Introduction: $50 Plastic Shredder / Grinder / Recycler

Everyone in the DIY community and especially those who work with 3D printers, have one issue - plastic junk. It can be failed prints, project scrap leftovers, or maybe you are just looking for a way to shred and recycle your plastic at home.

There are a few projects on here:

Most commercial grinders and their DIY derivates work on a simple mechanism of counter rotating wheels with grooved teeth to grab and tear. Check out some of the videos below

There are many more links on youtube if you want to build a beast. Most of my plastic waste comes from failed prints and leftover strands of filament which I want to recycle into fresh filament using Filabot.

Also, with 3D printers in the <$500 zone and filament spools in <$30 zone, the logic of spending $1000< for essentially recycling <$1 waste and all the time and labor didn't particularly entice me.

It turns out that paper shredders also use the same mechanism. Check out some of these videos:

Time to hack a paper shredder to grind up my waste plastic. From the time the shredder arrived in the mail to putting together this instructable, the entire project has taken me 48 hours. If you follow all the instructions to the T, this is what you should be capable of grinding in about 24 hours-

Step 1: BOM

STRIP CUT PAPER SHREDDERS WILL NOT WORK for this project (3 types of shredders). I already tried to bust open mine and replace the inner wheels with grooved washers and the like but its just not worth the effort.

We will be working with a CROSS CUT SHREDDER. If you have one already and don't mind busting it open, this instructable should work for you. If not, here is the only real expense involved in the project:

AmazonBasics 12-Sheet Cross-Cut Paper, CD, and Credit Card Shredder

Go to amazon:

Click Add to Cart and checkout.


When I ordered mine new, it was <$50. There may be other economical options and I'm not Jeff Bezos, so go for it. Bear in mind, to chew and grind up plastic, we will need a pretty powerful motor and a gear drive train thats mostly metal or as little plastic as possible. This shredder seemed to have both so it worked for me.

Also, the CD shredding capability is completely useless for this project, so if you can find a powerful, economical/free one without it, thats perfect. We will be getting rid of the CD shredder completely.

Besides the shredder, the only other tools you will need are:

1) PH Screwdriver with a longish narrow shank

2) Basic electrical tools, wire, stripper, tape

3) Saw or drill. I just used my jigsaw and am happy with the results

4) Patience

Read on for details.......

Step 2: Test

First we need to test the shredder. Ignore this step if you are using the same shredder. The opening is too small for any part to fit through, so flip it over and run it in reverse. This step came in handy to realize that if the bottom grooved carriage allows for parts to go through, it might be worth keeping intact (which is a nightmare later during hacking). If it barely grinds even the smallest of parts, make note that it is expendable and move on.

Step 3: Dismantle

This is fairly straight forward. Take note of the electromechanical systems and electronics. Unscrew and dismantle carefully. More details in pictures.

Step 4: Hack - Electronics

For lack of a better term, let's call this "hack". The IR sensors and microswitch under the flap are vestigial and can be harvested for use in other projects. The IR sensor and receiver can be directly cut off the board. The flap microswitch can be cut off and the wire spliced with the alignment microswitch. Look at pictures. Test your circuit.

WARNING: We are dealing with AC. Be careful. If you consider any body parts expendable, feel free to keep them in proximity to the grinding rotors.

Upon successful testing, extend the wiring to the alignment switch like the last picture. The tube is optional to keep the wiring neat and tidy.

Step 5: Hack - Mechanical

This part gets a bit tricky. The objective is to get rid of the top plastic cover over the rotors. Go though the dismantling process methodically and avoid using unnecessary brute force. This is the longest and most tedious part of the build and I apologize for the lack of pictures. But if you are at this stage with grease smeared hands, you will understand why.

You will end up unscrewing the end cover, the screws holding the plastic covers together and the screws holding the steel rods in place. I had to unscrew 3 of the 4 steel rods in order to get the covers off.

In order to get to one of the screws, the CD shredder became expendable. It comes off by bending the little clasps and pulling it out through the slots.

Take your time and be patient. Again no unnecessary brute force. Follow the assembly logic.

Once the two plastic covers are off, you have a choice to get rid of both or just the top. I suggest keeping the bottom to add rigidity and since it barely interfered with reverse grinding(Step 1), why not? The pictures make it seem like you should take both off. I changed my mind later and decided to dismantle again to add the bottom plastic cover. So you can skip that unnecessary step.

Carefully reassemble the gear drive train and rotor assembly. Make sure everything is snug and rigid and the rotors move freely.

One piece of advice, don't work on a glass table like I did. This assembly is pretty heavy and the with the number of times it dropped on my table top during dismantling (the copious amounts of grease didn't help), its a miracle it didn't shatter.

Step 6: Lid Slot

For this part, I used my handy jigsaw with the thinnest blade I could find. Remember to cut off the plastic flap on the bottom back edge. Use the pictures as a reference. Make sure your grinding rotors are completely exposed. Test fit once done.

