Shredder converted to Imperial system (Inches)

Hello everyone 🙂

After several days learning CAD and some 3D modeling tools, I have finally finished my conversion of the Precious Plastic Shredder to imperial units.

This is a request that tons of people have been making for months and there are a few machine builders who have managed to convert the drawings to inches, but for some reason no one else has shared the converted files with the community (something I consider very selfish).

These files have been checked from every single angle to make sure they will fit correctly. While these have not been used to build a real shredder yet for their final test, I will send them myself to a laser cutting company soon and will post the results here as soon as possible.

Without further ado, here are the technical details:

Steel equivalents
3mm = 1/8″ = 3.175mm
5mm = 3/16″ = 4.7625mm
6mm = 1/4″ = 6.35mm

Original metric design (inside lenght)

14 x 5mm rotating knives = 70mm (BOM shows 15 knives but only 14 are used in the shredder)
13 x 6mm spacers = 78mm
70mm + 78mm = 148mm total hex length (plus 85mm on each side of the hex bar)

New imperial design (inside lenght)

14 x 3/16″ rotating knives = 66.675mm
13 x 1/4″ spacers = 82.55mm
66.675mm + 82.55mm = 149.225mm total hex width (plus 85mm on each side of the hex bar)

Parts that had to be resized:

*Hex bar
*The original Hex bar had a total length of 318mm, with a central hex length of 148mm and 20mm diameter round ends with a length of 85mm each end.
*The imperial Hex bar has a total length of 319.225mm, with a central hex length of 149.225 and 20mm or 3/4″ diameter ends (you chose) with a length of 85mm each end. You can round this number to 320mm, or just do what I did and buy 1ft of hex bar, since you only need one end of the bar to hook up the motor, there’s no need to have 85mm of round bar on each side. Buying 1 ft of bar is normally cheaper than getting a custom cut. With a 1ft bar (304.8mm), you will end up with 85mm on one end of the bar, 149.225 in the center and the remaining end of the bar will be 70,575mm.
*Side panels (front, back)
*The front and back panels remains the same except for the slots where the middle panels are connected.
*The 1/4″ “side” (front, back) panels have 2 slots on each side, and those slots were originally 3.2mm wide to allow the 3mm middle panels to fit in and have some clearance. In inches, those middle panels are 1/8″ thick (3.175mm) and I made the slots 3.3mm (0.130″) wide to allow for 0.125mm clearance
*Middle panels
*The middle panel needed to be extended to fit the increase of length. The original panel was 149mm wide, the new panel is 150,8125mm wide (5.9375″).
*Also, the holes at both sides of the panel had to be enlarged, from 3mm to 1/8″
*The side inserts that connect the middle panels with the side (front/back) panels had to be enlarged a little bit, from 6mm to 3/16″
*Finally, all the slots (3 from the top and 5 on the bottom) where resized, repositioned and aligned to adjust to the new panel dimensions
*Side 1
*Adapted top and lateral inserts for 1/8″ thickness
*Side 2
*Adapted top and lateral inserts for 1/8″ thickness
*Bottom 1
*Resized from 149mm to 150,8125mm wide (5.9375″)
*All slots resized and repositioned proportionally to the new part length
*Bottom 2
*Resized from 149mm to 150,8125mm wide (5.9375″)
*All slots resized and repositioned proportionally to the new part length
*Top 1
*Length increased to 5.9375″ and all slot dimensions resized to fit into the middle panel slots
*Top 2
*Length increased to 5.9375″ and all slot dimensions resized to fit into the middle panel slots


*Additional notes

*IMPORTANT: For the imperial version of the shredder I decided to use the 1″ hex bar files modified by @keesdeligt, since it’s much easier/cheaper to get 1″ hex bar than 27mm. Also, make sure to read the changelog at the bottom of this post, it shows important information about the hex bar and bearing spacers.
*Original BOM shows that for the part “Fixed Knife Small” 15 pieces are needed, but actually only 14 pieces are needed
*Original BOM shows that for the part “Knife3″ 5 pieces are needed, but actually only 4 pieces are needed. The total amount of knives used in the shredder is 14 not 15.
*This redesign of the shredder was made for black steel which is available in 1/8″, 3/16″ and 1/4”. It is my understanding that Inox Steel is available in different gauges. If you are interested on an imperial design of the shredder using inox steel gauges, just contact me and I might design a new set of files for inox steel gauges. I have zero knowledge on whats available for inox steel so you will have to tell me.
*This shredder design is based on the 2.0 version of the shredder, however, all the changes from 2.1/3.0 are fully compatible (new hopper and new sieve design)

