[TheForge] rigid vs. springy steel

[Jerry Frost]

Pete's point is valid, that is an aggressive temper for a speed bar but 
spring steel is pretty tough stuff unless you get carried away. It's 
also why I recommend dark straw as a DEPARTURE point and testing coupons 
to get it right. Drawing back to a spring temper, blue will be too 
springy to conduct force from a hammer blow and flex. Too stiff and 
it'll work harden and break. Dark straw is the hardest temper I'd draw 
to and I figure you'll end up close to purple but I've found spring 
stock drawing into the purple is onn the soft side, for hammer faces 
chisels, etc. they deform from hammering and it's pretty unusable on the 
working edge/face/end.

Bruce: I may have made a mistake thinking you were going to have one of 
your smith friends work on this with you and assumed more than I should. 
Good catch Pete, it's good to have backup.

For example do you know how to use test coupons and evaluate the 
results? to start they need to closely resemble the product, not a pry 
bar resemble but mechanical characteristics and more importantly they 
all need to be consistant every variable changes everything. So, using 
the target stock forge it down into thin section of the same width. 
Using kiss blocks is a much better method than eyeballing thickness. Cut 
to the same length and harden them individually being as consistent as 
possible. Now draw the tempers as carefully as you can, again, one at a 
time starting at the departure point temper color. Med dark straw in 
this example, mark it, clamp it in the vise lay a rag over it as a 
scatter shield and give it a smack with a hammer. Remember how hard you 
hit it, this is important, heck critical, use the same hammer, same arm 
swing, etc. Note the result if it snaps off it's too hard, if it bends 
it's too soft, if it deflects and springs back you're close and it's 
time to judge how much flex you want. And so on, drawing the temper of 
the next coupon a step farther. This is a case where drawing the temper 
in an oven with a good thermometer is a preferable method.

As I said, you may want to get together with a balcksmith or bladesmith 
friend Bruce, it's better safe than sorry. Heck I just buy speed bars 
and I know how to forge ad heat treat the things. <hint hint>

Jer


On 7/25/2013 11:34 AM, Peter Fels & Phoebe Palmer wrote:
> Jerry's temper recommendation is a bit less conservative than mine, but makes sense.
> The question is the failure mode...Do you want it to hold up with little wear till you finally abuse it and it snaps abruptly,
> or would you were rather it was tougher, softer, and fail by bending?
>
> On Jul 25, 2013, at 12:12 PM, Jerry Frost wrote:
>
> You're on the right track Bruce, a little thicker and more tightly wound AND don't put a spring temper on it, only draw it back to medium to dark straw and you'll be good to go. Oh yeah, spring steel is a good choice as it's more forgiving in the heat treat so little differences in temperature don't have major effects.
>
> I guess I'll *never *learn and keep on replying before reading the whole post. <sigh>
>
> You're wanting to make a speed bar,  great tools, I have a few though I've never made one. I'd forge it down from spring stock and temper it to medium straw. springs are typically drawn back (tempered) well into the blue. You'll want to make a couple test pieces (coupons) to get the temper right, they WILL be struck with hammers so do a few tests.
>
> A good alternate stock is found in tire irons, lug wrenches or (big surprise!) pry bars, yard/garage sale stuff. Again, make some test coupons as a departure point I'd draw the temper down to the straw and adjust from there depending on the test coupons.
>
> Jer
>
>
> On 7/25/2013 1:06 AM, Bruce . wrote:
>> Here's a question you metal munchers might be able to field:
>>
>> I have had a few applications in which I need thin but rigid steel.
>> What steel is best?
>>
>> Consider for example a corkscrew -- it's a helix that holds its shape,
>> it's rigid.  But a spring with a comparable shape is flexible.  What's
>> the difference?  I suspect that it's simply the relative dimensions --
>> a spring is relatively thinner wire wrapped on a relatively larger
>> mandrel, and vise-verse the corkscrew.
>>
>> But is that all there is too it, or is there a metallurgical difference as well?
>>
>> Although I've contemplated making corkscrews, the immediate
>> application is a prybar for roofing and siding nails and similar
>> stuff.  It would be flat, like these:
>> http://www.homedepot.com/p/Dasco-Pro-Pry-Bar-Set-3-Piece-91/202585548#.UfDoym1cWgw
>> but of thinner steel.  (If I can't make it thinner, I'll just use a
>> commercial one.)
>>
>> I'd like it as thin as possible for a number of reasons, but I don't
>> want more than minimal flex to the thing.  So I'm wondering what steel
>> to use.
>>
>> I have, BTW, considered using thin steel and putting longitudinal
>> bends ("ribs" or "nerves" or "corrugations" -- whatever you want to
>> call them -- as are used in larger HVAC ducts to prevent oilcanning of
>> the large flats) in it, but this partially defeats the purpose, as the
>> result would effectively be thicker -- so why not use thicker metal
>> and be done with it?
>>
>> This is not any sort of critical problem, but I've had similar
>> problems before and left them unaddressed.  This time I thought I'd
>> ask....
>>
>