Posted by: @chmax

I thought it would be on the speed setting and not on the structural one, at least reading some of the posts in the forum in the subject...

Posted by: @gb160

I did both accelerometer-based tuning but I still see VFA when printing pcblend with .15 structural setting.

 

I think some VFA is always going to be present on structural profile on this printer.

 

Nah, there's a certain range where VFAs appear the most, but generally speaking print fast to avoid bad VFAs. 

Posted by: @gb160

Make sure you're always checking with the printer at the same temperature (eg always cold) as I'd imagine some variance is to be expected depending on thermal expansion.

Posted by: @gb160

I did both accelerometer-based tuning but I still see VFA when printing pcblend with .15 structural setting.

 

I think some VFA is always going to be present on structural profile on this printer.

Posted by: @wdlandry

I’ve been checking once a week. I have noticed I’ve had to adjust slightly nearly every time. Some initial settling/stretching of the belt is expected but I would have assumed it would have stopped by now. Starting to wonder if something else is causing it to loosen but don’t have enough hours on the printer yet to flag a concern. If this is still the case in a few weeks I’ll likely look more into it

Posted by: @samael

I assume there is no general rule, but how often do you tighten the belts?
Depending on the accelerations/decelerations and overall moved meters of the head, its hard to judge imo.

As this is my 1st printer, i fiddle with it every 2 weeks or so to check, and always find that the tuning has changed slightly, is that normal if used almost daily?

 

I did both accelerometer-based tuning but I still see VFA when printing pcblend with .15 structural setting.

I think some VFA is always going to be present on structural profile on this printer.

Posted by: @samael

I assume there is no general rule, but how often do you tighten the belts?
Depending on the accelerations/decelerations and overall moved meters of the head, its hard to judge imo.

As this is my 1st printer, i fiddle with it every 2 weeks or so to check, and always find that the tuning has changed slightly, is that normal if used almost daily?

I did both accelerometer-based tuning but I still see VFA when printing pcblend with .15 structural setting.

Posted by: @newprinter

Are you all just eyeballing this or are you squaring it some other way?

Posted by: @jurgen-7

Posted by: @gb160

Side note, I think rather than these brackets actually bending, some aren't perfectly square to begin with. I don't think the forces the printer is putting on them is enough to bend steel.

Agree. I measured mine before installing them, and they were certainly off by a degree or two.

The material is quite soft; the brackets are easily bent while holding them with two fingers. But I agree that plastic deformation during printing seems unlikely. Some elastic deformation is another matter, as witnessed by the fact that unequal belt tension can easily "adjust" the gantry. 

 

Are you all just eyeballing this or are you squaring it some other way?

I used a machinist square to measure the brackets before assembly and bend them to exactly 90°. I still had to do a small in-place correction after the gantry was installed (and before the belts were added), checking that both end stops were hit at the same time.

At that time (gantry installed, but no belts), I also made sure that the two Y rods are parallel and at the right distance: Loosened the screws which hold the mounting blocks  for one of the Y rails, pushed the X gantry all the way back and forth to nudge the Y rail into place, gradually tightened the mounting block screws. That's a strep which is missing in the build instructions. (Unless Prusa has since added it?) I have been wondering whether some of the homing problems might be due to increased friction and tension in the Y drive if the rails are not properly aligned.

As this is my 1st printer, i fiddle with it every 2 weeks or so to check, and always find that the tuning has changed slightly, is that normal if used almost daily?

Posted by: @gb160

These are the reasons the recommendation is to attempt to return the L brackets to 90degrees by bending. This is really the only consistent way of suggesting a fix to customers without having to ship out new brackets… which could just bend again if belts are tightened inconsistently. The flaw is in how easily those brackets bend.

You're absolutely right but I think we're wasting our time here. There's an old saying 'You can lead a horse to water, but you can't make it drink' 

Side note, I think rather than these brackets actually bending, some aren't perfectly square to begin with. I don't think the forces the printer is putting on them is enough to bend steel.