Modified (larger) shredder
My name is Wes. I am an engineer with quite a bit of product development experience, and I decided to build the shredder machine. After reviewing the documentation, I decided I wanted something larger (mainly so I could throw in a whole trash bag full of plastic instead of feeding it a few pieces at a time). I basically took the same concept that you could download here, and used my CAD software to re-design and make everything larger. I also did some FEA to confirm the component sizing and ensure nothing is going to break.
This is powered by a 5HP (3-phase) motor and a 22:1 reduction gear box (about 76 RPM). I am using a VFD basically as a phase converter so that the motor can be powered on either single phase or 3 phase (I am using 240V single phase from my house). It turns out that 3-phase motors are a lot cheaper than single phase motors, so it was almost (within $100) the same price to get a 3-phase motor + VFD compared to a single phase motor, plus then all my controls are built into the VFD to keep wiring simple.
Plus, I programmed the VFD so that if it detects an overload, it will reverse the direction for a specified time period (to clear a jam), and then start rotating the opposite direction.
So far, I’ve found a couple things based on my experience. First, I designed the teeth using a 3-bladed tooth, and kept all the teeh the same. I found this doesn’t work very good (because you have so many teeth cutting at the same time), so I will design the teeth with 2 blades so that you can alternate them so only 2 teeth are cutting simultaneously. Secondly, I found that 76 RPM is a little faster than I’d like, as shredded particles tend to get thrown around quite a bit. Third, I found (after subsequent FEA) that my machine can handle a lot more torque than my motor/gearbox was supplying. I plan on getting a higher reduction ratio and keeping the motor HP the same, so I’ll have more torque and slower speed, plus if I wanted to speed it up a little bit the VFD can safely turn up the speed.
See attached images. If anyone would be interested in purchasing a kit, I would be happy to help out. I have some pretty good suppliers for the motor setup and the laser cutting/forming, and everything can fit on a single pallet for easy shipping…
Hi is that stainless steel?
No I decided to use standard A36 steel for this build, just mainly due to cost.
Hey Wess…im curious as to what components of your shredder you modeled using an FEA software. If you still have them would you mind posting some screen shots??
@ramdhan2805 it is a lenze VFD. I ended up with a 10HP drive for 5HP motor based on some simple up-rating.. Since 3 phase power is defined as P=(sqrt 3)*(voltage)*(current)*(PF), and single phase power does not include the (sqrt 3) term, and assuming voltage and PF are nominally the same (safe assumption), you multiply your motor’s FLA by 1.73 to get the full current carrying capacity of the VFD. Pretty much any 3P VFD can do this, so just select whatever one is cheapest and easiest to get for you.
I also like your inline reducers, found those are cheaper and more robust than the angle gearboxes (either helical bevel or worm gear), at the expense of taking up more footprint.
@jonn, I used FEMAP. The only thing I really did was model the teeth and the shaft. Basically I did a fixed constraint on the end attached to the motor, did “rolling constraints” where the bearings sit. Overall it was a pretty basic analysis.
My email address is [email protected] if anyone wants to contact.
Hi @wess! Great work out there, congrats! 😀
Will you be up to give me more info about what made you do something like this and answer some questions? We’d really like to write an article on our community news. Let me know if you are interested and will send you a private message with more detailed info.
Sure. shoot me an email!
I think your 3-blade design might work very well if you offset the blades.
As they are set up now, every blade grips at the same time if you put in a large piece.
Offsetting should put less strain on your motor, and chances are that it will easily churn “anything” you throw at it.
I did try offsetting the blades, and while it did help I still think I have issues with it trying to cut too much at a time. For testing purposes, I think I’m going to cut off one of the blades on the teeth so I can offset them more like how the original design (from here) is done.
I also had a failure of the gearbox. Fortunately the MFG is covering it under warranty, and I’m going to be upgrading it a unit with a lot more torque. My original gearbox had an output of about 4000 in-lb torque @ 75 RPM. I went back and reviewed my FEA results, and I think I can handle up to about 20,000 in-lbs torque. The revised gearbox is going to be around 20 RPM and about 13,000-16,000 in-lbs torque. Also, instead of using a solid shaft coupling, I’m either going to incorporate a torque limiter (clutch) or a belt drive to help reduce shock on the gearbox.
Update to my project. I finally got my bigger gearbox in and I modified the frame. In the pictures the blue one is the old one, orange one is the new one. I increased my torque about 3x (under 3,000 in-lb to over 10,000 in-lb), and reduced the speed from about 75 RPM to 25 RPM.
