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Shredder converted to Imperial system (Inches)

This topic contains 87 replies, has 24 voices, and was last updated by  henry 1 year ago.

Olivier xxxolivierxxx

Shredder converted to Imperial system (Inches)

04/02/2018 at 02:08

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 https://goo.gl/7Bg2WP

*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.

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04/02/2018 at 04:56

Adding some people who might be interested:


10/04/2018 at 19:02

@dixon Ah, I see.
If it helps, this is the amount of material I was asked to provide by my local water jet company:

1/8″ = 250 x 700mm sheet
3/16″ = 500 x 700mm sheet
1/4″ = 480 x 500mm sheet

In the pictures below you can make yourself a better idea of how to arrange the parts:

05/03/2018 at 07:43


24/05/2019 at 13:03

After many hours of machining/sanding/design tweaking (I learned a lot of things making this for class) I finally have my fully functional plastic grinder ready to go and help break down usable material for my thesis. Much thanks to this community I wouldn’t have been able to do it without your help. As a side note: yes that dress is made out of recycled upholstery fabric AND the grinder also shreds fugitive rubber from old molds like a dream (although its a bit fleshy when it comes out…).

05/03/2018 at 06:55

Some pics

07/08/2018 at 00:11

@ewanenj yes, mild steel rusts. But this is not rotting-type-rust, is more like thin rust stains that you can clean even with your bare hand. I keep my mild-steel shredders coated with a few sprays of WD40 and it protects the steel agains rusts pretty good. When the shredder is working the friction between the metal knives and the plastic actually helps to polish them and keeps them clean from rust.

05/03/2018 at 07:55


05/03/2018 at 07:46


25/11/2019 at 16:27

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 http://onearmy.world/community/forums/topic/shredder-modifications/

08/08/2019 at 09:30

@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.

30/04/2019 at 07:40

@msnmsk seems like they changed the link or ran out of stock for that item. Here’s an alternative https://www.onlinemetals.com/en/search/results?q=stainless+steel+sheet+0.125%22%3Arelevance%3AMaterial%3AStainless%3AShape%3ASheet&checkbox=on#

17/04/2019 at 09:17

@msnmck all these shredder versions are the same thing, the only difference is that the newest version has a square hopper instead of a piramidal one, and an easier to remove mesh filter. The base of the shredder box is the same in 2.0/2.1/3.0 so you can use these files without any fear

26/01/2019 at 08:46

Hello @superhhapychris

5/16″ is a typo, I just made the correction. The correct thickness is 3/16″

When I say “black steel” I actually mean “mild steel”. In Costa Rica we call this type of steel “Hierro negro” which literaly translates to “Black Steel”. I learned later that the correct name is mild and not black.

You can buy the sheets of steel in many places, but my favourite is Online metals
Some examples:
Mild: https://www.onlinemetals.com/merchant.cfm?pid=13973&step=4&id=944
Stainless: https://www.onlinemetals.com/merchant.cfm?pid=9806&step=4&id=793#

03/10/2018 at 23:48

First of thank you for this informative thread and for the converted files.

I am spearheading a PP initiative at my university in the US and they have agreed to fund the shredder and injector with more possible upon completion. I’m studying orthotics and prosthetics and the program throws away a few pounds of raw clean plastic a day. So i figured this would be a good way to try and find other uses for the waste, and possible injection mold prosthetic components to bring to developing nations (thats why its funded).

My question is on whether or not having an imperial machine will limit future upgrades or fixes. This machine will get a lot of use so using inches (while unfortunate) will allow for replacements and easier sourcing. Is there any risk of stagnation due to the sizing difference or will the community find a way?

29/05/2018 at 18:17

@nimrodmachine Link below:

It can be found right above the youtube video, in a link called “DOWNLOAD”

28/04/2018 at 18:27

Hey there. I got the info from this post to share with the printer I found.
This is what they gave me for the quote:

1Side Plate – 8.27” x 5.31” – Plus .25” 304 Stainless Steel – Laser Cut: $33.25 ea – X 1

2Bearing Spacer – 1.35” OD .8” ID – Plus .25” 304 Stainless Steel – Laser Cut: $5.50 ea – X 1

3Knife Spacer – 1.97”OD – Plus .25” 304 Stainless Steel – Laser Cut: $7.50 ea – X 1

4FixedKnife Small – 5.2” x .96” – Plus .25” 304 Stainless Steel – Laser Cut: $9.25 ea – X 1

5Knife 1 – 3.89” x 3.89” – Plus .1875” 304 Stainless Steel – Laser Cut: $10.50 ea – X 1

6Knife 2 – 2.76” x 4.36” – Plus .1875” 304 Stainless Steel – Laser Cut: $11.25 ea – X 1

7Knife 3 – 2.89” x 4.72” – Plus .1875” 304 Stainless Steel – Laser Cut: $11.25 ea – X 1

