Burrs Sharpening

Grinders are one of the keys to exceptional espresso. Discuss them here.
Rodion

#1: Post by Rodion »

How many times could you sharpen the burrs of your grinder?

cdo

#2: Post by cdo »

It really depends on the cost of burrs, I think for anything other than Ditting/Mahlkonig/SSP resharpening would make no sense financially. Mazzer burrs can be had for quite cheap. WIth home use, it would be pretty difficult to wear out burrs as well.

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cafe102
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#3: Post by cafe102 »

And be satisfied with the results? Probably none, unless the burrs are going back to the manufacturer where they are set up to sharpen the burrs to the proper geometry. I worked for a tooling resharpening company for 15 years, the machine set up time alone would make it cost prohibitive to grind a matching set of burrs.

zero610

#4: Post by zero610 » replying to cafe102 »

I have to think a legitimate burr resharpening service (SSP, especially for MK or Ditting) will do an excellent job of resharpening. They've been doing it for many years and are well known for this service.

cafe102
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#5: Post by cafe102 »

I was responding to the burrs for the grinder the OP has listed on his profile. Cost of new burrs are $75 or $145 depending on which model he owns. Also, SSP doesn't sharpen burrs that are smaller the 64mm.

myke2241

#6: Post by myke2241 »

When you factor in the manufacture will have to clean every burr coming in to ISO standards before even running any QC is telling. Also, keep in mind the sharpening process will introduce more heat to the part. That can be a bad thing depending on the material.

Rodion (original poster)

#7: Post by Rodion (original poster) »

So, as I understand special equipment is used for sharpening? What kind of equipment is used?
And what is the answer on my question? D.Shomer writes that burrs could be sharpened 1-2 times and then you have to buy a new one.
We have Fiorenzato F64E in our coffee house and burrs cost around 30 EUR.

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GeorgeP922

#8: Post by GeorgeP922 »

Never knew this was a thing.
My 2 cents, if the burrs are truly worn in home use (or bought used) I would buy new.

I would only do resharpening if the new edges were unique to their original form, that would be cool to unlock new profiles with the unique burrs.
I doubt that's possible but the thought is nice.

Also is this done by hand, or machine?

jpboyt

#9: Post by jpboyt »

When it comes to sharpening you have to understand how burrs are manufactured. Most burrs have machined teeth and then go to heat treat. Final sharpening is done by surface grinding to set outfall depth. So you have a hardened burr that can't be machined. So the only machine shop equipment that can be used is a grinder. The next thing you have to determine is whether you have a case hardened burr with shallow hardness or a through hardened burr. The larger burrs 80mm and up for grinders like the Ditting and Mahlkonig for example, have burrs that are machined or have "as cast" teeth and then the final teeth are produced by grinding after heat treat. Talking bulk grinders,the cast burrs you see are a "white" cast iron with large amounts of carbon (very hard) and the steel burrs you see have large amounts of tungsten. The tungsten steels would fall in the category of hot work tool steels.
So if you have a normal low cost burr it probably is case hardened. So more than a few thousandths of an inch of material removal would possibly drop you below the hardened layer. If you want to touch up your burrs just lap them a bit. To completely sharpen you would have to remove enough material to return the tooth corner to sharp. That means you have to remove enough material to remove the radius that is created by use and is what one sees as wear. A through hardened burr, such as my D2 offerings, could be surface ground to restore the sharp corner. The problem is that you just changed the outfall depth of the flute at the outer diameter, possibly to zero, and the burr now won't grind beans or is extremely slow.
Wear occurs at a decreasing rate due to the increase in molecules in contact with the beans. It is point contact. First one molecule is removed leaving a few exposed. Then this area looses a few more molecules and then some more until one ends up with a radius contact area with a subsequent decrease in pounds per square inch pressure. Cutting efficiency decreases to the point where coffee ends up being crushed like a bulk grinder and not cut in a scissor fashion that espresso grinder burrs typically use.
The lowest cost burrs from Italy are a commodity like nails. And like straightening nails, trying to sharpen low cost case hardened burrs is just not profitable or recommended.
jpboyt

Coffcarl

#10: Post by Coffcarl »

Wow. Just wow.