What could go wrong with my design?

[Abenakis]

Hi

I have looked at many homemade power hammers and I came out with something from my own salvage yard. But before getting deep into the fabrication of this little monster, I have decided to submit my design to all this wonderful experience that lies around here. (experience doesn't lie, does it????)

As you can see on the drawing, I am planning to use a motorcycle shock absorber; the one I would use comes from an old motocross racer of the early '70s, when the suspension was mostly done by your arms and legs! Compression damping on these should insure a good hit while the spring would make sure that the shock is back in its full length before the next cycle.

If I find one with adjustable compression damping on an outside body (yes, it exist) that does not cost too much, then I could even adjust the force of the impact. As for speed, I guess that a pedal, as the ones used on sewing machines, should be able to control the electric motor.

I also want the hammer stem to move between a set of bearings to get a free movement and keep as much impact speed as possible.

For the crankshaft part, I think I could mate a disclosed part from my racer to the eye of the shock mount with either a needle bearing or a bronze bushing with a grease nipple at the end of the shaft.

According to your experience, where could that design fail? (Yep, you can beat on this one!)

Thanks, everybody.

[Chris Pook]

You don't want dampening IMHO. The spring is suppose to be compressing on the up stroke so that on the down stroke it tries to throw the TUP away from it, causing it to speed up and hit with more force.

[dablacksmith]

and the speed control from a sewing machine wont handle the power needed for a power hammer...that is why a lot of rigs use slack belt or clutch...anything that can control the speed on a 1/2 hp or bigger electric motor is gona be costly..not sure the shock is gona work but it can be done without a big cost so try it !if you dont like the dampening action later try drilling a hole is the shock oil resevor and draining it... you would then have the spring without shock absorber .basic dezigh looks good tho.... good luck!

[Abenakis]

The idea I had behind the usage of the spring was not to act as an energy storage device but rather as a way, for the system, to live with the difference in thickness of the beaten steel rod being hammered; then, compression damping was a way to counter the bouncing of the spring and, thus, leave as much energy as possible to hit the steel part. I see that I was using only one of the possiblities it gives me.

Chris: if I understand your idea, you would want no damping at all. That way, the spring would be compressed at the end of the up stroke by the weight of the parts underneath and would have to rebound while the crankshaft is going downward, speeding up the hammer. Very interesting. I believe that, if it's light enough to compress at the top of the up stroke, it will be able to extend only at the end of the downward one; but, that's perfect because, anyway, since this part of the movement has the least amount of vertical speed (the crankshaft direction is almost horizontal), that could help keep the speed of the hammer at its maximum. I have a completly worn out shock with liter spring gauge and that's the one I'll start with!

dablacksmith: a clutch! The donator motor has one that could be used; but I think that the electric motor mounted on a spring loaded plate (a la mini-power hammer on youtube) would be easier to construct and maintain... but I am interested in understanding why a foot control for a sewing machine would not work, if you have the explanation. I will research anyway because there are multiple places where I would want to use that type of control

Thanks, both ofd you, for your input. I knew I could count on people here!

[ThomasPowers]

Abenakis; why a sewing machine speed control won't work---it can handle the current draw of a motor large enough to effectively power a powerhammer.

Like trying to pour 4 liters of water in a 1 liter bottle, sure it's made to hold water but not that much!

[Chris Pook]

One thing you haven't mention is how heavy the TUP is going to be.

I'd also be concerned about the shock being able to handle the forces of being stretch and compressed with the weight hanging off it. Its not unheard of to rip shocks apart in my 4x4ing/rock crawling hobby. Depending on speed and weight you can get a lot of energy spinning around.

[Abenakis]

Thomas: I get the picture! Thanks (lol)

Chris: that might be the reason why I would HAVE to keep the oil; it slows down the piston inside the reservoir and makes the top out or bottoming less of a concern! As for the capacity to sustain heay load, I remember that, once, by error, I went airborne for a 50 feet high drop from a cliff and the shock has handled it very cleanly! Motocross are very sturdy. But, I'll watch in case; your experience, here, is telling me to be careful

I haven't yet been able to make up an intelligent serie of words with TUP; can you help me on that too?

[arftist]

Shocks have been tried and proven to not work well. However, all power hammers use springs in one form or another. While most mechanisms can be improved in some way, there is no need to reinvent the wheel. For more info on shocks, check anvilfire.com. In my opinon, a flat belt clucth is the way to go, but a lot of people like the spare tire clutch method.

[Dale Russell]

Abenakis ,
Don't discount usin' a " clutched " industrial sewing machine motor .It's what i'm using on my height adjustable helve hammer .

1/2 hp 240 V ( AUSSIE single phase ) RPM's from around 1300 to 2800 ( approx ) Just find 1 to suit what you need

Dale Russell


BTW , by trade i'm a sewing machine mechanic

Edited June 11, 2008 by Dale Russell
Fix a " spelling mistake "

[ChrisB]

I think you'd be better off getting the tire hammer plans from Clay Spencer. The diy hammer wheel has been invented plenty of times.

[Abenakis]

Dale: Very interesting ideas in your hammer; takes more space than I can afford but there has been some clever thinking put in that machine. Thanks for your post.

[ThomasPowers]

"Tup" is not an acronym, its a word for the upper moving die/holder/weight/etc.

I second the suggestion that you read about the experieces they had using a shock absorber over at anvifire on their junkyard hammer section.

[Bentiron1946]

If you want to see some interesting discussion on power hammers, albeit, light weight ones go to MetalMeet as they build a multitude of them for shaping sheet metal but many of the ideas will work for heavy stuff too.

