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# Will it shred??

This topic contains 30 replies, has 19 voices, and was last updated by  Stan 1 year ago.

4

The questions often come up, “will this motor work?” “How many rpm do I need, how much power?”

There are several other threads about finding suitable motors and gearboxes
In truth there is no single answer to these questions and it can be quite bewildering to anybody not familiar with building machines.

I have created an Excel calculator into which you just enter as much information as you can, motor power, speed, gear ratio etc. and it tells you how likely the combination is to work, and gives advice on how to improve it. If you don’t know all the parameters it can calculate them from ones you do know. (Just type the numbers you know in the green boxes)

You probably don’t need to use this if you have a degree in mechanical engineering, but hopefully it will provide answers if you don’t know where to start.

I’ve based this on real world measurements taken by @timslab (thanks Tim) and also other people’s experiences in the ‘Share your Shredder motor experience’ thread. If you have built a shredder and can enter your parameters and the calculator gives a wildly different result, please let me know.

###### Attachments:
1. Will-it-shred-v1.xlsx
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### In reply to: Will it shred??

warrior
12/12/2017 at 21:13
10

(download the spreadsheet using the link at the bottom, Will-it-shred-v1.xlsx)

### In reply to: Will it shred??

starter
13/12/2017 at 10:36
6

Wow! THANKS for the hard work! I stayed up light into the night watching videos on youtube about basic motor design, and functions. I learned how to read the label plate! Well, at least I have a much better idea. Hopefully, I can figure this out.:)

### In reply to: Will it shred??

helper
14/12/2017 at 16:27
4

Great work!

### In reply to: Will it shred??

new
14/12/2017 at 17:12
4

Good work

### In reply to: Will it shred??

dedicated
14/12/2017 at 21:35
3

I have a question : the plastic’s type, thickness and flexibility affect the ability of a motor to shred it, don’t they ? If so, it would be interesting to know what thickness for what material you could put in a shredder made from the V3 blueprints.

Will it shred ? the answer might be in both shredder characteristics (speed + torque) and material properties (thickness, hardness, etc …)

I think the current shredder design is limited in plastic thickness because of the diameter of the blade, the larger it is, the bigger the stress zone, the better it can capture plastics, an then more force or less speed would be required to provide the same torque… We can’t get a clear idea unless somebody checks this in practice or has enough knowledge in this field 🙂

Can anyone who has a working shredder try and explore the limits of these parameters to enrich our open source knowledge database ?

### In reply to: Will it shred??

warrior
15/12/2017 at 10:38
5

Hi @armbouhali
Yes, yes and yes, all three matter! Unfortunately it is impossible to post such information about the maximum thickness per material etc. because there are too much variables playing a very big part here…

some of th variables:
material group (PP, HDPE, PS,…), thickness, bigger structure of the material to shred (sphere, bar, block,…), other objects shredded the same time (needs some force of the motor too), motor power, speed, material of the blades, exact position of the material relative to the blades, sharpness of the blades, additives of the plastic (can vary the properties a lot!), level of efficiency of your motor,…
to name only a few :’D

So yes, it would be nice to have a sheet saying e.g. if you have that torque you can shred PP up to 6mm, etc, but it is just too complex of a system with too much variations to simplify it like that.

The only thing I can tell you: My motor (2,2kW, 56 rpm, 280Nm) got stuck at a 24*24*70mm injected PP block. Everything well below a constant thickness of 10mm should work with that configuration of mine but as I said, it’s not that easy to generalize.

I hope that helps anyways,
all the best
Flo

### In reply to: Will it shred??

helper
15/12/2017 at 11:38
3

That right there is an inredible piece of work. thanks so much!

### In reply to: Will it shred??

helper
19/12/2017 at 07:49
3

found this motor and according to the calculator its looking superior, just posting here for anyone else looking.

If anyone sees any issue with this motor choice let me know

### In reply to: Will it shred??

warrior
19/12/2017 at 13:54
5

Yes, that looks like a good motor @willyk. Though it’s important to note that the rating given by the calculator depends on the gearing ratio as well (which you have set to 50:1).

### In reply to: Will it shred??

helper
19/12/2017 at 14:06
4

yeah i have went for the flanged version of the motor with the same spec for the worm gear.

### In reply to: Will it shred??

hero
19/12/2017 at 19:21
4

This is great, thanks @andyn
Something that would be useful to add in the future is another field to enter the worm gear efficiency. Most reducers I have seen are around 90%-95% efficient.

Regards

### In reply to: Will it shred??

warrior
19/12/2017 at 20:32
3

@xxxolivierxxx There actually is a field for that, but it’s hidden, I thought it best to keep it simple. I’ve set the efficiency to 75%, a little on the conservative side perhaps, but that’s better than giving an overoptimistic result which might not pan out in reality.

