Skew on only half of the bed

[xojins]

I'm having something weird happening. Let's say I print an object that has a footprint of 20mm x 20mm. If I position it within the first 70mm (about halfway) of the Y-axis, it will print great. However if i position it where y > 70mm, then I get skewing every layer. The skew is about 1-2mm every layer.

Here is a picture:
[img]https://lh4.googleusercontent.com/-EWmL ... mage43.png[/img]

Anyone ever see anything like this or know what might be causing it?

H-1.1
Ramps 1.4
Repetier Firmware 0.73

Thanks!

[Polygonhell]

It's almost certainly a mechanical problem. Probably something rubbing or misaligned, I'd start by moving the Y axis by hand and see if it's harder at one end of the bed, if it is the most likely cause if the Y rods not being quite parallel.
The reason it's likely mechanical is that all the steppers rotate multiple times to cover the front of the bed, so there is no "difference" to the electronics from front to back.

[xojins]

interesting... I know the rods are parallel.. spent a lot of time measuring/adjusting to get it perfect... I have a luggage bag scale that I can attach to the bed to see how much force needs to be applied when the bed is at y min and y max.

Thanks for that tip

[Polygonhell]

You don't really need to measure that accurately, just push it around with your hand, you'll feel it if there is an issue.
It could also be the Y belt walking as it moves and rubbing against the fender washers, you just have to watch it.

[xojins]

Ok.. well the distances were equal and there was varying resistances.. I did a little more homework and came up with this:
[img]https://lh5.googleusercontent.com/-R_tb ... mage45.png[/img]

Because the belt angle changes when the bed is moved, the resistance force applied to the pulleys increase/decrease.

My solution was to put a 15mm block under the plexiglass and affixed the belts to the block. This made the resistance force constant as the bed moved.

This fixed my issue and now I have no skew

[stienman]

You might have made the same mistake I made. The y axis bars go under, not over, the bars on the front and back of the printer. This causes the bed's belt attachment points to be above the belt path, leading to problems as the bed approaches the limits of its travel.

The block solution you present will fix it, but putting the y axis bars below the threaded rods is the ideal solution, and will give you another few mm of z height as well.

[xojins]

Oh crud.... I just saw your thingverse post with the picture of your machine.

Looks like i'll be rebuilding my printer a 4th time