Slow Down Your First Layer (Do This Every Time)
Last lesson covered the five settings that matter. This one is the first of them, and it's a habit more than a setting.
Slow down your first layer. Every time. No exceptions.
Here's my position, and I hold it close to fact: the first layer is the whole print. Everybody wants speed. They see a six-hour estimate, bump the speed to make it four, and the first layer suffers first. That's backwards. Get the first layer stuck down flat, even, no gaps, and the 300 layers on top behave. Botch the first layer and perfect settings everywhere else won't save you. Nine out of ten problems people bring me trace back to the first layer.
Why the first layer is different from every other layer
Every layer after the first bonds plastic to plastic. Same material, similar temperature, it wants to stick. The first layer bonds plastic to your bed. Different material, usually cooler right at the surface, and it gets one shot to grab. Miss it and the whole print is loose from the ground up. Corners lift. The nozzle drags the piece around. You get a shipwreck. Mine's on the shelf, my very first print, looking like a candle that melted in the sun. My bed wasn't level and I didn't know enough yet to slow down and watch.
So slow down. Specifically:
What to actually change in your slicer
First layer speed. Most slicers have a separate setting, sometimes buried under "speed" and labeled "initial layer speed" or "first layer." Cut it to around 20mm/s, even if your normal print speed is 60. Some slicers do this by default. Check it anyway. Don't assume.
First layer height. Slightly thicker than your normal layer height, not thinner. Printing at 0.2mm layers? Set the first layer to 0.24 to 0.28mm. That gives the nozzle room to squish the plastic down and get good contact with the bed. Counterintuitive. Do it anyway.
Bed temperature, first layer only. A couple degrees warmer than the rest of the print, if your slicer lets you set it separately. A warmer bed helps that first layer adhere. Then drop it slightly for the rest so things don't get too soft up top.
Watch it happen. Not the whole print. Just the first layer, usually around 5 to 10 minutes depending on the size of what you're printing. Stand there. If it's not going down clean and even across the whole plate, stop the print. Don't let it keep going hoping it fixes itself. It won't.
What "clean" actually looks like
Look for lines that lay down next to each other with no gaps, no see-through spots, no little beads catching on the nozzle as it passes back over. Look close, don't touch. Plastic looking translucent or stringy in spots means your bed's too far away there, or too hot, or your first layer speed still isn't slow enough. Squished flat with almost no visible lines means you're too close. Aim for the middle: lines you can see, no gaps between them.
When a student gets this right I tell them "that's a clean first layer, dang" and move on to the next thing. That's about as much praise as you're getting from me, and it means something when you hear it.
A word on skipping this because you're in a hurry
I get the temptation. You're excited, the print's queued, you want to walk away. Take Elijah, my nephew. He came to me at like 8 o'clock at night needing something printed for a school project due the next morning. Zero notice. Normally I've got no patience for that kind of last-minute scramble, and I told him so. But I printed it anyway, cranked the speed up to something like 7x what I'd normally run, first layer included, because there just wasn't time to babysit it properly. It came out rough. Held together exactly long enough to get turned in and graded. I brought up the deadline math to him for weeks after, because that's not how you do it when you've got the option to do it right.
That's the exception, not the rule. You had a printer sitting there and a deadline, so you made a call. Most of the time you don't have that excuse. Slow down the first layer, watch it, don't walk away until it's laid down clean.
Before next time
Run one print this week where you change only the first layer settings we covered, nothing else, and watch that first layer the whole way through. Tell me next class whether it looked different from your usual.