Shredder modifications – 1″ Hex Hole parts

Finally found some time to update and add some shredder issues, I’ve read in some topics.

For “Oldfashioned” 😉 countries not (yet) working in Metric.
The rotating knifes and spacer, with a 1″ Hex. Hole. Easier to find in some countries I guess.

And to reduce the lasercosts a little, I took a older prototype frame from the shelf, made from Square tube and some flatiron. Worked well and strong enough, but we opted for the lasered version in the end, because it is easier to align and always square.
The ‘older’ version is also easier to change, being it smaller or wider to Fit when 5 and 6 mm sheet is not available. Do the Math Yourself, and adjust the tubelength a little.
On one side You need to close the gap between sieve and frame with piece of sheet, should be no problem.

How do I load this in FreeCAD?

I upgraded my current specs to 1.25 inch aka 32mm hex bar and 1 inch bearings.

M14 grade 8 bolts that have the heads cut off and TIG welded on with lock nuts.


BTW you MUST I can not stress it enough use lock nuts or lock washers and the best grade of bolt you can source/afford


Earlier machines had issues with nuts constantly vibrating loose and one time a loose nut somehow got into the cutting blades from the hopper.




heyy thank you so much for this,

So if i used the blueprints from the precious plastic portal, I cant use a 1″ hex bar? Because I just cut my laser parts, and I see the hole in the  cutting blade is 1 1/16″,

The blue prints ask for a 27mm hex bar, i am confused

What software do you use for the 3d model, to download and thus be able to observe the model?
Did you also want to know what software you use to make the code for laser cutting? since I have aspire 8.0 and I do not know if I can open it in the

Apart from hex rod length and hopper size/mesh length etc. No reason why shredder can’t be made bigger by simply adding more blades. 14 blades needs 200-300Nm to do its job as discussed elsewhere, but I expect only 1 or 2 are ever needing maximum torque at once with this number of blades.
If 14 blades needs 2kW at 70rpm then:
28 blades at 35rpm would also be 2kW and same output rate achievable.
28 blades at 70rpm would be 4kW with double output rate.
Likewise 7 blades at 70rpm would work with a 1kW motor assembly or
7 blades at 35rpm would only need 0.5kW.

Power [kW]=(blade thickness/6mm) * #blades * rpm /490

You are asking for too much buddy @goodandbasic 🙂
In the official Precious Plastic Kit you can find all parts in milimetric steel with 27mm hex holes. If you want to use 1″ hex bar instead then just download the files from this topic and replace the ones in the official PP kit.

If you want to use imperial steel (1/8″, 3/16″ and 1/4″), I made a conversion and can be found HERE. On my conversion, I use 1″ hex holes

I’ve got an idea. Could someone here compile a program that allows the user to drag and drop different sizes of material, numbers of blades, blade type, size of hex bar, box or tube frame, etc, and then have the program spit out the dxf files for the shredder? There seem to be a lot of mixes between metric and imperial sheet steel and the above mentioned options. The program could simply have the models for all the options pre-designed, and then compile them into a single file from the intersection of the factors. The program should be visual drag and drop to make it easy to use, and it could be built into this website. The program should also calculate the combined thickness of the blades and modify the sides of the box or tube frame. Output could be divided into two sets of files, dxfs for cutting and pdfs for the remaining blueprints.

Yeah, thank you for the info. I’ve already calculated that mismatch on the blueprint)

@listva There is are only meant to be 14 moving knives for some reason there is an extra one! and also for fixed one I’m not sure why this.

Hi guys!
Sorry for stupid question, but how many knives are there actually in the shredder?
There are 3 individual .dxf files for 15 moving knives (3 types x5), but in the “overall” .pdf blueprint there are 14 moving knives. The same thing with fixed ones (15 vs 14).
I tryed to find exact answer here on forum, but I couldn’t. On different photos here people has also different number of blades.
Please, could somebody make it clear? Thanks

@dotcom22 The knife are all the same, the lñittle holes are just to help when mounting on the e bar but if you want you can choose and try different settings.

Hello everybody

Please I’m unclear about Knives piece… It seem Knives 1/2/3 have exactly the same dimension/specification except the fact they have 1/2/3 small hole “for help?” when mounting the shredder. Could you confirm please ??

I looked the video but I don’t get well the concept and the use of theses hole and for what exactly is necessary. Is not possible to have 14x of any knives?

Probably a stupid question or I miss something somewhere….

Thank you

i am also looking to design a bigger shredder. how do we upgrade this existing design? and does anyone know the output of the original shredder?

Hi @xxxolivierxxx,

Thanks for the link!

I had originally looked into changing the whole design to imperial units, but decided against it since the replacement of 5mm and 6mm knives and spacers with 3/16 and 1/4 inch would have left a significantly bigger gap, rather than 1mm total (0.5mm on each side), it would have been almost 1.6mm (0.8mm on each side).

I really don’t know what effect this would have, but I assumed that it was designed this way for some reason so I didn’t want to mess with it too much. Maybe the plastic would bend rather than cut and would jam the shredder or something. Anyways, since I went with the 3/16 and 6mm combination, my gap will still be a bit bigger, but less so, around 1.24mm (0.62mm on each side). I’ll let you guys know how it works, and if it’s no big deal then the switch to full imperial might also work.

I also looked at the design you linked, and it seems to have much bigger gaps between blades, with the 1/4 and 3/8 combination they are a full 1/8 inch (more than 3mm, 1.6mm on each side). So if that is a potential issue, then it might be a problem.

If anyone is interested, I would be happy to make and post the dxf files for the switch to 3/16 and 1/4 that I initially proposed, but I won’t be cutting or testing it myself. It will take me a bit of time since I’m still new to CAD software and I do it manually one point at a time, but give me the word and I’ll get right on it.

I had trouble finding a 27mm stainless steel hexagon bar in the various visited ironworks. I found a carbon steel rod in this dimension. I would like to know if it is acceptable to use this bar for machining the hexagonal shaft of the shredder.


I did see that one, but thought it would be nicer to adjust the laser files, to make sure it is perfectly square and aligned. If you do have some time to make some modified DXF’s it would be great, as I still haven’t figured out how to do it myself. I will keep trying though 🙂


I see what you are looking for….
Have you seen the above modification with the boxtube?
That’s a lot easier to adapt different sheet sizes….

Regards Kees

Hi @keesdeligt,

Thanks for the quick response! We would love some on-site help, might need to work together on the funding to get you here, but we’ve got a place for you to stay for sure 😉

The DXF’s would be awesome if you have time to make the changes. I’d also love to learn how to do it myself, do you know any good tutorials for starting out with CAD?

Thanks again, let me know if you need any more details / clarification on the changes.


Hi @tonyman,

Aruba……. Need any help on site ;), this morning the first time to defrost the windscreen :(…
I think I could post some modified dxf’s tomorrow if you want?

regards Kees