I’m trying to get [Tulio’s Marble Machine #3 on Thingiverse][/https://www.thingiverse.com/thing:1385312] to print in PLA and I’m have a heck of a time.
The main issue right now is the bottom layer. It’s a big circle with several full coverage layers and after they print and I remove the object (pulled it off early to check) the bottom layer extrusions are not fused. They pull apart like spaghetti squash. 
The individual filaments are not fused together nor are the fused to the next layer.
I’ve tried several variations of speed and so far I’m very frustrated. Any ideas? Other objects seems to print fine. Thanks
My guess is you’re a little too far from the bed for the first layer. Try using a little negative Z-offset, or adjusting the bed if it’s not a Mini or Taz6.
Could also be a lot of underextrusion.
I have a TAZ 6. It’s printing smaller items perfectly. The first layer seems to be right on target in terms of Z. Could it be crappy filament? It’s basic PLA from Lulzbot I got on my first order. I’ll have to try another.
I thought perhaps it was because the default bottom speed is like 15 mm/s which was very slow. Perhaps the PLA was cooling too quickly? I bumped up the bottom speed to 50 mm/s but that didn’t make any difference.
Wonder if anyone her has printed the marble machine and was willing to post their Cura 19.x profile they used for PLA?
I don’t see any reason a particular model wouldn’t be close enough. If you have smaller items dialed in, it should be about the same. It’s possible that the model itself has a gap on the bottom. You could try looking into that. Perhaps tell Cura to drop the bottom to the bed. Even a fraction of a mm is enough to do what you’re seeing.
It’s also possible you’re cooling too fast, but a proper first layer even with the fan on max should still fuse if your Z is right. Any bed heat set up? I doubt the speed has anything to do with it, slower should actually be more accurate, but 15mm/s seems a bit slow.
Could try to increase the initial layer extrusion width parameter…
Well watching it print the filament is printing in rows adjacent to each other on the first row. I let one run and the subsequent layers were fused to each other as well as the perimeter but in the center the first layer still separated into individual strings.
I’ve done a bunch of stuff with rafts for example and the rafts are all solidly fused. I did the Venus box and all the parts printed out perfectly, some with rafts and other without but the first layer was solidly fused in all cases.
It’s only this one object. Hmm… Something Cura 19.x is doing?