That is because of the much wider variety of available materials with which we can print. While in theory, one gap could, potentially, meet every need, I've not found it quite so simplistic.
The Goals of a Proper Gap
The role of the gap between the print head and the printing surface is to satisfy two competing needs. The first need is for the object being printed to adhere to the print bed with enough adhesion as to not come loose during printing. But. this goal has a bit of a conflict with the need to be able to remove the piece from the print table once the print job is down.
And, this is compounded by the fact that different types of materials have greater tendency to stick than other materials. This largely due to different melting temperatures.
The trick, therefore, is to be able to find the proper gap that effectively balances both needs for a particular material.
The Tool To Test Balance
To initially test a particular gap setting, it would be a mistake to print a larger object. I use a small, round disk that is just 20mm in diameter and 3mm high. In addition, I chamfer the bottom edge so that I have a lip of 1mm under which I can insert a palette knife for removal.
|Gap / Removal Test Tool|
It's a simple object that only takes minutes to print. Yet, it quickly allows me to determine if the gap is small enough to produce the adhesion I need during print jobs and if the gap is wide enough to allow for relatively easy removal of printed objects once the print job is completed.
There is little value of printing an object only to have it broken due to it sticking to the print plate too tightly.
Watch the Gap Tool being printed
The first layer is critically important. If you see layers that don't lie flat, then the gap is probably too wide. When you remove the test print, check to see that the bottom beads of filament have a uniform flatness. (You will see the individual filament lines and that is OK.)
Remember the Chamfer Trick
Creating a chamfered lip around the bottom of your design goes a long way to helping you safely remove items from the print table. But, even that won't help if there is too much adhesion. There should be some,; but, not a huge amount of resistance when removing items from the print table.
The Starting Place
Using a piece of 20lb bond paper to measure the gap is a great place to start if you are printing standard PLA 3D Ink. But, when printing with Tough 3D Ink or other more exotic materials, the paper gap might be too small. I have found that, in fact, objects printed with Tough Ink can be very hard to remove if printed with a gap that worked perfectly fine for regular PLA.
So, when switching materials it probably isn't a bad idea to reset your gap based on your own experience with that material.
Fortunately, the M3D print client offers a very convenient way to adjust gap height without having to go through the entire gap setting process. More on that later!