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While 3D printing continues to decrease in cost, it is still a large investment. Even after the initial purchase of a printer, purchasing plastic filament still remains a costly affair. One of the best goals now in the printing community is to allow the user to lower the cost by producing their own filament. Many companies and individuals are trying to fine-tune designs on filament extruders, including some excellent designs seen on this site. Eventually, the settings and methods for printing will allow for almost any type of plastic to be used, making any recyclable plastic a source of printing material!

One item that seems to be lacking is an efficient means of granulating plastic in order to feed into an extruder. Most designs use pre-formed plastic pellets, which are also expensive. If a person could shred waste plastic or failed prints to feed into an extruder, the cost of printing material would be greatly reduced. Searching the internet reveals some impressive and well-build plastic shredders, but the complexity and cost are significant. This Instructable will show a proof-of-concept of a simple, low-cost, hand-operated plastic shredder for starting the process of reusing waste plastic for printing.

Step 1: Concept

Two coaxial hollow cylinders (steel pipe in this case) are used as a cutting mechanism. The outer cylinder remains fixed in place, while the inner cylinder is free to rotate within. A slot is cut into both cylinders, such that when aligned, plastic from a hopper above is allowed to fall into the opening. The edges of the slot on the inner cylinder are sharpened to create a cutting edge. As the inner cylinder is turned, the plastic will be caught between the stationary outer cylinder and the rotating inner cylinder, and will be cut much like using a pair of scissors. The cut plastic will be contained within the cylinders, and by mounting the cylinders on an incline, the pieces will be able to fall through the cylinders and out to a collection container. By varying the size of the opening, larger pieces of plastic can be restricted from falling into the cylinders, giving control over the size of the plastic pieces produced.

Step 2: Materials and Cost, Tools Required

Depending on what tools and materials you have on hand, or your level of resourcefulness, this device can be built for anywhere from free, to about $30!

Cylinders: Any two pieces of pipe made of a hard material that can be sharpened and hold an edge can be used. One piece of pipe must be able to fit inside the other and rotate smoothly. For this proof-of-concept, I used one 1-1/4" and one 1" black steel nipple, both 6" long. While this worked, the gap between the two pipes proved to be inefficient, much like loose scissors.

Handle: I used a piece of 1/2" round steel rod

Hopper and Body: I used some scrap wood and screws for no other reason than because I felt like playing with it! This shredder works best mounting it in a vise, and it is perfectly suitable to simply clamp the outer cylinder directly in the vise, with no body required! Also, because the force is only exerted on the two cylinders, the hopper does not need to be made out of any rigid material, or be mounted rigidly. A plastic jug and duct tape would work just fine!

Retention pin: I first used a piece of all-thread rod, but ended up using a nail

Tools:

Angle grinder

Metal cutting disc

Drill

Drill bits

Tape measure

Marker

Rotary tool

Grinding stone

Safety glasses

Gloves

Other helpful tools:

Drill press or drilling guide tool

Center punch

Hammer

Square

Aluminum channel or angle iron to use as a straight edge

File

Reciprocating saw with metal blade

Piece of paper

Piece of pipe to help hold items being cut

Jigsaw for cutting wood (or scissors or utility knife if using plastic jug for hopper)

Hole saw bits

Step 3: Making the Cutting Cylinders: Outer Cylinder

The threads extend about 1" in from the ends on both pieces of pipe. Starting at the end of the threads on the larger pipe, measure 3" down the length of the pipe (4" from the end). Use a piece of paper to draw a line around the pipe at this spot. This line will be 2" from the opposite end of the pipe.

Use a straight edge to draw a 3" line from the circumferential mark up to the threads. Bend a tape measure around the pipe, and make a mark 1-1/2" from that line, and mark a parallel line. The threads will make the fourth line marking out the slot to be cut.

Wearing safety glasses and gloves, use the angle grinder to cut out the slot along the marks. You will probably need a vice or some creativity to hold the pipe while cutting. Keep your fingers intact. Since this was just a proof-of-concept, overcuts and lack of precision were acceptable.

From this point on, the end of the pipe that the slot touches the thread will be referred to as the short end, and the end that the slot is one inch away from the thread will be referred to as the long end.

