Nozzle Size vs print speed

OK!

Have concluded that if
I have a 0.4mm nozzle using 1.75mm filament at a max print speed of 100% (hypothetical speed)
And I change to
I have a 0.8mm nozzle using 1.75mm filament the max print speed should be about 50%

A 40watt hot-end heater can only melt 1.75mm filament at a given rate regardless of nozzle extrusion size.

Is this correct, If not please point me to somewhere that will explain.

At 40W power, the amount of surface area available to heat the filament is likely to be the limiting factor. That's why the E3D Volcano is longer than the E3Dv6, and their forthcoming super Volcano is longer still. It's also why a Diamond hot end can print fast when you feed filament at the same rate into each of the 3 or 5 inputs.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The wonder of area versus diameter.

A .8mm hole has about 4 times as much area as a .4mm hole. A .8Ø hole would extrude 4X the material as a .4Ø hole. If you used a 1mm hole it would have over 6.2x volume!

It's not quite as simple as that, because of the time taken for the filament to conduct the heat to its centre. So a larger diameter doesn't necessarily help.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

It gets better. A thicker diameter hole also allows a thicker extrusion height. Since the layer height is (often) a percentage of the diameter, you can use up to 8 times the material by doubling the nozzle size.

However, what you can extrude comes down to how much power does it take to melt the plastic. It takes about 1 calorie of heat to raise the temperature of ABS plastic up by 2 degrees C. 40W produces (give or take) about 10 calories per second. if we need to raise the temperature of the plastic by about 200 deg C, then we can extrude about 0.05g/s, or about 2cm of 1.75mm material if we're using that heat at close to 100% efficiency. This means that if we exceed that speed of extrusion, we either need more power, or the hot end temperature will start to drop. Assume a much lower rate of efficiency though, since we have to transmit that heat into the filament right to the core, and plastic is something of an insulator. This is the reason for the change in design for things like the Volcano heat blocks, even using the same heater cartridges. The problem becomes transfer of that energy to the plastic. (At 0.8mm by 0.6mm height this is a shade over 48mm/s print speed.)

So double the nozzle diameter (And increase the layer height) and you should be able to extrude material at 8X the rate, however, this really only halves print time, more due to the doubled layer height, although if you're printing solid parts, it will be 8 times faster for the same print head speed.

Whether or not you can maintain print head speed is all up to your heat block's ability to melt filament at 8X the rate.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

Quote
dc42
It's not quite as simple as that, because of the time taken for the filament to conduct the heat to its centre.

That's why I propagate a new filament diameter standard like 0.8mm. It has many advantages like better melt rate and extruder motor can be smaller etc.

In traditional extrusion (at least single screw extrusion) as extrusion rates increase the difference between materials increase. With some materials under high extrusion rates the heated zones are not needed, the friction and shear in the material is enough to generate the heat to melt the polymer. I wonder if we are getting close to that. Live view of the duty on the heater may give some indication.

Edit: I've done a load of extrusion tests with PETG recently and found increase in die swell (extruded polymer bead is larger than nozzle diameter) and the extruded bead was matt in apperance at high speeds (up to 180mm/sec) compared to 30-60mm/sec. The extruder was set at the rate that would be required to print at these speeda with a 0.4 nozzle, 0.5 width, 0.2 layer.

Edited 1 time(s). Last edit at 06/24/2018 06:25AM by WesBrooks.

i am using a .8mm nozzle on my main printer. installed this for extrusion speed but i understood that it was a big mistake. not only it requires a different hardware approach ( as it has been pointed earlier in the post) but due to the amount of plastic it extrudes ( abs in my case) it shrinks more and faster as it cools down making prints going slowly than slow.

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Delta Printer
Duet 0.8.5 firmware 1.19

My understanding is that larger nozzles are for greater part strength, since the individual lines of extrusion are thicker. The total volumetric throughput is determined by your hotend's ability to melt plastic, which is partly to do with heater power (but not reliant on it as the heater is typically maintaining temperature using about 10w - larger wattage heaters just heat up more quickly and respond to changes in temperature or extrusion rate more quickly) but mainly to do with length of melt zone and diameter of filament (smaller is easier to heat through). E3D joked that fins in the melt zone would help, but of course they would increase friction greatly.

I've found nozzles with better thermal conductivity also help (tungsten for example).

So use a 0.8mm nozzle for strong parts, but you'll see not much reduction in print times, unless you get a hotend that can really melt a LOT more plastic than what we currently use.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

the reason that drove me to go slow was that the parts were more fragile with the layers bonding being poor to no acceptable . i was going for thicker lines and i were getting them but the temperature of the filament wasnt high enough for the required bonding.

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Delta Printer
Duet 0.8.5 firmware 1.19

I'd steer clear especially with large nozzles of trying to use the "75% of nozzle width" guidelines, and go for setting the thickest layer height to 50% of nozzle width so 0.4mm for 0.8mm nozzle. More temperature helps to extrude faster and improve interlayer bonding.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Thank you

For all the information you have provided

One thing no one has mentioned here is that when you use a large nozzle to lay down more plastic, faster, all that hot plastic takes longer to cool. So when you were printing with a 0.4 mm nozzle in 0.2 mm layers and you had to print multiple copies or a sacrificial part to allow the print to cool between layers to maintain print quality, that problem is now multiplied by the increased volume of plastic being extruded with a larger nozzle printing in thicker layers.

I have also found that print quality goes down when using the larger nozzles, at least when printing ABS (no print cooling fan). When you are printing in thin lines with a small nozzle, the plastic hardens almost as quickly as it comes out of the nozzle. When you use thicker layers and wider lines, the plastic takes longer to cool when it comes out of the nozzle and tends to slump. You can't expect a large nozzle print to look like a magnified small nozzle print. This may be less of an issue if you print in PLA and have an adequate print cooling fan blowing.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I use a part fan with ABS, just at a much-reduced airflow (except bridges/overhangs) than with PLA/PETG. But yes surface area is smaller with thicker extrusion and it cools much more slowly. Perhaps I didn't notice it much as I rarely print small parts with big nozzles only large parts where there is time to cool a layer before the next layer begins.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions