Bow Spring Linkage Power Hammer

[PaulKrzysz]

Hello everyone,

I will be soon making my own power hammer.

 

I would like to make a bow spring linkage as seen in the pictures below.

 

From what I have seen and read the springs need to be bent far more than what is commonly available in the form of trailer springs.

 

My Question:

How would you bend a trailer spring into a near 'U' shape? Can it be done safely?

 

Please let me know what you guys think.

 

My idea was, worst come to worst, I will just bend them in the forge while hot, and leave them unhardened.

[Geoff Keyes]

There are a couple things to think about.  I built a hammer with a design like that.  We had access to a 300 ton press, and, with some patience and a few broken springs, were able to bend them cold.  We also heated and rolled the ends of the longest spring in the pack and left them as forged.  Those rolled ends have not moved in 15 years of use.  You could also leave the springs as found.  It would give you a different motion (longer and lazier) but would also work.  I have seen a design that used 2 spring sets, one facing down, once facing up, with the tup attached to the upward facing springs.

 

I would bite the bullet and buy new spring stock, old salvaged springs may have hidden cracks, which could fracture unexpectedly, creating a hazard to life and at the very least, a Brown Trouser Moment (BTM).  You might investigate spring shops that make springs for cars and trucks.  They might be able to make just what you want for not too much $.

 

Geoff

[Frosty]

If you have or can make good drawings as in blueprint type mechanical drawings most any decent spring shop can make up a stack like that. They don't need to be a blue print, just good, to scale, dimensioned drawings. A quick sketch on a napkin is too unreliable. Heck, if you know the performance specs and parameters you could probably spec a stack and get what you need. I wouldn't try that though, it's an art and craft specing things like that.

 

There's nothing really special about that stack, just not a common shape. They'll probably arc them cold, then heat treat them with the next batch through the furnace. Spring shops do it all the time so they usually have the heat treat oven going. AND like so many specialty shops they LOVE something new.

 

Frosty The Lucky.

[onetreeforge]

I bent a stack of 7 leafs in one go for my hammer, I bolted them in the center and heated one half and bent them inch by inch in a half open vice and used a patton to keep them the same, then I sent them to the spring shop to make them hard, don't forget to compinsate for preload. 

 

Here is a pic of my hammer.

 

[PaulKrzysz]

Thanks for the input guys.

 

I am only planning on doing a small hammer, something in the 25lb range, no more then 30lbs. It needs to be a quite little bugger so the neighbors don't complain. (Suburb)

 

I cannot order new 5160 because I live in Canada. If I was to do it with bought flatbar with would be 4140. I could also buy a spring and re-bend it to my purpose.

 

I might go with the bowspring design, or maybe a dupont linkage (Like the tire hammers).

 

If I ended up doing this bow spring linkage out of mild steel do you guys think it would hold?

Of course it would have to be beefier then if done with alloy steel, but the spring does not bend too much and the amount it does bend should not be too much for mild to return to its position.

 

 

I also have a question concerning what is considered the ram weight on such a hammer, does the flywheel count? or is it just whatever is attached to the flywheel?

[Judson Yaggy]

Why can't Canadians get 5160?  

 

If you are after quiet a power hammer is not the way to go.  Yes, a mechanical is the quietest type of PH but they are still pretty noisy.  Especially a hammer welded up out of structural sections and plate steel rather than one with a bunch of cast iron in the frame.  Have you thought about presses?

[PaulKrzysz]

Why can't Canadians get 5160?  

 

If you are after quiet a power hammer is not the way to go.  Yes, a mechanical is the quietest type of PH but they are still pretty noisy.  Especially a hammer welded up out of structural sections and plate steel rather than one with a bunch of cast iron in the frame.  Have you thought about presses?

 

I have talked to a couple of steel suppliers and they say the demand is just not there for them to stock 5160. If I really wanted some 5160 I could do a special order ($$$). This is why I might just rebend a new spring. I can pick up a new trailer spring for ~$25, but the same material would cost me over $100 from the steel supplier. ( I got charged $12 for a 12'' piece of 3/4'' O1)

I plan on filling the empty spaces with sand and oil in the structural parts to hopefully reduce some of the noise.

I have considered a press, I am buying a No.5 Fly press. But I also need a tapering machine, hence the mechanical hammer.

[Geoff Keyes]

I would go with your first idea and buy new.  Old springs (which I have used and with few failures) are liable to have hidden cracks, leading to the dreaded BTM (see above).  While I am a fan of picking through junk yards, I would not do it here, and the cost is pretty much zero for new springs, in fact, you won't need all of them for a #25, so you'll have some stock to work with afterwards.

 

Just my .02

 

Geoff

[JNewman]

Go to a spring shop that services tractor trailers as well as cars.  They will have new spring stock and have the capacity to bend it if you want them to do it.  I don't know if what they have will be 5160 and they may not be able to tell you but it will be good spring stock. 

[basher]

I would add another cautionary about using old spring stock for this aplication, power hammer springs are a guaranteed failure eventually, I've had 3 go on 3 different hammers, old spring stock is just too risky in my mind.
Concider lether wrapping hem as well.
Cheers

[PaulKrzysz]

Thanks guys.

I will buy one new trailer spring and rebend it myself, leaving them unhardened.

 

I'm gonna pick this one up.

 

http://www.princessauto.com/pal/en/Springs-And-Components/1300-lb-3-Leaf-Double-Eye-Trailer-Spring/2080031.p

[eseemann]

Good Morning All, 

 

I was wondering if you folks thought that some of these Cultivator "C" Shank  tines would work stacked together for a bow linkage? I do not have access to any of the equipment to bend the spring without killing myself. I am not wedded to this one tine but something like it. 

• Width: 1-3/4 in.
• Thickness: 3/8 in.
• Dimensions: 16-7/8 in. Long x 16 in. High
• Curve begins 8-7/8 in. down the shank
• 117° curved angle
• Heat treated 5160- RC 38-42 steel
• Curved end has a 1/2 in. and 1/4 in. bolt hole
• Straight end has a 21/32 in. bolt hole
• Used on a wedge or V-shaped cultivators
• Can be used on ASC 10398 and ASC 65067 cultivators