Problem with holes

I have a problem with my holes that I can't seem to fix. Basically they are to small. I have been printing for properly for about a month and the outer surfaces and dimensions are pretty good but the holes are not right. They seem to be getting to little material so when the nozzle goes round it looks like it drags the plastic towards the midle of the cirle leaving a to small diameter and a gap between the circle and the infill.

I have a mendel with gen6 board and I use skeinforge for gcode and repsnapper as host.

Which settings do I have to fidle with in skeinforge that would affect this??

I'm having similar hold trouble. My holes look good but print way too small.

I've heard that using stretch in skeinforge solves this issue but haven't found a guide to what to set it to for .35mm nozzles.

Also I red where someone suggested using polygons instead of round circles for creating holes. I believe he recommended creating 2 vertices for every 1mm in diameter. So a 3mm hole would need a six sided polygon. I haven't played with this idea yet.

Yes, that was nophead with his blog post entitled "Polyholes".

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

I have been printing on a makerbot using skeinforge for a few years now and I cannot solve this problem. There is a setting in skeinforge "Perimeter Inside Stretch Over Perimeter Width", but I fiddled about for ages and still have had no luck getting the holes to the correct size.

The way I print now is to widen the vertical holes in my model (I work at increasing them by about +12% for holes 4 - 10mm) going down to about 3% for +30mm diameter holes. Every hole I make I log the sizes in my notebook, so I can record the shrinkage for each size hole. I am lucky to have a cad system which makes the resizing easy, but it wouldn't be too hard to do this in blender 3D, by grabbing the hole vertices and scaling them up 1.12 around the centre point.

I aim to be slightly under size and drill ream them out to size, but if you don't make this size correction there isn't enough wall and you tend to break into the hollow infill which is bad news. I always print with 3 top and bottom layers and 2 perimeter layers to give me a nice solid wall in case I have slight hole size issues.

Another tip that I found was to plot the inner perimeter first, then the outer perimeter and then the infill. Slow the outer perimeter speed down a lot, It takes a little longer to print, but you get much better holes. Printing the inner perimeter first, gives the extruder time to begin on a new layer, so you get much better holes without a bad pulled start point.

You could also check your extruder temperature, you may be running too cold. I run at 255 degrees, as hot as you can without denaturing the plastic, this way its less viscous and pulls less around holes. Also try upping the extruder speed a little as this reduces pulling inward.

Edited 1 time(s). Last edit at 10/03/2011 08:31AM by martinprice2004.

Ok. Thanks for the advice. It looks like it is a general thing with too small holes. I guess I just have to fidle som more.

I'm printing my first 3mm diameter holes using polycoms tonight. We'll see how it goes.

Try increasing the infill percentage.

It appears you are not extruding enough filament, or have your width/thickness settings too small. The hole issues are a byproduct.

What version of SF are you using?

My first suggestion is to make absolutely sure your mm of filament extruded perfectly matches the value in firmware.

Second, print a test cube [www.thingiverse.com] with infill at 100% and no extra shells

If the threads have gaps, or squish too high and the nozzle drags through them, you need to re-calibrate your speed/flow/Width over thickness. There are a lot of threads around which can tell you how to do that.

Take a close and clear picture of the cube and I can help more. (some opaque PLA is better to see if you have it)

Using polygons solved my issue. My holes look great.

Overall my print jobs look good, though I'm sure there's room for improvement.