Shredder build guide (for experts)

After building and fixing a dozen of shredders, it’s time to share our observations for the v3 precious plastic shredder. This guide is intended for machine builders with good equipment and we are aiming to get the max. precision, rigidity and durability out of this design. It’s important to make it precise as possible. Only with a well assembled shredder and the modifications below you can increase motor power and thus you’re able shred PET bottles or thicker HDPE or shampoo bottles with not much wear out or damage. Please note that details and order of the process have a great impact on the entire assembly and quality of the shredder. You also save lots of time that way. 



Good welder, a TIG welder gives best results.

Good measurement tools : 

The height gauge makes a big difference when layouting the shredder box mounts but also to measure errors as on the hex-bar. Please also use a machinist level. 

Before you start

  • please grind everything, it’s important. If you see any bur anywhere, remove it ! If you don’t there will be lots of friction. The shredder drive shaft has to spin freely with no friction anywhere at all. 

Changes in design

Hex bar

to guarantee best results regarding rigidity and durability we strongly recommend to use 32 mm hexbar and a 30 mm drive shaft. The motor drive shaft should be also at least 30 mm. Please see below the difference. There are reports about broken driveshafts and it’s no surprise looking at this cute 20 mm bar. 


with a bigger drive shaft of 30 mm we also need bigger bearings (UFCL206) : 

The needed changes in the CAD and laser files are in the ‘Resources’ section.

The hex bar

the best results and accuracy can be archived with an adjustable 4 jaw chuck. A good 3 jaw chuck can do too but please consider 0.5 mm + run out as useless.


Please dial in the hex bar as best you can ! Any run out will create wobble and vibrations. 

If you purchased the hex bar, please measure the run-out with the height gauge, send it back if there is a run out of 0.5 mm on each end.

The hex section should be slightly smaller than the shredder box with (149 mm), 148.2 mm is a good fit. It prevents that the hexbar’s edges collide against the side plates. This is important !

What’s also important : the drive shaft / coupling side should be as short as possible ! The other side too for security reasons but please consider also that you could use the other side to run another actuator as the extrusion !

The hex bar – sleeves

with a bigger hex-bar we need also to modify the washers/spacers for the hex-bar. Currently custom sleeves with a width of 16.75 mm are a perfect match, also considering the new space to the bearings. The sleeves help us also align the shaft in the chamber as well it provides extra security. Please consider to use or create bushings.



The sieve

This component can be troublesome ! There are reports that the sieve got entirely pulled into the shredder due to bad welding or the sieve is just too close to the blades. With the current design it is best : 

  • max. 1.5 mm thickness
  • good weld and finish up with a grinder
  • do a complete test that the clearance between sieve and blade is at least 1.8 mm
  • do even more tests with smaller and bigger chunks of plastic that the sieve doesn’t bend

The shredder chamber / enclosure and side plates

To have no damages and ease also machining, we recommend to use steel. It’s more forgiving material than stainless, especially when it comes to welding. 

The housing

It’s important you grinded all bur off. Make sure that the 3mm fit really really well together. If not, it can push the side plates out of square. 

After you made sure it’s fitting well together, please pre-assemble the shredder box and tie it up with bolts and then weld. Don’t weld it together on the table, there is lots space for errors. Make sure you clamp everything in away that you maintain squareness of the entire shredder box when welding the 3mm sheets in place. After you tagged the sheets together, de-assemble it again and continue welding wherever you can. It’s also important to weld the outer corners . Again, please use steel and a TIG welder, make sure you go slow and nothing deforms !

The side plates

Also here, best results can be archived with a TIG welder and steel. The updated CAD/Laser files are in the resource section. It’s important to weld the side plates first on a metal plate before you weld the bearing support mount blocks on it. If you weld this too strong, it easily bends the whole plate. 

The bearing support blocks are  pre -drilled before welding and they are 6 x 4 x 1 cm with a M10 (M12 is better) thread which also goes through the side plates.

The shredder mount blocks

Please don’t use angle brackets or tubings to hold the shredder in place. It’s bending easily and will cause coupling wear out and all sort of distortions and skewing. The best results we have archived so far was with solid steel blocks of 10 mm thickness. We also recommend to mount motor and shredder box on one solid metal plate of at least 15 mm thickness. 

This is the moment where you should test the shredder chamber for squareness. Please make sure that the 3mm boxes didn’t push the side plates. Please tie up everything to simulate the final stage. If you see mis-alignment of over 0.5 mm, please re-do the parts ! 

After everything looks and feels good, it’s time to align the shredder to the motor to drive shaft. It’s important that you do this with no blades inside the shredder.  

Our little machinist jacks help us to align the shredder to the motor. At this point make sure it’s the shaft (hexbar) you align to the motor and not the shredder box only. Use a height gauge to maintain also all other planes to each other.

We use a real machinist level which gives much more accuracy.

After you have everything perfectly aligned, please weld now the mounts on the plate. Do this with the bolts only slightly tied up. If you tie them up to strong, you may have it hard to get the shredder out. 

Please note : do not use ACME rods to hold the 3mm boxes in place. That will cause skewing of the box as well.

To be continued

  • shredder testing and fixing
  • shredder blade grinding
  • wiring & grounding
  • 3 phase & inverter ( over-torque and auto-reverse )
  • motor mounts
  • the hopper