[Abenakis]

You don't want dampening IMHO. The spring is suppose to be compressing on the up stroke so that on the down stroke it tries to throw the TUP away from it, causing it to speed up and hit with more force.

Following this comment on the usage of spring, I began to think that there could be other ways of achieving acceleration of the hammer. More so because a cranckshaft is at its lower vertical speed around top and bottom dead center. So, in reality all the movement between 11 and 1 and 5 and 7 (on a clock) generates almost no vertical movement to something attached vertically to it like my shock absorber. So I went to the drawing board and began to play with geometry. When something came out, I tried it with my son's mecanno toy. I have attached 2 photographs: one shows the upper position of the accelaration arm and the other, the lower one. Now, if you compare the position of the small wheel (which represent the cranckshaft) in the two photos, you can note that all the vertical down movement is done within 1/4 of a turn, compare to normally 1/2. This means that the speed has been, at least, doubled.

The accelarator arm could be replaced by a leaf spring as long as it is attached to the frame via a link, not directly as what is usually seen. The lenght of that link must be greater than the diameter of the crankshaft.

The way I plan to try this out is with the shock attached to the end of the accelerator arm, the shock acting as a compensation device for the difference in thickness of the iron piece as it is being beaten by the hammer.

Edited June 14, 2008 by Abenakis

[Abenakis]

If you want to see some interesting discussion on power hammers, albeit, light weight ones go to MetalMeet as they build a multitude of them for shaping sheet metal but many of the ideas will work for heavy stuff too.

Bentiron, you are true! There some pretty nice ideas ther too. I liked the neatness of the off-axis wheel that turns inside what looks like a large bearing housing; probably balls between the two.

I have also seen a wheel at the bottom of what is probably and height adjusting screw; I wonder how large and long a bolt and its nut would have to be to be capable of handling the bang of a 50kg hammer hitting it at speed! I like the idea of being able to vary the distance between the top and botton for different applications.

[arftist]

Have you seen designs for apalacian style hammers?

[Abenakis]

On anvilfire? Yes. It's a quite neat version of the leaf spring principle. Do you know any specific for it? Like: how much is the spring compressed when the hammer hits? I guess that it needs to be compressed at rest when at the bottom of the crankshaft rotation otherwise there would not be a powerful hit; am I wrong?

[arftist]

Yes, I am quite familar with the construction and opperation.Actualy, the sping should not be compressed at all when the hammer hits, quite the oposite, it should be extended if set for maximun power. The reason for this, is that the crank throw is only seven inches, the maximun stroke is about eleven inches. The tup height is adjustable, maximun impact is achieved when the tup height at rest is set one inch above the work, this increases the available throw, the spring is compressed on the up-stroke, hurling the tup down on the down stroke and extending the spring. If the spring were to be compressed with the crank in the lowest position, it(the spring) would have had to absorb energy that should have gone into the work, which is part of the problem with using shocks: you don't want to lose any energy from the tup. Shocks ABSORB energy!

[arftist]

Also, you have to get past the idea that the shock is going to compensate for the thickness of the iron. This would be fine if all you were making were a mechanical flatter. In no time at all, you are going to want to strike hand held top tools, place bottom dies with varios thickness, etc. You MUST have an adjustable tup height or you severely limit the usefulness of your hammer.

[Abenakis]

So, you say that the spring, in fact, continue to swing once the crankshaft has past his bottom end thus releasing its stored energy into the hammer! I think I understand the idea. And, in this case, you don't even want the accelerator linkage I have tried because the slowed up movement (it takes 3/4 of a turn to move up) would not store the energy you want to release later. Is the $500 bucks still a valid number?

[Abenakis]

Arftist, I have looked again at my accelerator linkage and found out that both part of the movement, the up and the down parts, benefit from the acceleration; and they are right after the other with a very slow moving moment after the hit that is lasting almost half of the crankshaft rotation. On both side, there is also a very short stopping moment when the amount of movement is converted into energy (storage in the up part and release in the down part). And since the energy stored in your leaf spring is in direct relation with the speed of both movement, there would be a significant gain in the strength of the hit.

On top, I beleive that it is possible to move the attachment point of the link on the frame so that it would produce higher or lower acceleration thus lighter / stronger hit at the end. I'll work on that.

And since my shop is quite small, I will work on a version that will use half length leaf spring and place the motor between the support column and the anvil one; I have seen one like that so I know it's feasable.

By the way, it's true that the shock absorber eats energy, that's the only reason they exist, but it would have been only AFTER the hit that it would have happen.

[arftist]

Good Luck. Your initial design looks promising in its simplicity and small foot print. Acomodation for height change can also be acomplished through stacking removable plates on the sow block. As for the 1/2 spring helve, sounds like a project to engineer, but probably a worthwhile task. I spent about year deciding exactly what I wanted, then about 4 months to build. What I am trying to say, is try to look at every design possible. For example your roller guide tup. Research this design thoroughly.

Edited June 14, 2008 by arftist
Thought of more stuff to say.

[Rich Hale]

Build it like you wiosh and see how it works. the basics you have drawn are fine,,If the shock does not work you can go to a more proven design. My concern is the shock is made from light weight steel tubing for the shell and the eye on one end is welded to that. If that were to fail you would have a loss of the oil inside spraying around. MAke sure you have not only safety glasses but a face shield on when you gie it a run. And a shield of metal in front of the shock and spring would be a good thing.

[Abenakis]

Thanks a lot, everybody. All those terrific comments are what I was wishing for; challenge of the ideas, points to be careful with, better understanding of others' design, all to push me further through this very funny and creative moment of designing and building my own tools! 20 years in computer programming helped in finding different solutions for a problem but it's nothing like putting the hands in there. I will make sure to gather as much data as possible so that my experiments serve as many people as possible.