Straightening Leaf springs--can someone explain?

[Mike Romo]

I've decided I want to build my own power hammer.  I have settled on the design very much like Stormcrow's Gunnhilda--really nice hammer.  Mine will be much smaller, closer to 25#.

 

My first real question is about the leaf springs.

 

 

 

I see many build referencing "straightening the springs" or "straightening the spring package". 

 

What does this mean?  How is it done?  Sounds like a job for a suspension shop?

 

What is the difference between straightened springs and curved springs?

 

Thanks much folks.

 

 

[arftist]

Yes, it is a job for a suspension shop; a good one will have a press capable of straightening them cold. A suspension shop is also where you should buy your springs, used springs are a very bad idea. Curved springs can be made to work but add a lot of slop to the linkage between the tup and the spring, it is really worth straigtening them and it is likely they will do it free if you buy the spring from them. 

[Mike Romo]

Thank you.

That clears up a bunch.


Any idea how to ask for the proper size of spring? Terminology or by weight?

[Geoff Keyes]

I thought I posted here, but it seems to have gone, I'll try again.

 

"Spring steel" is carbon steel with a springy heat treat, which you might describe as semi-hard.  Most carbon steel, particularly cold rolled steel, is just that, semi-hard.  So why not buy flat steel of the right type?  5160, 80crv2, 10xx can be had at knife makers supply houses. Admiral or the New Jersey steel baron come to mind.  That way you save yourself the hassle of trying to find a plate to flatten them for you.

 

Second, the spring rate of mild steel and carbon steel is the same (pretty much) for the same cross section, the difference is the yield point.  Once a steel passes the yield point, it takes a "set".  You might be able to build the spring with mild steel, maybe beef it up a couple of leaves to make up the difference.

 

I built a power hammer some years back, based on a Champion with a DuPont toggle.  The springs we had were not bent enough, so we adjusted them in a 300 ton press, cold.  We broke a number of the short leaves, but we had plenty.  We took the longest leaf and took a heat on the ends and rolled it around a wrist pin.  We left them as forged, no HT at all.  Those ends have not moved at all.  The hammer has been in use since 2000 and has hundreds of hours on it.

 

We didn't have a clue how much spring to use, so we made a WAG.  It has worked just fine since the day it went into service.

 

My point is, you may be over thinking your design.  19th century springs may not have been all that uniform, but lots of those hammers are still in use.

 

Just my .02

 

Geoff

[HWooldridge]

As an added comment to Geoff's note, I made a coil spring for a 25 lb Little Giant from mild steel about 20 years ago that is still in service. I forged tapers on each end of the stock and rolled it hot onto a mandrel then adjusted the length (also hot) by laying it in a large piece of angle iron and tweaking the coils with a wedge. When I thought it was the right length, I let it air cool then reheated to bright red and quenched in Gunter's original Super Quench lye solution, with no tempering afterwards. The spring took about 1/2" set after assembly so I removed it, reheated and extended the original length by another 1/2" then went back through the heat treating process. The second time, it took the set and stayed put so I left it in place and started using the hammer. I ran it for several years then bartered it to another smith who is still using it. I told him it had a mild steel spring and he might want to consider buying a new one from Sid Sudemaier but he never got around to it. The spring never took any further set after the initial movement.

[Mike Romo]

Geoff, the idea of a spring from mild steel is intriguing. Are you basically saying I should find some flat bar and build a leaf spring with perhaps a couple of extra leaves and use that?

Maybe some 1/4" x 2" by 5 feet long or so? Tup weight close to 25-30 lbs and no more.

I'd love to see a pic and some specs on this.

[Geoff Keyes]

That is exactly what I'm saying.  I saw a demo some years ago, and I cna't remember where or when, but they took a flat bar of mild 1/4 x 1.5 x 3ft and a HT and tempered bar of 10xx the same dimensions and clamped them to a table with about 2.5 ft of overhang.  Weights were then attached to the ends.  The curve and rebound of each was the same under the same weight, and each returned to straight when the weights were removed.  Eventually, the weight on the mild steel bar exceeded the yield point of the steel, and it took a set and did not return to straight when the weight was removed, but it was a lot of weight.  I would like some brain to explain to me the science, please.

 

I don't have the tools to calculate what the spring package needs to be, or how it behave to tell you that it was under/over sprung.  I suspect that withing broad limits it wold be hard to tell.  If you can, biuld your hammer so that you can try out several different spring packages and see which one hits harder or has better control.

 

 

This is the hammer in action, the "U" shaped package were small car springs which we had bent to shape, cold, in a 300 ton press.

 

Geoff

[swedefiddle]

A spring is rated at how many pounds pressure it takes to move one inch. A coil spring is rated at the pressure on a gauge/meter of when it is compressed one inch. Two inch is twice the pressure of one inch, three inch is three times the pressure of one inch, etc.....

Leaf spring is measured the same way, the center is held firm and the pressure gauge is at the eye of the leaf. How much pressure to move the eye one inch is the spring rate. A 350 lbs. spring, means that it takes 350 pounds to move/compress one inch.

 

It is not magic.

 

Neil

[Mike Romo]

Thanks Geoff. Something to ponder for sure.

Swede, I figured it was straightforward.

Any idea how much spring my concept would need? Just a ballpark. Tup at 25-30 pounds max.

