Thanks for your input Mike. What you say makes a lot of sense.PartierSP wrote: ↑Friday 10th December 2021 10:22pm Yes. But since the first pass on a printer is always at a non zero height, the program is expecting to have that gap as your first pass, nothing more. And this makes sense compared to traditional CNC programming/machining practices in general (Z zero is usually top or bottom of the part, generally not somewhere in between).
So essentially your first pass wont have enough plastic resulting the expected pressure against the bed and/or each pass on the first layer will be spaced out too much not getting enough pressure against each other. Now the shim you're using is a very thin one so I don't expect you'll notice too much. Its just you're not at the 'theoretically perfect'. And if you use glue on your bed you may be easily making up for this extra gap and some. But one thing I've learned with automated equipment, if it works for you, then it works for you.
I have heard of people getting so called 'elephant's foot' error on their prints. This is where the first layer (or first few layers) bulge out at the bed. I'm not sure if this is a sign of the nozzle being set too low on the first pass, or a temperature issue, or what. But its something to look out for if you try new techniques.
I thought we'd better wander into the Lounge to continue our chat, since this is more about 3D Printing than Gambas programming.
I moved away from using copying paper to set/check the gap because it is compressible. Hence I'm using a 1960s set of steel feeler gauges, which were made before we introduced the metric system, over here in the UK. The 2, 3 & 4 thou gauges are very approx equal to 50, 75 & 100 micro-metres. From my comparative checks, it looks like a sheet of 70gsm paper is around 80um (0.08mm) thick.
Earlier this year, I did a few tests with my printer where I compared results with the the nozzle-to-bed gap set to 2, 3 & 4 thou. I was printing with a 0.4mm nozzle and a layer height of 0.2mm. My printer seemed to print OK with a 3 thou gap, but when set to 2thou, the first layer was smeared on the bed. My conclusion was that the nozzle was too close to the bed, although it was not touching it.
I rationalized this by thinking that the bead of molten PLA was being 'pulled' slightly at 90 degrees to the nozzle, maybe at a rate slightly faster or slower than the x/y movement of the bed. (sounds a bit crazy now I've written it down!). But of course, if the extruded PLA does curl very slightly (due to this small extra gap) and stick to the bed, subsequent layers will do exactly the same, and all layer heights will be roughly equal. In my earlier example, the final layer will still be printed approx 0.075mm below the nozzle.
However, the next time I have a spare evening, I'll run these checks again and also try the 'no-gap' configuration. Have you noticed any smearing? How do you compensate for the paper thickness when you dial in a Z value?
Re: using glue, hairspray, blue tape... to help stick prints to the bed... I've always thought that a crazy idea. I have a glass bed and just keep my fingers off of it. I clean the bed with isopropyl alcohol (IPA) from time to time, and that's all I seem to have to do for good adhesion.
Elephants foot generally seems to be caused by either lack of cooling or too high a bed temperature (the first few layers should be printed with the cooling fan off, then the rest with it on.