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jumpmobile

What does it do when I change the Nozzle diameter in Cura?

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Hi

I have measured the string that comes out of the nozzle. it had 0.65mm diameter. Would it help to set the Nozzle diameter in Cura to 0.65mm and lowering the flow to sth. like 65% so it calculates the distance of the lines differently?

I have problems with parts not fitting to each other.

Greetings Jumpmobile

 

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If you set nozzle width to .8 instead of .4 it changes several things. One thing is it outputs twice as much plastic (e.g. 200% flow). Another is it spaces the lines farther apart (.8mm apart instead of .4mm apart).

A third thing is that it moves the head further from the edges when printing. You probably don't care about this but let me explain anyway: if you print a 10mm cube with .4mm nozzle, then it actually prints the cube .2mm smaller on all 4 sides to account for the radius of the nozzle. So the path of the gcodes will be 9.6mm by 9.6mm resulting hopefully in a 10mmX10mm cube. Same for interior holes and all edges - the head is moved towards the solid part of the part by .2mm. If you set nozzle to larger values it compensates further.

Anyway, you could try increasing flow but not increasing nozzle size if you want.

What do you mean by "not fitting"? Parts can be out of tolerance for many reasons. The biggest reason is shrinkage but there are other issues. Pictures?

Usually if I make a part with important tolerances, I often just print the first layer, then measure the important distances, and then go back to CAD and adjust the model and print again.

There is no simple formula to fixing these distances but the more you design and build the more often you can get it right the first time. You can even remove the "elephants foot" by printing the bottom few layers with a chamfer.

http://en.wikipedia.org/wiki/Chamfer

 

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I would send pics, but i don't have a camera (jep, my phone is rather dumb compared to the ones from that fruit-company). My problem is that onhttp://www.thingiverse.com/thing:27233 nautilus gears the push fitting doesn't work. I measured the pin had a diameter of about 5mm and the holes were 3mm. That is way to much for me to file of. I would be busy for like half an hour to get everything working.

This has different reasons than the nozzle diameter, for sure. E.g. I print with two shells and 100% infill overlap, maybe this causes overextrusion on the outline causing it to swell, but i don't want to change this setting. (You are using large overlaps, too, right?)

I have tried this now and it seems to work. I had those gears printed out at .8 scale and it fit better even better than the bigger ones though the tolerances should be smaller (right?).

Do you / Does anyone know someother tricks to improve dimensional conformance of prints? (except for tightening the belts again)

P.S: Here is my profile. Just in case you want to have a look.

[profile]

layer_height = 0.2

wall_thickness = 1.3

retraction_enable = True

solid_layer_thickness = 0.8

fill_density = 100

nozzle_size = 0.65

print_speed = 50

print_temperature = 210

print_temperature2 = 0

print_temperature3 = 0

print_temperature4 = 0

print_bed_temperature = 55

support = Everywhere

platform_adhesion = Brim

support_dual_extrusion = Both

wipe_tower = False

ooze_shield = False

filament_diameter = 2.85

filament_diameter2 = 0

filament_diameter3 = 0

filament_diameter4 = 0

filament_flow = 65

retraction_speed = 40.0

retraction_amount = 4.5

retraction_dual_amount = 16.5

retraction_min_travel = 1

retraction_combing = True

retraction_minimal_extrusion = 0.1

bottom_thickness = 0.3

object_sink = 0

overlap_dual = 0.2

travel_speed = 150.0

bottom_layer_speed = 20

infill_speed = 0

cool_min_layer_time = 6

fan_enabled = True

skirt_line_count = 1

skirt_gap = 3.0

skirt_minimal_length = 150.0

fan_full_height = 0.5

fan_speed = 25

fan_speed_max = 100

cool_min_feedrate = 0

cool_head_lift = False

solid_top = True

solid_bottom = True

fill_overlap = 50

support_fill_rate = 15

support_xy_distance = 1.5

support_z_distance = 0.2

spiralize = False

brim_line_count = 20

raft_margin = 5

raft_line_spacing = 1.0

raft_base_thickness = 0.3

raft_base_linewidth = 0.7

raft_interface_thickness = 0.2

raft_interface_linewidth = 0.2

fix_horrible_union_all_type_a = False

fix_horrible_union_all_type_b = False

fix_horrible_use_open_bits = False

fix_horrible_extensive_stitching = False

 