Step 4: Making the Cutting Cylinders: Inner Cylinder

Insert the smaller pipe into the short end of the larger pipe, such that all of the thread of the smaller pipe sticks out. Use the marker to trace the slot onto the smaller pipe, then cut out the slot on the smaller pipe with the angle grinder. Both pipes should now have a short end and a long end.

Step 5: Making the Cutting Cylinders: Drilling the Hole for the Handle

Now to drill some holes for the handle, and to create a way to adjust the cutting size of the shredder. All the holes were drilled in the threaded areas of the pipes. Had I been smart, I would have filed or ground a smooth surface into the threads and used a center punch to mark the spot. Since I didn't, I broke several of my smaller drill bits trying to start a hole between the threads.

The handle for turning is attached to the smaller pipe. I aligned the holes such that the handle would be vertical when the slot of the smaller pipe was facing upward, as I liked the position this would give when the smaller pipe would start cutting the plastic. Measure in from the LONG end of the smaller pipe one inch minus half the diameter of your handle, and mark the location of the hole (in my case, 3/4" in for a 1/2" handle). This way, the handle will just touch the end of the threaded area. When the inner pipe is inserted into the larger pipe SHORT end first, the handle will keep the slots in both pipes aligned. Using a drill press or drill guide, and another pipe inserted into the small pipe to hold it still, drill a pilot hole into the smaller pipe. Let the bit pass all the way through the pipe and find its own resting point on the opposite wall, and continue the pilot hole through the other side. Increase the size of the bits used incrementally until the hole is the desired size for the handle.

Step 6: Making the Cutting Cylinders: Drilling the Cutting Size Adjustment Holes

Next, drill some holes into the thread on the LONG end of the larger pipe. I drilled 3 sets of holes passing through the pipe, spaced about 1/2" apart, and 1/2" in from the end, with the first set of holes being horizontal when the slot of the large pipe is facing upward. These holes will allow a pin to be inserted through the base and through the larger pipe, keeping the pipe stationary with respect to the base. By having a few sets of holes drilled, the larger pipe can be repositioned to decrease the size of the opening that the plastic falls into. I drilled these holes out to 1/4" because I planned on using a 1/4" rod for the pin, but I ended up using a nail for the pin instead.

Step 7: Making the Cutting Cylinders: Making the Cutting Edge

Using a rotary tool with a grinding stone, sharpen the long edges of the slot of the smaller pipe, such that the edge slants toward the inside of the pipe. If both edges are sharpened, the shredder will be able to cut in both directions. If desired, the larger pipe can also be sharpened with the edge slanting outward. Wear gloves. I didn't and ended up picking metal splinters out of my hands for 2 weeks.

Step 8: Making the Cutting Cylinders: Add the Handle

The last part of the cylinder assembly is the handle. A two-foot-long handle gives some good leverage for cutting thicker plastic. If the handle does not slide nicely into the holes in the smaller pipe, encourage it with a hammer. I used 1/2" diameter round steel rod.

Step 9: Building the Base: Inner Piece

As stated before, the base is not necessary if you are not planning on varying the size of the plastic shredding, but it does make operation easier. If not making a base, the cylinder assembly can simply be clamped in a vise.

Using a scrap of two-by lumber, I marked out and cut the inner portion of the base so that the cylinders would sit with the handle end tilted upward. This would allow for the shredded plastic to fall down through the pipes into a collection container. The only important part of the base design is that the base does not extend past the short end of the outer cylinder, so as not to interfere with the handle rotation.

Step 10: Building the Base: Outer Pieces

To make the sides, lay the inner portion of the base on the material to be used for the side, and use a square to make lines perpendicular to the direction the cylinders will be laying. I used some scrap on 1"-thick wood, but as this is not load-bearing, any size will suffice.

Cut out this shape using a jigsaw. I wanted a larger hopper on the system, so I planned on adding more wood to the outside. To allow plastic to be guided toward the cylinder slots, I cut the top of this piece at a 45-degree angle slanting inward.

Make a mirror-image of this piece for the other side, cutting the slant at a 45-degree angle in the opposite direction. Now, the larger pipe can be seated onto the inner base piece, and sandwiched between the outer pieces. Because the 1-1/4" of the larger pipe is the inside diameter, and because 2-inch lumber is closer to 1-1/2", there will be some gaps when everything is put together. Srcrews or nails will hold everything tightly.

