Extrusion speed

I run with a 0.5mm nozzle, and am in the process of building a new printer for which I have already purchased 2 0.35 mm orifice J-heads.

Recently my 0.5mm J head jammed, so I temporarily switched over to the 0.35mm and I had nothing but problems with it. I assumed that all I had to change was the orifice size within slic3r and everything would work OK, but in retrospect, maybe that was a bad assumption. The ratio of the orifice openings between the two hotends is (0.175*0.175)/(0.25*0.25) = 0.49 - so the 0.5mm nozzle has twice the opening size as the 0.35. This would make me think that I'd have to halve my maximum extrusion speed. I'm thinking that by pushing it too fast that the hobbed bolt dug into the filament to the point where it lost purchase and then the filament stopped advancing

I've since moved back to the 0.5mm hotend, and everything is working OK again, but someday I'll get to the point where the 0.35mm hotends are going to have to work. I just want to know that my thinking is correct here.

Thanks

Quote
jbernardis
I run with a 0.5mm nozzle, and am in the process of building a new printer for which I have already purchased 2 0.35 mm orifice J-heads.

Recently my 0.5mm J head jammed, so I temporarily switched over to the 0.35mm and I had nothing but problems with it. I assumed that all I had to change was the orifice size within slic3r and everything would work OK, but in retrospect, maybe that was a bad assumption. The ratio of the orifice openings between the two hotends is (0.175*0.175)/(0.25*0.25) = 0.49 - so the 0.5mm nozzle has twice the opening size as the 0.35. This would make me think that I'd have to halve my maximum extrusion speed. I'm thinking that by pushing it too fast that the hobbed bolt dug into the filament to the point where it lost purchase and then the filament stopped advancing

I've since moved back to the 0.5mm hotend, and everything is working OK again, but someday I'll get to the point where the 0.35mm hotends are going to have to work. I just want to know that my thinking is correct here.

Thanks

No it isn't your extrusion speed (steps/mm) will stay the same but you will need more torque from the motor as it will require more pressure with the 0.35mm nozzles.

I moved from a 0.4 to a 0.8 and did not have to change anything at all the Slicer should calculate the right amount of feed to suit the setup.

Doug

If your hobbed bolt is stripping on the filament, you can increase your extrusion temp a bit to reduce the viscosity of the melted plastic, which will make it easier to extrude, requiring less torque. if you're using a geared extruder, motor torque usually isn't the problem, but idler gear pressure may be.

---

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

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

Quote
dougal1957

No it isn't your extrusion speed (steps/mm) will stay the same ...

I realize the steps/mm will remain the same. That's not the extrusion speed. The F parameter on the G1 statements gives the number of mm to extrude. All the steps per mm does is to convert this into steps. I'm thinking that the number that ends up on the G1 statements should be smaller because the orifice only allows half the plastic through than the original hotend. Also, I wouldn't think youd have these problems going UP in size like you did. In that scenario, you ought to be able to increase the max speed.

I think some experimentation with the temp is in order, but all increasing the torque is going to do is to grind the filament even more.

Quote
jbernardis

Quote
dougal1957

No it isn't your extrusion speed (steps/mm) will stay the same ...

I realize the steps/mm will remain the same. That's not the extrusion speed. The F parameter on the G1 statements gives the number of mm to extrude. All the steps per mm does is to convert this into steps. I'm thinking that the number that ends up on the G1 statements should be smaller because the orifice only allows half the plastic through than the original hotend. Also, I wouldn't think youd have these problems going UP in size like you did. In that scenario, you ought to be able to increase the max speed.

I think some experimentation with the temp is in order, but all increasing the torque is going to do is to grind the filament even more.

OK think you have slightly the wrong end of the stick

the slicer should compensate for the change in nozzle size (as long as you changed it in the Slicer config) and then you must re-slice your object and it should know how much filament to extrude to cope.

think of the size of gap you try to squeeze say your body thru and then reduce that gap by half you need a lot more force which is where the torque comes in. It is a fairly well accepted point that direct extruder's suffer from this badly (if the motor is low torque hence why people used geared motor's) and will skip and chew filament.

You don't actually say what extruder you are using?

This is actually a mind field

My I3 was supplied with a direct drive extruder and I could not get it to work at all got loads of this skipping and chewing filament I changed it to Wades Geared extruder which is about a 5 to 1 reduction ratio and my problems disappeared instantly.

HTH Doug

I am using a wade's geared extruder, so there is a reduction, and I have never had a problem with the 0.5mm nozzle.

With a 0.35mm nozzle, I get slipping and grinding.

I just assumed that I need to slow things down. The F parameter is a representation of the filament going into the extruder. From what you are saying, I guess the slicer is supposed to know that it should slow things down because it is physically impossible to force the same amount of material at the same rate through a narrower opening. If I keep the same rate, I would need to increase the temperature so that the extrusion is easier, but all other things being equal, if I just increase my pushing force beyond the maximum speed of the hot end, then grinding and slipping is inevitable.

When I get home tonight, I'm going to slice the same object with 0.35 and 0.5 and see what the differences are.

Interestingly enough, (if I remember correctly) skeinforge does not ask for the nozzle diameter - the idea being that if you put so much plastic into the hot end, the same amount of plastic has to come out at the bottom. While I don't dispute that fact, I think the maximum rate has to come into play. If I keep increasing and increasing the speed, I will reach a point where the hot end cannot keep up and slipping will occur. Once I reach the maximum point, If I do anything to restrict the flow - such as reduce the temperature or shrink the nozzle - then I would think I'd need to reduce the speed accordingly.

BTW, I am using the term maximum rate to be the maximum speed in the firmware. The slicer is not aware of what this value is, but my expectation is that if the slicer asks the firmware to exceed this speed, then the firmware would scale back all speeds until it was in compliance with ALL (not just E) the maxima. I never really calibrated my maximum E speed. Mine is currently set to 25 mm/s (?) in marlin - I believe that value was already there. This is the number I'm thinking I need to change. Of course if my expectations of the firmware imposing the speed limits is wrong, then I'd need to rethink everything.

You can't use the firmware to limit the maximum extrusion rate because the motor needs to go much faster during retract and restart than it can sustain extrusion at.

The slicer doesn't know how much force your extruder can handle so the only thing you can do is slow down the feed rate in the slicer until it works reliably.

---

[www.hydraraptor.blogspot.com]

Thanks nophead. Although you shot holes in my thought that the firmware would enforce the speed limit, you have validated my thought that I need to slow things down (and/or raise hot end temperature) until the feed rate is in concert with the flow rate. My focus was on slowing down the extrusion; of course the X and Y axis movement would also need to slow down.

The maximum filament width and layer height you can use with a smaller nozzle get less, so you need to use smaller settings and the slicer should then reduce the flow rate to match. In fact if you didn't use smaller settings for more detail there would not be much point in having a smaller nozzle.

But also you may need to reduce the XY feed rate to account for the fact that the pressure needed to push the filament though the small aperture is inversely proportional to the fourth power of its diameter but only linear with respect to flow rate.

---

[www.hydraraptor.blogspot.com]