Two slicing questions - benchy

[Mak]

Evening all.

I've got two slicing questions please as I try to fine tune my printer performance (see attached images).

1) On the benchy model, there is an open-topped box behind the cabin. When printed, I have a hairline gap running around the top face in the middle. Upon looking in S3D, I realised that's because it is exactly how it is sliced. I've tried playing with perimeter overlap but I haven't found a way to make it cover this gap, please can anyone tell me how?

2) Getting bridging to trigger. I've been trying to improve my bridging performance but I wasn't having any impact to the top of the arched door or the circular porthole. When looking in S3D, even if I drop the "unsupported area" threshold right down for bridging, and try enabling "bridging for perimeters", I cannot get it to recognise the top of those shapes as unsupported regions. Clearly I could address this through using a support, but a bridge would be much less printer - any ideas how to achieve?

Many thanks.

[wirlybird]

On the gap try changing the extrusion width to see if you can get rid of it or on the Other tab on the lower of the two drop downs on the left switch from gap fill to single extrusion and see if it helps.

What nozzle size and what extrusion width are you using?

I think on the bridging deal it is just too small an area and bridging really isn't needed.

[Mak]

Thanks for the reply. You're right, it was on manual width so I'll play with auto. Single extrusion gap fill didn't help, it's too small a gap.

I'd agree on bridging except I'm trying to get rid of the slight lumpiness I'm getting on the underside of the arch, which I assume will be full temperature uncooled filament being unsupported even though it's only a few mm.

Cheers for the reply.

[wirlybird]

Manual is fine. What is you nozzle and extrusion width at now?

[Mak]

Sorry I forgot that. 0.4 nozzle, 0.45 width. It's the recommended abs profile from prusa for my Mk3, and I've got a question on their forums as to why fixed, and why below 120%.

[wirlybird]

OK, Prusa uses 0.45 since it is a compromise between a layer width that is not overly wide but still good adhesion, especially on ABS.

Go with 0.4 and see how it looks in the preview. Also you can run up to 0.5 and see.
Also since the MK3 has a variable speed fan you could add some gentle cooling right at that bridge layer, maybe 15-20% then back off after that layer but not really needed.

What is "fixed" and 120% about?

[Mak]

So set up cooling on that profile at the specific layer rather than trying to get it recognised as a bridge? Nice thought, had completely passed me by.

BT fixed I meant manual rather than auto where it will vary in a print. I understood 120% of your nozzle width to be the rule of thumb for extrusion width?

Cheers.

[wirlybird]

Yea, sometimes you can use some careful cooling with ABS to help thin areas or areas that will have an issue with the heat.

Ok, I see on the 120. Yes, 120% is a default or go to value based on nozzle size. I usually run .4 (same as the nozzle) for PLA and ones that generally bonds well. I'll do the same on smaller or pretty solid ABS parts. On most ABS though I will run it up to 0.48 if all the walls do ok at that thickness to get the extra layer bonding.

One caveat is that when you run up the extrusion width and or layer thickness then slow down some so it extrudes ok.