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Stainless Steel in Shredder

This topic contains 6 replies, has 4 voices, and was last updated by  Mirco Graenert 2 days ago.

Bill billa14

Stainless Steel in Shredder

11/07/2018 at 15:20

Using Stainless Steel in the shredder is a real NO NO
I have been using mine for about 6 months now and has worn badly
The teeth have about an 1/8″ gap in front of them now so not cutting well at all and the sides well there is about 18thou gap on each side of the teeth to the guide
If you are going to build one please make sure you use a lot harder steel of some sort to lessen the wear

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11/07/2018 at 16:58

could you please add some pictures please ? it’s a sensitive topic for many of us…

11/07/2018 at 17:53

for now you could reduce wear as described here. i have no long-term data on this but using classic cutting tool basics seems definitely feasible.

@davehakkens, @xxxolivierxxx, would be nice to have at least a link to hand picked list of important forum topics in the public ‘machines’ section of the site to avoid exactly this sort of desaster. 200 euro average price tag on the laser cut with 6 months lifespan is more likely what most of us can’t effort :-). I am already afraid about that my clients re-claim their money from me…

11/07/2018 at 19:28

I’ll set this topic as sticky. Unfortunately, I can’t speak on regards of inox steel usage on the shredders because all shredders I have build are made with torched Mild Steel and they show zero signs of wear, even without applying Guenter’s knive upgrade

13/07/2018 at 01:03

There are different types of Stainless Steel, however the fact that a lot of stainless is non magnetic already creates a problem for the machine shops as the baled thickness can not easily be ground.  The chuck that holds the pieces are generally magnetic based.  The next item is the process used to cut the material, laser cutting actually produces a harder edge, however it also produces a burr, unlike the waterjet.  It would seem sensible to use a tool steel such as American grades A2.  O-1 steel is less expensive and can be oil quenched and tempered in a home shop.  A2 is best hardened at a proper heat treat shop.  Hardness process requested should be Vacuum Harden, Temper to 58-60RC, process for cutting either waterjet prior or after heat treat, leave .010 on the thickness for grinding.  Wet Grind on a proper surface grinder if available.  O-1 will warp during treatment and a good tool shop can grind it flat and take the warp out, oversize may need to be .035, depending on the warpage per test.  European materil equivalants can be found in “the Key to Steel” global material conversion book.  The cheapest would be to use Mild steel, use it and if there is wear, then it can be carburized to induce a hardness.  We are in the process of building a stainless shredder and it is not simple, especially as we are reducing the cutting clearances, so everything has to fit perfectly.  I hope this helps,
cheers, Mirco, Ontario Canada.

15/07/2018 at 22:03

@mirco Indeed, making a shredder is not as simple as cutting the parts and assembling them, there is a LOT of adjustment needed, grinding, shimming, dissasembling, reassembling, tightening, before your shredder is ready to use.

Finding perfectly calibrated steel sheets is pretty much impossible, so a belt grinder comes pretty handy for reducing the thickness of the parts as close as possible to the design measures.

17/07/2018 at 04:59

Hi Olivier,
agreed the fit up needs careful planning, a good CAD system and methods to manufacture the plates so the stack up works out.  We are currently working on reducing the cutting clearances tolerances and altering the blade designs slightly in order to attempt to increase efficiency.  I am a Tool and Die maker by trade and worked in Tooling Engineering for one of the largest Auto Parts manufacturers in the world.  The materials are available in the correct sizes, especially in imperial units here in Canada.  So the design needs to suit the supply, ie. Europe metric and North America Imperial (Yes even Canada) Imperial, stock materials are often imperial sized.  And yes if you are real good with a belt sander and have a week to spare you can likely get it done.  Even bolts and nuts are generally cheaper in Imperial units.  I work in either measuring units and understand the advantages.  The key is knowing a few things about metallurgy and the availability of the thicknesses and tolerances, including the manufacturing method.  Cost plays into it of course.    Less than .001″ (.0254mm)  is the type of tolerance that will be required for each blade and opposing cutter if you are looking for a .010″ or less cutting clearance (distance between the moving shredder blade and opposing fixed cutter) between the blades.  Careful  planning and material selection can avoid much sanding and fitting.   As with 13 or 14 blades the stack up error will accumulate and then the shimming and adjusting will never end or take another week….  Planned and accurate sizing will allow the stack to work without shims or belt sanding.   Which size is the best cutting clearances we have not determined, but generally in steel cutting it is a function of the type of material and the shear strength.  I am going to take a guess here and say that .010″ or just over .25mm per side will be suitable for most materials, if the clearance is to large or to small the efficiency window may be missed.  Changing the cutting clearances involves a basic re-design of the overall cutter box, shaft and or number of blades used.  We will be adding 2 or 3 additional blades when we complete the refurbishment of ours to fit into the current box.  We are also adding two counter blades on each end as a blade just running on the outside does not have an opposing cutting edge in the current design – that can`t be the best we can do for efficiency and stopping the thing from jamming.  A reversing switch and an E-Stop is a must have on the motor.  Once we figure out a nice method we will post…
Food For Thought…. Best Regards,

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