I've had the Rancilio Silvia+Baratza Vario for <6 months. I've had some issues throughout that time with channeling but eventually perfected my technique somewhat to get nice and even extractions. However, for the past 2 months I've been consistently getting channeling and uneven extractions.
I've changed many variables over the past 2 months to try and trouble shoot this including:
Buying new baskets (VST 18g) and a flush shower screen; Updosing in increments of .5 from 17-19 grams; Adjusting my tamp method and distribution (this includes tamping lighter vs. harder, and the WDT distribution technique); Adjusting grind settings; Cleaning the Silvia (backflushing and descaling);
I'm not sure what else to do at this point. The only thing I can think of is that there may be a problem with the grinder? Is it possible the burrs are misaligned? I've noticed overtime that sometimes when you adjust steps on the Vario it doesn't grind predictably as if the burrs don't move when you move steps. Has anyone had an issue with the Vario similar to this before?
I didn't use the WDT method for distribution in this one for time sake but I've used it previously without it helping.
Any ideas would be appreciated. Thanks!

When was the coffee roasted?

this particular coffee is 12 days old. I only use coffee between 3-14 days of roast and this is how it consistently turns out irregardless of the roast date unfortunately.

Do you have the same problems with Silvia stock basket and 14gr dose in it?

Yes I do

I was having some channeling problems and tried a new tamping technique I saw in a coffee bar...you lightly rotate the tamper over the grounds while holding the tamper at an angle, like a coin that has been spinning and is falling down. This creates a slight convex surface to the puck, then I tamp as usual. I almost never have any channeling problems now.

If it's hard to understand let me know and I can try to explain it a different way. Maybe this is a common technique for everyone else but it was new and helpful to me.

This is called nutation, it was quite common but has lately seemed to fall out of favor. Here's an old thread from 2009 that explains the technique.

Nutation: how to do it right

m1key wrote:I've changed many variables over the past 2 months to try and trouble shoot this including:
Buying new baskets (VST 18g) and a flush shower screen; Updosing in increments of .5 from 17-19 grams; Adjusting my tamp method and distribution (this includes tamping lighter vs. harder, and the WDT distribution technique

I'd go back to the old basket, and slowly start mixing things in. Changing a lot of variables all at once can often cause confusion. WDT is good thing, and will help things. It very well could be the VST, as it being less forgiving of you prep.

m1key wrote:I'm not sure what else to do at this point. The only thing I can think of is that there may be a problem with the grinder? Is it possible the burrs are misaligned?

Regarding the grinder alignment. I feel partly to blame on this. Everyone keeps trying to blame the grinder.

Just to clarify things: no grinder is perfectly aligned, don't let anyone tell you otherwise. There is always a tolerance. Frank at Titus is the best out there with <.01mm both radially and axially.

Even if yours is at .05 - .075mm (which many are), this will actually make the puck/preparation more forgiving when pull a shot. As the wider the grind distribution, the easier it is to get a good flow rate without channeling.

Headala wrote:I was having some channeling problems and tried a new tamping technique I saw in a coffee bar...you lightly rotate the tamper over the grounds while holding the tamper at an angle, like a coin that has been spinning and is falling down. This creates a slight convex surface to the puck, then I tamp as usual. I almost never have any channeling problems now.

If it's hard to understand let me know and I can try to explain it a different way. Maybe this is a common technique for everyone else but it was new and helpful to me.

The technique is called nutating or nutation.
If I recall correctly Jim Schulman coined the term about 10 years ago, and Matt Perger popularized it with his 2013 WBC routine.

I'm currently experiencing similar issues with a Rancilio Silvia V3 and a new HG-1. Getting better but I've yet to pull a shot that doesn't have at least a little spritz stream somewhere...and that is a couple months of this experience. I'm very frustrated but learning. I'm feel like I really need expert training but have no clue where to find it. Counter Culture has a training facility here but seems not to have any classes over the summer.