8FixedKnife Big – 2.14” x 5.2” – Plus .1875” 304 Stainless Steel – Laser Cut: $6.75 ea – X 1

9Bearing Spacer – 1.59” OD .88”ID – Plus 11 ga 304 Stainless Steel – Laser Cut: $2.75 ea – X 1

10Sieve Bracket – 4.77” x 2.00” – Plus 11 ga 304 Stainless Steel – Laser Cut: $6.00 ea – X 1

11Side – 5.32” x 1.18” – Plus 11 ga 304 Stainless Steel – Laser Cut: $6.50 ea – X 1

12Bottom – 1.30” x 5.87” – Plus 11 ga 304 Stainless Steel – Laser Cut: $9.75 ea – X 1

13Top – 1.18” x 5.87” – Plus 11 ga 304 Stainless Steel – Laser Cut: $6.50 ea – X 1

14Middle – 6.34” x 5.31” – Plus 11 ga 304 Stainless Steel – Laser Cut: $13.25 ea – X 1

15Side – 5.32” x 1.61” – Plus 11 ga 304 Stainless Steel – Laser Cut: $8.00 ea – X 1

16Bottom2 – 1.61” x 5.87” – Plus 11 ga 304 Stainless Steel – Laser Cut: $8.25 ea – X 1

17Top2 – 1.61” x 5.87” – Plus 11 ga 304 Stainless Steel – Laser Cut: $8.00 ea – X 1

Will these work in order to fit well with other pieces and designs? This is my first job with a laser cutter, and first step into Precious Plastic work.
I’d love some reassurance that they will work out okay.


30/03/2018 at 20:13

Would someone please send me or direct me to any prints to make the shredder in standard English units? I found the CAD, thank you!

I’m working with a possible machine builder in the midwest, I’ll post something once we identify lowest cost options.

17/03/2018 at 06:34


13/02/2018 at 01:09

@lukeryberg25 All that info is on the main post. The hex bar has to be 1″ (original design used 27mm) and then it is up to you if you want to mill the ends of the bar to a 20mm diameter or 3/4″. I included bearing spacer files for both sizes so you can use the ones you prefer. For the motor, you just need to find one with a minimum of 300n.m (around 1.5kw)

10/02/2018 at 00:05

What motor did you use to attach to this imperial shredder? Would That cause issues with the hex rod not fitting?

09/02/2018 at 17:28

Awesome! Keep us posted on how those turn out. Continuous improvement makes the PP program more and more accessible, which is awesome.

05/02/2018 at 10:32

Thanks a lot for checking the files @javierrivera, I really appreciate it.
After spending a while trying to find out what was wrong, I discovered that 2 pieces where off by 0.007″ and that was causing that the parts could not fit correctly. Also, some constraints were set incorrectly.
I just fixed the problems and uploaded the files again 🙂

Your suggestion of using 3/4″ instead of 20mm for the shaft bore makes sense, I included an additional hex shaft design and 1/8″ spacer for both 3/4″ and 20mm bores. I just want to make sure that if someone already purchased ucfl204 bearings with a 20mm bore or if someone already got their hex bar machined, they will still be able to use these files without having to get another set of bearings or another hex bar.

I’m not familiar with cad formats and don’t know which ones are more common than others, but following your suggestion I included .stp and .igs CAD assembly files as well.


16/06/2019 at 04:51

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.

24/05/2019 at 20:00

@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 😊

24/05/2019 at 13:05

One of the techs made me lock out the machine because people can’t seem to stop putting their fingers near the blades… … …

20/01/2019 at 04:08


hi Charlie    here an example of a PDF with standard measurements i did scale 1 to 1 so if  you  print  this pdf in a regular  printer will be real size (make sure  go to the printer setting  and  check is in 100% scale)

this is  only the  blade  number 1 that  you  need to cut 5 of them  … if  you are still in Barriles BCS mexico .. i can send you a EPS file you can take the EPS file  to somebody that have a vinyl plotter .. i know a guy  who makes stickers in La Paz  …if you think that would help

please  tell me  if  this is what  you  need  and  i will continue  to export all the CAD files to PDF and  EPS  …

cheers  from  vallarta .. i will be at  la Paz   by  May, hope  i will saw you  machine done  by  then  … i sent the  files to a company here at Guadalajara  they have a waterjet ..but just ask  for  estimate hope  will be a good  price  .. i ll keep post ..

17/01/2019 at 20:29

Ok, lemme rephrase that. Can someone please share these in a .pdf format as I do not have the programs or knowhow needed to open and export each file. Sorry for my obvious ineptitude and thank you for your help!


17/01/2019 at 20:02

Yes, that’s possible. You can open the files in Autodesk Inventor or Autocad and export each file to a PDF.

20/07/2018 at 23:33

@unratonloco yes, it is needed. That small knife is designed to hold plastic when the rotating knive is cutting. If you remove it, the rotating knive will just push the plastic through that slot, instead of shredding it.

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