would seem that you had all the gear and information to build a working chassis. I wonder if there could be some serious difference between the coupling rod centres. Did you use just one set to set up the Avonside jig? If the other one of the pair had different distance between the crank pin holes, then the problem you describe could be caused by that.

 

Different radii of the crankpin centres would have a similar effect, but I would think that was very unlikely with Romford/Markits wheels.

 

Perhaps a fresh set of eyes will spot something.

[SWTDriver]

The sad thing is that I also have another chassis on the go and have made the same mistake of compensating that as well. This time it is the High Level kit for the Collett Goods, in all honesty I am not holding out much hope of it going right despite using the Avonside jig - think I'll just go back to ready to run 00, I'm wasting my time and money on EM.

[N15class]

The sad thing is that I also have another chassis on the go and have made the same mistake of compensating that as well. This time it is the High Level kit for the Collett Goods, in all honesty I am not holding out much hope of it going right despite using the Avonside jig - think I'll just go back to ready to run 00, I'm wasting my time and money on EM.

Compensation is not the problem unless you have made the horns and bearings too sloppy. but then that's a construction fault not the compensation. As above its axle coupling rod centres not matching or moving. Or the crankpins being tight or sloppy in the coupling rods, or the pins at out of position either from centre of wheels or out of upright.

[hayfield]

The sad thing is that I also have another chassis on the go and have made the same mistake of compensating that as well. This time it is the High Level kit for the Collett Goods, in all honesty I am not holding out much hope of it going right despite using the Avonside jig - think I'll just go back to ready to run 00, I'm wasting my time and money on EM.

 

As peter has said it might just be a case of opening a hole(s) a tad with a broach. How about making the chassis rigid ?

[Siberian Snooper]

The sad thing is that I also have another chassis on the go and have made the same mistake of compensating that as well. This time it is the High Level kit for the Collett Goods, in all honesty I am not holding out much hope of it going right despite using the Avonside jig - think I'll just go back to ready to run 00, I'm wasting my time and money on EM.

As peter has said it might just be a case of opening a hole(s) a tad with a broach. How about making the chassis rigid ?

I think that you would have had the same problem in 00, but a rigid chassis in EM gauge should still be OK, if you decided to go down that road.

[Dave John]

Its worth keeping on trying SWTDriver. Compensated chassis do work. All the above advice is good, I read up about them and talked to folk before I tried one. Half a dozen bad compensated chassis later I built one that ran like a dream. Thirty years later it still does. 

 

So whats my advice ? Simply that when you do crack it the satisfaction more than makes up for the learning curve. 

 

The thing that I finally realised I was doing wrong was the coupling rods. The cure ? Buy a box of 1.5 mm drills and never use them for anything else. ( or whatever size, they fit gibson crankpins ) Make the rods up and drill the first hole of both pairs into a block of good wood, preferably formica faced. Leave the first drill bit through the rods and the wood. Next drill bit, second hole through both, leave it in place. Next drill bit etc. Mark the rods , I dot a bit of paint on the rear. Then reference everything else from the rods. I have a set of old romford axles with the ends turned down to 1.5 mm, use the coupling rods to set the axle bearings up. 

 

Its not my Idea, I borrowed it from lots of other folk. Try it, might help. 

[43078shildoncountydurham]

 

Keep on going SWT Driver, you have already done brilliant, it will come good

 

I am just trying to rewheel a Hornby K1 from 00 to em and guess what I've got the similar going on

 

Take care

 

Craig

[Brit70053]

Something else to try is replacing the axles one at a time. I've had a couple of instances out of dozens of Romford axles I've used, where one threaded axle end has not been true and resulted in similar problems to those you describe - loosening and scoring crank pins because the wheel isn't secured at a perfect 90 degrees to the axle - and this on rigid chassis.

Its one of those things that is very difficult to see unless you prove it to be the case by substituting an axle which is 'true' in all respects.

