Cardboard Perforator / Shredder Machine - Paper Shredder Hack

This Instructable describes my process for converting a heavy duty cross cut paper shredder into a very capable cardboard perforator for packing and shipping.

What is perforated cardboard?

If you haven't seen it before, it's a sheet of cardboard which has been cut into a waffle like weave, or mesh. It has most of the benefits of cardboard, but not the rigidity. Instead, it is very flexible and can easily be bent and twisted in any direction. The benefit of the perforated sheet verses the little confetti chips you would normally get when you put it through a cross cut shredder is that the sheet stays put, its good for wrapping around things, and it isn't messy for the recipient. The shredded confetti shifts in transit, so what may have started out as an inch of padding, could be two breakable things knocking together on a truck. If your shipment survives, the recipient isn't going to be happy to have to dig through little chips of messy cardboard.

I am a potter and discovered perforated cardboard a number of years ago. I really wanted a machine for my studio to use for shipping my ceramics because cardboard is free, upcycled, and recyclable. So by reusing it, the cardboard gets one additional life of use before being sent to the recycling plant. It's a green as it gets. It will help keep your recycling bin from filling up, and you will never have to order shipping supplies.

The problem? Cost of the machine. There aren't many companies making cardboard perforators, and while they are really nice, they start at around $2,500. I can't rationalize that kind of expense for my one man shop, so I decided to make my own using a common paper shredder which I disassembled into about 400 pieces, modified about 115 of those, and then reassembled. This project is not going to be something everyone can do, but if you are mechanically inclined, patient, and good with puzzles, it's a great way to build a machine to make your own green packing material, and do so with very little cost (mine was $20).

Supplies

You will need a paper shredder - obviously. The more heavy duty the better. The one I chose is a Fellows 99Ci, which I recommend. It is a beast of a machine. It has solid, heavy parts, a strong motor capable of quite a bit of continuous running, and can easily handle thick cardboard boxes and double thickness of Amazon box cardboar, so you can stitch together smaller pieces. It worked out great for me, and was relatively easy to work on.. It states that it has a 17 sheet capacity, which is about as high as you are likely to find. These sell new for about $250, but they are pretty common on the used market. I got mine on craigslist for $20 and there were others of the same model for $50 and $60. Mine is a slightly older model, and has a plastic bin. I understand the new ones have some type of flimsy cardboard bin, but I can't say if the mechanism changed over the years.

You will also need a bench grinder with a grinding wheel and some kind of soft abrasive wheel. I have one of the little orange ones from Harbor Freight. I think it's about a 3" wheel diameter. They cost about $30 (use the coupon), and you will use up at least two grinding wheels in this process, so get a couple of packs of replacement sets. The last time I bought them they were $7 a piece.

You will also need eye protection. I recommend a full face shield for all the grinding involved, maybe combined with safety glasses. HF sells both of those for cheap as well.

You will need a dust mask.

Finally, you will need some basic hand tools, such as screw drivers and pliers (Needle Nose and Channel Lock) . I also found my cordless impact driver to be particularly helpful in removing some tricky screws. It may or may not be a necessary tool for this project, as I did not attempt to remove them with a standard drill or screwdriver.

Step 1: Remove the Lower Housing

This should go without saying, but unlpug the shredder. Also, you do this at your own risk. I take no responsibility for injury or loss of property.

I didn't photograph this part, but you will need to remove the storage bin and then the lower housing. The lower housing is just clipped on, but it's a little tricky. Turn it upside down and look at where it connects to the top section. Look on the inside with a flashlight and you'll see two clips on each side. You will need to use a flat screwdriver to separate them from the inside of the housing. There will be a little bit of popping when it separates, but if you're careful and patient, nothing will break.

Step 2: Remove the Lower Cover to the Shredder Mechanism

Once you have the top of the shredder mechanism isolated, flip it over and remove the 7 screws holding it on. There will be 5 main screws, plus 2 smaller screws on the plug side. Once those are all out, the lower plastic section should come right off. Mine was slightly stuck, but easy enough to pull off. There were two wires connecting the lower cover that I had to disconnect, one orange and one black. They are simple wire connectors, just push the button and pull them apart.

Step 3: Remove the Shredder Mechanism.

The mechanism is not physically connected to the housing. It is held in place with 10 little rubber bumpers (5 above and 5 below). They may be on the mechanism, or they may have stuck to the bottom cover. Find them and put them somewhere safe so they don't get lost (hopefully you're putting your screws somewhere safe too). You can now lift the mechanism from the rest of the housing, but be careful as it is attached with wires. Stand it on end with the gear side down.

Step 4: Remove the Cover Plate on the End of the Assembly, and the Circlips. Disassemble Cutters and Plastic Guides.

While the assembly is standing on it's end, there will be a flat plate on the top with a plastic insert. You will need to remove this first. There are 2 larger screws and 2 smaller screws holding it on. I used my 1/4 impact driver to back the screws out while holding the metal guide shafts with pliers. These screws were quite tight, and if you don't hold the guide shaft, the screws and the shaft will spin together, not doing anything.

Once the plate is removed you will have clear access to the ends of the main shafts. Take photos of the cutting disc and guide assembly before removing anything for referencing during assembly. There are over 350 parts that you are about to remove, so make sure you have a good record of where they go and you have a place to put them so they don't get lost.

There is an E-clip at the end of each shaft. Use a small flat screwdriver to work them off. Remove all cutting discs and guides. The teeth on the discs are sharp, so you may want to wear gloves.

