one corner of the printbed leaves horizontal gaps

[andrewhodel 0]

I assume this is a belt tension problem, but I have been adjusting to no avail.

The front left corner of the print bed always leaves gaps when drawing circles, this problem does not occur in the other 3 corners.

Here's a photo illustrating the problem.

The issue mainly causes problems with de-lamination when printing a tall rounded wall on that side of the printer.

 

[illuminarti 18]

Try powering off the machine and moving the head by hand, using light fingertip pressure on the sliding blocks. Both axes should move fairly easily and smoothly, and with equal pressure for both. Is there more friction in that corner of the bed?

 

[gr5 2,265]

Does this happen on higher layers? Above 3rd layer? If not then maybe it's a "bed leveling" issue: If that corner of the bed is slightly lower then the first layer isn't squished as flat and wide as on other parts of the bed. More likely illuminarti is right and things aren't lined up. Looking from above, see if the long belts line up with the rods perfectly parallel. Move your eye around until the edges line up. Do this under good, bright lighting. You might need to move a pulley a few mm to either side to get it to line up better. Try moving the print head and see if the belt is always straight or starts to head towards the pulley at a steeper angle as it gets closer.

 

[andrewhodel 0]

Thank you for the replies.

This happens all the way up the print, I've seen it 5-8cm up on prints which may seem to indicate the table is level. I've also spent much time leveling the bed so I hope it is quite square.

Based on this bit from gr5, "Try moving the print head and see if the belt is always straight or starts to head towards the pulley at a steeper angle as it gets closer." it likely has something to do with that. Thinking about the way this works, technically with a belt tensioner that raises the belt you will have a non linear plot of the belt speed at a constant pulley speed.

I added printed belt tensioners to all 4 blocks to make them properly tight in the past, this certainly changes the angle of approach as you get closer to the pulley on each end.

It seems, if I am thinking right, that this would exactly cause this problem. It also seems, thinking in this way, that any belt tensioner design which drives the belt upward and changes the angle of approach could be causing more harm than good.

I guess I need to get shorter belts that will be capable of being taught with the standard "tensioner" that pulls the belt down into the block and does not raise the edges causing this angle of approach problem.

I'm in Uruguay so getting belts is a slow process, but I will update this post with the results of this once finished.

 

[andrewhodel 0]

I also want to mention that I have spent much time aligning the "squareness" of the X and Y axis with an accurate caliper so I hope it to be correct.

On this point, it would be an awesome update the Ultimaker to see each block with a raised notch that is perfectly level to the top plane of the top plywood part of the frame. Add a distance marker etched with laser on the same plywood top of the frame top and one would easily be able to pull a caliper to square the printhead on all 4 corners.

You can do this now, kind of, and as the build manual suggests there is a wooden cap part to use to measure this... but those who try to account for the very slight angle difference and apply Pythagorean might drive themselves mad trying to properly measure this.

 

[gr5 2,265]

are your tensioners on the left and front parts of the belts? That would explain why this happens on the front left corner.

There are some clever tensioners on thingiverse that don't affect this angle.

 

[diabolov 0]

Just a thought but are you using the ultimaker acrylic bed ? have you measured the thickness of the acrylic at each corner. I know from experience that acrylic sheet is never the same tolerance over its length/width. Also have you tried

turning the acrylic bed around so front becomes back and does the problem now occur in the rear right corner?

If you can eliminate some possibilities then you can narrow it down.

Regards