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Changing the nozzle size tells Cura the natural size of the bead of plastic that you can extrude. If you set your shell thickness to be an exact multiple of that size, then Cura will adjust the spacing of the lines it prints with, and the amount of plastic that it uses to print each line, on the assumption that each line is going to be a rectangular block, 'nozzle-width' wide, and 'layer height' deep. (Which is an oversimplification, but generally good enough).

If you extrude into free space, the size of the string that comes out of the nozzle is larger than 0.4 usually for several reasons; firstly due to die swell, which is mostly the resolving of elastic tensions in the plastic before it hardens. The other is due to how fast you are extruding; you can basically be piling up plastic faster than it is moving away from the head to some extent.

But if the nozzle is 0.4mm wide, and the head is moving away at the appropriate speed, then you always have exactly the right amount of space under the nozzle for a 0.4mm wide bead of plastic. If you set the extrusion width to 0.65mm, then that is what you will get, but only because the printer is pushing out plastic much faster than normal, so it spreads out under the flat tip of the nozzle as it moves. That's probably a less precise process than leaving a trail that is exactly the width of the nozzle hole, and requires higher head pressure to push out the extra plastic. It probably doesn't make much difference overall, so long as you keep the linear speeds low enough.

Small holes are notoriously difficult to get right. Partly because of shrinkage, and also becuase circles are really made from straight line segments that tend to cut the corners internal to the hole and so leave the opening smaller than it should be. I printed the same Nautilus gears without a problem when I tried - but I recommend getting a decent set of small drill bits in half mm size increments, and just drilling out holes on things like this. So much quicker and easier than messing around with the print size to get small holes to fit.

Looking at your settings; you aren't using 100% infill overlap. You have it set to 50%. Which is still too much. I think. The infill overlap affects how the infill extends into the perimeter lines: It is measured based on the nominal centerpoint of the semi-circular end of each line of infill. A 50% infill overlap means that that centerpoint is positioned 50% of the way across the first perimeter bead. Allowing for the fact that the infill has a semicircular end on it (the shape of the nozzle hole) the actual physical end of the infill line will actually go all the way across the first perimeter line. And that's only if the infill and perimeter meet at right angles. If they meet at an angle, the infill line can actually go all the way through the perimeter and stick out the other side. And in practice, when this happens, you are extruding plastic where there is no room for it, so you end up with some excess plastic that blobs out somewhere and makes a mess. It could certainly tend to make small holes close up even more. An infill overlap of 15% is more usual, and even that can be too much with some single-perimeter shapes if the infill is parallel to the perimeter in some parts.

You're also printing with solid infill - 100%. There's really no need for than on a part like the nautilus gears. I printed it with 40% infill, and could probably have gone lower. Using 100% infill is always going to be a little challenging, because there's simply no room for error. if you're making the shape totally solid with plastic, then there's nowhere for any over-extrusion to go at any point on the print. It can work; but doing it when there's not a mechanical need to do so is just over-constraining the system - and making every print take a heck of a lot longer than it needs to.

 

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I recommend the defaults: .4mm nozzle, 15% overlap, 20% infill.

50% overlap is okay, but I like 15%. 100% infill is too much. Better to set the shell to 30mm. That does 100% infill but with a safer pattern. .65mm nozzle - not sure how that will come out. I never tried it. It *should* work as long as you print very slow. But .4mm makes more sense.

But I also have problems getting parts designed by other people to fit.

 

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