Step 11: Building the Base: Adjustment Pin Hole

Now mark the location for a through-hole in the base for the pin. It is easiest to place the 3 parts of the base and the larger pipe together, and reach the marker in through the end of the pipe into the horizontal holes. Or, you can just measure onto the base itself. Drill these holes through the outer parts of the base.

Step 12: Building the Base: Eliminating Gaps

This next part is not necessary, but did allow for the hopper to be made without unwanted gaps. With the 3 parts of the base and the larger cylinder together, the location of the slot was marked onto the inner surface of the outer base pieces.

The sides were trimmed down in front of and behind the slot location in order to let the front and back of the hopper to sit snugly against the cylinder. The fancy notch was just a result of my using thin scraps of wood for the back of the hopper, as well as trying to stay away from the pin hole.

Step 13: Completing the Base

Now, the base parts can be assembled. First, insert the pin through the sides and the larger pipe to get everything aligned. Place the inner base piece underneath, and slide everything together tightly. Screw or nail the three base sections together. The pin and cylinder may need to be removed after the base is assembled in order to complete the hopper construction.

Step 14: Building the Hopper: Sides

For the sides of the hopper, cut two pieces of wood about the width of the cylinder slot, and of the height desired. Fasten these to the side of the base perpendicular to the cylinder orientation.

Step 15: Building the Hopper: Front and Back

The front and back were formed by cutting a piece of wood to width, and marking out the curvature of the pipe at the bottom. I used a hole saw to cut this rounded portion, but a jig saw would be suitable as well. Now that all the pieces have been cut, everything can be fastened by nails or screws.

Step 16: Final Assembly

Place the larger pipe into the base/hopper assembly, insert the pin, and insert the smaller pipe and handle into the larger pipe, and the plastic shredder is now completed!

Step 17: Adjusting the Cutting Size

To vary the size of the plastic shredding, remove the pin and rotate the larger pipe to one of the other sets of holes, and re-insert the pin. This decreases the size of the slot opening to the hopper, which restricts larger pieces of plastic from entering the cutting region.

Step 18: Shredding

Mount the shredder in a vise, and place a collection container under the rear of the cylinder assembly. Drop the plastic to be shredded into the hopper, and rotate the handle to begin shredding! Larger pieces may need to be cut so that they can fit into the slot. Or, you can just build a bigger shredder!

Once the plastic has been cut on one size setting, the opening can be decreased, and the plastic can be shredded to smaller-sized pieces

If the inside of the cylinders become clogged, push a rod in through the handle end of the shredder to push the shredded plastic through.

Step 19: Improvements

It was difficult to find suitable sizes of pipe at a hardware store that would fit together nicely. This left little choice as to the amount of gap between the cylinders. It rather was like trying to cut paper with loose scissors. Some pieces of plastic would fall into the slot, and the top would bend and get squeezed between the larger and smaller pipes rather than being cut. This is the most significant factor that could be improved upon.

Another possible improvement could be to make various-diameter inserts for the cylinders, so that the shredding size can also be adjusted by limiting the depth to which the plastic can fall into the cylinder.

Hopefully by presenting this design, someone can get an idea for an improvement, and in the future we can re-use waste plastic as a cheap source of 3D printing material!

