infill optimization

Am printing an image that takes a lot of time and uses a lot of filament. It could be optimized by changing the infill. In sli3er there is an option to infill only where needed, but seems like if I check that the infill is the same. OK maybe I don't understand where the infill is required , so I am open for education. I have tried changing the option to connect infill every n rows.from 2 to 5 with not much change. So I'm sure it is a simple cse of not understanding the software or filament. Anybody know what I'm talking about?

I've tried the "infill only when needed" and had it make a small difference. I think it only kicks in when the top surface of the object can self support (because its on a steep slope) and so doesn't need the infill to hold it up as it's filled in. It didn't seem that worthwhile for the amount of filament/time the few times I saw it make a difference. You might be better off with the "Infill every n layers", this lays down thicker infill every 2nd (or 3rd or whatever) layer but keeps the perimeters at the original layer height. I don't use it, but the theory is that it halves the amount of time spent infilling.

In my experience, Opus is correct...Infill only where needed only changes the result under a sloping side face.

As for infilling every n layers, I don't know how much checking is in the code...It may specifically not be doing it if n times your layer height is more than your nozzle diameter.

You can manually create internal voids in the model, provided you give some consideration to having adequate support.

IIUC the "Infill ever N layers" works only if N multiplied by layer height is equal or less than the nozzle diameter (BICBW). For most prints that means that N cannot be larger than 2. It is used mainly to get a good outer finish by setting very thin layer heights (for the outer perimeter) while effectively having a thicker more usual layer height for the infill. The reason is that the infill layer thickness has to be N times the perimeter layer thickness, and layer thicknesses greater than nozzle diameter do not print very well. It can also be a "swings and roundabouts" situation with more usual layer heights, because unusually thick infill needs to pump a lot more plastic, and so you may have to slow down the infill speed to prevent the extruder skipping and so gain no overall improvement in the time taken to complete the print.

Reducing the infill percentage will always improve print time by reducing the total amount of plastic in the part, so you could think about how little infill you can get away with and still have the part strong enough. You could also set the infill extrusion width thicker ("Print Settings" > "Advanced"). The thicker the infill extrusion, the fewer infill lines will be laid down for any given infill percentage - but again you could end up having to slow the print due to the extruder not being able to pump plastic fast enough. Simply speeding up the print speed for infill to the maximum your extruder can handle may be a solution - the XY position of the infill does not need to be as accurate as the perimeter position. At the end of the day the fastest print time possible is equal to the total volume of plastic contained in the part divided by the maximum rate your extruder can feed the plastic, and whatever your settings you cannot get past that limit.

Dave