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Q: Print Nozzle Hole Shape?

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Ed Duffner31/07/2019 21:46:13
811 forum posts
91 photos

Hi guys,

I'm looking at getting a 3D printer, not sure which one or type yet. However, whilst looking at the various tests and reviews online, a thought crossed my mind regarding print quality on filament deposition (FDM) printers.

Why do the print nozzles on FDM printers have a round hole? Why not a square hole? Wouldn't a square hole lay down a flatter sided filament? and subsequent layers create a better/flatter side surface?

With todays' manufacturing abilities, a square hole should be relatively easy to accomplish.


Jeff Dayman31/07/2019 22:13:30
1915 forum posts
45 photos

Hi Ed,

Ender-3 machines are low cost and do great prints. I bought one a while ago and have had a lot of fun with it. It worked fine right out of the box. If you want finer resolution / less ridges on part sides you can a) change the layer height to 0.1 or 0.15 mm, b) change to a 0.2 mm dia nozzle, from the stock 0.4 mm dia one. Of course these adjustments will slow the printing down.

Round holes are cheapest to make in nozzles and work fine for the majority of work done with FDM. This is probably the main reason round holes are used, especially in the very low cost machines available today!

Stratasys in USA in the late 1990's tried various square and rectangular nozzles in their industrial FDM machines costing multiple hundreds of thousands of dollars - nozzles failed and split out - this wrecked a lot of the beds by dragging metal fragments across them, and the different shape made virtually no difference to print quality.

Versaboss31/07/2019 22:25:51
458 forum posts
51 photos

Uh-oh- if using a square hole in a printer nozzle, wouldn't it be necessary then to rotate the nozzle so that it is always tangential to the movement of the print head...?

Kind regards,

Edited By Versaboss on 31/07/2019 22:26:06

Ed Duffner31/07/2019 22:37:38
811 forum posts
91 photos

Jeff, thanks for the info. Seems strange the nozzle would split out unless they were thin-walled.

Versaboss, Indeed I thought of that too, but if the nozzle had outer edges which were made square to the inner, then setup could be achieved.


jason udall31/07/2019 23:06:51
2026 forum posts
41 photos

Printers print in *all* a circle cross section will present a constant profile at all directions in the day plane.

Any other profile would give no advantage in an arbitrary angle even if a slight advantage in X or y only feed

The theoretical 0.4 mm dia nozzle would give corners of 0.2 rad. In practice the smoosh of the plastic gives a shape that is at this scale more to do with fluid dynamics than nozzle geometry.

Thus for no gain we change from simple drill/team to broach...more complex for no gain

Bob n About01/08/2019 10:03:36
48 forum posts
1 photos

A square hole would have none laminar flow in the corners, this would promote the plastic to decompose quicker where heat is more concentrated and result in rapid blocking of the nozzle. You don't tend to see many square section pipes in engineering. A printers smallest output is a blob, not a defined shape, but a defined volume. the nozzle both extrudes and smooths out that blob to form a ribbon of plastic. A square nozzle, whilst it worked would produce a different width ribbon corner to corner.

Edited By Joules on 01/08/2019 10:04:46

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