<p>Hi guys, i am an industrial design student in my final year, i need something like this for my design so bottle caps can be ground down, but i would much prefer it to be motorized. Can this be motorized safely? and if so with what kind of motor?<br><br>Any help would be appreciated, Thanks!</p>
It would be very easy to add a mottos to this, even if it was a drill or a motor with a controller board.
<p>I am currently in a debate about if we should get a 3D printer for our school and I just have to say, this helped SO much prove my point</p>
<p>Perhaps 2 opposing large drill bits setting a hairs breadth away from each other would be good for grinding as well. Most of the extruders on here use a single bit as part of their design.</p>
Thanks! Stay tuned for version 2, in progress ;)
<p>I think my wood chipper works much better and is safer and cheaper. I can shred hundreds of pounds of plastic scrap in an hour. If i shovel it back in for another pass it makes plastic snow.</p>
<p> I like your off the shelf esthetic.</p><p>My suggestion for closing the gap between two loose fitting cylinders is to coat the inside of the larger pipe with a release agent and clamp the slotted side of the inside pipe against the inner surface of the larger pipe.Then fill the space between pipes with concrete.</p><p>The result would be a inner pipe that was closely fitted against the outer pipe.</p>
Thanks for the suggestion!
<p>I recently had another project that required concentric pipes of close tolerance, and found good cheap ones at autozone and my local muffler shop. They have a surprizing number of sizes and I got 2 pipes that were made for each other...</p>
Oh wow, thanks! That would be a little thinner-walled, but this whole project is just to see if the concept is worthwhile... I think I'll try that.... Thanks!
<p>Wouldn't a cheese grater do the job better and easier? </p><p><a href="http://www.walmart.com/ip/22080765?wmlspartner=wlpa&adid=22222222227015943585&wl0=&wl1=g&wl2=c&wl3=42973918832&wl4=&wl5=pla&wl6=69920711540&veh=sem" rel="nofollow">http://www.walmart.com/ip/22080765?wmlspartner=wlpa&amp;adid=22222222227015943585&amp;wl0=&amp;wl1=g&amp;wl2=c&amp;wl3=42973918832&amp;wl4=&amp;wl5=pla&amp;wl6=69920711540&amp;veh=sem</a></p>
Hi! Thanks for reading and commenting! I've had a lot of feedback suggesting the use of various blenders, food processors, mills, etc. I think the problem would be long term durability. Even the infomercial food processing devices that can withstand a minute of grinding concrete are most likely not going to have a good long life afterward. And if they are repeatedly used on hard objects, I would not expect the blades and motor to last long at all.
<p>I think a Straight Tooth Side Milling Cutter (used for cheap) would be your best bet. Maybe a few in a row on a common axel. Check this one out from ebay. </p><p>http://www.ebay.com/itm/UNION-4-x-5-8-x-1-1-4-STRAIGHT-TOOTH-Side-Milling-Cutter-/291489172151?pt=LH_DefaultDomain_0&amp;hash=item43de1bcab7</p>
<p>Or use quite a few and simplify this design. </p><p>https://www.youtube.com/watch?v=Lze-UDPPyYk</p>
<p>Ok yeah I saw that video before I started and had actually wanted to replicate it, but I couldn't source gears within my budget that would work with the parts I wanted to use for the rest. So it was either spend a lot to get gears that worked with the other materials I had, or go cheap on gears locally and have to buy additional materials for the rest. </p><p>What I was going to use for the cutters was just a bunch of large fender washers, and take the angle grinder to them, making 3, 4, or 5 notches into the edge at even spacing around the washer. That would pretty much make the same idea as the cutters on industrial shredders. I may still do that in the future when funds allow the purchase of appropriate gears, and to have someone weld them and the cutters onto shafts. </p><p> Thanks for checking out my project!</p>
<p>Think about recycled bicycle sprockets and chain instead of costly <br>gears. The sprockets don't need to be exactly the same size as the two <br>axles of the grinder don't need to be rotating at the same speed. They <br>just need to be rotating in opposite directions.</p>
And cheap is good so I'm curious!
Thanks for the feedback! It's gonna be a little while until I can check out your link, but I will!
<p>Nice idea. Is this an original idea or is it based on another design? How well does it work? And are there any changes you would make?</p>
Thanks! This is my original design. I had wanted to make a cheap copy of the multi-bladed counter-rotating design, but without a lathe, mill, drill press, and welder, it seemed rather daunting. The real kicker was the gears.... Without the resources to make my own gears to a specified diameter and strength, I was limited to purchasing. Nothing found locally, and without paying a lot, all the other dimensions would have to be based off of gear sizes I could afford, which further limited the availability of locally-sourced parts for the rest.<br><br>So, that began a series of changes in design concept. One cutting shaft instead of two meant no gears. No second meshing cutters meant gaps between disks (good idea for that below), so the series of cutters became a continuous shaft with a slot cut in. The slot became increasingly wider and deeper, until the sketches suddenly seemed more like a pipe. Using a pipe caused issues with a central axle, so the body became the exterior retention system. That meant issues with the load on the walls, so things started getting reinforced to the point it just seemed to need to be surrounded. That's where the second pipe came in.<br><br><br>As far as how well it works? At this point not well. The sloppy tolerances lead to the plastic bending and tearing in chunks, and getting caught between the two pipes. But its a start, and enough to feel good about.<br><br>And changes? I listed some in my last step, and we've been having quite a good discussion below!
