Someone know the WHY of the design of the shredder

I have the idea of making a project about the shredder machine, but I have to fully understand the WHY of every part of it. Being more specific, I want to know the considerations that had to be taken into account when Precious plastic make the blades, the shaft and the separators of the blades… Things like why they choose that length of the shaft and how that affects the behavior of the machine if is longer or shorter, how the curvature of the blades that they choose affect the shredding of the plastic, and so on…

I’m trying to understand these considerations to maybe think in a way to change the design a little, I’m not an expert in this area, but I want to learn how a design engineer would think when he saw this machine and what would go through his mind to change something. Maybe someone with more experience and knowledge about this can give me a hand?, I’m from Venezuela and I’m looking a way to make this machine cheaper to be built here… How I can start???

I would appreciate that if anyone knows how any consideration of design affects the behavior of the machine, leave it in this post no matter how small the contribution can be. I want to learn as much as I can about the design of this machine, not just see the video of how it is built and understand it. Any calculation needed to the design process, or maybe a step by step method to redesign the machine in according to the needs that I have can be useful. (I already see the post about “calculations needed to the shredding machine but I end up with more doubts than answers, in fact, the questions that I have about this topic are still there, If anyone could answer any of them, I’d appreciate it, too.)




i think there wasn’t much thinking or classical engineering per-se, it just turned out to work better than the other trials, the rest, well … that’s how a design student would do things though 🙂

So if I’d be you,
– just copy the blade design (with customizations)
– find a cheaper way than that hexbar approach, ie: just bolt blades together and weld it on a cylinder
– get rid of the 3mm fancy side plates, they just look nice but that’s it. build the housing from simple steel plates, min. 6mm thickness
– to get around the bearings blocks, you can harvest big bearings from old motors, just find a way make them sit on the side plates

no big deal if you’re patient; have a simple stick welder, an angle grinder (with lots of discs) and a drill press as well a bench grinder. that is what you need first in any way, no matter the design. once you’ve done some stuff, things come by self …

apologize my ignorance but I strongly believe that certain individuals are able to make a fe** car with a welder and angle grinder alone 🙂

2. alternative shredder
hopefully help 🙂

but, there are more alternatives i’ve collected from forums like …
1. shredder blade
2. alternative shredder

1. shredder blade

hi @thefranky
i’ve read your post, something about looking a way to make this machine cheaper to be built, i’m still new here but very happy knowing that so many people interested in recycling 😀
i agree that cost can be annoying problem, but i suggest to not forget about effectiveness.  I would recommend join group order. in my country, join group order can lower shredder kit cost up to more than 50%. you can see in here…

problem was rather that the author has little means and/or ways to get those to Venezuela… apparently there problems with the bazar, we had similar problems with other projects getting money in and out of brazil …

and yes, if patient and a better drill press you could do all blades (but not side plates) in a day, followed by another day of filing and grinding. i made for fun one blade in 20 minutes, til finish, accurate 🙂

130 is indeed a great price, we pay 360 here in Catalonia but top notch quality.

Group orders per continent would be great, if we could organize this our own on the main page (visibility is key here), in all languages needed, with a speedy server which could work with average 2G-3G, this could be definitely a big win for PP, more people getting active = more people invent = more people find a way to pay the bills, we’re just at the feet of a huge mountain though 🙂 having a kinda guaranteed sheet thickness would also help tackle the current shredder issues, requiring quite some time to tackle and fix during the assembly.

Hi guys.

Just a simple question for those, whi have tried this method to create blades with drilling. Is it really that cost, time effective ?

Because its requiring lot of drilling, brushing , and the precision will go down probably also.

Just asking.

Maybe group order of laser cutted parts like 10-15 sets at once could solve this.

With this solution a bought (thanks to Katharina from Germany, currently working on Flip Flopi project) all laser cutted parts for 130 euros (shipping incluced ) from German company to Slovakia.

Cheers, Martin

btw, what always helps – especially when on a budget – is to visit agriculture, technical and even math museums. there is always something to gain there. we often stop by old mills somewhere in pampa… in the library there is also tons of stuff, i am not sure it exists in your country, but we have here a 5 band ‘technical encyclopedia’ in germany, basically going from stonage to now, very detailed, takes 6 months to read, enjoy 🙂

if you have some hippy camps around, give them a visit, they usually harvest meters of DIY and technical books. these guys are also helpful to get general direction, contacts, help, etc…

@thefranky your profile says you are a mechanical engineering student. Do you have access to a machine shop at school?

hey there,
@s2019 is right, if you can’t get at least hands on a old but good drill press (please find an machine auction place, not the shopping malls!!), welder (try to get a cheaper MIG welder) and some power & hand tools, this won’t work.

hexbar: with this technique you could basically do anything you like; if you’re patient 🙂 hexbar is great and traditional because of the amount of contact points which prevents wear out. you could also make a square, no worry 🙂

we’re currently looking for a way to make couplings but as you’ve seen in the other article today, there are often classic parts in the agriculture you could use, farmers are often your best friends btw., they hack the sh** out of stuff, you can’t imagine what this guys get done 🙂

for the transmission, I’d also opt for pulley and belt (2 drives), you need at least 7 cm contact around the pulley, more likely 2 belts. for the motor, I’d checkout @btmetz on facebook or his posts here in the forum. he has done a gas driven shredder. otherwise, If you’re lucky to harvest motor bikes, there are sprockets and chains.

i hope you started putting enough $$ on the side, in either way, it’s eating your wallet quickly 🙂

@thefranky, @pporg has given you some great ideas for fabricating the blades . It may help if you can list the specific tools and resources that you have available to you at a reasonable cost. Then the modifications can be directed towards your capabilities.

WOW, I see what you mean now. So, that method doesn’t really need the laser, thanks!!!, but I have still some questions in mind, how I can start to think in customization of the blades? , and can you explain to me better the idea that you give me about changing the hexbar design?? You can see my comment above 🙂

ahm, little update for step 5. : don’t polish all the outer edges. I think this little triangles will be of benefit and may avoid plastic from slipping away as it does in version 3.0 🙂 The tip however should be sharpened as any other cutting tool, there are some angles to be applied. I will illustrate this later on the website.

here the rest of the pictures

hey there,
here the first low cost shredder build variant.
needed :
welder, drill press, angle grinder, bench grinder (to sharpen drills)

1. make a template of the blade, the first can be from wood
2. weld the template on a metal sheet
3. now drill holes along the edges of your template, per blade this makes around 10 – 15 minutes only
4. if you managed to drill the holes near each other, it should be easy to kick out the blade from the sheet.
5. use a bench grinder or angle grinder to sharpen and polish up the edges of your blades

I am continuing this tutorial on our website later this days, also covering motor and pulley-belt system.

I will be waiting for you. 🙂

hey, I am back to you tomorrow 🙂
all this hard to explain to someone who never hacked some stuff together with a welder 🙂

pporg, thanks for your answer again. I have some doubts about your reply:
1._ How I can start to think in customization of that blades??
2._  Can you explain to me a little better the idea about the hexbar ?? You’re trying to say me that I can think in a design where I screw the blades to the shaft and then weld them? (I don’t understand you here so well because of my English level, so I have to make sure that the idea that I caught is correct) How is that approach cheaper?