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I have an Anet A8 printer for about 4 months, set up pretty well (or so I thought) and printing a number of models pretty well. I made a large 3" x 6" box with a sliding lid yesterday and when it was done there was a gap on one side when the lid was slid on. I checked the parts and it turns out they are not square - which means the X and Y axes are not square to each other.

I'm wondering how to adjust this - I'm thinking that extending the distance between the back of the frame and the front by adjusting the threaded rods that separate them to a wider distance on the side where the angle is obtuse. Obviously one of the first things I'll check is that the distance between the front and back is the same (I can't imagine why I never checked that before, come to think of it).

Does this sound like a sound plan?

DarkTerritory
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  • Please post a picture or two of the print. It may be a matter of slack in the drive belt(s) rather than the physical mounts of the carriage. – Carl Witthoft Mar 29 '18 at 14:29
  • Ended up being rushed last night and didn't have a ruler of sufficient length to check the whole printer. I was able to determine that the distance between the front wall and the intermediate wall was exactly the same. Ruler wasn't long enough to reach all the way back. – DarkTerritory Mar 30 '18 at 15:29
  • I managed to print a 20 mm cube, and it showed that there was a difference of about 0.6 mm from one diagonal corner to corner than the other. Also showed my X dimension was about .2 mm thicker than it ought to be. Y was withing 0.05 which seemed good to me. Z was spot on. So it looks to me as though it's definitely skewed from X to Y. I'll know more when I can get a longer ruler on it. Then I need to figure out how to correct it. – DarkTerritory Mar 30 '18 at 15:29
  • Pretty difficult to say on such a small cube. Print this: https://www.thingiverse.com/thing:2280529 and measure the diagonals. Have you replaced the belts already? This is probably your main problem! – 0scar Apr 02 '18 at 09:06
  • Thanks for the thing. I'm in the process of adding new frame braces and X/Y belt tensioners, the work should be done tonight and this is the first thing I'll try. – DarkTerritory Apr 04 '18 at 19:38

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I recently went to the same issue on my CoreXY printer (culprit was uneven belt tension in the 2 belts), but you have a Prusa style printer like my first Anet A8 printer.

If you just found out (because you are printing large models now) but always had this issue it could be frame related. You should check your printer and try to fix the geometry that is causing this. If this is impossible you could fix this by changing the firmware (see below). If large prints used to be accurate, but are now skewed, you could be facing stretched belts. Replacing them will fix the issue.

Skewness compensation in Marlin: When X-Y are skew (or any other plane like X-Z or Y-Z) you can fix that through the firmware software in Marlin Firmware. Please go into the Configuration.h file and look at the instructions; please search for "Bed Skew Compensation".

Basically you are required to print a giant square and measure the diagonals, these should be the same, but apparently are not in your case.

0scar
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  • No, an AnetA8 has belts to drive the bed and the extruder carriage. Not sure what Prusa model you're thinking of – Carl Witthoft Mar 29 '18 at 18:51
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    @Carl Witthoft I also have an Anet A8 which is a Prusa clone, I have no clue what you are asking here! The Y axis is not properly aligned to the X axis here, therefor he needs to check the frame. Or the belts. – 0scar Mar 29 '18 at 19:20
  • Sorry -- your phrasing seemed to intimate the lack of belts. It's pretty difficult to assemble a Prusa clone in a way that causes X-Y not to be perpendicular. – Carl Witthoft Mar 30 '18 at 13:21
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    @Carl Witthoft No problem, the frame is acrylic, reasons enough to introduce non perpendicular movement when improperly fastened (allthough tough I admit). Even the original Prusa itself has X-Y compensation it the firmware. The lack of information of the OP does not state if this problem was present in the beginning. But most probably the OP's belts are stretched. – 0scar Mar 30 '18 at 13:28
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To correct x-y axis alignment to 90 degrees: Loosen the nuts on the two threaded rods at one end and in the middle. Lower the Z-axis to its lowest level. Place a square block of wood or metal so that it rests on the table and is snug against the X-axis rods. Slide the table so that either its rear or front edge is under the edge of the block. There you can clearly see any misalignment by comparing the edge of the block and the edge of the table. Now the 'fun' part: rack the entire assembly, pulling the diagonal corners to square the table and block. You may have to tape the assembly down to keep it in place while you spin the threaded rod nuts back into place....gently,then carefully snug the nuts while watching the table and block to insure they stay put!

Gordon L. Scott
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  • Actually this worked and is pretty much what I ended up doing in a roundabout way. I added a set of braces on the frame to stiffen the front and back, and when I was done I checked the ends against each other diagonally and slowly tightened up the frame until everything was right and square. Now when I print objects they are coming out square or nearly so. – DarkTerritory Oct 15 '18 at 22:18
  • Neat trick with the wood block, but I don't like forcing the frame. What I did was widening the holes for the threaded rods in the front plate (e.g. with a Dremel milling or sanding bit). This way, I can just loosen the front-most nuts, and then slide the front plate left or right, which causes the "guide rods" to move with it. This way, I can directly change the X/Y angle without requiring any force. Then just re-tighten the nuts carefully et voilà -- square! – Fritz Dec 22 '21 at 13:19