Thanks

[Stormcrow]

The smaller Rusty-type hammers use pickup leaf springs, the larger ones use truck springs.  I'm sure there's an exact science to it, but it's beyond my scope, or that of most folks who build these.   :)

 

Here's a video just posted by a fellow up in Wyoming, Joe Calton, who built a 50 lb.hammer based on my Gunnhilda.

 

[Geoff Keyes]

Trying to post a reply, but keep getting rejected

[ThomasPowers]

1/4" x 2" may not be sufficient in mild; seems like I can put a permanent bend in something that size fairly easily and I'm not even trying to whip a 30# weight up and down fast.

[Geoff Keyes]

Why can't I post to this topic?

 

Geoff

[Geoff Keyes]

Short posts work, apparently

[Geoff Keyes]

I wanted to say a couple of things.

 

1)  You want to build the anvil out of a solid piece, no tube filled with concrete or lead.  You need the rebound.  OTOH, in my build I used two pieces, a 12" round with an  8" round bolted to it through welded ears.  It works well enough that I've never changed it.

 

2)  The tup can be built up out of pieces, many of the commercial hammers were built that way.  Apparently, the accelerated mass acts like a solid, where the anvil loses engery to vibration.  You might even be able to build the tup out of a tube filled with shot.

 

3)  The size of the die has an effect on the work the hammer can do.  Mine has small dies (for a 50# hammer) and so seems to hit harder.

 

I used bronze wear strips in my guide, they don't show any wear after 14 years.

 

Geoff

[arftist]

Sorry but I question this entire line of reasoning. 

The spring for my 75 pound spring helve cost 60 bucks including straightening. It is at least 5160, scientifically heat treated in an expensive oven, came with the one eye I needed already made, and is at least 1000 times less likely to break than a homemade spring, which will cost as least as much for steel alone due to the economy of scale. (you can't buy 30 pounds of steel for the same price the spring company buys 40,000 pounds.)

 

 

  I would like some brain to explain to me the science, please

 

Sure. The same reason that this is a bad idea. Work hardening. Enbrittlement caused by repetitive bending. 

Springs in a power hammer get more abuse than springs in a vehicle. 

 

Use mild steel for a spring for your post vise or hold down dogs. 

Use highly engineered tool steel for what it is designed for. 

[forgemaster]

You can bend/straighten heat treated spring steel easier if you heat it up to the greasy stick heat, (heat your steel up on top of the fire, or just in the door of your furnace) while heating it rub it with a hammer handle made of hickory or spotted gum, when the stick starts to feel as if it has a greasy feel on the spring steel, the steel is at tempering temperature, (at this temp is when spring shops will set springs), you too can also use this temp to alter the shape of the leaves without fear of them cracking.  Normally it pays to disassemble the spring before hand, set all the leaves, then reassemble.  If you search for greasy stick you will find other posts I have refered to with it.

 

Phil

[Mike Romo]

glad this thread got more input.

 

Stormcrow, I'll watch the vid at home this weekend.  Excited to see what others have done.

 

 

Geoff, I think I am going to go with the commercial spring idea--I don't know enough about fabricating/substituting for the spring.  Your anvil advice is spot on, and I have a couple of local scrapyards looking out for large diameter round or square stock for my anvil.

 

 

arftist, would you mind posting the dimensions of your spring on your 75# hammer?  Mine will be less than half that size and certainly no larger.  I'd just like an idea of what I should start the conversation with at my local suspension shop.

 

 

This project has me very excited, but as always, better to know more and do it right the first time than re-engineer because I got in a hurry. 

 

 

Thanks again friends.

 

Mike

[ThomasPowers]

Note that if you go to a good spring shop to straighten a used spring they should be able to sell you straight spring stock fresh off the stock rack---and heat treat it to boot.

[arftist]

glad this thread got more input.

 

Stormcrow, I'll watch the vid at home this weekend.  Excited to see what others have done.

 

 

Geoff, I think I am going to go with the commercial spring idea--I don't know enough about fabricating/substituting for the spring.  Your anvil advice is spot on, and I have a couple of local scrapyards looking out for large diameter round or square stock for my anvil.

 

 

arftist, would you mind posting the dimensions of your spring on your 75# hammer?  Mine will be less than half that size and certainly no larger.  I'd just like an idea of what I should start the conversation with at my local suspension shop.

 

 

This project has me very excited, but as always, better to know more and do it right the first time than re-engineer because I got in a hurry. 

 

 

Thanks again friends.

 

Mike

3 leaves, 5/16" by 2 1/4. Only one is full length with a shorter leaf above and below. 

 

Talk to Jerry Allen at The Wizards Forge. He will tell you exactly what you need. 

 

The only major change I made from Jerry's plans was to add a flywheel between the motor and the crankshaft and use a slack flat belt clutch instead of vee belts. 

[ptree]

The difference between 5160 and mild steel in a leaf spring is significant enough that all of the automakers pay the premium and the replacements are also 5160 Triangle spring company, the supplier of the spring stock I use in my powerhammer and to supply the stock for my veggie choppers uses only 5160. The 2" by .237" I use for veggie choppers comes with a  slight pre-arch. The slight pre-arch makes no difference in use on a powerhammer like mine. No extra noise or slop. All of the rusty type, that use rollers at the ram will have slap noise as there has to be clearance.

 

But in reality spring steel is the steel you made the spring from and tool steel is the steel you made a tool from. Alloy steel taylored for a particular use simply makes for higher performance. A plain high carbon twist drill will drill steel. A "High Speed" alloy called that becasue the speeds and feeds were higher for that group of alloys will greatly outperform the plain steel.