First to second layer adhesion issue

Hi

I'm struggling with an issue of poor adhesion between the first and second layers of my prints, there always seems to be a gap that develops between the first two layers of the prints, even though the rest of the print is pretty good quality. The edge of the first layer then tends to split off at the weak seem if it's a part that handled a lot.

See the attached picture for an example, can anyone suggest possible causes to investigate?

My set up is a Prusa i3, printing in PLA at between 200-215oC onto heated bed at 65oC first layer, then 60 for subsequent layers.

Raise bed temp to 70 and keep it like that for the whole print, lower your hotend temperature to 195, slow down your first layer to 50% of regular printing speed and finally use a layer height not bigger than 60-70% of your nozzle size.

Don't know what speed are you trying to print at, but don't go beyond 2400 mm/min, I usually print at 1800 I know is slow but have never had a bad print.

Check the gap between the bed and nozzle. Put this value in your slicer. Your first layer seems a lot larger than the others so I am wondering if you are just dropping filament on the bed. If you are deliberately over extruding the first layer as is often suggested you may mask the issue.

Thanks for the ideas, I will try them out tonight.

Quote
ggherbaz
use a layer height not bigger than 60-70% of your nozzle size.

I've got a 0.4mm nozzle and printing at 0.3mm (if I recall correctly), so that's 75%, otherwise it's printing at 0.2mm which is obviously 50%. Which of slightly-above or far-below is preferable?

Quote
MCcarman
Check the gap between the bed and nozzle. Put this value in your slicer. Your first layer seems a lot larger than the others so I am wondering if you are just dropping filament on the bed. If you are deliberately over extruding the first layer as is often suggested you may mask the issue.

This sounds plausible, how do I go about measure the gap between bed and nozzle? Do I need feeler gauges? I don't have any, I've just been using the nozzle-grips-a-sheet of paper method, do I need something more precise?

I'm certainly not deliberately over-extruding, but I will check the settings on that too

You might try looking at Triffid Hunter's Calibration Guide, [reprap.org], if you haven't already.

The general rule of thumb is that you want your layer height to be less than 80% of your nozzle diameter and your layer width (typically set automatically by the slicer software) to be at least 1.2 times your nozzle diameter. I am currently printing at 0.2mm x 0.48mm with a 0.4mm nozzle without issue. You should be able to go as high as 0.32mm with that nozzle, and some people will just set a default width of 0.5mm. So you should be fine at 0.3mm unless you want to print finer details.

I doubt the heated bed is your issue if only because I print fine without one. Definitely try increasing the temp to 70 (and keep it there throughout the print) as the temperature is the reading at the thermistor, not necessarily the top of your build plate where the print sits. My guess about your layer bonding would be the temperature of your hot end and / or possibly cooling on the first layer.

If your PLA needs 210-215 temperature range to bond correctly throughout the print, try increasing your first layer temperature to 220. I recently started printing PETG and had to set the temperature for my first 3-4 layers to 250 before dropping it down to 240 to finish printing.

Also, make sure that your print fan...the one pointing towards the build plate, possibly at the nozzle of your hot end...is turned off for the first layer or two. Once the first layer is down, you can have your slicer activate your cooling fan as needed. In case you have an all-metal hot end, you should also have a second fan pointing directly at the fins on your hot end, above the nozzle and heat block. This fan MUST be turned on whenever your hot end is active to prevent heat from creeping up and jamming your hot end. I configured my firmware to activate the fan at 35 degrees to turn it on and off automatically, but a lot of people will just wire the fan directly to the 12V power rail.

This evening i tried a few of the suggestions, I have made a little progress but the issue isn't resolved.

First I tried increasing the bed temperature, reducing the extruder temperature and reducing the first layer print speed further (I was already printing at 30mm/s and I dropped it to 20). None of these really made a difference to my issue, though the reduced temperature slightly improved the finish of the rest of the part.

Next I looked at first layer height, I can't measure the gap between nozzle and bed in any meaningful way, but i did discover the slic3r settings gave me a first layer height of 0.35 and the rest of the print 0.3. I reduced the first layer height to 0.3 and saw an improvement in the adhesion on another test of the small part shown above. On a slightly bigger print, I still saw a significant gap between first and second layers.

I reduced the layer height to 0.2mm and saw some improvements on the next print. While the overall print quality was better, the first layer wasn't laid down particularly well and the time increase on larger prints would mean that I would prefer to stick with 0.3mm for now.

Finally, I tried reducing the first layer to 0.28 and increasing bed temperature to 75. This again seems to have made a small improvement, the gaps between the first layers are smaller but are clearly still present. Also, in some cases there have now been small gaps forming between the second and third layer, where previously it was only the first and second layers that were the problem, perhaps this is a result of the increased temperatures?

I also usually print at 30 mm/sec, so 50% for first layer is 15 mm/sec. The first layer is the foundation for the print and it's better to wait longer for a completed print than rush a failed one, once you have completed successfully an 84 hours print with a 0.2 nozzle you will understand it.

0.3 for a 0.4 nozzle is in the limits, it can be done but will depend on the bottom shape of the nozzle, if pointy will fail if flat might succeed. Try a small print with a 0.2 layer height all around and see if there is any difference.

Going higher on temperature on both bed and hotend will only increase your chances for failure, get to know your filaments, do test prints increasing 2 degres every 5 to 10 layers and observe the changes, pick the best 3 ones and now play with speed. Once you have found out the limits of your filaments and printer, you have eliminated 80% of possible failures.

It might be a good idea to check your Z calibration and to find what layer heights your Z threaded rods can do, it is an M8, T8 or a ball screw?

you shouldn't really keep you bed at 70 degrees with printing pla, and have change to lower few layers up, as the bottom layers will swell you end up with elephant foot issues, i used to print 70 throughout print and wondered why i was get dis-coloured first three to four layers and a wider foot print when i was printing test cubes and it was down to bed temperatures so i start at 70 and then 50 degress

Edited 1 time(s). Last edit at 06/12/2016 09:04AM by chris33.

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