Leaf Springs

[ivanj]

What is the best way to make these as dummies. I have used mild steel strip and brazed it together which is not that easy. Is it better to make leaf springs which work and how do I get the rate right if I do that?

[waggy]

Ivanj,

I fabricated some tender leaf springs using steel banding from packing cases or palletised goods. It doesn't really matter what you use providing the material will take the weight of the machine you're springing. What you must do is chamfer the edges of the plates so they look radiused, as are "proper" leafs. If you don't do this they look false!

If you fancy making real leaf springs, don't use Tufnol for all the leaves, it isn't strong enough for a working spring. It's fine for the lower, shorter leaves as in our sizes they don't do much.

I made a set for a 4-6-0 loco, the top five leaves being made from Sandvik bowsaw blades, the rest from Tufnol. I found out about this type of material purely by chance, had a couple of old ones about and tried out, bingo! It is easy to drill and shape. I ground the teeth off and cut to width by holding in a machine vice and shearing the unwanted bits off using an old wood chisel. Crude but it works! You must grind the teeth off as they are induction hardened and will defeat the chisel! I bent the leaves around a piece of 3" cast iron I have, this seemed to set the curvature well, it springs back to approximately 7" diameter when released.

To ascertain the weight setting of the spring you need to know the service weight of the beast to be sprung, ie, full of water, coal or whatever you put in it. In the case of the 4-6-0 there are four weight bearing points, the driving wheels and the bogie centre. Each needs to hold about a quarter of the machine weight, this figure then divided in two as there is a spring either side of the bogie and each driving axle. (As a rough guide, my loco has springs capable of supporting 26lb at each point.) The bogie is of the DeGlehn type so the springing is through an equalising beam between the axles.

I'm afraid it takes a bit of trial and error before you get things right, hope the above is of help.

[Deleted]

Waggy,

How much should the springs deflect when under load? I'm just fitting the main springs to my Modelworks Britannia - they are all steel, 11 leaves - and they only deflect a couple of mm with a load of about 30lb on one spring - is this enough movement? I guess the aim is just to even out the load on each wheel, rather than cope with big irregularities in the track?

Regards, John

[waggy]

jj,

The spring needs to flex about the same amount that the axlebox lifts in the horns from normal running position until it hits the top of the horn.

The normal position is usually when the 'box sits in the horn with a near equal gap at the top and bottom of the box 'twixt frame and keep. The spring also needs to allow the box to drop as the wheel goes into a dip, however this movement will be taken up as you adjust the springs to get the loco balanced or "weighed" correctly.

Have a look at the Model Engineer index for a simple weighing device, you need to get fairly equal loads on each side of the axle or the engine may slip, caused by uneven weight on each wheel.

I had to put pieces of lead under the cab floor of said 4-6-0 to counterbalance the mass of the three cylinders. Putting extra strong springs on the bogie to lift the front end wouldn't have worked as weight may have been taken off the leading wheels, causing a slip under power.

A good guide for the weight of your loco can be found in the IMLEC results, they record loco weight. Standing a big lump of metal on the bathroom scales can lead to domestic discord!

As I said, trial and error will pay off.

Good luck,

Waggy.

[greasemonkey]

Hi JJ
Go carefull with the weights of IMLEC locos! I know a couple of the regular entrants have added a lot of addtional weight to their engines, as the limiting factor in the adhesion of a minature loco is its weight. I would sugget you have a look at the weight of a range of Britannias and you will see what I mean. To give an example the 2-8-2 of Lionel Flippance has main frames which a first glance appear to be standard 1/8" plate. Look again at the frames beneath the running boards and you wil see it is 1/4" plate, the front was milled away for effect!!
As Waggy has said it is as important to allow the wheel to drop as it is to rise and the cylinders will usually cause the front to be heavy, add weight under the footplate to counter balance it.

Andy

[Deleted]

Waggy, Andy,

Thanks for your advice. I'll try to establish the likely all-up weight of the model and load it up accordingly. It would be nice to get the springs right before painting the frames. I think the axleboxes will sit somewhere near the middle of the range, but I don't think they will travel anywhere near the top of the horns.

Regards, John

[chris vine]

Hi John,

The only trouble with them being too stiff is that they won't push the wheels down into a hollow. This could mean derailments because a wheel is not kept in contact with a lower piece of rail.
Just something to watch out for.
Chris.

[Phil Sutton]

It is the opinion of one or two of our members that springs should be softer rather than firmer,that way they'll follow irregularities in the track better(or so I'm told)

Phil