Chassis building

[hayfield]

Give me a few lengths of rail and sleeper strip and I am in my ellement, but the black art of chassis building leaves me shaking.

 

I look ay RTR chassis and the coupling rods slop about all over the place but they work fine. Then get an etched chassis and whilst the wheels rotate fine on their own, put the coupling rods on and they bind. I have been told that ridgid etched chassis have the centre holes 0.5mm high (to stop rocking), should the centre hole in the coupling rod be eased out a bit.

 

I have a couple of flexi chassis (not made by me) and when the axles float why dont the axles bind as the distance must increase and decrease as they move up and down.

 

Help please

 

Also I am just doing a chassis for a GWR 1854 pannier tank with 18mm wheels, what is the best gear ratio please

[James]

Also I am just doing a chassis for a GWR 1854 pannier tank with 18mm wheels, what is the best gear ratio please

Have a look at High Level Kit's website and see which boxes may fit - I'd go for 54:1 with their range. Otherwise I'm a huge fan of the gearboxes which Branchlines supply with 50:1 Ultrascale gears.

[gordon s]

John, I'm still a beginner on chassis construction, but I have gone through the same loop as you just recently. The first thing to check is that the quartering is correct. The jig from GW models does the job really well. Once you have the quartering correct, fit the coupling rods and check if that's cured the problem. If they still bind, look closely at the rod holes and see if the crank pins are central in the coupling rod hole. I bought a set of taper broaches from Eileen's Emporium which cover 0.6mm through to 3mm from memory. These will allow you to gently open up the holes and remove the tight points. Take your time and try to work on the wheels in pairs. For instance, the front and centre and then the centre and rear on each side.

[hayfield]

Gordon

 

Thanks, I am using Romfords in an old Wills cast chassis with 1 piece coupling rods, should I open them up slightly? I did this to the centre ones should I do the same to the outside ones?

 

Chassis runs freely without a motor, but binds when the motor is added, it runs off the front wheels.

 

Cannot fit a gear box as its a whitemetal chassis.

[Metropolitan]

Give me a few lengths of rail and sleeper strip and I am in my ellement, but the black art of chassis building leaves me shaking.

 

I look ay RTR chassis and the coupling rods slop about all over the place but they work fine. Then get an etched chassis and whilst the wheels rotate fine on their own, put the coupling rods on and they bind. I have been told that ridgid etched chassis have the centre holes 0.5mm high (to stop rocking), should the centre hole in the coupling rod be eased out a bit.

 

I have a couple of flexi chassis (not made by me) and when the axles float why dont the axles bind as the distance must increase and decrease as they move up and down.

 

Help please

 

Also I am just doing a chassis for a GWR 1854 pannier tank with 18mm wheels, what is the best gear ratio please

 

Hmmm! The thing with an etched chassis is to use the coupling rods to set the wheelbase before soldering in the bearings. You can, however, to stop any binding, ream out the holes in the rods a la RTR to get over any stickyness. Just keep going until the chassis runs free. You won't notice the slop. With a flexi chassis the same applies.

 

Fitting the centre driver 0.5mm higher is fine for 0-6-0's but quite honestly it ain't worth fiddling about with. Add weight instead!

[R A Watson]

Using the "old" format as you are, Romford wheels / solid chassis, the only adjustment that could be carried out was to the holes in the rods; BUT the answer to your problem is in the throwaway line. "It all works until the motor comes into the equation", 10 to 1 on the problem is the mesh between motor worm and axle gear. Check this out before trying any other surgery. A fine gap between the teeth when at rest and no movement of armature forward and back leading to binding when rotation starts.

 

H T H

 

Wally

[micklner]

Check wheels in fours once they are run without binding , then add the next set of crankpins to the wheelset any binding should then be in the last pair coupled rods

[Nicktoix]

If your centre axle holes are 0.5mm above the line then you will get binding. There is no good reason to have this arrangement all the axle holes should be in

a straight line on a rigid chassis.

Nick

[James]

There is no good reason to have this arrangement

The OP does state the reason why in his first post - it does help prevent rocking. In theory only three wheels on a fixed 0-6-0 chassis are in contoct with the rail, so keeping the centre axle slightly above all of this means that rocking around it unlikely. I think John Ahern mentions it his book on loco construction.

[Bruciethefish]

Hi John, To check the rods on this kind of chassis, rotate the wheels so all the cranks one side are in line with the axles, then try moving the rod that side backwards & forwards;- if there is enough slack in the rods, you should just be able to get a small amount of movement. If you can't move them, examine which side of each hole is closest to the crankpin, I.E. if the rod is either stretched or pinched between two particular pins. If this is the case, use a fine rat-tailed file to ease the hole on the tight side only, then restore to roundness with a broach or twist of the file. once you're happy with the running, add the motor again, & if binding occurs, it has to be the gear mesh, in which case ease the motor upwards a little, until you can just move the geared axle slightly before the worm prevents further movement.

