Sharpening coffee grinder burrs!

AlexyL · Mar 6, 2018

Hi guys, I have about 12 blades that need to be re-sharpened and the company that was re-sharpening my blades stopped the program. I am starting to look at the option of buying a mill and doing it myself since a new set is 750$ each(was 350$ to resharpen). I asked a machinist friend to come and see if it would be a viable option but I was wondering how would you guys go about re-sharpening them?

Any tricks or tips would be really appreciated!

Thanks alot
Alex

rklopp · Mar 6, 2018

A mill is the wrong machine. You need some kind of tool and cutter grinder. I imagine cutter grinder shops exist that would be willing to bid this, especially in multiples.

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DDoug · Mar 6, 2018

I'll bet the Italians have a specially made machine to do the job....

Barry Weeks · Mar 6, 2018

Hard to say without actually having a part in my hands, but I do a lot of grinding. I would think with a surface grinder (6-12 or larger), a compound sine chuck, a small rotary table, and a shopmade fixture to hold the part to the rotary table, you could sharpen these. I think the $350 price is low, and why they discontinued that service. If the price to resharpen approaches the new part price, the part becomes disposable.

AlexyL · Mar 6, 2018

rklopp said:
A mill is the wrong machine. You need some kind of tool and cutter grinder. I imagine cutter grinder shops exist that would be willing to bid this, especially in multiples.

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Totally makes sense to use a ginder, im heading out to get a couple quotes!

Thanks for the quick reply!!
Alex

AlexyL · Mar 6, 2018

digger doug said:
I'll bet the Italians have a specially made machine to do the job....

Those are actually Swiss made hahaha its from Ditting!

Barry Weeks said:
Hard to say without actually having a part in my hands, but I do a lot of grinding. I would think with a surface grinder (6-12 or larger), a compound sine chuck, a small rotary table, and a shopmade fixture to hold the part to the rotary table, you could sharpen these. I think the $350 price is low, and why they discontinued that service. If the price to resharpen approaches the new part price, the part becomes disposable.

Ill take a look if i can find some used tools around! And yeah they discontinued resharpening those exactly because it was not profitable anymore!

Thanks alot for the reply guys!!
Alex

HuFlungDung · Mar 6, 2018

Looks to me like you'd need a VMC with a flaring cup grinding wheel in the spindle, and a 4th axis set on a sine table to get the required angle. CNC would be far easier to apply the complex motion required to get the wheel in and out of the cut safely. I think I'd go nuts trying to do that on some sort of manual grinder.

That being said, I don't want to grind in my VMC

EPAIII · Mar 6, 2018

I can't see just how dull the edges are in your photos, but if they have a small edge radius, I would consider an acid dip. This is how files are sharpened. Probably a shallow amount of acid so only the working side of the disks are in the acid. And you will need some kind of supports, possibly glass beads or marbles.

upthebikes · Mar 6, 2018

Send them out for sure. A good friend of mine was the maintenance/espresso machine guy for a real high end coffee shop with 6-7 locations. He consulted me about the best way to get them resharpened, and after holding them in my hands I knew I couldn’t do it without tooling up. I gave him some numbers of tool and cutter grinder shops, and he called around and found some shops willing to bid. A very well equipped “old school” shop can do it, as would a shop with a cnc tool grinder; your best bet for a good price is to not be in a hurry, and send all of them at once.

AlexyL · Mar 6, 2018

EPAIII said:
I can't see just how dull the edges are in your photos, but if they have a small edge radius, I would consider an acid dip. This is how files are sharpened. Probably a shallow amount of acid so only the working side of the disks are in the acid. And you will need some kind of supports, possibly glass beads or marbles.

I think the outside part is grinded flat! heres a close up picture maybe you can see better! Cant seem to get my phone to focus well lol!

Thanks for the idea!!
Alex

AlexyL · Mar 6, 2018

upthebikes said:
Send them out for sure. A good friend of mine was the maintenance/espresso machine guy for a real high end coffee shop with 6-7 locations. He consulted me about the best way to get them resharpened, and after holding them in my hands I knew I couldn’t do it without tooling up. I gave him some numbers of tool and cutter grinder shops, and he called around and found some shops willing to bid. A very well equipped “old school” shop can do it, as would a shop with a cnc tool grinder; your best bet for a good price is to not be in a hurry, and send all of them at once.