Step 7: Hopper

Get creative with your hoppers. I was originally going to print one but something of this size would take hours to design and print. I decided to go with an inverted conical hopper, to minimize the amount of plastic being spit out. I had a sheet of 3mm polypropylene lying around so I used it to cut the shapes.

If you cut out your hopper like me, here's what you will need:

a) 2 rectangular pieces 22.5X12cm

b) 2 isosceles trapezoids with 4cm top edge, 6cm bottom edge and 6cm height. Basically theta of 10 degrees.

Assemble like in the pictures and test fit for snugness. Blue painter's tape is what I had handy (thank you ABS printing). Make sure that both the long edges go around the steel rods and touch the lower plastic cover which we added back. Essentially make sure that the plastic bits flying around during operation don't make their way out of the grind chamber to the motor, gears and electronics.

Step 8: Final Assembly

Time to start putting things back together. Screw in the electronics and clean up the wiring like the pictures. Close up, put in the 6 original screws and mount on bin. Load the hopper. I had an extra piece of PP which I decided to use as a lid. We are almost done.

Step 9: Cosmetics

Print the little clip. Shouldn't take more than a few minutes. Glue to the side and clip on the switch. Stand back and take pictures. Project complete.

Step 10: Grind

There is one and only one golden rule to this operation. Short slow pulses. If it sounds like the motor is being strained; stop and pulse in reverse once, flip back to forward and start pulsing again. I will eventually work on a hack to reduce motor speed drastically in order to eliminate pulsing all together. But for now, monitored pulsing has its advantages.

Here are some of the grind videos

First grind-

Multiple Small Parts-

Mid-Size Parts-

Large Part-

Dino skull fail regrind-

1st Grind Quality- The grind varies from dust to long strips and ribbons. This is characteristic of 3D printed parts as entire layers get delaminated. Keep in mind I have been running this continuously and ground up about 1kg of black ABS parts. The only breaks have been when the motor overheats.

2nd Grind Quality- Drastic improvement in consistency but some big chunks still remain. Easy to sort out by hand. Heat is starting to become a huge issue. Friction = heat. Not only does the motor overheat, the real big issue I am noticing is that the rotors have heated up. Also, the undercarriage has taken a bit of a beating, some of the rotor teeth are misaligned. Now the heat issue while not a big deal for plastics like ABS(high glass transition temp), might be a huge issue for PLA(low g-t). Cooling the motor is easy, its the rotors that have me concerned.

3rd Grind Quality- Ground the bigger pieces twice and smaller pieces once. Product is relatively consistent. At least to the point that the filabot extruder screw will spit out bigger chunks. Check out the pictures.

Step 11: Summary & Future Work

Total product 840gms. Assuming we began with 1kg, thats a yield of 0.84. I'm looking around and all the spillage barely amounts to 100gms. There is definitely a lot of debris in the shell. Most of the real damage seems limited to the plastic undercarriage shell that we left in place. Considering that most of the plastic on this machine is ABS and we ground up ABS, contamination isn't an issue.


1) Physical: The huge downside of this hack is that we are using a single set of rotors which imposes massive strain on the drive train. Also, the grinds need to be reground a couple of times to ensure semi-uniform consistency.

2) Heat is a monster. An immediate upgrade is a computer fan for the motor. Will post more later. The rotors need a bit more thought. Liquid cooling poses the risk of leaks. Fans will just generate dust and require filters which is a perpetual consumable and fire hazard. This is the plate and fin cooling problem from transport phenomena, but reversed.


Don't grind up huge batches at a go but rather grind as you go along and store for later use. My honest opinion is if you intend to grind about 1kg batches at a go, perhaps you need 2 - 3 of these machines running simultaneously. For an outlay of $150 for 3 machines producing 1kg a day and a profit margin of $5 per kg of product, the machines pay themselves off in 30 days. If you intend to go bigger, then you are in the recycling business and the $1000< beast is for you.

An upgrade in the short term would be to couple this with the $100 micro-shredder off amazon. This should help with the regrinding problem.

True Solution:Here's the market void that needs to be filled ASAP

1) A small 3-stage plastic grinder comprising of 2 rotor top stage of about double the diameter of this shredder, 4 rotor 2nd stage like the one we are using, 8 rotor 3rd stage of half the diameter. In fact that gear ratio would be a great starting point with load sensitive speed control speed control rather than the "clicky" end-stop switch. There are some coffee grinders that use this concept.

2) It should be capable of grinding huge parts to fine grains in a single pass. No regrinding.

3) Mostly importantly be <$150. Let's face reality, if recycling is expensive then there is no incentive to recycle.

Essentially we need a device transformation like from to Having built the first one, I decided to buy the second one.

If you are reading this, I'm assuming you either liked / thought about / want / intend to build or intend to contribute 'USEFULLY' to this idea. I will be posting upgrades and observations as I go along. If you have any suggestions / feedback / comments / build schematics / upgrades / mods or anything 'USEFUL' to contribute please message me. Use youtube comments as a benchmark for 'USEFULNESS".

Thank you,


Maker Olympics Contest 2016

Participated in the
Maker Olympics Contest 2016

Metal Contest 2016

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Metal Contest 2016