hi gr5,
thank you for your very comprehensive and informative reply it has given me a much better understanding of the principles involved. I did notice that the problem occurred more on the cooling fan side of the print and also on the side of a very cold draught as I am operating in a cold draughty and unheated garage and as you say the problem occurred more on angular surfaces with thin sidewalls. I think that you have also hit on the bonding between layers as being a possible cause. I also had another issue and posted a question (oversize prints) in one of the other topics, this was due to large a setting on the x and y steps / mm, so I would also be suffering from weak horizontal bonding as well poor vertical bonding.
you have given me the best possible answer on this problem and how to reduce it just has the contributer on the other topic and would like to thank you again and this site/forum for expanding my knowledge and understanding in the world of 3d printing.
dave
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gr5 2,224
Yes!
First you have to understand why it's doing this. ABS has a much higher "softening" or "glass" temperature. About 100C versus 60C for PLA. To get good layer bonding you have to get the ABS well above 100C - the plastic on the layer below that you are printing on top of. This is trivial with PLA because the plastic coming out of the nozzle is about 200C and the air is about 20C and heating existing plastic to 60C (PLA) is much easier.
So the solution is heat. One common solution is to turn the fan off. If you print at the same speed and so on that you had been printing but simply turn off the fan you will get MUCH better layer bonding. The problem is if you print overhangs or bridges the quality will suck. But if your part has only vertical walls (like a gear flat on the bed) then this is a great solution.
Another technique is to simply lower the fan to 30% max. This usually is not good enough and you will get layer bonding issues still but not as bad. Not nearly as bad. Older slicers before Cura were very good with ABS and would only turn on the fan a few seconds here and there for overhangs and bridging.
Another technique is to heat the air to about 50C. The difference between 100C and 50C is much less than between 100C and 20C and is usually enough to get good bonding even with the fan at 30%. This is a very simple technique - just put a spare cardboard box on the top and cover the front with saran wrap. It will be nice and warm. Don't seal the back of the cardboard box - you don't want it getting over 50C or the servos start to suffer.
Another technique is to remelt the layer below by slowing the head down to 5mm/sec. Not a great way to do it, but it works great. With very thin layers - say .05mm you can print a bit faster.
I would think thicker layers in general would help - say .2mm layers versus .1 because now you have more thermal mass to melt the layer below. But many ABS experts claim that .1mm works better for layer bonding.
You might think hotter nozzle temp would help but the difference from 100C to 240C versus 260C is not a huge difference and above 250C it starts to get very easy to bake the ABS into nozzle clogging gunk if you aren't printing non-stop and not too slowly.
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