infill & perimeter not joining

I was never quite able to get all sides of the perimeter to join to the infill without setting the overlap so high that it ruined the outside finish. Adding shells and tightening my belts helped substantially, but there are still some sides that do not connect well unless I use excessive overlap. After trying to find the sweet spot for a while, I gave up and decided to live with slightly deformed outer layers.

Having looked at the extruder path close up, I think I now see why it has to be that way. In the picture, you can see how the lines don't actually connect to the shells at the one edge despite completely overlapping it on others. Has anyone managed to change that via settings without using too much overlap on other sides?

I assume this is due to round off error or perhaps an overly simplified algorithm that doesn't work as well on angled/rounded surfaces. If it is, then fixing it might require changing one of the skeinforge modules, but I'm hoping there is a simple fix via skeinforge parameters.

I have tried using a combination of stretch and overlap, but I can't find very clear documentation on what the stretch parameters are changing or how one parameter affects the others. I'm guessing that if there is a setting that can help, it will probably be one of the stretch parameters but I don't understand it well enough to tune it. Stretch might also shift the ends of the infill, so maybe I'm barking up the wrong tree here.

How did you get that image?

I just hit the "print screen" key with skeinlayer open. The scale is set to 60 or something like that so you can see the detail better. After that I just pasted it into paint.net and saved it as a jpg.

If you need that much overlap with ABS or PLA then I think you must have a backlash problem, or your flow rate is a little low.

I generally set the overlap to 0 because otherwise a) it distorts the outline and b) you get too much plastic on narrow sections.

I don't use stretch because I also don't know what it does.

Edited 1 time(s). Last edit at 01/26/2011 04:27AM by nophead.

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[www.hydraraptor.blogspot.com]

I don't think this is purely a backlash issue. Admittedly, my extruder does have to rotate some odd number of steps before engaging the gear, but there is a pretty clear cut difference in how the edges of that hexagon are joined to the infill. If that one edge would overlap the same way the others do, there wouldn't be a problem.

Even the extrusions that are ending at that edge rather than starting there are not joining. If extruder backlash was the overriding factor, it doesn't make sense to me how all of the lines on that edge would miss. Backlash should only come into play when starting an extrusion and building up pressure, which is only the case for half of those extrusions.

Edited 1 time(s). Last edit at 01/26/2011 05:58PM by dazed.dnc.

I meant axis backlash, not extruder.

Yes SF is not doing the overlap correctly, but what I am saying is overlap isn't necessary with ABS unless you have backlash, or the flow rate is too low.

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[www.hydraraptor.blogspot.com]

Hmm. My belts are as taught as I can make them without being so tight that it stresses the motor. The motors are quite rigidly mounted, nothing is able to rattle or slide around. What else would cause backlash on the axes?

My only guess would be the build plate springs. It takes more force than I should think an additive manufacturing process would exert but my build plate is really the only thing that can shift around.

EDIT:
After looking at the build plate closer, I'm noticing that the bearing blocks are too flimsily mounted to the build plate. I should have thought of this earlier because I knew they were probably going to be too weak during initial assembly. Up till recently, I was using a lighter build plate. I had to add some insulation and a glass sheet. The extra weight seems to be too much for the puny little wood piece that connects the bearings to the frog plate. I haven't been using the purge plate for anything and it is the only wood I have on hand that will clear the rods under the Y axis, so I cut it in half and glued them to the bearing carrier and frog plate. Now that the bearings are supported from the top AND bottom, it should be plenty rigid.

Edited 1 time(s). Last edit at 01/26/2011 08:13PM by dazed.dnc.

What do you have for these settings?

infill w/t
perimiter w/t
infill perimiter overlap

It is the infill that strikes the perimiter at an angle that isnt meeting which makes me think that skeinforge thinks the width of something it too large. Remember that that line is the centre of the extrusion, so the edge of the extrusion may meet the perimiter without the center touching it.

Edit:
After seeing how the edges were sliced differently, I assumed this was causing that edge to be printed differently every time.

I set overlap to 0 as nophead suggested, and now I realize this is also an edge where my extruder retracts. Parallel extrusions have always joined quite well, so I trust that my width/thickness/feed/flow are well adjusted to one another. Perhaps some combination of stretch and dimension tweaks will fix the problem.

Edited 2 time(s). Last edit at 01/28/2011 07:12PM by dazed.dnc.

This is possibly a SFACT issue.

I resolved the problem by using the newest "daily" version of SFACT.

https://github.com/ahmetcemturan/SFACT/tree/Daily_Updates