How to avoid strands with printing support

I have printed an object to test support material. See attachments.

But after printing I don't see a solid layer after removing the support material. I see strands (if this is the right word for it).
On the picture the top is laying down.

Is there a way to get a solid layer there?

Edited 1 time(s). Last edit at 02/21/2016 06:13AM by glsf91.

Support material works by allowing controlled sag - it provides a lower limit for the sagging material that would otherwise be printing in free air. You can adjust the spacing between the support material and the print, but if you get too close, the two merge and become very hard to separate. The thickness and diameter of the overhanging material will be the diameter of the extruder nozzle, not whatever layer thickness and line width you have programmed, because there's nothing underneath to squish the plastic against. So the short answer is that overhanging material is always going to look different from the top and bottom surfaces of the print. It's a characteristic of FDM printing.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Yes, I agree with the previous poster. If you need to prevent it you will need to use a dual nozzle and print solid support in a soluble material such as PVA (see [www.3ders.org])

Dave

In designs where that surface is critical you may have to print your item as multiple pieces to be assembled after printing, either glued or screwed together, with that surface printed as either a top, bottom, or side. It's OK, it's not cheating.

Why didn't you print that object flipped over, with the large surface of the part on the print bed? You would not need support material for it at all.

When printing a wall you have the problem of it being small, so the print head comes around very quickly and keeps printing on previous layers before they've had time to cool and solidify, resulting in an ugly print. You can tell the slicer to slow down on small area layers, but that often doesn't work for very small area layers. If you're printing PLA, you use a print cooling fan, but not with ABS. With ABS you just print multiple copies of the part or add a sacrificial part to give the extruder something to do while the part you care about is cooling.

That's what I did with this ABS part that I used to tune up retraction settings on my printer:


I printed four of these parts at the same time and spread them out on the bed so the extruder would take a while when moving between them. The tips of the cones are 2 mm in diameter. I may have also slowed the non-print movement speed to drag it out longer.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

IMO a "pause between layers" would be a good feature to add to any slicer as an alternative to slowing down when layer time is below the minimum set. This should result in the head moving a distance away from the print, pausing, then moving back for the following layer.

Dave

I think you can do that with slic3r using custom gcode in the printer settings tab, but I've never tried to do it.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
Why didn't you print that object flipped over, with the large surface of the part on the print bed? You would not need support material for it at all.

It was just a test for printing support material.

For me it is now clear that what I saw is normal. I didn't print with support material before.

Edited 1 time(s). Last edit at 02/22/2016 11:33AM by glsf91.

I agree with "the digital dentist" regarding printing in multiple parts. I do this frequently with my parts, not only to avoid needing support but also in order to make the part stronger in the direction it is needed - FFF prints are strong in the XY plane but the layer bonding (Z plane) is far weaker. To print a column for example, I will often print two semi-circular sections lying down and glue them rather than build it vertically, which makes a far stronger rod. As I mostly print in ABS, I use acetone to form a chemical bond that is at least as strong as a single part. I also glue parts together instead of using fastenings whenever possible. This makes the design simpler, but of course prevents disassembly so is not suitable for everything.

Dave

Quote
dmould
I agree with "the digital dentist" regarding printing in multiple parts. I do this frequently with my parts, not only to avoid needing support but also in order to make the part stronger in the direction it is needed - FFF prints are strong in the XY plane but the layer bonding (Z plane) is far weaker. To print a column for example, I will often print two semi-circular sections lying down and glue them rather than build it vertically, which makes a far stronger rod. As I mostly print in ABS, I use acetone to form a chemical bond that is at least as strong as a single part. I also glue parts together instead of using fastenings whenever possible. This makes the design simpler, but of course prevents disassembly so is not suitable for everything.

Dave

How do you "glue" this with acetone?

And how about PLA?

Quote
glsf91
How do you "glue" this with acetone?

And how about PLA?

For ABS, I simply generously coat some acetone onto the mating surfaces using a small syringe, then press firmly together and hold for about 10 minutes or so. I hold many parts manually while the "glue" sets, but in some cases I use elastic bands, clothes pegs or bulldog clips to keep the faces pressed firmly while they melt together. For some awkward parts and to repair splits in the layer bonding (caused by minor warping), I dribble acetone into the crack or join and press together for some minutes. The join reaches full strength in an hour or two. Then clean up the join and any other bumps with a needle file or sandpaper and polish the whole part with a paper towel soaked in acetone to give a nice shiny appearance.

Acetone will not work for PLA, and the chemicals that will dissolve PLA are rather nasty, so probably best to use thin superglue (cyanoacrylate), which I believe forms a strong bond (but I do not use PLA so cannot confirm)

Dave