Bed Leveling

The diagram shows a top view of the heatbed on my Prusa Mendel. S = the position of three adjustment screws for leveling the bed. The spots are the test results with green = good and red = poor.

My heatbed is glass then aluminimum then PCB then lasercut wood.

I don't see a way to correct the problem using just the screws. Any suggestions on how I can get it level? Shims under the glass perhaps?

Thanks, Andy



Edited 1 time(s). Last edit at 08/22/2012 04:53PM by ajayre.

why glass alu and pcb.....? the alu only deflects the heat

i would remove the alu as that can be deformed then use the glass right on the pcb and measure again

why are you using only 3 screws to hold the bed ? prusa I2 uses 4 screws to hold the heated bed to bottom plate then the glass is held on using bulldog clips

you can then alter the height in each corner is needed but normally i dont see why you would. if your prusa frame is all level then the base should be level therefore the heated bed. i dont use springs i just raise the bed 4 m4 nuts form the bottom plate and bolt it down tight.

if you dont want to alter your setup the other way i can think is the alter the frame it self on the foot vertex move the vertical rod up and down will alter height in the corners.

To answer the questions - I don't know why aluminium and three screws. It's a kit from RepRapPro aka Adrian Bowyer and I assumed there is a good reason it is why it is.

It's not a large variation towards the problem corner, just enough to make adhesion poor on the first layer.

Andy

Edited 3 time(s). Last edit at 08/22/2012 05:34PM by ajayre.

It uses three screws because four screws over-constrains the bed. With four screws it is easy to make the bed warped. With three screws the bed will always be flat. If you want to level your bed as you have it shown there, simply lower the bottom left screw point and raise the right screw point.

I just skimmed through so not sure how helpful this will be but I would put the side that has two adjustment screws parallel to the x axis, from what I can see that would make adjustment easier.

I would bet the issue is the Y rails not being parralel, so the bed twists as it moves end to end.

I recommend reading this. Mostly, just print (or otherwise acquire) the thumb screws. I have them on mine with the four screw setup. Leveling was a cinch; I placed a sheet of paper on my print bed and used pronterface to move my extruder to each corner and the middle of the plate. Just turn the thumbscrews until you can move the paper from under the nozzle with just a bit of resistance.

4t1fy Wrote:
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> I recommend reading this. Mostly, just print (or
> otherwise acquire) the thumb screws. I have them

That method involves four screws, but my question is how to use the three screw system.

Thanks for the suggestions. I understand that four screws could warp the bed, but perhaps it is already warped and I need to apply the opposite warp to get it back into shape? I'll try adjusting the two screws as suggested by Cameron.

Andy

If you adjust any screw, it makes the bed pivot about about a line between the other two screws. So, in the case above, I would start by altering the bottom left screw.

FatFreddie Wrote:
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> If you adjust any screw, it makes the bed pivot
> about about a line between the other two screws.
> So, in the case above, I would start by altering
> the bottom left screw.

Ah - yes, of course - now I can picture it in my head what an adjustment to one screw will do. Thanks!

Andy