ROK grinder burrs rubbing

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

Postby AlexCA » Oct 10, 2018, 5:51 pm

I can't seem to get the Rok grinder's burrs to stop rubbing against each other when the adjustment is down to an espresso setting. I get decent espresso shots out of it but I can hear the burrs rubbing as I use it and there's some slight resistance. When I adjust it to no longer rub the grind is too coarse for espresso. I have twice done the inner burr realignment and this doesn't seem to change anything.

With the burrs rubbing will they run out more quickly? Also, is the grind not going to be even as it only seems to rub for 1/3rd-1/2 of the cycle. Has anyone experienced the same problem and able to remedy it?

Beaniac

Postby Beaniac » Oct 11, 2018, 8:29 am

Been that way since the start of production. Its a poor quality burrset, some sets rub, some dont.

walt_in_hawaii

Postby walt_in_hawaii » Oct 11, 2018, 1:03 pm

Alex, I don't think you should worry about it. The only time you need to worry is if you can't get it fine enough for a good pull... although ideally you should have enough adjustment to choke the machine, it isn't necessary. If it grinds fine enough, you're ok. The nature of the burr set is always going to produce grinds that vary in size slightly, and the amount of runout (unevenness in your burr's surfaces that cause the rubbing on one spot but not another) is probably smaller than that natural variation in size in your grounds, so it probably makes no difference.
That being said, if it REALLY bothers you, here's how you fix that:
Get a height comparator, or a dial gauge set up vertically and build yourself a very sharp indicator pointer on it. You'll have to set up your burr on a round turntable or very even, flat surface and simply rotate by hand. Measure the bottoms of V cuts on the burr to see if there is any variation in height, then to flat surface on top to see if there is any difference as you rotate it. If there is, you cannot change the depth of the V cut; but you CAN change the back face, the flat mounting surface on the bottom. You'll have to mark the highest V cut, mark that point and how much the V cut height differential is, then flip it over and grind that part of the mounting face down by the amount you measured as the height differential.
Would I do it? nope. too much trouble. if you can't live with it, chuck it and get a set of SSP burrs, they are pretty good quality and trued up reasonably well.

mivanitsky

Postby mivanitsky » Oct 11, 2018, 1:15 pm

SSP has burrs for Rok?!

walt_in_hawaii

Postby walt_in_hawaii » Oct 12, 2018, 5:43 pm

:)
I've never actually seen one, my bad. I assumed it was the standard run of the mill (ha, pun intended) ubiquitous flat disc grinder.
pulled up a picture of one and wow, that thing is a modified egg beater!

mivanitsky

Postby mivanitsky » Oct 12, 2018, 6:27 pm

Well, to call it a grinder around here might be a bit of an overstatement. Discard or sell on CG the Rok, and buy a Helor 101 or Kinu M47 or Hiku or Aergrind, depending on funds available.

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Ursego

Postby Ursego » Oct 15, 2018, 9:20 pm

AlexCA wrote:I can't seem to get the Rok grinder's burrs to stop rubbing against each other when the adjustment is down to an espresso setting.

I had this problem with a couple of kinds of beans. The produced coffee powder was a little bit coarser than I needed, so I partly compensated that by loading 17 gr (instead of the usual 16 gr) and super-hard tamping. :lol:

AlexCA

Postby AlexCA » Oct 16, 2018, 10:08 pm

Beaniac wrote:Been that way since the start of production. Its a poor quality burrset, some sets rub, some dont.


That's unfortunate. I actually bought it off a HB member and he gave me a preciso burrset with it. I swapped it out for the standard one. Will the preciso burrset grind fine enough for espresso? In reality I wanted this to be a single dose grinder as I also have a Fiorenzato F4E. Maybe I'll just use it for the occasional pour over or french press instead.