Hey Flat users!
I'm running into something and wondering if anyone out there is experiencing the same thing.
I started noticing a pretty decent variance in grind when using the same settings. I'm pulling shots on a Decent1, so I have the ability to see flow and pressure rates for each shot. Using same setting, same bean, same batch, same dose, same metered tamp, same week (if not day), same flow profile, I've been getting a variance in pressure from 3 to 11.
So I started paying attention and found a slight amount of vertical play in the adjustable hopper. It's small, but clearly enough to matter.
Some of the problem is due to how I use it. When I grind for an immersion brew, the setting is pulled back so coarse as to be off the 1-10 chart. This setting allows the grinds to gather around the lip of that three-studded flange that sits on the upper burrs, and when I dial it back down to espresso settings, those retained grinds get compressed, pushing up on the hopper that has play in it, and changing my grind.
When I've cleaned the burrs recently, it grinds finer. The longer it goes between cleaning, the coarser the grind gets.

So my question is: does anyone else have a slight amount of vertical play in their hopper? I don't remember it ever being there when I first got the grinder.

I do not have the original version with the tightening collar, or counter-clockwise tightening.

In general if you are hopping between brew grind settings and espresso grind settings you want to run the grind while you are adjusting finer again, for the very reason you mentioned about coarse bits getting compressed. I learned this the hard way many years ago on a Baratza Vario.
Run the grinder while resetting to espresso range and this problem shouldn't occur.

What you may want to do to validate / reset your alignment is remove the top burr carrier, brush everything out, then remount the top and tighten the screws snugly. Hopefully that should get rid of your current issues.

If you are talking about the round hopper itself having play, I'm not exactly sure what your issue may be. I don't have any play, but my unit is the original kind with a tightening collar; yours isn't so I'm not sure what is creating the friction that should keep it from having vertical play. A low effort fix may be to add teflon tape to the threads to eliminate the play. I've seen it do wonders on other grinders.

As Dominico says, and to further emphasize, whenever you move from a coarser grind setting to a finer grind setting, it's best practice to run the motor while you make the adjustment. This way, any residual grinds sitting between the burrs will get crushed and pushed out while you bring the burrs closer together and you avoid adding unnecessary pressure on the burrs, burr carrier, and screw threads that hold everything together. The funnel should also spin much more easily.

The general rule with any mechanical is that you should never have to force anything unless you're trying to tighten something down. And even if you are tightening things, it's best practice to use a torque limiting tool so you don't damage threads or over torque. If something that should move easily doesn't want to move, there's usually a good reason and it probably shouldn't be forced.

Also, if you have a concern, you should hit up Dennis. He's usually quite responsive.

Thanks for the responses.
In short, I do run the grinder when adjusting to finer grind. It's pretty much required. Doing so only eliminates the grinds between the burrs and doesn't not the buildup on the flange that eventually prevents it from moving to a finer position.
What I really want to know is if others with this generation flat (non collar) have any vertical play in their funnel, like I do.

Maybe send this info to Kafatek. Other manufactuers added an extra mechanism to their grinders to prevent this problem.

Here is a link to time on a video with Ceados mechanism: http://www.youtube.com/watch?v=Mm1TFjBK8Cc (time is 5min 41 sec)

I have no play in the burr carrier. A bit of play in the pour funnel, but that does not affect the carrier. I have not seen any inconsistency in grind. Very repeatable settings.

No idea if this is your issue but, in my experience, the flat is very sensitive to grind retention. If your beans are at at all oily, grounds will compress and cause trouble. For example, it will be impossible to turn the adjustment to the finer range because residue gets in the way. Unlike my Eureka Mignon, which will just freeze up when the burr hits compressed grounds, the motor in the flat will keep the burr spinning. The problem is still there, however.

Easy enough to keep it clean. Denis suggests moving the adjustment back and forth while running. That helps. I prefer poking a bristle brush into the chamber (through the exit hole) and twirling it around. REMOVE BRUSH and run. Grounds will spit out. Repeat a few times and good to go.

I also have a DE1 (v1.1) and a Monolith Flat with SSP burrs. While I haven't noticed any play in the build of my grinder, I have noticed similar inconsistencies with the flat grinder. I'll pull 3 shots in a row, and they'll all be slightly different in terms of their timings.

I've e-mailed with Denis and he offered a few perspectives ranging from the burrs are still seasoning to inconsistent puck preparation -- to just that Flat burr grinders are way more demanding than conicals. I believe all of these are valid points -- especially when I compare and contrast using my conical on the DE1.

But the real issue I think that is at hand that both Denis pointed out -- and from my own experience -- is that the water dispersion in the DE1 is less than optimal. I often get "crater-style" channeling, which is worse using my flat than my conical.

That channeling has dramatically improved for me by implementing some feedback on the internal Decent Forums (Diaspora). I've been using the IMS SI200 shower screen to create more space between the head and the shower screen. Others have designed 3D and brass spacers to create more space with the factory shower screen. For me the change of using the SI200 and the next size up basket was dramatic.

You might want to do some experimentation on the dispersion front in tandem with your Flat research.

Although I agree a larger flat burrs set is more demanding to chase the grind setting in no way should you have inconsistency from the same bean in the same day.

The best way to test this is a very consistent machine like a comm. spring lever comparing weighed doses. As these machines are very forgiving to technique particularly tamping.

I have not read all of the replies, so sorry if this has been answered. I do have some play in the adjustment funnel (OP calls this the hopper?), however since I have the latest model which has spring force that acts on the upper burr plate, my adjustment stays consistent even when switching to/from coarse brew grinds. The same setting always yields the exact same results. The play that is in the adjustment funnel comes from play in the male/female threads, however as I mentioned, the upward spring force prevents variation when grinding.

I believe this spring mechanism mirrors the design in the Compak burr carrier system (and other grinders) but still requires the threads be shielded from grounds with the spring and burrs sitting inside the carrier.

I might have photos but I sold my 83mm Compak. I kind of miss it, brilliant grinder just massive and tricky to single dose without a decent weight on the beans and some fiddling.