A set of 3 new axles won't cost a fortune (you may only need one) and even if this proves not to be the case, you'll always have use for a spare set of axles as you progress with other builds or conversions.

 

Regards,

 

John

[ROSSPOP]

 No... Don`t give up SWTDriver......................but   you will have to start this chassis again from the very beginning....

 

There are a few basic principles to follow to build a working loco chassis that is hasle free in ANY chosen scale.  They are all to do with accuracy.

 

It matters NOT A JOT  whether you use  fixed bearings, compensation or sprung hornblocks.

 

 

 

1.

 

start by making the coupling rods first.

 

Your chosen crankpin bearing holes should make an easy fit, no slop or oval holes.

 

 

 

2. assemble your chassis frame , adjusting/modifying for your chosen bearing type.

 

 

 

3.

 

Purchase this simple axle alignment tool  from (was Metalsmiths now Midland Rail Centre)

 

 

4

 

Make your coupling rods do all the accuracy.

 

 

 

Bob`s your  Uncle,     Fanny`s your    etc, etc .........

 

 

A working chassis everytime..............................

[John_Hughes]

Its worth keeping on trying SWTDriver. Compensated chassis do work. All the above advice is good, I read up about them and talked to folk before I tried one. Half a dozen bad compensated chassis later I built one that ran like a dream. Thirty years later it still does. 

 

So whats my advice ? Simply that when you do crack it the satisfaction more than makes up for the learning curve. 

 

The thing that I finally realised I was doing wrong was the coupling rods. The cure ? Buy a box of 1.5 mm drills and never use them for anything else. ( or whatever size, they fit gibson crankpins ) Make the rods up and drill the first hole of both pairs into a block of good wood, preferably formica faced. Leave the first drill bit through the rods and the wood. Next drill bit, second hole through both, leave it in place. Next drill bit etc. Mark the rods , I dot a bit of paint on the rear. Then reference everything else from the rods. I have a set of old romford axles with the ends turned down to 1.5 mm, use the coupling rods to set the axle bearings up. 

 

Its not my Idea, I borrowed it from lots of other folk. Try it, might help. 

 

I know this works because I've done it myself! But I would caution against the idea that any simple twist drill gives a truly round and accurate hole.

 

Why not buy a decent set of reamers up to, say, 2mm? Mine saved me hours of frustration!

[Pebbles]

If you are using the Comet system and components you can't easily relocate the bearing - removing the area defined by the half etch lines has to be done very carefully! If you have not already done so, as a simple test to check the crankpin throw, try each wheels in a different location to establish whether the problem is linked to a specific wheel or combination of wheels.

[Jol Wilkinson]

More good advice above.

 

I would also suggest, as already mentioned, going back to basics to find what has caused the problem. It will be either a mismatch in the parts or something has gone awry in the assembly. If the former, then  any chassis - rigid, sprung or compensated - won't work.

 

Parts first.

 

Do the rods match each other , centre to centre?

Do the axle bearing holes in the frames match the rods and are they consistent with each other? - The tapered axle jigs shown (available from several sources. I use the London Road Models version) will show any rod/axle bearing misalignment.

Do the crankpin "throws" match?

Are the wheels accurately and consistently quartered?

 

The last two should be okay with Romford/Markits wheels, but it is worth checking

 

If you take off the rod on one side and rotate the wheels until the crankpins are fore and aft (as in the LH picture in the OP) and the rod is not binding, then those axles and rods are matched. Then do the same for the other side. If that is okay, then it would seem to point to a wheel quartering and/or, crankpin throw problem.

 

.

 

Assembly process.

 

Were the axle jigs in the Avonside jig set up accurately and checked? I have read that they can move when finally tightened.

Did you use one set of rods to set up? If there is any mis-match in the different rod centres, then that could cause the problem.

 

There may be other issues, although I can't think of anything else significant at the moment.

Edited September 4, 2017 by Jol Wilkinson