Ive been reviewing and practicing a lot of the distribution techniques posted to the forum, since stumbling upon this place the quality of my shots and my understanding of "the process" have improved greatly.

Ive since been met with a problem with my Rocky/Silvia combo setup.

No matter what variable I change, I get channeling in the exact same spot in the filter for every shot. I change grind setting up and down, under and over dose the shot, combo the distribution techniques, tamp with the basket in and out of the portafilter, pre-infuse, surf longer/shorter, etc. Everything I can think of.

The beans are 4 days off the roast.

I've cleaned the machine inside and out, descaled and buffed, he machine is pristine.

Every shot results in channeling at the 10 O'clock position on the filter, just to the North edge of the locking tab, and immediately beneath the locking slot on the grouphead. No matter which of the above variables were altered, the same channeling occurred with blonding at the last 10 sec of the shot.

Any ideas if this may be a method related problem, or a possible problem with the machine? Double shot filter basket is brand new from a retailer, and the grouphead gasket is flawless (as far as I know), all internals have been disassembled (within reason) and inspected. I honestly don't know whats causing this.

Ive even used a laser level to ensure the machine is completely level on the counter.

The shot quality isnt terrible, I still get some minor mottling and a cinnamon/red hue to the crema, with a well timed shot for volume. Minus this channeling I think these shots could be better.

Anything? Anyone?

Is the basket in the same position in the PF each time? The basket can rotate as the PF is inserted and removed.

If so, the basket may be suspect. When held up to the light, do all the holes appear very, very similar?

If not, what does the water flow look like from the group w/o a basket? Is it even all around the screen?

I've inspected the filter basket pretty thoroughly, its brand new and appears to be pretty uniform, Ive held it up to bright light and used a magnifying glass to look pretty closely.

I've been rotating the basket before every shot, a different direction every time and at various degrees. With the same result. The slot in the machine screw for the shower screen bisects the angle of the channeling at a right angle.

By using a grease pencil, I managed to deduce that the channeling occurs precisely where the North edge of the left locking tab lies beneath the South edge of the left locking slot, Im not sure if this really means anything.

Running the pump minus the PF results in fairly ideal water flow, 6-7 individual smooth streams of water radially around the end of the shower screen.

I've been debating filing the edges of the locking tabs a little bit to see if perhaps there is a small gap created by a raised edge, a sloppy left over from when they machined the handle. Dunno if this will work. I will be buying a smaller machine screw to see if this helps the problem any , as the channeling occurs just as the puck should be expanding up into the screw itself.

Can't imagine the locking tab could be a problem as it's outside the basket / gasket interface.

Have you had the screen out?
Perhaps the screen is distorted / bent. The screw should be just tight enough to hold the screen in place so it doesn't loose with the PF removal puck friction

Ive inspected the screen, seems fine. I'm sure its likely to do with some minor habit in tamping or distribution.

I was initially just concerned that with the consistency in the location of the channeling there may be a physical defect to the machine or other hardware.

I'll keep playing with settings, my methods are far from perfect and perhaps these kinks will disappear with time. If anyone can suggest some methods to help iron this out or perhaps get to the bottom it'd be great.

I'm currently sticking with WDT for distribution and Im a former employee of the roast master I get the beans from, so as long as the money holds up I can expect a few long nights of caffeine headaches until this goes away.

If the tamp is level, WDT pretty much precludes having a distribution flaw in the same place every time.

Assuming you've checked the puck is not touching the screen on lock in and has a nickels worth of clearance, how level is your tamp? Leave the tamper in the basket and look at it at eye-level. Is it tilted towards the rear?

I have a container of junk espresso grind Im going to use for the nickel test (why put a dirty nickel in what could be a good shot), to test the level and dosage. Ive yet to incorporate the use of a scale into the mix, so the dosage isn't as consistent as it should be.

As for level tamping, Im 6'3" and have a really low counter top, so I tend to tower over and hunch when I tamp, which I can see leading to subtle slanting towards the leading edge of the PF. I try to use the rule of locking the arm at a 90 degree angle , forearm vertical and upper arm parallel to the tamping surface. I also tamp with my finger tips rather then grasping the handle with the full palm, this tend to lead to better control over weight distribution for me.

Between postings I pulled another shot with the same channeling in precisely the same spot, after rotating the filterbasket in place before locking the handle. It ran to full shot in 20 sec and was 'coffee n' cream' blond almost instantly, given, I used two week old beans for this one.

Just trying the nickel test. With the stock Rancilio PF there seems to be no way to avoid contact with the dry puck from the large hex nut coming from the screen, even dosing such that the puck sits below the midline in the filter after tamping results in a big drill hole in the middle of the puck.

Im leaning towards switching out the OEM hex nut as being a possible solution, as you said as long as it is just tight enough to keep the screen in place vs. friction from the puck when locking.

As per the responses in the million other posts regarding errors in distribution techniques, its just going to have to come down to practice. I'll keep at this.

Thanks very much for you responses, they've been helpful. I look forward to hearing any other tips or bits of wisdom regarding this machine the community may have.

Chris,

This certainly sounds frustrating.

Did this just develop, have your results been good in the past? If so, maybe your burrs are worn to a point where one step goes from choking the Silvia to not consistent enough for even pours. Combine that with your observation of the screw head in the puck and it may make some sense. Do try a reduced screw head if you can.

I was just having a series of shots favoring the front center. Tried a few things that didn't change the conditon. Stopped polishing the puck after tamping and the shots are pouring much better.

Good luck, espresso is weird science!

George

Have a look at this...http://coffeegeek.com/forums/espr...machinemods/358311
countersink the distribution screen and the water diffuser, change the screw and no more bulky screw head sticking out...