Introduction

Bed Levelling is only the beginning of getting prints to reliably stick to the print bed and getting a perfect 1st layer.

The next challenge that presents itself is the 1st layer thickness and getting it to stick. With dual extruders this becomes even more of a complicated issue.

If the extruders are too close to the bed, the second extruder will scrape off whatever’s put down by the 1st extruder because there isn’t enough clearance. Too much clearance and the print won’t stick.

Bed Surface

The two most common print bed surfaces are aluminium and glass. Both of these are unforgiving when it comes to 1st layer tolerances. If the nozzle is too close to the bed, the extruder will struggle to extrude filament. If it’s too far, the extruded filament simply won’t stay in place. With glass in particular, there’s also a danger zone where the plastic sticks too well, and can’t be removed without smashing the glass. I’ve had this happen enough times that I no longer use glass on top of the print bed.

There’s another factor at play here more critical than 1st layer height when it comes to adhesion. If the filament has nothing to grip onto when it’s extruded, layer height alone won’t help. Short of the filament being squashed down by the extruder, glass and smooth aluminium are often too smooth for good adhesion.

A simple magic formula that roughs up the surface nicely is PVA watered down to the consistently of full-cream milk. People have spoken about sugar formulas and the threat of ants. It’s not so much the “stickiness” of a treatment as it is the texture produced.

Many of the commercial bed surfaces that can be purchased and applied to the bed are textured. What’s really needed is something for the extruded fliament to hold onto to, vs sticking to per se.

To this end, watered down PVA produces an excellent texture when brushed onto glass, aluminium or any other smooth bed surface. This textured foundation allows far greater 1st layer tolerances where the filament will still adhere, but doesn’t need to be pressed into the bed. With a higher 1st layer height, clearing a 2nd or 3rd extruder nozzle is far easier.

Commercial bed surfaces offer a really effective texture. Roughly the equivalent of painters tape which is ideal, but tends to stick a little too readily to finished products. Tape also gets damaged by the extruders and the prints themselves when they’re removed. In short, tape is quite high maintenance and doesn’t take long to get expensive.

Summary

Many articles I’ve read focus on how sticky the print bed is. Once I started experimenting with texture and layer height, 1st layer adhesion became far easier to consistently calibrate for.

I’ve written a separate article on the virtues of calibration which will help vastly improve the quality and reliability of your prints.