RepRapPro Mendel aluminum heat spreader not flat

Hi,

I have a RepRapPro Mendel that I've been struggling with to get the print bed to be completely level with respect to the head.

I mounted a digital dial indicator to the X carriage where the nozzle assembly usually goes, and I was using it to measure the flatness of the aluminum bed.


I can get three out of the four corners to be level between each other within around 0.05-0.08mm or so.

However, one corner is way off - it's about 0.65mm higher/lower than the other corners.

I also get similar results if I perform the same test with the glass plate on top of the aluminum heat spreader.


The corner that is too high/low is on the side of the bed where there's one leveling screw supporting it in the middle, and it shifts from either the front right corner or the rear right corner depending on how I tweak the leveling screws.


I can print reasonably well on bare glass with a 0.12 1st layer height and a 0.2mm normal layer height - but only on certain sections of the bed.

An entire 1/4 of the bed is completely out of whack and I can't figure out why.


Any ideas?

Thanks!

Are your X and Y axes' smooth rods perfectly parallel?

Is the plate actually flat? A piece of glass comes with the kit, this is pretty much guaranteed to be flat, so if the plate is bent it should be obvious to spot any gaps by putting the glass ontop of the aluminium.

However, in my experience of the Mendels, if the 2 Y smooth rods aren't perfectly parallel and aligned it is possible for the Y frog to twist giving the symptoms you describe.

I don't think the X and Y rods are level to each other...

I measured the left-hand Y rod this morning against the two X rods, and the Y rod appeared to be sloping downwards from back to front - the vertical gap between the rear X and front X rods and the Y rod differed by at least 2mm.

I had installed these Y rod leveling adjusters, but they couldn't bring the Y rod end high enough to correct it:

[www.thingiverse.com]

They're installed upside-down with the screw facing up, with the Y rods underneath.

I had found that the printed U clips that originally came with the kit would shift downwards when you tightened the nuts against it - the clips bent inwards at the top and formed a wedge.


I suspect that my Z rods are not aligned perpendicular to the front-back horizontal M8 threaded rods, and that slight angle is throwing off the X rods - they're shifted at an angle instead of being horizontally parallel.



And yes, I have the glass plate - with the plate on the bed, I was getting similar out of flat symptoms in the range of 0.5mm-0.65mm.

Does the glass bend or twist to conform to the aluminum plate at all?

Sorry I don't think I explained properly. If you sit the glass on top of the aluminium, without even clamping it and ignoring the extruder for the amount, it there any visible gap between the aluminium and the glass then the aluminium is bent and you need a new piece. If however there aren't any gaps then it then it is an alignment problem. RepRapPro sent you out a frame measuring jig. Double check all the measurements on the Y axis. I also find it helps to get the measurements on the Y axis right with the bearing holders on the Y frog a tiny bit loose, then clamp them up when on the bar as it ensures everything is lined up.

I had the exact same problem. Putting the edge of a steel rule diagonally on the plate clearly shows the warp.

RepRapPro replaced my plate with a new one under warranty and it is perfectly flat.

Andy

ajayre Wrote:
-------------------------------------------------------
> I had the exact same problem. Putting the edge of
> a steel rule diagonally on the plate clearly shows
> the warp.
>
> RepRapPro replaced my plate with a new one under
> warranty and it is perfectly flat.
>
> Andy

I put a steel rule diagonally across the plate in one direction - front left to rear right, and it appeared flat.

However, when I put it on the other diagonal, front right to rear left, there appeared to be a bow/gap in the middle of about 0.2mm.

Would that indicate a warped plate?

You said that one corner is 0.65mm higher/lower that the others. You should see that size of gap. My gap was about 1mm.

Andy