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Any disadvantages of having a big speed difference between inner and outer perimeters?

Posted by LMF5000 
When printing there's always a compromise. High speed means it completes faster, but ringing, ghosting and other blemishes become more evident.

By default most slicers seem to print inner perimeters at the speed you set (eg 60mm/s) and outer perimeters at around 50% of the speed (eg. 30 mm/s).

What's the disadvantage of having a bigger speed difference - like printing infill and inner perimeters at 75mm/s and outer perimeters at 33% (25mm/s)?

To me it seems perfect - you power through lines that are purely functional as fast as possible, and then finish off with slow high-quality ones where appearance counts.

Edited 2 time(s). Last edit at 03/23/2019 06:09AM by LMF5000.
Re: Any disadvantages of having a big speed difference between inner and outer perimeters?
March 23, 2019 08:14AM
Did you try ? Result ?

Edited 1 time(s). Last edit at 03/23/2019 08:15AM by MKSA.

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
I did, and got my first nozzle blockage in almost a year of operating two 3D-printers. I don't think it's related though?
I dont see a disadvantage, but the relationship between speed and looks of the outer layer is probably not linear.

So for the inner shells go as fast as possible. This is a science on its own and isnt talked about very much. [dyzedesign.com] Im hoping that CNC kitchen will do a test on that at some point smiling smiley but theoretically one could find that out with a micro scale and see at what print speed expected vs actual volume decreases below 99% or such value.
There was another older blog post about that (which im not finding atm). I used that to extrapolate to my old printer and the speed for which I dropped under 95% expected vs actual was surprisingly low.

For the outer shell, slower is better certainly but 25% seems too low imho. The highest speed here is probably determined by the acceleration artifacts. This relationship I assume also to be non linear but 2/3 of max speed seems a good starting point.

going for a .5 or .6 nozzle is worth a try. I found that the volume increase and print time reduction more than makes up for the slight loss in detail.
the outer layer is the one that is the most noticeable for deflections in motion from acceleration and slop. so depending on max speed of hot end system,
and on the rigidity of material, and how well it adheres to bed in theory you could go as high as extruder would allow for,
however there are issues at high speeds with jamming and keeping consistent flow pressure, especially when slowing down around corners. corners have aprox 3.14/4 space to put material down in and this causes pressure to built up.

you need large mass and good heater system to allow the equilibrium of feedstock temp. you could raise the temp but retractions or slow down between layers could mean the pla would burn and clog the nozzle.

if following criteria are met then printing really fast outside layers could be possible
rigid machine
tight slop free construction
material that sticks very well to bed
hot end designed with large mass heater
larger diameter nozzle prob at least 0.6 to 1mm
parts that have little retraction steps
parts that have few corners

your milage may vary,

any one else have anything to add?

Edited 1 time(s). Last edit at 03/30/2019 07:30AM by jamesdanielv.
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