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Old 07-15-2022, 09:25 PM
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Default Should I Case Harden Shredder Teeth?

I have some 1" plate I cut into teeth for a shredder / grinder. As far as I know it's mild steel (sourced from a junkyard). This steel doesn't harden well from heat treatment.

The shredder will be for processing meat, bone, hooves, etc.

I'm wondering how mild steel teeth would hold up to dense bone - lamb shanks, deer femur, cow femur, pigs feet, etc. Will the teeth eventually get warped and chip if I don't harden them?

Is it worth it to case harden the teeth?

Case harden then temper?

Setup will be extreme high torque, very low RPM so no high speed impacts. I don't care about grinding speed at all, only that it can process material.

See pic for tooth profile.
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  #2  
Old 07-15-2022, 10:16 PM
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In my experience mild steel doesn't case harden well either. The other problem you may have is with the depth of the case hardening itself. The surface of the material may harden somewhat but the underlying material will still be soft and, depending how much load and impact there is, the sharper edges may just break away while the softer material slowly deforms.

I would certainly have made those teeth out of a better material but, since you've already got them made you don't have a whole lot to lose if you use them. The time to ask questions like this is before you buy the material...
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Old 07-16-2022, 01:16 AM
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Originally Posted by LKeithR View Post
In my experience mild steel doesn't case harden well either. The other problem you may have is with the depth of the case hardening itself. The surface of the material may harden somewhat but the underlying material will still be soft and, depending how much load and impact there is, the sharper edges may just break away while the softer material slowly deforms.

I would certainly have made those teeth out of a better material but, since you've already got them made you don't have a whole lot to lose if you use them. The time to ask questions like this is before you buy the material...
Mild steel will not harden.

I agree use them when they fail, and the only unknown is when not if.

Buy some A2 tool steel and make your next set.
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Old 07-16-2022, 01:51 AM
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...Mild steel will not harden...
You can in fact create a very thin skin of hard material on a piece of mild steel by case hardening but it won't stand up to anything more than mild abrasion. If there is any impact involved it will fail quickly because the underlying core is soft and won't support it. So for all practical purposes Ron is right, you cannot harden mild steel--it's just not worth the effort...
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Old 07-16-2022, 06:49 AM
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Originally Posted by Shade Tree Welder View Post
Mild steel will not harden.
I think you missed the question.

Yes, Case harden will help but from the pictures there may be too much back clearance on the teeth.
as Keath mentioned "won't support", may not be enough back support for the pressure generated. "its hard to tell from the picture because I cant judge size or pressure angle.

I had a motorcycle sprocket case hardened, about 0.030-0.050 it did help but the teeth still bent.
its Hard to explain,
with case hardening the teeth bent symmetricly (all the teeth bent the same amount).
stock non hardened sprockets some teeth would bend more than others and stretch the drive chain in spots, the chain would slap up and down so you could not adjust the slack out of the chain.
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Last edited by GWIZ; 07-16-2022 at 06:59 AM.
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  #6  
Old 07-16-2022, 07:28 AM
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OH GOD NO !!!!!

"Hard Facing"

OH GOD NO !!!!!
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Old 07-16-2022, 07:41 AM
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OH GOD NO !!!!!

"Hard Facing"

OH GOD NO !!!!!
Doug, I did think about that but this is a shredder, so you have to have them somewhat sharp. So weld and then try to grind hard facing...

Run them like they are. The buy some tool steel and do it right.

(PS he likely is not going to want to spend that kinda cash on 10 lbs. of hard facing rod, I have never seen HF rod in small paks.)
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Old 07-16-2022, 09:28 AM
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Quote:
Originally Posted by Shade Tree Welder View Post
Doug, I did think about that but this is a shredder, so you have to have them somewhat sharp. So weld and then try to grind hard facing...

Run them like they are. The buy some tool steel and do it right.

(PS he likely is not going to want to spend that kinda cash on 10 lbs. of hard facing rod, I have never seen HF rod in small paks.)
I still have some 60 Rockwell tool steel welding rods, I paid $45/lb for them in the 80's.
But like Keith said, you should ask before you invest time and damage on making something like this. That is the purpose of the forum, not to help un-fuck a fuckup.

At this point you can hardface and hope for the best. I would have made these out of T1, it is amazingly tough and yet can be filed. I would cut them out on a CNC plasma table, but then I have one.
https://www.napaonline.com/en/p/FNY4...pressionRank=1

I don't know what you have in Onterrible for farm supply stores, but they can be a good source for small amounts of rod.
At some point it would be good to see your design as well. If I was going to do this, I would set up a roller system with bars to crush and break bones and then into the shredder.
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Last edited by Ironman; 07-16-2022 at 09:34 AM.
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  #9  
Old 07-16-2022, 08:14 PM
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Quote:
Originally Posted by Shade Tree Welder View Post
Doug, I did think about that but this is a shredder, so you have to have them somewhat sharp. So weld and then try to grind hard facing...

Run them like they are. The buy some tool steel and do it right.

(PS he likely is not going to want to spend that kinda cash on 10 lbs. of hard facing rod, I have never seen HF rod in small paks.)
OH GOD NO !!!
It was a joke, seeing how the OP can't even diagnose a problem with a simple 4x6 bandsaw....
OH GOD NO !!!
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  #10  
Old 07-17-2022, 08:48 AM
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At this point, I would suggest a hardfacing, but apply it to only one side of the tooth. The tooth will then, in essence, become self sharpening. I used to buy rock bits with that feature. They'd still have a sharp cutting edge with 80% of the tooth worn away.

Once these teeth wear out, I'd replace them with a different profile tooth of a better material. A quick YouTube search for HD grinders should reveal that the heaviest duty shredders have teeth cut in a modified C shape. I've seen shredders with that tooth shape shredding steel barrels full of material feeding a disposal process.

This shredder has multiple teeth on each cutter, but hasaprofile with much more support for the cutting edge than a simple star shape.
https://youtu.be/iWlJGFzjT-g
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Last edited by camdigger; 07-17-2022 at 08:57 AM.
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