Reciprocating Saw Impact Force
Reciprocating Saw Impact Force
(OP)
Hi,
I am try to figure out how to find the impact force that a Recip saw (Sawzall) can exhibit.
To better understand:
If you took the blade out of the saw and just used the reciprocating rod (.5" Dia) was held 1 inch off a block and then the trigger pulled so the shaft smashes into the block.
I had asked a friend of mine in materials and he thought you could use:
Power=Force*Velocity=Current*Voltage
And measure the peak current of the saw. Does this make sense?
Thanks for your help.
dreinert
I am try to figure out how to find the impact force that a Recip saw (Sawzall) can exhibit.
To better understand:
If you took the blade out of the saw and just used the reciprocating rod (.5" Dia) was held 1 inch off a block and then the trigger pulled so the shaft smashes into the block.
I had asked a friend of mine in materials and he thought you could use:
Power=Force*Velocity=Current*Voltage
And measure the peak current of the saw. Does this make sense?
Thanks for your help.
dreinert





RE: Reciprocating Saw Impact Force
jt
RE: Reciprocating Saw Impact Force
Mike Halloran
Pembroke Pines, FL, USA
RE: Reciprocating Saw Impact Force
P.S. That doesn't make sense to me. You would need to know a bit more then that to figure out the impact force. You could reference mechanical engineering handbook for example.
Alternatively, a quick solution is to strap a force transducer to something and 'wack' it with your saw. However, this method is not the best, just the quickest.
Fe
RE: Reciprocating Saw Impact Force
Fe
RE: Reciprocating Saw Impact Force
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Reciprocating Saw Impact Force
Then you have what you need to calculate energy anywhere in the stroke.
Or you know the strokes per minute and stroke length. You can calculate velocity.
Ted
RE: Reciprocating Saw Impact Force
C'mon Mike, even a mechie should know that's what a hammer drill is for. Why carry two tools when one does both jobs.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: Reciprocating Saw Impact Force
RE: Reciprocating Saw Impact Force
Thanks for the input.
The issue with the saw is that after it experiences several hard impacts gear teeth start breaking off.
I was thinking like TED and thought that with the motor specs and gear ratio we could calculate the velocity of the recip rod.
I also thought that upon the impact of the saw the amps would peak because the motor would stop "instantly" and still be appling power, operating higher than rated.
The problem with the transducer is that a force transducer setup is going to cost me $600+, unless anyone know of a cheaper place.
Thanks for the help.
dreinert
RE: Reciprocating Saw Impact Force
There is no give in the drive to allow the shaft to impact while the drive follows through. Everything in the drive comes to an abrupt stop at impact. Eventually something breaks.
One method used to estimate impact is to drop a steel ball onto the reciprocating shaft and measure how high the ball is thrown. Using the ball weight and height reached you can calculate the energy trasferred to the ball. Be careful.
Ted
RE: Reciprocating Saw Impact Force
Impact is not just a straight force calculation. You are developing kinetic energy in something, and then dissipating it into whatever it is you are hitting. The force is affected by the response of whatever it is you are hitting, and probably by the mass of whoever is holding your reciprocating saw.
The quick and dirty answer is that your impact is the abuse that voids the warranty of your saw. The long, complex answer requires a detailed study of what is holding your saw, and what you are hammering. It is probably a waste of time.
RE: Reciprocating Saw Impact Force
dreinert,
It seems obvious that the saw wasn't designed to put up with these "hard impacts", so what's causing them and can't they be eliminated?
If not, would it be possible to fit some protection for the gears in the form of a shear pin that will let go before the gears break or an adjustable slipping clutch that you find on the feedscrews of some lathes, you could adjust this until it transmitted enough power to cope with the worst cutting conditions but would let go on "impact".
RE: Reciprocating Saw Impact Force
ht
$15 from Digikey.
http://s
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Reciprocating Saw Impact Force
The power supply, amplifier, and FFT-capable recorder aren't.
RE: Reciprocating Saw Impact Force
Since a Milwaukee Sawzall costs a little over one hundred dollars, Wouldn't it be cheaper just to give the operator another saw?
Then if the guy keeps breaking the saws, replace the operator.
B.E.
RE: Reciprocating Saw Impact Force
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Reciprocating Saw Impact Force
RE: Reciprocating Saw Impact Force
Dreinert's problem is that indestructibility is a big part of the Sawzall brand.
If he's working on warranty issues for the real Sawzall, then he has to find and reverse the last cost-saving initiative on the gears.
If he's working on a faux sawzall, then he hasn't quite got it right yet.
Mike Halloran
Pembroke Pines, FL, USA
RE: Reciprocating Saw Impact Force
One test would be to reduce the cross-section of the blades so that the blades start to fail when the saw binds/grabs. Then compare blade tension and/or Charpy tests to get an idea how much energy is involved.
RE: Reciprocating Saw Impact Force
Obviously the impact is not as significant as lets say a bullet hitting a surface, the damage would still be significant due to the penetration of a thin blade.
RE: Reciprocating Saw Impact Force
What do you do after you measure the load? If you change your device and if any of its mass or accel or springiness changes then the load you measured with this setup won't be the same load you measured with the new setup.
How stiff do you make the impacting surface? For worst load cases it would need to be stiff (thick and well supported). But that would be a bit unrealistic for most cases in the field.
Have you considered strain gaging the rod and calibrating the strain with a known static load? Or if the the rod is a simple section you would'nt need to calibrate it. You'll still get some inertia effects but if it's a simple rod then the inertia effects can be easy to estimate within 5-10% I'd think.
RE: Reciprocating Saw Impact Force
Walt
w_f_strong@msn.com
RE: Reciprocating Saw Impact Force
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Reciprocating Saw Impact Force
Fe