tsackett wrote:It looks like the inner burr was once kept centered by little plastic nubs on the mounting, but these are worn down, leaving the inner burr hanging freely in the outer burr.

Tom,

I find it hard to believe that the plastic nobs were centering the inner burr, but it can't be told for sure from the picture. It looks to me those are rather to hold the outer burrs in place. Are those nobs clearly worn? are they worn differently along the axis of the shaft as one would expect. Is there even enough play of the inner burr to touch those nobs at all?

To my understanding the inner burr centers itself against the outer one as partly ground beans force it in position during grinding. This would be a very efficient way of forgiving imperfections of the burrs while keeping the construction of the bearings very simple.

ogatasan wrote:Tom,

I find it hard to believe that the plastic nobs were centering the inner burr, but it can't be told for sure from the picture. It looks to me those are rather to hold the outer burrs in place. Are those nobs clearly worn? are they worn differently along the axis of the shaft as one would expect. Is there even enough play of the inner burr to touch those nobs at all?

I don't understand your point about uneven wear, but I'm pretty confident that the nibs once acted as guides for the inner burr, which swings freely enough at the bottom end to touch them even in their worn state. The inner burr also has a wide, smooth band running around it below the grinding surface. This looks like it was meant to act as a bearing surface.

The nibs definitely were not there to hold the outer burr, which has the shape of an inverted cone and is locked in place in the plastic mounting by its shape. I've looked at a few different hand grinders, and have not see one that does not have the bottom end of the inner burr held in place by some sort of mechanism.

tsacket

What a great solution to your problem and keeping the adjusting screws inside as well! Maybe you can get the ends of the screws flat by fitting the screws into a slow spinning drill then file and polish the ends - a crude but effective lathe? You will probably end up with a slight sphericity on the ends of the screws which should give a broad and stable point contact.

Good luck with the grinding.

Geoffrey

Alright guys, I think I may have performed the first ever burr transplant for a hand coffee grinder. Check it out.

I used the burrs from my old La Pavoni Club, which had a built-in grinder. They are apparently the same set of burrs as used in the Ascaso I-mini, small but very high quality. I machined a new shaft, new bearings, and a new adjustment mechanism. Everything seems to be dead-center with absolutely no wobble. The only issue I'm having is the adjustment tends to back out while grinding, so I either need to find a higher tension spring or come up with something else. It's also very difficult to make fine adjustments, so I may ditch the 24 tpi screw altogether and go with some sort of worm gear adjuster. Hmm.

What do you think?

Very innovative! The friction betweenn the base of the lower burr and your adjuster set up seems to be too great. Remember on many of the old grinders they has a inset ball bearing between the base of the burr( with a half spherical hole) and the tipp of the adjusting screw( also with a semi hald spherical indentation to hold the lubricated ball bearing).

This would transmitt far less friction and twist that seems to be effecting your adjutments while grinding.

Did I say that in a way that was easy to follow?

Also I could be barking up the wrong tree!

oofnik wrote:The only issue I'm having is the adjustment tends to back out while grinding, so I either need to find a higher tension spring or come up with something else. It's also very difficult to make fine adjustments, so I may ditch the 24 tpi screw altogether and go with some sort of worm gear adjuster. Hmm.

From the picture, I'm guessing that the metal bracket is threaded where the tensioner bolt passes through it. This might not provide enough friction to keep the bolt from turning as the grinder is used. You might consider drilling out the threads and brazing on (or epoxy-ing on) a locknut with a nylon insert.

I'm really glad to see that someone is attempting this. The quality problems with recent Zassenhaus mills suggests that the era of the precision hand grinder may be at an end. Fabricating new hand mills using electric grinder parts may be the only way to keep hand-grinding alive.

Okay, fixed. And improved. I decided to go with the worm gear idea. As a kid, I was fascinated with moving parts and would spend hours disassembling fax machines, VCRs, tape recorders and all sorts of stuff with gears and motors. And I would save all the cool parts. The majority of them remain in a box in my basement until today. One of these cool parts just happened to be a worm gear assembly. Who would've known it would eventually find its way into a coffee grinder?

I'm running out of beans, and it's past midnight, so the test will have to wait until tomorrow morning.
It's looking good.

edit: This is definitely the best grinder I've ever used, including electric. Very adjustable, stepless, no clumps, reasonably fast, doesn't back up, and super smooth flavor.
We have a winner. I hope more people will do this.

oofnik-

How is your grinder working? The worm gear mechanism looks great. I've been taking a look at some of the other grinder pictures on this thread, and noticed that some of them have adjustment knobs on the back or in a corner on the top; I wonder if they use a solution similar to yours.

-Tom

Tom,

that was nice looking grinder that I was watching on ebay and saw you threw a bid at.... Oh well there are plenty of fish on the sea!

I have one of those side knob grinders and actually the adjustment is an adjustable wedge that advances and retracts from below the center burr( at least thats how mine works. )

mogogear wrote: that was nice looking grinder that I was watching on ebay and saw you threw a bid at.... Oh well there are plenty of fish on the sea!

Which one were you watching, the "Danish Modern Eames Era" one? That was definitely one of the cooler-looking ones that has been up for auction recently. I actually bid a bunch of grinders, and one two. One is labeled "Columbia," but is almost certainly a Trosser that was rebranded for sale in the U.S.. The other is a larger Trosser in really good condition (it looks almost unused). My wife thinks I'm crazy, but she can't complain because the coffee we've been making is really good.