[frisby]

The OP does state the reason why in his first post - it does help prevent rocking. In theory only three wheels on a fixed 0-6-0 chassis are in contoct with the rail, so keeping the centre axle slightly above all of this means that rocking around it unlikely. I think John Ahern mentions it his book on loco construction.

Surely unless one of the following occurs:-

1. the middle coupling rod hole is 1mm oversize

2. the rod is bent to be 0.5mm high in the centre (or the hole is drilled 0.5mm higher), in which case it has to be the 'right-way-up'

3. the rod is jointed

then it is guaranteed to bind!

[Metropolitan]

There are a host of reasons why a chassis may bind or rock (including wheels that are not round). If you look at any RTR chassis (as per the OP's question) you will see that the rods are jointed and there is an amazing amount of play, side play and slop in the joints.

 

However, with built models, such generous clearances are frowned upon for some reason. By far the easiest and stress free remedy for a chassis with unjointed rods that bind at one part of their rotation (which usually indicates an error in setting up the axles ) is to open out every con rod hole (the effect compounds along the rod) to a good 0.4mm oversize. You honestly wont notice the play with the loco in motion.

 

On the question of lifting the centre axles by 0.5mm to avoid rocking on a rigid chassis I would have thought that 0.5mm is extreme and that around 0.1mm would be plenty. In other words, just a smidgen. Better still, spring the centre axle? Not that I bother with either.

[James]

It will work, but you'd have to open up the coupling rods until you acheive a running fit. It's not a wonderful engineering solution but it will work!

[34theletterbetweenB&D]

Chassis runs freely without a motor, but binds when the motor is added, it runs off the front wheels.

 

Cannot fit a gear box as its a whitemetal chassis.

 

 

... the answer to your problem is in the throwaway line. "It all works until the motor comes into the equation", 10 to 1 on the problem is the mesh between motor worm and axle gear. Check this out before trying any other surgery. ...

 

Absolutely. The addition of the motor may cause problems in another way also in a whitemetal chassis, the attachment may be distorting the chassis block. Glueing the motor in place with Evostick or silicone putty type adhesive can be a way forward if the chassis distorts when the motor is screwed on.

[hayfield]

Thanks for all the replies, I found the answer last night just before I went to work 34 got it right. I am using a 5 pole replacement (of the Hornby) motor which must have a slightly different bodt shape than the Hornby one.

 

As I tightened the rear motor retaining bolt it distorted the chassis (centre wheel lower than the outer 2)I have straightened up the chassis a thich brass washer between the motor and chassis stops the motor distorting the chassis and also improves the meshing as I am using the older type worm gears.

 

Thanks everyone for the information.

 

I did ask about what is the better gear ratio for this loco, I have a choice 30-1 40-1 & 60-1. just to remind you its a pannier with 18mm wheels.

 

Thanks

[34theletterbetweenB&D]

I would go for 30:1 in these circumstances. A five pole motor of roughly XO4 dimensions should have adequate torque for decent low speed control with the relatively small wheel diameter of this loco, the coarser gearing will be more tolerant of the fairly rough and ready meshing alignment that is likely with the chassis construction of this model, and the lower motor shaft speed for any given rate of progress on track will likely make it quieter if it is a direct drive arrangement (motor shaft worm drives axle mounted pinion).

[ArthurK]

 

I did ask about what is the better gear ratio for this loco, I have a choice 30-1 40-1 & 60-1. just to remind you its a pannier with 18mm wheels.

 

Thanks

 

With a rigid chassis and the "older style" open framed motor I would never use a gear ratio of more than 30:1 in a single stage gearbox. Above this the gear efficiency drops rapidly. I have never understood why anyone would opt for worm ratios of 40:1, 50:1 or even higher for this combination.

 

The story is different if you use a flat can and HighLevel style of gearbox. Then you can go much higher than that as only the first gear in the chain is worm driven. 54:1 is my standard and allow the wheel diameter to take care of slow goods or fast passenger.

[hayfield]

Thanks 34 and Arthur,

 

I have changed the gears to a coarser set and its a bit smother,

 

I have 2 more of these chassis built by others, one which has the same coarser gears which came with another 1854 (cheap Ebay buy as it is missing 2 bufferheads and the pickups were bent out of shape).

 

The other which I brought for an 1804 saddle tank body (also a cheap Ebay buy which had a poor description) has a finer set of gears but still runs OK.

 

Now making the pickups for both.

 

Thanks again

[hayfield]

Thanks everyone,for all the advice sorry for the delay in replying but Virgin.net has been down for 2 days.

 

The chassis is now running well,just need to but some axles washers before I solder up the crankpin bosses, with the internet down I also fitted new wipers to 2 other chassis and repaired 2 other ones.

 

Thanks again.