New economic plastic Shredder design

You might have already seen the DIY “Auger shredder”
and the “Pipe shredder” designs for plastic shredders, which get the job done but are a little rustic.

A new idea was proposed today on Instructables (link here) that allows you to build a shredder under $60.
Dave’s shredder is much more efficient, but way more costly as well, so this is a good shredder idea is you are with a tight budget

PDT: “Auger Shredder” and “Pipe Shredder” are not the official names of those machines, I made them up 😉

I am brand new here, so please forgive if this has already been mentioned countless times already, but has anyone had any luck modifying office shredders?

I think the assumption that it has to be slow is somewhat faulty. If you browse the websites of industrial recycling equipment suppliers, they have a variety of models.

Some are slow, high torque “shredders”, others are higher speed grinders or granulators. The tend to be used in series – with the slow, high torque as an initial size reduction, then the high speed ones doing the final granulation.

Since we are unlikely to have massive chunks of trash to pre-crush before final size reduction, the high speed ones are more likely to work better. IN that regard, surely the plentiful agricultural shredders available cheaply on the market are sufficient.

I did way more research months ago, and cant find where I stored all the links, but here’s a couple to check out.

All About Plastic Shredders: From Applications to Advantages

there is another approach here, using an angle grinder :

with a standard big angle grinder (1500 watt) and the right blades, the build would be under 200e,

We built a PP shredder which hasn’t done a bad job but now wearing badly and blocking more I think we should have got the blades hardened before we put it together, that might have been the answer perhaps

@ralinaresg good suggestions, but seems that @lyricalpolymath already sorted out his shredder problem 😉
The problem was that there were about 2 extra milimiters on one side of the shredder, because the metal pieces did not have a perfect thickness, and these extra MM caused the shredder to “bend” when the nuts were tightened


“1- the motor has to be slow
what if if wasn’t? the faster the motor the more Nm it delivers.”

A few clarifications. Given the same power P, the faster the motor the less torque. P = T*omega where T is torque (Nm) and omega is speed (Rad/s). Power is in Watts.

It seems to me that the issue is that it jams due to peak torque issues (hard spots). This would be cheaply addressed by an inertia wheel. It seems to me that this machine would be a lot better with a belt drive system instead of a gearbox, since the belt drive would have more inertia.

You can easily address this by installing a large disc (the heavier the better) on a shaft. Start up will be slower, but also won’t get jammed.

yes indeed 🙂
but unfortunately, since I need it for an educational workshop in september I will have to find an alternative solution if I can’t fix it :S

One solution I’m considering is to bring the plastic to a professional wood shredder. we have one here in the village. We have accumulated a lot of plastic for the workshops and it would be easier with an industrial shredder.

keep us posted on your fixes…and good luck

@lyricalpolymath if you want my opinion, we have already spent too much on this machine to give up 😉
I sen’t my shredder to a machinist to see if he can get it aligned and soldered. Unfortunately, I don’t have a welding machine at home and my tools are very limited as well (I had to buy an angle grinder a few weeks ago to get the parts cleaned), so I just decided to let a professional fix it (or try to….)

@xxxolivierxxx from your interest in other shredders, and from the other message, I deduce that your shredder doesn’t work very well right? :S

I too might need to look for another alternative.

by looking at your links I found yet this other shredder.

I think there is one assumption in @davehakkens shredder that we might try to change:
1- the motor has to be slow
2- the shredder’s design

**1- the motor has to be slow
what if if wasn’t?
**the faster the motor the more Nm it delivers.
it’s true that also the plastic bottles might come flying out of the cone, but that is probably why the industrial versions have an angle on the cone where you insert the pieces, instead of a vertical dropdown, so that flying pices fall back down into the machine

2- The shredder design
form your links we see that there are other ways to shred the plastic, even using cheap power tools that already are used for that kind of work (Another reminder that the motor does not have to be slow)

my “PreciousPlastic Shredder” works at 85%: it’s usable, but very slow, it keeps clogging and you need to switch the motor to the other direction in order to make it get unstuck
(that however might be an issue with my motor which might not be powerfull enoug :S (1.5Hp, 1.1Kw, converted to Monophase, with a gearbox output of 60Nm and 70rpm)

what do you think?