Skeinforge Stretch - Holes too small

Hi Everyone,

I am having some trouble getting my holes to print the correct size. I am printing a 2mm high simple ring, ID 22.4mm OD 34mm.

In order to get my ID to the correct size I have to enter VERY high numbers in the stretch page, but this introduces strange 'artefacts' such as that seen in pictures 1 and 2. These artefacts make the diameter of the hole smaller in that particular spot so the bearing I want to put in it no longer fits. I have tried playing with the other settings but don't really know what I am doing and there is not enough information in the SF manual for me to understand what is going on. Can anyone suggest how I can overcome this problem? It seems to me that my numbers should not be as high as they are so I must be doing something wrong.

Thanks

Andy

Perhaps your diameter is not correct for a different reason?

Stretch is practically unnecessary for 20mm holes.

I'd focus your efforts more on how well your width/thickness is calibrated, and making sure tour x/y axis are calibrated correctly.

Do your calibration cubes turn out the correct size? Are your print walls well aligned? (wavy walls will alter the dimensions)

It could also be to much fill which can make the holes shrink. I had that problem initially

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Experimenting in 3D in New Zealand

How fast is your feed rate? If you're printing too fast (>30 mm/s), then you're probably getting segment pause which around circles. The head slows down which would make holes smaller since it ends up extruding more plastic in places where the segments are short.

Thanks for the replies everyone. In answer to your questions:

@ brnrd - My feed and flow are both set to 25 - I can't imagine this is a major issue given that pretty much everyone I have read about uses a number in this region.

@ NelsonRap - My fill is more anaemic than bulging so I am sure it is not this.

@ Andrew - My 20mm cubes come out with near perfect dimensions and the walls are not wavy so I am happy with the hardware setup. I ran a print of the thin walled box and my width/thickness is not correct so perhaps this is the issue.

My layer height is 0.4mm. PWoT set to 1.7 I get >1mm walls, at 1.5 I get 0.88mm walls and 1.2 I get 0.6mm walls so obviously something is not right.

I have tried looking for SF40 calibration guides but to no avail. They all suggest that as long as you get E steps/mm correct (mine is) and measure feedstock then all you have to do is set flow=feed and decide your layer height and PWoT and SF figures it all out for you. This is what I have done but I get walls that are too thick (which is undoubtedly why my holes are too small).

Can anyone explain/point to a GOOD explanation of how one should calibrate SF40 please?

awmt102 Wrote:
-------------------------------------------------------
> My layer height is 0.4mm. PWoT set to 1.7 I get
> >1mm walls, at 1.5 I get 0.88mm walls and 1.2 I
> get 0.6mm walls so obviously something is not
> right.
>
> I have tried looking for SF40 calibration guides
> but to no avail. They all suggest that as long as
> you get E steps/mm correct (mine is) and measure
> feedstock then all you have to do is set flow=feed
> and decide your layer height and PWoT and SF
> figures it all out for you. This is what I have
> done but I get walls that are too thick (which is
> undoubtedly why my holes are too small).
>
> Can anyone explain/point to a GOOD explanation of
> how one should calibrate SF40 please?

I agree that you're problem is that you're extruding too much plastic. You're not too far off. You can increase the filament packing density ratio (FPDR) in the Dimensions plug-in to correct this. Since your observed PWoT ratio is 1.29 and 1.25 times the desired value, the average would be 1.27. Just multiply your current FPDR by 1.27 and try again. I hope you measured this at the top layer and not at the bottom layer which will be affected by how flat your bed is and how you set your clearance.