<p>You could fit some kind of shim in the bottom of the outer tube, so the inner tube is pushed up to the slot in the outer one. Not perfect but it would help with your &quot;loose scissors&quot; problem. Bias it to one side or the other so that one set of edges closes properly, depending on which way you want to wind it. With a bit of thought you could probably come up with an auto-biasing version...</p>
I did think about a shim, but I was picturing more evenly spaced around the circumference. Putting it just on the bottom to force the top together is a good idea.... I'll probably try that. Thanks!
<p>The mechanical cutter concept is excellent. Next step is to make an extruder for heating this shredded plastic and forming it into filament for use in 3D printers.<br>If you want inexpensive 3D printer filament it might be interesting to try weed-eater string. </p>
<p>Ok good, I don't have to lose sleep.... here you go <a href="https://www.instructables.com/member/arvevans/" rel="nofollow" style="">arvevans</a>:</p><p><iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/SzUGHrEqEUk" width="500"></iframe></p><p>http://forums.reprap.org/read.php?1,141946,141946</p>
<p>Some weed-beater string is high density PVC, but I am not sure about all of it.</p><p>Seems that an extruder could be something as simple as a 3D printer with heated hopper to melt chopped plastic and a ram for forcing it out a nozzle to &quot;print&quot; the filament into a water bath (bucket) for cooling. Print in a circle to automatically coil the filament in the bottom of the bucket.</p>
Thanks! I'm hoping to eventually make an extruder, and will probably follow one of the Instructables covering that... There are some awesome designs out there! <br><br>Weed whacker string.... wow, I wonder if anyone has tried that... I think you just cost me some more sleep lol
<p>How about using old skill circle saw, one that you can put multiple blades in it 3-5 or more (use longer bolt )have a metal plates on both sides of blades, with just part of the blades sticking out. then a wood frame around that for hopper . use long bolts with wing nuts to hold together ...I'm going to play around with some ideas and will post results .....I'm thinking a shaft with bearings with a stack of circle saw blades 10-20 with jam hopper.</p>
Great! Please keep me posted!
<p>Just to picture what others have said, to make cutting easier:<br>Inward angle on inner cutter edge, <br>Angled inner (or outer) cutter slot.</p>
<p>Thanks!</p>
<p>As far as the pipes not <br>fitting together well, the angled cutter may cut better and fit the pipes <br>together better, too. If you take your grinder and cut a flap on the <br>inner pipe that you bend up and sharpen the edge of, it can take up the <br>gap between the pipes. I, too, thought <br>about the eccentric pattern but that would definitely take some precision not always <br>easily come by in the garage shop.</p><p>I am fortunate to have one <br>of the super-duper 5hp Vitamix blend anything blenders and I have tried it on <br>some plastics. I saw another user use his on straight-up plastic, and I have to <br>say that while it is more work (because of straining and drying the plastic), I <br>put water in mine along with the plastic to keep the plastic from melting in <br>the blades and to help it maintain motion and hopefully hit the blades more <br>times. It still didn&rsquo;t cut it up as much <br>as I wanted, so more work is to be done there on blend time/ speed/ water level/ <br>etc. </p><p>A dedicated filament grinder <br>would be nice if it can get the shred small enough for a filament extruder. Industrial <br>shredders use counter-rotating meshed blades, so maybe using a simpler version <br>with a set of fixed blades with a rotating second set of blades would work or <br>simply a fixed, slotted plate with the rotating blades that go through the <br>slots. That wouldn&rsquo;t have to require <br>welding- just space saw blades on an axle with washers/nuts but I'd make it <br>drill/ motor powered for sure.</p>
<p>Apparently I didn't put my reply in the right box, so you didn't get a notification of my reply, <a href="https://www.instructables.com/member/wilwrk4tls/" rel="nofollow" style="">wilwrk4tls</a>:</p><p>Here it is:</p><p>You have some good ideas there, and some good CAD work as well :) Yeah, I'd love to make a multiple cutting blade device, and I like your idea of using the single shaft to eliminate gearing (lowering cost). I may look into that as well! I never expected so much feedback, but I'm loving the ideas!!!</p>
