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

[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.