Wall thickness too high. (solved)

I am completely stumped here, my prints are coming out slightly too large and I can't work out why. If I print a cube it's 0.1mm too big, if I print a square hole it's 0.1mm too small. I know this isn't much but it's such a reliable figure that I know it isn't just down to part to part variation! (I would expect a 10mm cube to be 10mm +/-0.1mm however mine is always +0.1mm)

What I have narrowed down is it isn't a steps/mm problem - the x/y/e and z movement are perfect.

If I explicitly tell my slicer to use a 0.5mm track width and I print a 0.5mm wall thickness object it comes out as 0.58-0.6mm wide. This adds up to probably be where my error is coming from. However if I reduce the flow rate, there is clearly not enough plastic in the part so I have no idea how to solve this! I thought it could be filament variation - but I can't get that to account for a consistent 20% error!

The problem is that I like printing with a 0.55mm wall thickness (gives a smoother finish) - but this just seems to make the error proportionally larger!

I have tried kisslicer and Slic3r - both have the problem.

Heeeeeelllllp!

I should say - I'm using a 0.5mm JHEAD mk5

Edited 2 time(s). Last edit at 03/14/2013 03:20PM by konwiddak.

Check your filament first, although it usually runs small which would be the opposite effect.
The other adjustment Slic3r has is the extrusion multiplier. I have see this adjusted to get the correct walls.
See this guide using that method. [solidoodletips.wordpress.com]

I think the flow rate maths is wrong in kissslicer and slic3r. To get things the right size I have to use skeinforge, where you can set the perimeter flow rate separately from the infill. I then set it up using the maths here: [hydraraptor.blogspot.co.uk].

I also apply an XY scale to allow for the plastic shrinkage.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> I think the flow rate maths is wrong in kissslicer
> and slic3r. To get things the right size I have to
> use skeinforge, where you can set the perimeter
> flow rate separately from the infill. I then set
> it up using the maths here:
> [hydraraptor.blogspot.co.uk]-
> flow-rate.html.
>
> I also apply an XY scale to allow for the plastic
> shrinkage.

I am now getting nice prints, I increased wall thickness to 0.6mm - this results in a single wall print having a wall thickness of 0.8mm! Then I reduced the flow to 83% which took my wall thickness back down to 0.6mm. I can't believe my printer has a 17% error anywhere so yes I think you are correct, there must be something fundamentally wrong with the maths used. Most likely, the filament doesn't fill 100% as your article implies.

@Spk64: I had tried adjusting the flow for correct wall thickness in the past, but this always resulted in terrible prints. However your link inspired me to try again. I think the problem was I was using a 0.5-0.55mm extrusion width which bulges to 0.6mm. When the flow rate is reduced, I think the resulting track was narrower than the nozzle width, causing nasty prints. By increasing to 0.6mm track width, the track width is still wider than the nozzle even with the flow adjustment.

Edited 1 time(s). Last edit at 03/14/2013 03:25PM by konwiddak.