Data for Minimum Torque Required with Shredder

Hi everyone,
So @andyn had asked me a while ago to gather some info with my hand powered shredder to find the minimum amount of torque needed for the shredder to function… I have finally put some time into getting this info (Sorry for the wait)
Now I’m no engineer and I think my system (with gears, flywheel et al) complicates matters a bit, so instead of doing the calculations myself I will share my findings and hopefully someone can work it out with better accuracy…

Method: In these tests I used only HDPE. The plastic was placed into the shredder and the blades turned until met with resistance. At this point I attached a bucket to the lever and slowly filled it up with water until the blade passed completely through the plastic. I slightly varied the thickness of plastics from a thin wide bottle top, thick fat bottle top and the thread of a detergent bottle.

Different materials and thicknesses can now easily be tested in future…

1: Thin wide bottle top… scale reads 6.818kg

180mm from crank center to force
turn that into meters .180m
turn measurement on scale to newtons kg*g = 9.81*6.818= 67N
first multiply that time the moment arm so 67N * .180m = 12Nm
5 to 1 ratio
5*12Nm= 60Nm of torque

This looks interesting… Subscribed 🙂

Thanks @andyn cool, yea that does seem low… I’ve read in the past that 100Nm has been the estimated torque needed.
I suppose in functioning conditions there would be far more plastic between the blades. For sure, I’ll go chuck all that plastic into the shredder and see what I need to unblock it all.

Quick calculation… The numbers all seem quite similar for different thicknesses and work out to approximately 60Nm at the shredder shaft, I was expecting more. Perhaps in normal running there would be plastic being compressed and about to be cut even though only one tooth is actually piercing at a time.

Tim, I don’t suppose you could try jamming the shredder full and seeing what’s the most amount of water you can get in the bucket before it cuts?


Thanks @timslab I will do something with these numbers.

3: The thick thread of a detergent bottle… scale reads 6.804kg

2: Thick small bottle top… scale reads 6.789kg