Mazzer Super Jolly completely stuck/jammed - Page 3

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
jwCrema

Postby jwCrema » Jun 03, 2018, 11:58 pm

Scott_G wrote:If it's a matter of the burrs being pressed together due to the collar being overtightened, couldn't you remove the bottom of the grinder and bottom of the motor, loosen the nut holding the lower burr carrier on by about 3/4 turn and tap to drive the shaft down until the carrier spins? There should be at least 1mm of clearance between the lower burr carrier and the case.


+1

Soaking isn't likely to help jammed burrs. I would go in from the bottom.

mixuala

Postby mixuala » Jun 04, 2018, 10:27 am

Nothing moves except the center bolt.

But I may try the freezer before I try a heat gun. I'll have a look at tapping the center bolt to unstick the burrs

User avatar
Jake_G

Postby Jake_G » replying to mixuala » Jun 04, 2018, 12:01 pm

Did you remove the lower cover of the grinder and the lower motor bearing retainer plate? This should allow the motor rotor to be tapped downwards, providing the needed clearance to allow the lower burr to rotate freely and hopefully help the collar come loose.

Freezing will make the carrier tighter in the housing because the thermal expansion of brass (the adjustment collar) is less than that of aluminum (the grinder body). Because of this, the aluminum will shrink more than the brass, and grab the threads tighter. Heating it, even modestly with a hot compress around the top of the grinder housing will yield better results.

Good luck,

- Jake
★ Helpful

User avatar
sweaner

Postby sweaner » Jun 04, 2018, 12:41 pm

Jake_G wrote:Heating it, even modestly with a hot compress around the top of the grinder housing will yield better results.


Won't heating it expand all of the metal and increase the jamming?
Scott
LMWDP #248

www.coffeefreek.com

User avatar
Jake_G

Postby Jake_G » replying to sweaner » Jun 04, 2018, 3:04 pm

When heating objects, they grow according to their coefficient of thermal expansion. Holes in objects grow, rather than shrink like a donut, because the the perimeter of the hole expands. Likewise, the threaded adjustment collar will grow as well, but since it is brass, it will grow less than the aluminum housing. As such, the clearance between the threads will increase at a rate proportional to the difference in thermal expansion coefficients.

E.G. if two objects are the same material, the clearance between them may not change appreciably, and if we had an aluminum collar in a brass housing, the fit would get tighter with heat. Since our materials are favorable, we can heat the housing and increase the clearance, even if the collar expands with it.

Cheers!

- Jake

mixuala

Postby mixuala » Jun 04, 2018, 8:12 pm

Jake, that is good to know. For heating, I have a hair dryer or an oven or a butane kitchen torch. Any suggestions on a meaningful temp to target? I suppose it's possible to quickly heat the external body while the brass collar is still frozen...

User avatar
Jake_G

Postby Jake_G » Jun 04, 2018, 10:24 pm

Start with the hair dryer, aim for hotter than steamed milk, but not crazy hot. 125C or so should be enough to make a difference with aluminum. You can put a bag of ice in the throat after the housing is good and hot to shrink the adjuster collar away from the hot housing.

mixuala

Postby mixuala » Jun 05, 2018, 8:52 am

Jake_G wrote:That's a really good idea. This post has a good walk through of removing the bottom of the motor.
- Jake


I got the bottom off, but the screws holding the base plate in were so tight that I stripped a few of them. So I took off all the little bits I could and have the body in the oven. I hope to hit about 140F and then give the collar a whack. wish me luck.

UPDATE: got the body to 125F and started with the hammer. I was able to rotate the collar about 3/4 inch before my sleepy daughter put a stop to it. I'll try again tomorrow during the day...

User avatar
Jake_G

Postby Jake_G » replying to mixuala » Jun 05, 2018, 3:45 pm

Good news!

Next time, put a bag of crushed ice in the throat of the grinder before you start "massaging" the collar. Heating the grinder whole gave you ~.001" additional clearance in the threads, because the brass grew, as well. Shrinking the brass back to room temperature will get you over 5 times more clearance (~.005"-.006"), given a rough estimate of 80mm diameter threads and 75 degree increase in temp. The added clearance of cooling the collar should really help loosen it up.

Good luck!

- Jake
★ Helpful

mixuala

Postby mixuala » Jun 06, 2018, 12:27 am

Victory is mine!

The recipe was: bake in oven until body temp reaches 125F, stuff a bag of ice in the collar, lay the grinder on its side and hammer little M5 bolts (which I screwed into the collar) until loose.

Image

Thx Jake and everyone else—I couldn't have done it without you.