Soon I will be sharing as well a new set of files in Imperial units for a Shredder twice as big, something like THIS



*Fixed minor sizing issues with frame parts
*Appart from the .iam assembly file, I also included the assembly in .stp and .igs format
*Added pdf files with hex bar measurements, one for a 1″ hex bar with 3/4″ bores for 3/4″ bearings, and another for a 1″ hex bar with 20mm bores (original).
*While it is true that this design is made for Imperial units, there might be some people who already purchased UCFL204 bearings with 20mm bores, and that’s the reason why both hex bar designs were included.
*Added 2 additional files for the 1/8″ and 1/4″ bearing spacers for 3/4″ bearings in the DXF folder.
*If you are planning to use 3/4″ UCFL204 bearings then you will need to lasercut the files “1-8inch 2x BearingSpacer for 3-4inch Bearing.dxf” and “1-4inch 2x Bearing Spacer for 3-4inch Bearing.dxf”, and delete the files “1-8inch 2x BearingSpacer for 20mm Bearing.dxf” and “1-4inch 2x Bearing Spacer for 20mm Bearing.dxf”
*If you are planning to use 20mm UCFL204 bearings then you will need to lasercut the files “1-8inch 2x BearingSpacer for 20mm Bearing.dxf” and “1-4inch 2x Bearing Spacer for 20mm Bearing.dxf”, and delete the files “1-8inch 2x BearingSpacer for 3-4inch Bearing.dxf” and “1-4inch 2x Bearing Spacer for 3-4inch Bearing.dxf”
*Added 2 additional files for the 1/4″ bearing spacers for 3/4″ bores in the DXF folder.
*In case anyone is interested, found this deal on UFCL204 3/4″ bearings

*Fixed 0.007″ offset on “Bottom2” and “Top2” parts, updated download package with new dfx, ipt, igs and stp files

*I was told by my waterjet cutting company that they had problems opening the DXF files because they were in 2018 format and they only supported AutoCad 2013, so I added an separate folder into the download package with AutoCad 2013 format files and kept the 2018 files as well because why not…

*Finally received the water cut pieces and after a visual inspection and a few measurements with my caliper they look perfect. I’ll upload some photos soon and will report back once I have assembled the shredder

*I finished sanding and grinding all the parts and also milled my jimmy-hex-bar (more info HERE). So far everything looks perfect and all the pieces fit as expected, you can see some pictures at the botom of this thread HERE. I’ll upload more content in the next 1 or 2 days once I finish the shredder and it’s fully assembled.

*Habemus shredder 🙂 I just finished assembling the shredder and it runs smoothly, so we can call this design a success! Some pictures down below.

Adding some people who might be interested:


i sent the DFX files to a machine shop. they said they were 10 feet long when they treated the measurements as inches, and when they treated the measurements as metric, they said that some of the parts had holes smaller than the width of a  human hair.

I opened the files in fusion 360 with the dimensions treated as inches, and they look fine.

what am I missing?

i’m having the same problem as @nimrodmachine
the dimesions in the DFX files are all messed up

@jeana Don’t trust in the blueprint measurements. I have found that they were probably created and never updated, while the CAD files received multiple updates over the time (For instance, the blueprints will tell that you need 15 knives but only 14 are used in the shredder).

About the Imperial conversion, its not as easy as just using a converter. Metric steel and Imperial steel are different. For instance, you can find 3mm metric steel, but you will never find a 3mm imperial equivalent, the closest is 1/8″ which is 3.175mm. That difference in thickness means that the shredder files (walls, screw holes) had to be resized, not just converted to imperial.

Okay thank you. I’ve read all the info about the conversions and am very impressed and extremely grateful. The strange thing is Knives 1,2,3 are the only ones that don’t have the same dimensions as are listed in the blueprints, even in Dave’s files. The ones in Dave’s files are 84.5mm x 104.38 mm while
the blueprints say 120×120. Every other file except those three knives is spot on. I downloaded Dave’s files back in September so maybe he updated them before September but not the blueprints.