I will call some shops around here and get some bids!

Thanks alot for the suggestion!
Alex

AlexyL · Mar 6, 2018

Example

Here's an example of how one of my supplier is doing his sharpening. He can only sharpen one size of blades tho and i have 2 sizes. Is that a surface grinder?

Alex

Milland · Mar 6, 2018

I just checked out the Ditting website, and it's interesting how they specifically demand that no "aftermarket" grinding disks be used, under loss of warranty. I'm not sure that would be legal in the USA. Also, they've stopped offering regrinding of their disks, seems they want replacement only.

Grinding Discs

Compared to the website pictures (granted, they're small), it looks like the OP's discs have been ground a number of times. I wonder what the practical limit is.

johansen · Mar 6, 2018

AlexyL said:
I think the outside part is grinded flat! heres a close up picture maybe you can see better! Cant seem to get my phone to focus well lol!
View attachment 222372
Thanks for the idea!!
Alex

i think that is from metal on metal wear.

the cutting edges appear to be significantly rounded as well which means a lot of metal will need to be removed. this will probably reduce the capacity of that disk, which may or may not be a good thing. the heat generated by the grinding process has a significant impact on the coffee flavor...

TDegenhart · Mar 6, 2018

The grinder is a #2 Cincinnati T&C grinder.

Tom

upthebikes · Mar 6, 2018

Here is how mahlkoening does theirs, on a tool and cutter grinder.

AlexyL · Mar 6, 2018

Milland said:
I just checked out the Ditting website, and it's interesting how they specifically demand that no "aftermarket" grinding disks be used, under loss of warranty. I'm not sure that would be legal in the USA. Also, they've stopped offering regrinding of their disks, seems they want replacement only.

Grinding Discs

Compared to the website pictures (granted, they're small), it looks like the OP's discs have been ground a number of times. I wonder what the practical limit is.

Ive had em for more than 10 years. I dont think they are still under warranty lol! And yeah thats the reason im looking to maybe re-grind my own disks! When i used to send them for regrind they would send shims with it (im guessing for the amount they removed).

Thanks!

AlexyL · Mar 6, 2018

johansen said:
i think that is from metal on metal wear.

the cutting edges appear to be significantly rounded as well which means a lot of metal will need to be removed. this will probably reduce the capacity of that disk, which may or may not be a good thing. the heat generated by the grinding process has a significant impact on the coffee flavor...

Yeah they are pretty worn out! that is jus one of the sets tho! if i can save a couple maybe itll be worth the investment!

Thanks!

AlexyL · Mar 6, 2018

upthebikes said:
Here is how mahlkoening does theirs, on a tool and cutter grinder.

Awsome!! Thanks for the picture!!

HuFlungDung · Mar 6, 2018

I'd assume these are center feed, and that the bigger gashes are spaces for the whole bean to get in between a pair of plates. Are they precisely shimmed so that the blades don't contact, or do you have a specified clearance for a particular grind coarseness?

I can see after extensive or repeated resharpening, that you'd loose some capacity if the larger beans cannot fit into the big gashes, so you might have to regrind that part a little deeper if much material is removed.

However, I still think a flaring cup CBN wheel could be configured to work on a VMC, but that's not a DIY project either. Sounds like you're only paying about $10 per blade, ($350/12)? That is so cheap you'd have to automate it. T&C grinding with a soft pink toolroom wheel would have you pulling your hair out, IMO. Nice to grind with, but the stone wears quickly. Round and round and round, you'd go, trying to keep the wheel flat so it doesn't turn over the edge. Or am I wrong?

A super-abrasive like CBN would probably not wear significantly. I don't see any need for a razor sharp corner in the bottom of the flutes, so maintaining an acute corner on the wheel wouldn't be a big priority, perhaps.

Sharpening coffee grinder burrs!

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