Gaps near through-holes in ABS

MarkG · Post by **MarkG** » Thu Jun 26, 2014 8:23 pm

I was printing Jim's fan covers (http://www.thingiverse.com/thing:267921) in MG white ABS, and I'm getting gaps near the holes in the corners. The gaps are so much that the inner "Holes" actually fell out of the structure. I have taken a photo (below) which shows the result.

I am using the High quality ABS fff configuration, adapted with slight temp changes and using two shells and 90% infill. I usually use an Extrusion Multiplier of 0.95, and have tried .92 all the way to 1.00. These changes did not seem to close the gap at all. I'm printing at 245C on a V3b using 4800 mm/sec default speed, and 60% underspeed for outlines.

I did end up with the 0.95 extrusion multiplier by printing a number of calibration cubes and measuring the total dimensions as well as wall thickness to get the printed object

What I end up seeing in these photos is that the two shells that form the holes do not touch, and in addition, the larger structure does not seem to tie-in very well.

Any hints or directions to adjust the machine settings?

Appreciate it.
Mark

j-rod · Post by **j-rod** » Thu Jun 26, 2014 8:29 pm

almost looks like your extrusion multiplier is too low for the configured extrusion width. what is the width set to?

MarkG · Post by **MarkG** » Thu Jun 26, 2014 9:33 pm

j-rod wrote:almost looks like your extrusion multiplier is too low for the configured extrusion width. what is the width set to?

I see no differences in this problem for Extrusion Multipliers set to either .90. 95 (my normal) or 1.0. For the width, I use the auto setting.

Mark

jimc · Post by **jimc** » Thu Jun 26, 2014 10:31 pm

well the multiplier is for fine tuning and what you have there isnt fine tuning. did you measure your filament and set the dia. if its just a little off that will cause an over or under extrude far greater than you can make by moving the multiplier a little.

MarkG · Post by **MarkG** » Fri Jun 27, 2014 4:56 am

jimc wrote:well the multiplier is for fine tuning and what you have there isnt fine tuning. did you measure your filament and set the dia. if its just a little off that will cause an over or under extrude far greater than you can make by moving the multiplier a little.

Yes, I did measure the filament, and it's 1.74 or 1.73 for at least 3M samples. It's standard MG ABS. When you say that the Multiplier is for fine tuning, what do you think of for fine tuning. I assumed ,based upon instructions, that if you measured your filament at 1.70, then your multiplier would be 1.70/1.75, or about .98. I have found that .96 works best for me, and just don;t see much of a change between 1.0 and .95.

Also, I don;t understand your reference to "set the diameter" I see no setting in the slicer for the filament diameter, I thought it was part of the M2 basic configurations.

I have not played with Extrusion Width, however, what is the objective for controlling this manually? I had assumed that the rules for auto-width would follow the standard 1.2 ~ 1.5 of the layer height.

Mark

jimc · Post by **jimc** » Fri Jun 27, 2014 5:05 am

the multiplier does increase or decrease the extrusion but its minimal only. if you put a micrometer on your filament in a few spots over say a 3ft section then take an average. go into the other tab in s3d (assuming you are using it) and set the filament diameter. that needs to be set and or changed with every roll of plastic since they vary. the diameter makes the biggest difference the multiplier is as i said a fine tune. extrusion width wont help your current situation

MarkG · Post by **MarkG** » Sat Jun 28, 2014 5:12 pm

i wanted to folow up with some results for my problem.

First, the problem when away when I used a single shell, so it looks like the two shells were just not touching at all, but the infill in the field did end up touching the singel shell and making a good structure.

Second, I measured my filament, and use the filament size under the 'Other' tab (i had never really looked under than tab a lot), and while I used a multiplier of 1.00, and measured the filament at 1.73 or 1.74, it turns out that nothing changed until I went down to 1.70. then, there was some significant fill in, and the two shells touched. I looks like I was under-extruding. I'm not going back to some other calibration cubes and seeing if this setting would be better. I'm also going to be looking at PLA -- which did NOT have this problem. I could be that the ABS is underextruding due to low temps. PLA is runny, ABS is not, so it might need a higher temp for the proper extrusion.

Toby · Post by **Toby** » Sat Jun 28, 2014 5:22 pm

One thing that might have been happening is that when you had 2 shells the shells were touching, but the space between them was too small for any infill, i.e it has to be as large as the extrusion width. With one shell, the space was large enough for S3D to generate infill, and then the positional accuracy of the nozzle brought it close enough to the shell to merge.

When you went down to 1.7 that may have opened up enough space for the infill to be generated.

You can test this theory by looking at the gcode preview in S3D for the different cases. It will show you whether infill is being generated or not.

jimc · Post by **jimc** » Sat Jun 28, 2014 10:09 pm

well since you brought up temps, what were you running at? the same as your pla? abs is usually around 240-245. a temp too low and you will get clicking and under extrusion from the extruder

Gaps near through-holes in ABS

Gaps near through-holes in ABS

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