Need to duplicate an old flat spring

Most spring steel is plain-carbon steel. You have two steps in heat treatment: hardening and tempering.
To harden, you need to heat carbon steel to something like 1350 F to 1450 F. That's a medium cherry-red. You can get the idea by searching online.
Plain carbon steel has to be quenched very fast from the tamperature. Mostly, that means water-quenching. But a thin spring is better quenched in oil. It's less of a shock and less likely to damage the steel, while still allowing full hardness, or something very close to it. Motor oil is crappy for this but I doubt if you'll want to invest in quenching oil. Do NOT use used oil. It will leave too many bubbles on the surface of your spring and there will be soft spots under the bubbles. It will be weaker.
Then you temper it.That relieves some of the stresses from hardening and *slightly* softens the steel. But not much. It will make it much more resilient. With plain-carbon steel, it's best if you do this right away, after hardening.
I'll give you a temperature and time without explanation. It will give you what you want. Heat your kitchen oven to 400 F, lay the spring on a cookie sheet, and cook it for one hour.
That will produce a tougher and stronger spring than any of the quickie methods. 400 F is a medium temperature for that kind of work. You can go a little higher, probably, without hurting the performance of your spring. Anything much lower, and it will be brittle. For things like cutting blades, 350 F is usually preferred.
Good luck. Get GOOD quality spring steel, from Brownell's or similar.

Try feeler gauges.
BQ340 wrote:

Jim Stewart fired this volley in news:ktokfk$bps$1 @dont-email.me:
Good idea!
To cut them to size and drill them, you may have to first anneal them, then re-harden and re-temper.
If you have abrasive cutting methods, that won't be necessary.
LLoyd

Cannibalize a new or old set of feeler gauges...

You also can spot-anneal, which probably would be better.
Take a 10d nail and cut off the head. File the cut end reasonably flat. Insert in a drill press, as if it was a drill bit, cut end down. Clamp workpiece firmly. Bring the nail/bit down onto the work, pressing firmly, until the spot under the cut-off nail head is deep blue.
The spot will be annealed and can be drilled. This trick brought to you by the gunsmiths who used to drill case-hardened '03 Springfield receivers for scope mounts.

Ed Huntress fired this volley in news: snipped-for-privacy@4ax.com:
Ed, that only works for the holes. How about cutting the spring to size? Abrasives (carefully applied so as not to draw the temper) would be the best way.
Lloyd

For one like this, I'd use a Dremel or a die grinder with a cutoff wheel, and work slowly so you don't draw the heat treatment.
Ha! I'm becoming so impatient that I don't read even one line ahead.
Yes, exactly.
For a onesie or twosie, I try to avoid annealing the whole piece at all costs. You're just not likely to do as well. Even heating to transition temperature a second time, repeating what the manufacturer did, is likely to coarsen the grain and make the part brittle.

I'm listening, just not understanding!
So you are saying I can't change the properties of a spring, that I must find the same material as the original if I want the new spring to be the same dimensions as the old one?
MikeB

So I must find out what the original is made of & get that same type steel?
The speed it adjustable over a small range, but not much room to play with.
MikeB

BQ340 fired this volley in news:52001941$0$19313 $ snipped-for-privacy@ngroups.net:
Almost correct: You can change the properties by hardening/tempering... just not the spring force. It remains the same (nearly) for any given alloy, regardless of the hardness
The primary property you change by altering the hardness is the yield force, NOT the spring force.
You also can affect (positively) the durability of the spring by increasing the yield point IF the deflection is such that it comes close to the yield point when not hardened.
Someone recommended feeler gauges for stock. Also consider the rewind springs in cheap tape measures (don't use an old, discarded one, as it might already be severely fatigued).
Lloyd

BQ340 fired this volley in news:520019e0$0$20355$ snipped-for-privacy@ngroups.net:
AND tricky to adjust, probably.
But then, it's only a "music box" with a leaf contact in place of a reed. Unless you're transmitting the code to a compatible receiver, the exact speed doesn't matter very much.
Lloyd

You don't have to match the original grade of steel, they all have the same elastic properties, or Young's Modulus, below the yield point.
Can you adjust the weight?
jsw

Lloyd answered that clearly -- the spring rate will be almost exactly the same, no matter what grade steel you use (except stainless) and no matter how hard or soft it is.
What varies is the yield point (look it up) and, consequently, the fatigue life.
Maybe we can simplify this for you: How much, in inches or millimeters, does that spring deflect at the ends, when it's in use?
Be patient; you'll get it. By now you know that you started with some very common misconceptions. I've even known experienced machinists who didn't believe it when it was explained to them. So you're not alone.
But we'll enlighten you. d8-)

Greetings Mike, I'm pretty sure the springs, in normal use, don't get very close to the yield point. Based on this assumption most any steel hardened to a spring temper will work. You do not need the same exact steel. Differences in thickness will have a much greater affect on deflection that differences in width. Twice as wide will be twice as stiff. Twice as thick will be 8 times as stiff. So get some spring steel the same thickness but a little wider and trim until it acts the way you want. Someone here mentioned the use of feeler gauges. That's good advice. And Ed mentioned using a nail to anneal spots for drilling. More good advice. So buy a set of feeler gauges, trim to size with a Dremel tool and grinding points and/or parting discs, anneal the three spots you need, and trim the sides until it works the way you want. Eric

Hi, Eric
Regular feeler gauges are not nearly as stiff as I need, but I see some blue spring steel shim stock is available.
I will get some of that & from all the replies it sounds like that should work but I may need to tweak the width to get the results I need.
MikeB

BQ340 fired this volley in news:5200391a$0$49396 $ snipped-for-privacy@ngroups.net:
Again, I think you've missed the point. If the gauge is as thick, and as wide as the spring you've got, then it will be exactly as "stiff".
That is, it will be if the remaining spring is steel, and not (say) beryllium bronze.
Lloyd

I understand what you are saying, I'm probably not using the proper engineering terminology, but regular feeler gauges won't work.
Here is a video someone made of a different model but it has the same springs & speed regulator assembly in action:

Regular feeler gauge stock would distort under the forces, the brass weights are fairly heavy at the rpm's it operates at.
looks like what I will try.
I hope those links work!
MikeB

BQ340 fired this volley in news:52004658$0$5579 $ snipped-for-privacy@ngroups.net:
I don't know what you mean by "regular feeler gauge stock". It comes in all thicknesses, all the way up to "you can't bend it with your fingers", and down to "feels like metal paper". Feeler gauges have many thicknesses in one 'kit'.
Lloyd

The action of a fly-weight governor is controlled by two things. the weight of the fly-weights and the strength of the springs. Altering either alters the critical RPM.
So, you can make a couple of new springs and try them. If the speed falls in the right area you say there is adjustment. If not then make two more springs, either stronger of weaker as the case may be.
It's not rocket science and you can cut and drill most spring material with common tools. It is a guess but I'd think that once you obtain some spring stock, say a spring from a steel tape, and collected the tools you could probably make 10 or 15 pairs in an hour, or maybe more.