I’ll have to look into the shredder mods forum.

Just FYI, if you have access to CorelDRAW (you can get a free 15-day trial), they open the original files from Dave. And then you can tell it to convert to inches. No math, no fuss 🙂 Just save it as inches and send it to your cutting machine.

Thank you! I’m going to buy steel this week and get to cutting this weekend. Wish me
luck ❤️

Hello @jeana
All size proportions for the shredder Knives were left untouched in the new Imperial design, the only thing I changed is the thickness of the files, but of course you cannot see that on a 2D file 🙂

Just Fyi, the Knives and spacers used here are not the original PP files, I’m using the files redesigned by @keesdeligt where the hex holes are “1 instead of 27mm. You can see his topic at

I’ve taken steps here in San Diego to get this process going – taking a class tomorrow to learn how to plasma cut the parts for the shredder… Many people have told me that laser cutting is better, but I do not at this moment have access to a laser cutter suitable for metal.  People have also informed me it might be wise to farm out the blades… but… well… I quite enjoy learning how to do new things.  Especially because it might inspire some ideas for other future projects.

Wish me luck!
And if there’s anyone in San Diego looking to help build a shredder from scratch, look up @preciousplasticsandiego on Instagram and shoot us a DM (not sure how messaging works on this website).


It is extremely difficult for us to source for materials for machine production here in Ghana.Please we humbly wish to ask if anyone has information about where to source the materials for machine production. Getting to buy from outside the country is way to expensive for use to do as we are just a community based organisation working on promoting environmental sustainability through plastic waste recycling.We are also soliciting for anyone who has used or damaged machine which we can fix and use. Eve of it is outdated, we are greatly willing to accept.@All keep up the good works, as I have been following up on Dave for over 2 years now.

Dear Olivier,
Thanks for the information , It looks grate one . Is this a successful model after trial for PP   ?  what is the out put  size of expected from the shredder ?
Have a good day

@jamesindia there’s a big DOWNLOAD button right above the youtube video, at the beginning of this topic, that will allow you to download the shredder files in Imperial Units. If you want to use metric units, then download the original PP kit.

The above mail is confusing I suppose . I need a successful PP shredder model that works after trial , so that I can do it right at the first time . Any one may give a reply .


I am planning one PP shredder that works after trial . can any one share a move if available ?

Thanks in advance

It was a bit of an issue but I ended up cutting a few extra pieces out of 11 gauge material and mostly moved them around till they fit right. A little annoying but I fully expect to see that kind of issue when converting any file 😊 so not a big deal. Converting anything into rhinocad that isn’t rhino is always a hassle but that’s what our machines run off of.

We are just starting our operation, and we purchased an assembled shredder head on ebay (the cost of laser cutting services here are very expensive). Our unit’s knives/spacers were made with 3/16″ and 1/4″ plate. we have noticed many of the thinner plastics we are working with don’t shear consistently, it seams like lots of plastics wrap around the knives and slide in between the fixed and moving knives.

I did the math on the spacing, sorry for you metric folks my brain works in imperial.

the original design has a 0.0393″-1mm gap between the knives
our American plate has a 0.0625″-1/16″ gap between the knives

Our unit has over 150% of the gap of the metric design do you think this is enough to cause the issues we have been seeing?
please note our head never came with the screen under the shredder and is putting out very course shredded plastic similar to a traditional ribbon paper shredder.

@chicks Awesome
I would suggest uploading it to youtube, and then just put the link here

@xxxolivierxxx it was the imperial format. I was unable to open the original files for some reason but the imperial files worked well enough though I wish I’d been able to reference the originals. I do have video but I’m having a hard time uploading it places because it’s apparently too big. I’ll upload it when I get a chance to fix my file 😊

That’s awesome @chicks, congratulations. Do you have any videos of the shredder you can share?

By the way, did you build your shredder using the Imperial units files from this post, or the metric ones?

Wow, that’s a huge difference in price.
I have learned so many things I will never remember thanks to all of this community’s hard work. 😅

@msnmsk seems like they changed the link or ran out of stock for that item. Here’s an alternative