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Hand cranked shredder

This topic contains 36 replies, has 9 voices, and was last updated by  Herman 4 days ago.

Rhoy Guajardo rhoy2468

Hand cranked shredder

06/11/2017 at 19:29

Constructed the shredder utlizing a winch crank up the rejected 3D plastic prints. Drive shaft had a turned key that fit the spring loaded crank and testing is going on at the moment. Would prefer motor powered shredder for THICKER harder peices (ABS/PLA) but it does well on other less brittle materials.

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In reply to: Hand cranked shredder

08/12/2017 at 13:45

He also has another video about using an old meat mincer as a shredder, quite interesting.

In reply to: Hand cranked shredder

09/12/2017 at 12:41

@andyn he has some interesting videos and it’s handy for people wanting to start off without investing a lot of money the prob with the mincer is ya still have to cut the plastic up small to fit them in

In reply to: Hand cranked shredder

09/12/2017 at 19:08

I’ve been following your project on hand cranks. I am not a metal worker but I am very interested in raising money & distributing these in various countries thru a non profit organization to watch over & manage. When the kinks get worked out, many hands across the globe gathering & washing plastic could make a dent. What is your goal? I’m looking for help to get further down the road.

In reply to: Hand cranked shredder

11/12/2017 at 20:21

here are some calcs I did in another post for a bike powered shredder;
Well there are a few governing equations to sizing flywheels for this application
there are a few variables that are listed bellow:
1. Material that is being cut properties
2. Material that is being cut cross section
3. Flywheel design
4. Flywheel Material

So onto the equations:
First rotational kinetic energy units (Joules)
I = rotational inertia (moment of inertia) has to do with flywheel design
W = angular velocity
to find I just design a flywheel in a standard cad program and it will usually tell you what it is at center of mass
W is found by taking the tangential velocity on the outer rim of the flywheel and dividing it by the radius of the flywheel W = v/r

Next value that is important is the Tensile Impact Strength value of the material.
This is looked up from a table of your material for HDPE it is around 243KJ/m^2

example problem:
i designed this bowl on cad (not designed for flywheel)
and looked up its highest moment of inertia on cad which = .0004647 Kg m^2
r = .109
i need to find how fast i must rotate the flywheel to cut the material
impact strength of HDPE of 243KJ/m^2
and a cutting cross section of 1 inch x 1 inch or .00064516 m^2

impact strength needed is 243,000 * .00064516 = 156.77388 Joules of KE needed
so solving KE equation for velocity
1/2(W^2)(I)=KE W= V/r 1/2(V^2/r^2)(I)=KE ((KE(r^2)(2))/I)^(1/2) =V
plugging in
((156.77388(.109^2)(2))/(.0004647)))^(1/2) = 89 m/s or 200 mph lolz

a more important problem would be to solve for I as most people can pedal at 10mph
because you are solving for I you can determine what you need to model and using what material
to solve for I
however as you see you would also need to know the radius of your part as well so this equation has 2 unkowns.
basically the r would be limited by the machine that you are going to use to make the flywheel or the material you can get your hands on
you would then design around that.

I did some of the math for a 20Kg cast iron lifting plate
that would get you pretty close to cutting that 1 inch by 1 inch cross section
however that is only 1 tooth so you would need a 20kg plate per tooth /2
so if you have 12 i would do 6-8 20kg plates so 160kg of weight for flywheel.
reason why you would need a plate per tooth is that your flywheel would stop after only one tooth cut but you want to keep going indefinitely so you will need to have energy to spare so that you just spend energy keeping the flywheel up to speed.

so a 20kg cast iron lifting plate would be a good idea.

here is the original thread. https://davehakkens.nl/community/forums/topic/bicycle-shredder-costs-work-in-progress/

In reply to: Hand cranked shredder

04/02/2018 at 06:48

With no flywheel or gearing, this looks like an easy way to make your biceps explode XD

In reply to: Hand cranked shredder

12/06/2019 at 20:04

I tried getting in touch with some company here in Uganda that I think build machinery but the amount they told me for making an extrusion machine was really so exagurated that importing could really be the only alternative either from Kenya or any other country if I can get contact in Kenya that would be great

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