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Leaf springs

Highlander tender springing

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Thomas Pawley 125/01/2020 16:59:29
9 forum posts

I have to make a number of leaf springs. the material specified is 3/4 wide x 1/32. I find that this is prohibitively expensive but have sourced some reasonably prices steel which is 19mm x 0..4mm. I will need to double the amount of leaves to use this. How will this affect the springs performance ?? any advice would be much appreciated. Tom.

Perko726/01/2020 10:29:49
422 forum posts
33 photos

You may well find that double the number of leaves using a thinner material will make the springs much stiffer as not only will you have the spring action of the steel but also the friction between the leaves as the spring moves. If you have the opportunity, make up a test rig in which you can set up packs of leaves of various numbers, and load them to see how far they deflect with the weight of a loaded tender. Once you have determined the number of leaves needed to give the required load capacity, if the spring pack is much smaller than the original then you could make up some additional leaves from suitable plastic strip and place these between the steel leaves. They will not affect the load-bearing capacity but will reduce the friction between the leaves making them slightly more responsive.

As an option, many use the steel strapping used on pallets for springs, or else broken bandsaw blades and other similar items. You might find something closer to the required thickness from one of these sources.

Hope this helps.

HOWARDT26/01/2020 11:15:09
900 forum posts
39 photos

I found and bought some spring steel strip from Reeves at a reasonable price.

norm norton26/01/2020 11:18:15
183 forum posts
9 photos

1/32" seems rather thin for such wide 3/4" spring leaves. Is this for a model, a steam engine? Smaller 3/8" wide springs would use about this thickness.

M-Machine sell 3/4 x 16swg ( 1/16" ) spring steel strip for £3.30 per foot, and 3/8" in the thinner gauges. I would make 3/4" springs from this.

Edited By norm norton on 26/01/2020 11:18:54

Nick Clarke 326/01/2020 12:03:30
1392 forum posts
61 photos

Conventionally, when making leaf springs to scale they are far too stiff, so the solutions are either to slot the leaves, replace some or all of them with Tufnol or similar or to replace each leaf with a number of thinner ones, so I suspect your springs, if each leaf is made up of a number of thinner ones will be softer not harder than as drawn.

As a 7 1/4" locomotive the driver sits on the tender so it has to be able to take a reasonable amount of weight (particularly in my own case!!)

The club Highlander is off the rails at present awaiting a new boiler and repairs, but I can have a look at/take photos of the tender next weekend if it helps.


Thomas Pawley 127/01/2020 14:22:53
9 forum posts

My thanks to you all for your helpful comments. The size is as specified by the designer of Highlander, I have ordered a small amount of the thin material, enough to make one spring and see how it looks under load. There is something like 30 metres of the 1/32 material required, which equates to around £220 from the cheapest supplier found to date. I must investigate the steel strapping suggestion also. Thanks again to you all. Regards, Tom

Nick Clarke 327/01/2020 14:40:57
1392 forum posts
61 photos

A couple of thoughts - firstly the spring material you have bought will, according to some supplier websites, need to be heat treated and secondly you can perhaps work out the loading on each of the six springs on a best guess principle for a maximum water coal and driver load plus sprung weight of the completed tender.

Alternately input Martin Evan's spring design into one of the leaf spring desing formulas on the internet. These springs are of a relatively simple desigh with only one full length top leaf and single leaves of the other lengths so you should be able to obtain an approximation of their deflection under load to compare yours with.

Unfortunately your proposed springs with multiple leaves of each length are a harder problem to calculate (at least to someone who last looked at spring design at Uni nearly fifty years ago and never since!) so doing the same for yours may not be an option.

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