Help with Leaf Springs.

[rrmrd66]

Morning everybody.

Progress on the 5" Hunslet continues. I am now on with the spring assemblies.

DY's design calls for spring steel leaf springs 5/8" wide x 22swg and 5/8"x1/32" Tufnol strips.

The depth of the square shackle is approx 1/2" but there is a grub screw to nip it all together.

According to my rough calculation that makes about 12-13 elements, decreasing in length from the initial 4" down to, I guess, about 3".

Questions:

1. How do you form the radius in each of the leaves?

2. My normal materials supplier ( M.Metals Darlington. V. good BTW) can supply but only in the annealed state. What are members experiences with hardening and tempering? (I have a 2nd hand Tubal Cain booklet on the way)

3 Previous comments suggest that not all alternative Tufnol strips are necessary. Comments please.

4. is it necessary to know the weight of the engine , the max travel of the axle boxes, calculate the load/deflection of the spring and aim to set it about midway, or is that completely OTT?

Cheers

Malcolm

[Deleted]

Hi Macolm..

IIRC, for 'Doncaster' Don gave a figure of 1/4" deflection between the top of the leafs and the bottom arc. I made a wooden forming tool to match this, details are in my thread. I used annealed strip and hardened/tempered it after forming and drilling of any holes. As for the tufnol, I've found so far that more tufnol (less steel) leafs are needed than Don stated, however this may change as the chassis gets to full weight, for now I am leaving ut till then. The springs work very well so I'm happy with them.

Cheers

Pete

[rrmrd66]

Thanks for this Pete.

Which particular page is your wooden form tool on?

Cheers

Malcolm

[Deleted]

Hi Malcolm

Page 8 is one, there may be others when doing the loco. All it is, is a piece of timber that I drew an arc on to match the leaf size and 1/4" deflection and then cut out, can't recall if I did this carefully using a jigsaw or my bandsaw. Once cut, I then cleaned up both halves using sandpaper, think I first tried compressing the steel between them in a vice but later found it much easier to roll a piece of alloy bar over the leaf in the concave of the wooden profile, this is described on page 18.

cheers

Pete

[92220]

Hi Malcolm.

Form your leaves in the annealed state. You are using tufnol interleaves so I would suggest using an equal thickness mild steel strip to simulate the tufnol, and assemble them in the shackle. Place the assembly side on, on a sheet of 16 swg mild steel (or thereabouts) and heat underneath with a gas torch. Watch the colour of the spring assembly and when it reaches a dark purply blue all over, drop the s[pring assembly in a bowl of cold cooking oil. This should harden and temper at the same time. You can then dis-assemble and re-assemble with the tufnol interleaves. This is how I did my leaf springs on the 9f and it worked perfectly. The only difference is that mine are all steel leaves with no tufnol interleaves. I would suggest making up a spare spring assembly to go through the heating process before working on the loco parts. That way you can work around any problems you might encounter.

Bob.


Edit:      I've just found the page where I describe making and heat treating the leaf springs on the 9f tender. It's exactly the same as for the loco. I did make a mistake, above. I forgot to describe the hardening process before tempering. If you look at page 6 of my thread, it describes how everything was done for the springs. This is the link to page 6....http://modeleng.proboards.com/thread/11583/5-evening-star-works-drawings?page=6    Hopefully you can just click on it but if not, just copy and paste to find it quickly.

Bob.

[jma1009]

Hi Malcolm,

Don Young's 5"g Hunslet 'Quarry' loco is quite a big heavy lump in 5"g and on only 4 wheels, plus the cylinders are inclined which imparts a certain 'bounce'.

I would be inclined to make the leaf springs quite stiff to start with, and accurately test them when assembled on the finished loco (I can describe again how I do this at the relevant time). Be prepared to adjust - make new spring hangers of different lengths when the loco is finished, and do some dismantling and adjustment of the leaf spring assemblies.

The last thing you want is a 'bouncy' short wheel base top heavy 0-4-0 ST bouncing off the track!

Cheers,

Julian

[rrmrd66]

Thanks guys for all the good suggestions.

I assume from the remarks that obtaining the correct temperature of the spring steel strips with a Sievert Propane blow torch in a sort of "refractory brick oven" is not a problem?

regards

Malcolm

[92220]

Hi Malcolm.

Yes that would do but you have to be able to observe the change in colour as the steel heats up.

Bob.

[simon822]

Malcolm,

I have made several sets of springs, one set for a 3” quarry Hunslet and 1 set for a 7.25 Wren. The steel came from M-Metals, it was sheared strip, so the edges needed to be cleaned up first. The top leaves were drilled on the Hunslet to take the end bearers, then rolled to the correct shape as per the drawings. The ends of the Wrens top leafs were bent backwards over a former. The important part is that all the machining is done at this stage. The leaves were then individually heated to a very uniform night orange and then very quickly quenched in cooking oil. The heating was done using a sievert torch and fire bricks. Each leaf is then cleaned using emery paper, you must resist the temptation to test the spring at they are very brittle at this point. I then tempered the leaves in a bath of molten lead, leaving the leaves in till the lead ran off them when removed (well that is the theory). One tempered, leave to naturally cool and cleanup again to remove any lead residue. Assemble and paint the springs. I put a light oil on each spring to ensure they don’t rust together.

In the larger scales I have not used any Tufnol leaves, but have always wondered what the difference would be in the position of the Tufnol leaf would be on the spring.

Hope this helps,

Simon.

[92220]

Have a look at Mike Jack's thread. He has just posted about making his springs and what he did to get scale deflection.....and it works 'cos I've done it, and load tested the finished springs.

Bob.

Edit:    Mike Jack (44767), describing his build of the Class 3 tank