90% efficiency is quite high for a worm reduction, and also as the ratio goes up the efficiency goes down, you could probably only get that with a very low ratio, not between 20 and 50:1 that most people are using. You might get 90%+ using all spur gears, or a 2 stage planetary, and still get down to the right ratio. But as you know, worm reductions are by far the most common.

### In reply to: Will it shred??

dedicated
20/12/2017 at 10:54
3

Hey @andyn Thanks for providing the community with such a handy tool thanks for your hard work we need more of this stuff

### In reply to: Will it shred??

helper
20/12/2017 at 23:45
0

it all depends on the cross section of cut.

### In reply to: Will it shred??

starter
22/12/2017 at 03:09
2

Great timing, i had a feeling some bright spark would have utilised Excel for this purpose! Many thanks to andyn and everyone contributing data and experiences to the forums.

### In reply to: Will it shred??

warrior
23/12/2017 at 11:14
1

Awesome work @andyn! This is a very very useful tool.. perhaps even deserves a space in the main download kit

### In reply to: Will it shred??

new
07/01/2018 at 14:51
1

Hi Andyn,

Will your calculator work for both monophase
7 triphase or only for triphase?

Thks!

### In reply to: Will it shred??

warrior
07/01/2018 at 16:47
1

@gxxm

Both single and 3-phase. It’s the speed and power of the motor that are important. If you don’t know these enter as much as you can in the other boxes and it may still be able to calculate a result.

### In reply to: Will it shred??

dedicated
03/08/2018 at 05:54
0

you can find designing-bigger-shredder topic here

### In reply to: Will it shred??

helper
15/05/2019 at 18:27
1

I have just gotten round to thanking you for this tool!

We used it in the very beginning when looking at shredder motors, we finally settled on a 2.2kw 4 pole single phase with a 25:1 reduction after consulting our supplier and your handy dandy xcel tool.

Great job, great tool! Thank you

### In reply to: Will it shred??

starter
22/05/2019 at 05:54
1

Man, this thread and this tool just saved me in more ways than one.  I was just looking at what I thought was a great deal on a “5 HP” motor (“3.72 kw”), but at 320 RPM.  If that was accurate I would have to have a 4:1 reduction ratio in order to shred anything without damage to the equipment.  Something about it seemed off, though, so I left “power” fields blank, and sure enough, it was a sham.  It’s not “5 HP;” it’s .5 HP (a mere 0.372 kw) just as you can barely see in the listing image.

I can’t thank you enough for all of this information, @andyn!

### In reply to: Will it shred??

warrior
22/05/2019 at 12:20
1

No Problem, thanks for bumping this thread, the calculator is quite buried in the forum and a lot of people might not have seen it.

### In reply to: Will it shred??

starter
22/05/2019 at 14:26
0

@here, @andyn, i linked it within the library.

### In reply to: Will it shred??

starter
31/05/2019 at 01:29
0

Spent all this time looking for affordable motors locally and online and it turns out my stepfather has two broken air compressors, each with a functional 5HP motor.  Now I’ve just got to hope we can figure something out for a proper speed reduction.  He thinks he can build a pulley system but I’m also looking into gearboxes.  IDK, but at least I’m finally moving forward.

### In reply to: Will it shred??

warrior
31/05/2019 at 04:36
1

120V/15A isn’t 5hp but worth trying.

### In reply to: Will it shred??

starter
31/05/2019 at 07:19
0

The weird thing is that two of these say 5 HP and one says 5.5 HP but they all have the same info on the panel.  Still turns out decent on the calculator and it’s free so even if it isn’t ideal it will hopefully be good enough to start with.
Do air compressors have a different measure of horsepower or…?

### In reply to: Will it shred??

starter
31/05/2019 at 07:23
0

Welp, a quick Google search answered my own question.
Ah, well, gotta start somewhere, I guess.

### In reply to: Will it shred??

warrior
31/05/2019 at 12:35
1

Where does it actually say 5HP?

As S2019 said, 15 Amps (“Full Load”) at 120v is not 5HP, actually less than 2.5 and that will be electrical input power, the mechanical output is probably around 2HP, but at a 50:1 ratio looks good enough (the calculator does take into account the mechanical inefficiency of the motor/gearing).

### In reply to: Will it shred??

starter
31/05/2019 at 22:10
0

Where does it actually say 5HP?

One of these actually says it on the nameplate of the motor, but all of the compressors say “5HP” on the top of the compressor itself.

A little research suggests that the “5 HP” rating from the manufacturer comes from the maximum amps drawn for a few seconds before it shuts itself off to keep it from blowing up or tripping a breaker).  Basically when the compressor has almost done its job it might need a little boost to reach its maximum pressure output.  I don’t really understand this all that well and I’m paraphrasing what I’ve read, idk.

### In reply to: Will it shred??

warrior
31/05/2019 at 22:33
1

I think those are the same horses that were in a Fiat I had long ago

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