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Shredder converted to Imperial system (Inches)

This topic contains 87 replies, has 24 voices, and was last updated by  henry 5 months 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.

87 replies
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29/05/2018 at 20:33

That’s what I mean, it is sized at 25.4 inches. It isn’t converted to inches.

29/05/2018 at 20:07

Thanks, I got them.
I’m not sure what happened, maybe a glitch in autocad, but the prints are dimensioned oddly. For example, the hex hole is measuring 25.4″ when it should be 1″. It seems like the computer just switched mm with inches in the print instead of converting the numbers.

17/05/2018 at 05:43

Hey All,
I am looking for work as a machine builder.
I have a new shop and have space to build.
I am already working on some wind energy and recycling equipment for a recycling company I am a partner overseas.
I have more than 25yrs of manufacturing experience including design, prototyping, production and commissioning equipment. I have a good deal of experience with electrical and hydraulics systems.
I am going to start this project in my own shop first to get a good handle on the details. I have 10 yrs of SolidWorks 3D cad experience.
I am located in Edmonton, Alberta..
Looking forward to following along with this group and learning more..

04/05/2018 at 03:00

Hey @xxxolivierxxx, I’m not sure if this is easy to check, but do you know if these files are any different from the ones posted in this thread: https://davehakkens.nl/community/forums/topic/plans-in-standard-units-not-metric/ ? I’ve had people asking me for the imperial unit design and sharing those files but now I feel like I need to send them two links. Did you make any changes besides to the parts determining the overall width of the shredder, and the interlocking corners in the frame?

01/05/2018 at 23:54

You’re welcome @kidtasticplastic

Fyi, Justin Carven is selling assembled shredder kits in USA in case you are interested, you can find him here https://www.facebook.com/groups/293443417731185/?ref=group_header

01/05/2018 at 20:33

Thanks @xxxolivierxxx

I’m SO excited to begin my project!

17/04/2018 at 06:09

@yukonelius I’m sorry to dissapoint you my friend, but you are wasting your time. Your motoreducer will give you 48.11 minus efficiency loss, and that will has troubles even shredding veggies. If you don’t believe me, then watch for yourself, this is a 63N.m motor:

17/04/2018 at 01:49

Thanks so much for these. I have my material on order and will probably start to cut out the parts this week. I was able to source a motor and gear box (all the calculators say it’s under sized) but I’m hoping that I can make it work by pre-cutting out sections I know will be difficult.

Once I get some parts being made I will be sure to upload some pictures.

Thanks for converting them!

11/04/2018 at 00:03

That gives me a better idea, thank you very much!

10/04/2018 at 18:52

Sorry, I am referring to the length and width. I have a machine to use, but it’s owner is… prickly and won’t do the nesting prior to purchasing to tell me what size of material to order, and I have been struggling with nesting the parts to figure out what size I will need.


17/03/2018 at 06:11

Final result

05/02/2018 at 22:49

@xxxolivierxxx This is great! Awesome work on doing this. It really needed to be done. The lack of metric steel in North America really adds a large cost to those trying to start out, so this should really, really help!

04/02/2018 at 17:30

If you’re using imperial (which by the way should be erased from the face of the earth :P) then keep it consistent and use the hex shaft and any other dimensions in imperial, not mm. i.e, the bearings could be imperial too (3/4″?) instead of 20 mm.

If you can export the 3d files to .stp or .iges, they are more standard file types so that other people can open the design
There are some interferences between the sideplates, something not aligned correctly, there’s a difference of 0.1 mm between the tabs (see picture)

did a 2D drawing of the shaft as it is but may need some revision. As standard I’d machine it with a keyseat for a key, a plain coupling will slip.
see drawing attached or download pdf here:

good work !! thanks for sharing olivier

14/12/2019 at 23:35

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?

10/12/2019 at 23:25

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

25/11/2019 at 17:20

@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.

25/11/2019 at 17:12

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 ❤️

25/11/2019 at 03:25

I’m confused about a couple of things with the posts here… Someone posted that they sent the CAD files to be cut with the price points for each piece.

Knife 1 = is 3.89″ x 3.89″
Knife 2 = 2.76″ x 4.36″
Knife 3 = 2.89″ x 4.72″

This is confusing to me because the original blueprints say that Knifes 1, 2, and 3  are all 120mmx120mm, which implies they are square.

I figured when olivier did the original conversions, maybe he didn’t keep them square.  That’s fine.

The extra confusing part now is when I import the Knife 2 drawing, for example, for some reason the original size is 84.5″ x 104.431″… and when I keep the image proportional, then change the width to 2.76″, the automatic height becomes 3.397″.  I am wondering where conversion came from to A) no longer be a square, and to B) be so far off from the stated 4.36″?

Thank you in advance for any explanation on this.  I just learned how to cut metal and was going to start officially cutting the pieces, but then this really stumped me.

20/11/2019 at 00:58

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).


13/09/2019 at 03:41

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 [email protected] keep up the good works, as I have been following up on Dave for over 2 years now.

08/08/2019 at 11:41

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

08/08/2019 at 09:28

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 .


08/08/2019 at 09:08

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

Thanks in advance

17/06/2019 at 00:06

I am not sure what you mean buy using 11 gauge sheets, this is a factor of 1/4″ plate is a bit bigger than 6mm and 3/16″ plate being a bit smaller than 5mm plate. Our shredder head is sturdy we can shake the knives side to side a tiny amount but that is the only slop in the system.

By the way we are using a 3/4hp 1140rpm with a 39-1 gearbox 29rpm output/1617inch pounds and a chain coupling which seems to work fine. We tried a half coupling with a spider like your unit, but it crushed the rubber spider in seconds. Found out it was only rated for 120 inch pounds.

16/06/2019 at 04:42

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.

24/05/2019 at 20:13

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

24/05/2019 at 19:43

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?

30/04/2019 at 07:44

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. 😅

30/04/2019 at 07:32

So I was actually reading through the thread just now and wanted to point something out

You can buy the sheets of steel in many places, but my favourite is Online metalsSome 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#

The “Stainless Steel” link leads to an aluminum extruded thingy.
Thanks for all of the info regardless.

17/04/2019 at 09:52

That’s useful information. Thank you. I just remember the official assembly video saying something about less welding and mentioning the sieve.  I would kind of like the convenience involved with an easily removable sieve but eh 🤷‍♂️

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