<p>for the money, just go to a thrift shop and buy a blender or a food chopper. Faster, louder. and quicker.</p>
<p>I think you would be replacing it pretty quickly... unless you were referring to my cat litter comment below</p>
<p>In the lab we use heavy duty electric coffee grinder but we freeze the plastic in liquid nitrogen first. We also feed liquid nitrogen thriough the machine while we grind. Once I tried to use a domestic food processor but it couldn't handle it. I imagine some of the really heavy duty food blenders would work. But these solutions all require big money and are to hard to do at home.</p><p>I really like dmwatkins idea, I wonder how it would go powered by a hand held power drill.</p><p>Has anyone ever fed plastic into a garden shredder?</p>
Thank you! I appreciate that! Someone on HackaDay also suggested a garden (compost) shredder, and others liked that too! If somebody tries it, I'd love to know how it works out!
<p>If the method was to extrude plastic pellets, why not use the same sort of method as shredding meat? You would have to heat the extruding/shredding apparatus to ensure that the plastic would stay melted, but they have kitchen aid meat shredder apparatuses to experiment with for relatively cheap. The trick is to find one made entirely of metal. Good luck!</p>
Thanks for the read and feedback! I did think about the way a meat grinder works as well, and whenever I go to the store, I'm always looking at various items like that for ideas (for this project and 50 others as well lol)... I got inspired by various blenders for a way to grind cat litter for green sand for casting.... probably would've been cheaper to just buy a coffee grinder.... but where's the fun in that? ;)
<p>This is a great new idea. I have been searching for several years for an inexpensive way to grind plastic. I posted this thread in 2009<br><br><a href="https://www.instructables.com/community/Inexpensive..." rel="nofollow">https://www.instructables.com/community/Inexpensive...</a></p><p>The only home shredder available is the FilaMaker mini-shredder that costs about $400. <a href="http://filamaker.eu/" rel="nofollow"> http://filamaker.eu/ </a> A heavy duty &quot;will it blend blender&quot; might work but it is also expensive, a few hundred dollars. There has to be a better way.</p><p>An inexpensive home shredder is something there is a huge demand for that no one had come up with a design for. If someone could invent one that costs under $100 it would be revolutionary. No more buying filament. Just recycle plastic bottles, etc. 3D printing would essentially be free once you had a printer. I wish Instructables would have a design contest for it specifically.</p>
<p>Thanks for the read! Yeah, the amount of plastic we already buy in the way of packaging and cheap items that later break.... why buy filament? I'm excited that you're out there thinking about it also! Thanks!</p><p>I tried to open your link, but I got the 400....</p>
<p>https://www.instructables.com/community/Inexpensive-way-to-grind-plastic-bottles/</p>
OK thanks! I read through the post... funny thing is that I even searched Instructables quite a while ago, but I never used the search word &quot;grind.&quot;. I'll use that on Google when I get a chance...<br><br>I also started thinking about this during a previous project about injection molding. I had saved up a bunch of HDPE I planned on using, but after cutting one container into 1/4&quot; squares with tin snips, I knew I never wanted to do that again.
<p>This is a very clever concept you've created here! Now you've got me thinking and I don't have a 3D printer! I think your idea of scissor action could work instead of two tubes, have one tube and one blade, the tube can have a spiral slit instead of a straight edge and the blade would go on the side of the hopper. I hope this makes sense?</p>
Yes, that makes sense. Thanks for the feedback! I love the ideas that people are giving me.... it's putting my mind in overdrive, which is something I love!<br><br>If you are gonna spin your gears on it, a HackaDay reader suggested a flat disk like a circular saw blade, but with cheese-grater-like cutters on the disk face.... Then I started thinking about Tunnel Boring Machines....
<p>I think the hardest part about a cheese grater is sharpening the blades unless you make it interchangeable so you can throw out the old one and put in the new one easily. You are very good at drawing out ideas from people.......hmmmmm!</p>
What an amazing idea! You have put a huge amount of work in here.
Thanks for the encouragement! It really didn't take all that long... more time staring at it is blankly lol.
Nice and simple design! Good luck in your contest! You got my vote :-)
Thank you so much!
<p>Gee, thanks, now I have another project for my inbasket... :-)</p><p>A really nice idea! I am thinking of making a larger one to handle the milk jugs and other plastic we recycle---they take up lots of room in the bin. And it just occurred to me...if it's possible to make the cutting edge slanted instead of parallel to the pipe axis, it would reduce the effort needed. Hmm....</p>

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