The new gearbox has a bigger shaft, and I didn’t want to have a new shaft machined (would have been a big redesign). Originally I used a straight coupling, so now I’d need some sort of adapter coupling. After some digging, I found these couplings (many other brands make them). https://www.ibtinc.com/wp-content/uploads/2015/07/Martin-Sprocket-Roller-Chain-Couplings.pdf These are readily available all over the place, and pretty cheap! Basically it’s 2 sprockets, a roller chain and a cover. The chain coupling is pretty forgiving in terms misalignment, and allows you to connect two different size shafts very easily. Nice thing is if I ever change my setup, I will only need 1 coupling sprocket and I’ll be back in business.
First run was with my original blade setup (3 teeth, all identical). Despite the extra torque, it still binds up easily. So I’m going to have new blades manufactured. My machine has 26 teeth in total, so with my current design I have 13 blades trying to cut simultaneously (which obviously requires a huge force). If you feed it slow on one side it cuts, but if you fill the hopper, it binds up easily. New teeth will 3 different blades and only 2 teeth, so now only 4 teeth will be cutting at one time. I think that will make a big difference.
On the underside of my machine I have a 1/4″ mesh. I found that it cut everything the proper size, but the material would tend to stay on the mesh and not fall through. Plus, no matter what I did it seems like this thing always makes a mess. So I’m building a hopper to go underneath it to funnel the material close to the inside, and I’m going to attach a shop vacuum to the underside to draw the material out. I think this will help keep the mesh clean and help reduce the mess. The first image doesn’t show the attachment for the vacuum, I will probably try it without the vacuum first. To add the vacuum attachment, I’ll just weld in a small square piece and a pipe that I can attach a vacuum hose to. I think also in the future, using a rolled wire mesh of the proper size opening would work better than a plate with holes in it.
Below are a couple pictures of my final setup. I will post an update in a few weeks when everything is done being manufactured and I have a chance to put it together.
Hi Wess. This is a fantastic development / improvement. I am looking to obtain prices in the UK for the laser cutting of the cutters/blades etc. Would it be possible to obtain the CAD files so I can send to local workshops for pricing….
I am looking to setup a project with a local college to build the shredder as part of some available Grants to schools in my area under a STEM programme (Science Technology Engineering and Mathletics).
Hello Wess, it is a nice upgrade you are proposing for the original Shredder but as far as i know (maybe i am wrong) a Vector Frequency Inverter is able to compensate for torque at any speed so why are you using gearbox reduction? Eliminating the gearbox entirely is a huge economy for the whole project.
I’ve built the original Shredder and also had problems with the mesh, so i removed it and all chopped material falls flat on a basket, well, almost all of it.
The original design is not as powerful as i wanted but it is good enough for small businesses and residential use.
Anyway, let me know if you notice any improvements with your new design and good luck.
Can u send me the laser files for your machine ,please ?
Just a quick update:
Based on my testing I will need to do a complete redesign of my unit. Originally the gearbox I used was about 75 RPM, which was too fast.. Whenever it would jam it had so much momentum it was very violent. I got a larger gearbox which moved the speed down to about 25 RPM and over doubled the torque, but then it applied so much torque that it sheared the keyway between the shaft and the coupling, so I will need to use a larger shaft with a bigger keyway. So by virtue of needing to change the shaft size, I will need to have completely different teeth, shaft, bearings, which basically means my current unit will need to be scrapped. Additionally, I learned that you want to make the cutting teeth as small of diameter as possible to maximize the force applied on the material.
Sometime in 2018 I am going to design a double-shaft shredder. See attached images (this is a Franklin Miller TM8500, look up their website if curious). This particular unit will work nicely with my 5HP motor and reduction gearbox (if anything, my gearbox might be a little oversized, so less throughput but less likely to jam and handle heavier material)
The PP shredder design works good but it’s easy to overload it. Its a very simple design that is effective. You have to make the teeth larger diameter so it actually grabs the material (compared to a double shaft which grabs the material and forces it toward the center). The larger you make the diameter the easier it is to jam. The double shaft design should be a lot more efficient and really it won’t cost substantially more. My application demands something with a bit more throughput than the PP shredder, hence my original redesign.
I have a feeling (but have no data to support this) that even doing a smaller shredder with a double shaft configuration (similar size to the PP shredder), it may not end up costing a much more because it’s more efficient you could run a smaller gearbox and motor, which is a very substantial portion of the cost.
I like those blades. They look mean!
Please how can I get a VFD and overload detector?
If you were to produce for me how much can it cost?
What capacity of load can it take per hour?
Hey this looks great I look forward to seeing your next update!
Great ideas! Looking forward to hearing about your 2018 updates!
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