7 1/4″ Dart, John Smith design

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7 1/4″ Dart, John Smith design

This topic has 7 replies, 5 voices, and was last updated 20 February 2023 at 13:46 by Nigel Bennett.

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19 February 2023 at 14:07 #634185
Steve Bright 2
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@stevebright2
Work on my Dart is progressing, albeit slowly, the modifications to the chassis are almost complete and I'm working on getting it on it's wheels. The springs are built up of Tufnol and spring steel. I have done all the Tufnol leaves with the help of a Christmas cake tin and the kitchen oven, when she was not looking.

I'm having problems with the spring steel. I have managed to get some 15 x 2mm stock but the drawings require 1/2". Being spring steel I can't just mill the difference off but I'm considering angle grinding it off. That still leaves the problem of rolling it into shape.

I'm not confident I can do it so I'm seeking alternatives and maybe even a source of ready made leaves.
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19 February 2023 at 14:07 #34173
Steve Bright 2
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@stevebright2
Springs
19 February 2023 at 14:33 #634187
Clive Brown 1
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@clivebrown1
I've milled and drilled thinner spring steel for 5"g, at some cost to HSS cutters. Would carbide cutters do the job reasonably well? I've not tried for myself.
19 February 2023 at 14:39 #634188
Nigel Bennett
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@nigelbennett69913
I used a metal-cutting disc from the angle grinder, mounted in a suitable arbor on the milling machine and I machined some material to he thickness I wanted very easily. You can get the discs 1mm thick (thin?) so they'd cut the necessary sliver off.
19 February 2023 at 14:51 #634190
Steve Bright 2
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@stevebright2
Clive, I tried that and the spring steel was hardly touched and the carbide cutter ruined.

Nigel, I hadn't considered an arbour in the mill but easy enough to make one. I was thinking of using a flap wheel grinding disc. I have a stock of 1mm cutter discs, but I'm reluctant to use a cutting disc for grinding. To much time working with H&S i suppose plus I have seen a cutting disc explode and the damage it caused to the operatives leg, quite a few stitches!
19 February 2023 at 16:32 #634208
noel shelley
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@noelshelley55608
Thin cutting discs require a rotational speed of about 10000rpm I seem to think without looking ! At the speed a mill will spin all it wil do is break up the disc. So long as you are working on the edge of the wheel NOT the face it will be OK but DO NOT work on the face – it is a cutting disc. Are we not trying to reduce the width from 15 down 12.7mm ? Done carefully, letting the disc cut at it's own speed so as to avoid heating, it's what their made for. Clamp a length to guide, another bit of steel, even a lenght of 1/2" bar and run down it with a 4.5" grinder. Noel.
19 February 2023 at 16:40 #634212
duncan webster 1
Participant
@duncanwebster1
Anneal, machine, bend, harden temper. Sounds easy, but the heat treatment bit is not straightforward. Tubal Cain's book on hardening would be a good start
20 February 2023 at 13:46 #634327
Nigel Bennett
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@nigelbennett69913
I'm not talking those multi-tool cutting discs but the 4" diameter ones. Here you go:

As far as I recall it was doing about 1000rpm. You can just see a spark above the LH end of the job. The material is steel strapping, incidentally.
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