Bachmann 64xx compensation for RTR chassis

[outatime]

Hi,

 

i spent a lot of holidays in the uk during the last few years. Every year i brought some 00 models, the first one being a LT pannier tank.

After buying some different models, i tried to look for some kind of focus, because i didn't want to end up with models which do not really fit.

As a theme i chose a preserved railway, which is a great thing for me, i like the beautiful stations with flowers an all the old advertising.

It is totally different from what i am used to see on german preserved railways.

With this theme, i can also go for some models which could be on a visit on the preserved railway.

 

After some time i decided to focus on locos from the South Devon Railway in Buckfastleigh, which is where i bought the LT pannier.

As 6412 is one of the most used locomotives on the SDR, i had to buy one as well.

 

Sadly though, this model doesn't run as good as it looks and not as good as the LT pannier, which has a sprung middle axle.

 

What i decided to do was to built a 3-point compensation into the RTR chassis.

I also came across the highlevel chassis, but wanted to try modifying the model first.

If it would not work, i can still go for the highlevel chassis, which i will certainly do for the Hatton's 14xx, but that's another story.

 

At first, i have to say that english is not my native language and some things may not be described in the right way.

If you have any corrections, feel free to post them and i will edit this post accordingly.

 

So here is what we start with, the model as it comes out of the Bachmann box:

 

 

 

The loco is easy to disassemble, it just takes a few screws.

 

As you can see in the pictures belwo, the wheels have square brass bearings, but no springing at all, the chassis is completely rigid.

For a three-point-compensation, we need one rigid axle, which will be the middle axle because of the gears, 

and we need one sprung and one rocking axle.

To decide which one will be which, we have to find the centre of gravity.

Just put the loco on a small flat piece of wood and slowly roll it over the edge, forwards first and then backwards.

If the loco starts to fall down the edge of the wood, this is the side on which the centre of gravity lies.

 

For the 64xx, this was the case when it was rolled backwards, so the last axle under the cab has to be the rocking axle.

The first axle has to be sprung then. Before working on the chassis, the gears have to be removed, their axles can easily be pushed out.

 

 

 

The cutouts for the wheels are 4 mm x 4 mm in size, the axles are 3 mm in diameter.

As a new bearing for the wheels, a brass tube was chosen, which had 4 mm outer and 3 mm inner diameter.

Luckily the inner diameter was slightly above 3 mm, so the wheels could still turn.

Because of the outer diameter, the new bearings were a perfect fit for the Bachmann chassis.

 

 

The plan is to solder a 1 mm brass-wire to the brass-tube, so that this will become the fulcrum point for the rocking axle.

A small groove had to be filed into the brass-tube, for the soldered in brass-wire to sit flush with the chassis.

 

With a small proxxon milling-machine, a 1 by 1 mm groove for the brass-wire was cut into the middle of the chassis.

The brass-wire will be held in place by a small plastic piece, which will be glued to the lower plastic part of the chassis.

The lower part will then be screwed on the chassis frame.

 

 

The rocking axle will need some additional space to move up and down around the fulcrum point, so the cutout in the frame was widened up.

(Actually in the down-direction according to the picture)

 

Here, the modifications to the frame for the rocking axle are finished.

 

For the front axle, i simply did the same and widened up the cut-out for the sprung axle to move up and down.

 

The spring was also self-made out of a copper wire.

 

The longer the spring, the easier it is to adjust it, so i drilled a hole through the middle of the chassis.

The spring will go up to the boiler imitation but it will not be seen later because of the wheel splashers.

 

Here you see the brass-tube with the attached 1 mm diameter brass-wire.

 

The same piece sitting in the chassis-frame. Later on, the exact heigh of the rocking axle can be adjusted by bending the brass-wire.

 

 

Now we have to put the brass-tube pieces on the axles. I used a sharp knife to mark the position of the wheel to get the quartering right when reattaching the wheel.

 

Here, both brass-tubes are already attached to the axles. The four Bachmann brass bearings are not needed anymore.

 

 

Here are the three wheels next to their positions in the chassis frame.

 

To let the rocking and sprung axle also go down, we have to cut out some little pieces of the lower plastic part with the wipers and the brakes.

The middle axle is not modified.

 

When the loco is completed, go for a test-drive and see if it sits evenly on the track.

If not, adjust the rocking axle under the cab until the position is right.

Now 6412 can go on track with an Autocoach.

 

 

All the modifications could also be done by hand with a saw, a knife and some files.

A milling-machine is a nice addition, but i think it can be done without it.

 

Best Regards,

Bjoern

Edited December 13, 2018 by outatime

[Nile]

Great stuff, and your English is excellent, better than some of the gibberish that is posted on this forum.

But the most important thing is ..... how well does it run now? I hope all that work was worth the effort.

[outatime]

Hi,
 
it was totally worth it, now all six wheels stay on track, providing power to the loco to prevent it from stuttering or stopping.
Here you can see the loco running over a small screwdriver:

Kind Regards,
Bjoern Edited December 14, 2018 by outatime

[Barry Ten]

Excellent post. I also found that my 64xx isn't as reliable a runner as the 57/87xx variety., due to the over-rigid chassis. In my case I went for a cruder solution of increasing the vertical play in the rear axle, by cutting away a rebate in the keeper plate, which allows the rear axle a tiny bit of extra float, enabling it to cope with track irregularities a bit better. Your solution is far more elegant.

[Darwinian]

That is a most ingenious and simple solution.

I've been pondering how to sort out the lack of flexibility in my Hornby 42xx tank as it loses grip on the incline transitions on my layout because there is no flexibility in the chassis. Not sure how this could be made to work for an 8-coupled though. 

Oh, it's one of the original square axle cut-out, no bearings chassis.

[Gordon A]

Very nicely executed with a good result.

 

Gordon A

[34theletterbetweenB&D]

...I've been pondering how to sort out the lack of flexibility in my Hornby 42xx tank as it loses grip on the incline transitions on my layout because there is no flexibility in the chassis...

 First take the pony truck off and test to make sure it isn't doing either of taking load off the coupled wheels or having the flanges jammed against the footplate underside and acting as brakes. (Traction is not affected by the number of driven wheels in rail contact, but only by the total mass acting on the driven wheels. H-D's functionally 2-4-0 8F outperforms all current 2-8-0 models for traction except the simlarly weighty Heljan O2.)

[Darwinian]

I know what you mean about the Hornby Dublo 8f as I used to have one.

Maybe the issue with the 42xx is the tyre surface. I have a sprung 57xx of less weight that can pull more up the inclines.

 

I’ll try putting even more weight in the 42xx.