My new favourite 3D printer bed leveling method

Should I heat the extruder when bed leveling, or leave it cold?

 

If hot, how do I deal with oozing filament?

This is my new method which addresses these issues.

Whenever I've tried to level the bed with the nozzle heated to (say) 180'C, I get sticky plastic on my feeler-gauges.

I sometimes turn the printer on and check the nozzle-to-bed gap with the bed heated and the nozzle cold. This generally leads me to believe that the gap is too small. But actually the problem is that there is often a small bead of hard plastic at the tip of the nozzle, which formed and cooled the last time I used the printer.

Its quite difficult to see this small blob, even using a simple magnifying glass. But for the photo above, I used a 60mm macro lens on my Olympus E-M5.

I estimate this blob to be between 0.2 - 0.3mm high. So if I were to reset the bed height and not realise it was there, I would end up with a much larger nozzle-to-bed gap than required and would probably have problems getting my print to stick to the bed.

procedure

When using PLA, my new bed leveling procedure is as follows:-

• Pre-heat the bed (60'C) and nozzle (200'C)
• Remove the PLA filament from the extruder
• Manually advance the extruder to expel any residual filament
• Examine the nozzle to ensure that it is clear of molten plastic

Note: I use a strip of cardboard (typically the inside cardboard face from a cereal box) to wipe across the flat face of the nozzle, to remove any trace of plastic.

• Check and adjust the bed/nozzle gap in the usual way using a suitable feeler gauge (in my case: 3 thou/75um). Basically; measure > adjust > next corner > repeat... until no more adjustment is necessary
  
• Now refit a filament reel, print & test!

So the key to my new procedure is to remove the filament and ensure that there is no plastic on the nozzle which will affect set-up.

I did try to use a USB camera to view the nozzle on my laptop, but the image was too small/low resolution. You used to be able to get small USB 'microscope' cameras from suppliers such as Amazon, so I may investigate this further.

why print in the centre?

I normally print objects in the corner nearest the 'home' position. (OK, obviously if I'm printing an object with a very large base, it may have to be positioned near the centre).

One of the benefits of this approach, is that its much easier to make fine adjustments to the bed by just tweaking one corner, than to have to re-adjust all 4 corners.