Step 5: Grind the Cutting Discs

This step is the real work of the project. There should be about 116 cutting discs. You will need to grind the teeth off of all of them, as well as grind a groove next to where each of the teeth are. This is pretty time consuming. It took me about 3 hours, split over two days. You can see the before and after in the photo for reference of the shape you are aiming for. You must wear eye protection, and I recommend a face shield as well. A dust mask should be considered a must as well. I did this step outside for fresh air and to keep the grinding dust out of the shop.

As you go, the grinding wheel will glaze over and stop working as well, and the corner you are using to cut the groove with round over. Flip the grinding wheel around until you have used both sides, the switch to a fresh wheel.

One at a time, grind a tooth, grind the corresponding groove, then remove the burr.

Grinding the teeth off is pretty straight forward.

You will need to grind the grooves about 1/4" deep. You can put a couple of the discs back on the machine if you want to make sure you cut them deep enough. Mark the bottom disc against the edge of the disc above it and that is your minimum depth. You need to create spots on the discs where they will not overlap, and therefore leave that section of cardboard intact. Next to each tooth, there is already a little divot, use the corner of the grinding wheel to cut that into a nice V shape.

After the tooth and the groove are ground there will be a burr on the bottom side. This must be removed and made smooth or the discs will not fit back together on the shafts. I used the plastic abrasive wheel on the opposite side of the bench grinder, but be careful not to round over the sharp edge of the cutting disc.

Step 6: Reassemble the Cutting Assembly.

Reference your photos for the plastic guides and spacers.

This step definitely requires the most puzzle solving skills, so be patient, check your work as you go, and take your time.

Since the discs have three grooves, we know that one of those grooves intersects the cardboard for each 120 degrees of rotation. If you line them all up, you will have a solid seam of cardboard every 1.25" or so, and your perforated cardboard will still be fairly rigid. If you stack them so they alternate, you can achieve a more uniform cut. It will be much more flexible, stretchy, and expandable, like a net. I stacked my cutting discs so that the grooves alternate in pairs, so half the total discs will have grooves intersecting at a time, and they alternate back and forth.

Since the discs are stacked two thick, that means the grooves on the first 4 discs will line up (2 on left, and 2 on right), then the next 4 will line up after the shafts rotate 60 degrees.

You will quickly notice that the discs don't always line up. Since you no longer have the teeth to tell you the correct side up for each disc, there is a lot of trial and error. So if it doesn't line up, flip it over and try again. I found it extremely helpful to use the plastic clearing guides to reference my cutting disc alignment.

Each pair of discs gets a spacer and a plastic clearing guide. Every four pairs of discs gets a plastic rail support guide. Reference your photos for the proper orientation and organization of spacers, particularly the smaller rail support.

As you go, check your work often to make sure you haven't missed a support guide and that your grooves are lined up and alternating properly all the way down.

When you get to the top there will be one thin spacer and one thick spacer before the E-clips. Reinstalling the E-clips is very tricky, and will not be possible if you didn't remove the burrs on the cutting discs sufficiently. A second pair of hands may be helpful here, but I did it by myself.

There is some play in the main shafts. Lift them up or lever them from below, perhaps wedge a tool between gears. You will need to push the discs down tight, starting at the bottom to make sure there's no space between them. Then use a screwdriver in the groove for the E-clip to leverage a little more space for the clip. Once you get the clip started, you can use a pair of channel lock pliers to squeeze the clip onto the shaft (one jaw on the clip, the other jaw on the opposite side of the shaft).

Reinstall the end plate with plastic insert with the four screws.

Step 7: Deactivate Thickness Switch and Bin Switch. Reassemble Covers and Housing.

The auto feed will not work with the thickness of cardboard, though you can override it by holding down the forward button. That's a hassle.

In the mouth of the shredder you will find a little piece of plastic that sticks out. This is the switch that stops the shredder if you attempt to put too many sheets of paper through at once. Since cardboard is thick you will want to disable this switch. On the bottom side of the top cover you need to remove the 8 screws holding the cover on. When removing the cover, take note of the IR sensor (two LED looking things) and how they are placed - this is how the machine knows when something has been inserted, activating the auto feed. You will find the thickness switch held on by 4 screws. I just took it off and reattached it using 2 screws so it was off to the side and couldn't be triggered. You could probably permanently disable that switch by either cutting and taping off the wires, or cutting and permanently connecting them (I didn't test to see if this is a normally open or normally closed switch, so I don't know which would be the correct option). Replace the interior cover and 8 screws, making sure to get the IR sensor back in the correct slots.

The bin switch is easy to disable. You will usually want to have the bin removed while perforating cardboard so you can remove it as it comes out so it doesn't get messy. The switch has a metal bar that sticks out of the top assembly, on the side that the bin comes out. Just tape, tie, or wrap that bar down to the switch so that it is always depressed.

Finally, there is a bin overfill protection switch. I didn't disable this, but I wish I had, and I may go back in to do it, or find a way to mechanically lock it. This switch is on the bottom side of the lower cover. It looks like a 1.5x2" flap. It's purpose is to stop the mechanism when the bin fills up to that point. The problem is that the cardboard often makes contact with it without it being full. So I have to reach in and move the perforated cardboard and the shredding will resume. Since I haven't done it, I can't offer suggestions here, but it should be pretty straight forward.

Reassemble the covers and lower housing, plug it in, and you're done.