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Printing cracks....hmmm

Posted by antlvk 
Printing cracks....hmmm
April 21, 2014 02:59AM
Wonder why my printing cracks.... seems like the layer not sticking right? too cold of extrusion? I print at 220c abs
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Re: Printing cracks....hmmm
April 21, 2014 03:24AM
Because that's a big heavy print with lots of heat inside of it.
You can reduce the infill level to 0.1. Less Hot Plastic Mass means less trapped heat inside.
Have you an anti BackWash device or one of my Big Blue Fan-Ducts?


Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete
Re: Printing cracks....hmmm
April 21, 2014 05:51AM
I'll try the big blue, Thanks
Re: Printing cracks....hmmm
April 21, 2014 04:43PM
Welll, 220°C seems a little low to me. I print ABS at 240°C to get better line bonding, and this doesn't happen to me, even when printing big parts.
Re: Printing cracks....hmmm
April 21, 2014 05:55PM
Yeah Ant, I think you'll find it's because of the enclosed Mass of Hot Plastic, as it's a big old thing you have there....
You could try increasing the thickness of the Perimeters.... and reducing the fill density....
That looks like a serious bit of plastic... Are you going to park a tank on it?


Please send me a PM if you have suggestions, or problems with Big Blue 360.
I won't see comments in threads, as I move around to much.
Working Link to Big Blue 360 Complete
Re: Printing cracks....hmmm
April 22, 2014 10:14AM
Your print is warping - sometimes this causes the base to bend up and lift, sometimes it causes delamination at one or more layers. I've experienced both issues. The cure is the same as those used to minimise warping.

1) Use a hot bed - I find 110 deg best for ABS
2) Make sure the first layer is well stuck to the bed. If it's blobbly or the lines are too thin, stop the print, re-adjust the Z zero position and start again. I use a thin mix of ABS filament dissolved in acetone to coat the glass.
3) Keep the ambient environment warm - my large ABS prints warp if I print in a cold room. I keep the room at 22 deg C or warmer.
4) Most important keep draughts away from the printer. Opening a door or window for just a few seconds during a large print can cause it to warp. One solution is to put screens around the printer. I once put a bin-bag over the whole Ormerod to exclude draughts, though this can make it pretty hot inside the bag and give problems with things overheating.
5) Your hotend temperature seems a tad too low for ABS, which will result in poor layer bonding (the extrusion does not weld to the previous layer so well). I use at least 230 deg C for ABS, and 240 deg if there are no bridges or small perimeters.
6) Unless there is a good reason to have a high density infill, keep it low. The same goes for walls and other features - the thinner the walls the less warping. This is not a problem that applies only to 3D printing, but injection moulded parts have exactly the same issue. "Core out" solid parts of the design wherever possible - e.g. instead of a single solid thick support column, make a much thinner core column and add support ribs around it to give the necessary strength. Here's where we are better off than the injection moulded part designer - we can make completely hollow walls and other features that are not possible to injection mould.

In addition, I've found that some filaments have worse warping problems than others, so if all else fails try printing with a different colour filament.

Dave
(#106)
Re: Printing cracks....hmmm
April 22, 2014 10:43AM
I use a UHU & water mix to coat my glass and then I print to a 110° first layer and 100° other layer with a 240° extruder and a 10mm brim.
With this setting I have no warping but still have delamination and also some bloob problem that the noozle drag and alter the printing like a belt slipping (although retraction set to 5mm at 45mm/s and whipe on retraction on).

before increase temperature to 240° I have try 225° and then 230° with some crack like your, actually, after increasing the extrusion temperature it seems ok, but delamination over little stress and print fragility still remain
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