Nozzle ø in relation to filament ø experiences?

Good morning!

So, I'm printing 1.75mm PETG and 1.75mm PLA through a Merlin hotend.

Advantage with this hotend is that it is easy to change nozzles, and they are dirt cheap (and work really well!).

After buying a bag with 10 nozzles I've decided to drill out a nozzle to 0.7mm but I am not getting good prints with it. I am not sure why this is, maybe the drilling isn't done well enough. So I was wondering, what experiences do you all have with larger nozzles in relation to 1.75mm filament?
I know that things like pressure in the hotend can go wrong when printing with too large nozzles, and that too large nozzles can introduce new variables on retraction.

Want to try going bigger, but maybe 0.6mm is some kind of a limit for nozzle size with 1.75mm filaments? 0.6 has worked well for me, layer height of 0.5 was not super, 0.45 made a big difference, but I really wanted to get 0.5mm layer height so decided to step up on nozzle size.

Oh, and going to 3mm filament is absolutely not what I want. So if it's really hard to get a 0.7mm nozzle working with 1.75mm filament, I will just stick to a 0.6mm nozzle size

Edited 1 time(s). Last edit at 02/02/2015 04:34AM by Ohmarinus.

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http://www.marinusdebeer.nl/

I rpinted with a 1.54mm nozzle with 1.75mm filament FYI.. Here is proof. [www.youtube.com]

The main issue with larger nozzles is that at least for me the 3/4 rule of nozzle size vs layer heigh goes out the window. Its more of a 1/2 the nozzle diameter in heigh rule. So for .7mm, your really looking at .35 -.4mm layer heigh max. Your hot end also has to have a good sized thermal block as well as some decent insulation if you want to keep the speed up.

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Modicum V1 sold on e-bay user jaguarking11

Total noob to 3-D printing here but did have something worth mentioning.
Just to keep your size experiments more accurate, I would suggest drilling to size about .005" inside of the nominal internal diameter you want and then using a reamer of the desired size
to remove the final bit of material. It will make the hole much closer to round and within thenths (of thousandths) of the ID you were shooting for.
Drills are sloppy. I've worked as a machinist and a carburetor rebuilder and I've seen the damage people can do thinking the size on the drill is the size of hole you will get.

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Neybordave
Total noob to 3-D printing here but did have something worth mentioning.
Just to keep your size experiments more accurate, I would suggest drilling to size about .005" inside of the nominal internal diameter you want and then using a reamer of the desired size
to remove the final bit of material. It will make the hole much closer to round and within thenths (of thousandths) of the ID you were shooting for.
Drills are sloppy. I've worked as a machinist and a carburetor rebuilder and I've seen the damage people can do thinking the size on the drill is the size of hole you will get.

That is absoultly true. I measure my bits with a caliper. Usually I select undersize drill bits usually. My .5mm drill bit is actually .45mm, Also I use the shank of the bit to clear out the final swarf. One thing to mention is that the reamer is quite hard to find in these sizes, so I use high speed bits that I plunge into the cut surface. My oversize nozzles have come out quite good that way.

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Modicum V1 sold on e-bay user jaguarking11

Yoor accuracy may improve on larger diameter filiment if you drill into the tip with an oversized bit slightly so to concave the tip surface. This will help filiment from lumping and produce more even walls. Best of luck!

Hi, I've done exactly that with a new nozzle. Will install it tomorrow morning, I had some problems with the PETG filament jamming in my hotend, so want to fix that first. Maybe I'm printing too hot, not sure, as yesterday the filament didn't jam on the same print... Actually, the PETG doesn't jam, but it somehow creates backpressure, causing my extruder to jump back. At one point the PETG filament curled up in my extruder and all failed. My extruder is pushing really, really hard, and still it jams in my hotend.

Strange things happening!

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http://www.marinusdebeer.nl/

Drilling the Airbrush Nozzle of the Merlin is a bad idea. It is rather precisley machined and shaped.
If anything i would try very fine reamers of increasing size.
During the development of the Merlin hotend i built several variations with drilled nozzles instead of airbrush. One of these featured an 0.8 opening that i used with 1.75mm Filament. The results were very good, of course you could see a more coarse structure than with finer nozzles.
The over all print speed was very nice though, but you realy need a fast extruder with nozzles of that size.

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[merlin-hotend.de]
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Quote
Ohmarinus
Hi, I've done exactly that with a new nozzle. Will install it tomorrow morning, I had some problems with the PETG filament jamming in my hotend, so want to fix that first. Maybe I'm printing too hot, not sure, as yesterday the filament didn't jam on the same print... Actually, the PETG doesn't jam, but it somehow creates backpressure, causing my extruder to jump back. At one point the PETG filament curled up in my extruder and all failed. My extruder is pushing really, really hard, and still it jams in my hotend.

Strange things happening!

Ohmarinus, did you find a solution to your PETG jamming problem?

One other thing to keep in mind is the ratio of the orifice diameter to the orifice length. If the length is too short, you'll get more oozing and the filament might also not squirt straight. Too long and you end up with too much back pressure. My impression is that most nozzles have an Length/Dia ratio of about 2 or 3. Drilling out an existing 0.4mm nozzle to 0.7mm nozzle will obviously change that ratio.