External perimeter speed?
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@DocTrucker I think we must have been talking at cross purposes. You mentioned something about being concerned about swinging the weight of a direct extruder and I assumed that you were referring to the diamond - hence my mentioning the fact that it isn't.
And yes, filament is funny stuff. It's generally a poor heat conductor so one can get the situation where it is fully molten on the outside but only partially molten on the inside. Which is why I think that time in the melt zone is as important if not more so, as the surface area of that melt zone.
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@deckingman I meant to add a comment saying I think we are talking at cross purposes. To many things going on at once here!
Edit: I have said many times on here polymer is weird!
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I mention the E3D products regularly. In order to avoid sounding like a fan boy I'd like to pojnt out I am checking out the other options like Micro Swiss, Dzyne, Mosquito, and any others that I find which are substantially different to the J-head and E3D V6.
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@DocTrucker If I was looking for a single input hot end, I'd put my money on a Mosquito. I just like their approach to the heat break.
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@deckingman said in External perimeter speed?:
@droftarts said in External perimeter speed?:
True, but then you're flinging a lot of weight around, which causes other problems... but you know that, and have fixed it, already!
Ian
What problems?
Lots of weight on axis + fast speeds = backlash
That's why I said you'd fixed it; by separating the weight out onto independent axes.Ian
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@droftarts I guess that depends on your definition of "backlash". For me it's a varying clearance between mating components depending on the direction of travel, so unaffected by mass. Even though I've separated the mass onto two gantries, I still have 2Kgs on one and 3Kgs on the other which most people will say is very very bad.
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@deckingman said in External perimeter speed?:
@droftarts I guess that depends on your definition of "backlash". For me it's a varying clearance between mating components depending on the direction of travel, so unaffected by mass.
Lovely description, makes it sound so positive, almost intentional!
Ian
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@DocTrucker said in External perimeter speed?:
@Phaedrux said in External perimeter speed?:
Some of the filaments I use don't like to change speed very often, so print speed is held constant. Polyalchemy elixir for instance.
What are the symptoms of a polymer that doesn't like to change flow rate?
With the polyalchemy for example, it's a very spongy filament. When extruding into free air it creates a glob that sticks to the nozzle and keeps expanding rather than a single drawn out filament. When printing if the speed changes abruptly it can leave gaps at the transitions where not enough plastic is deposited.
With some PETG I find that it gets blobby and sticks to the nozzle unless speeds are consistent. If the print speed changes from 40 to 60 at different areas I get blobs. If I run the same print at 70mm/s it's nice and clean.
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MAX flowrates in slicers don't mean ANYTHING unless you calibrate the printer with a filament at a given temperature and even PID tune too properly at that temp.
IMO filament melt rates are non-linear and vary significantly between materials and physical hardware setups. Even the slightest draft on your printer will throw the numbers off for the same material and temp.
Here is a video example of what KISS does for flow tuning. Not my video, but pretty descent for the concept. It changes print speed to vary the extrusion rate. The gaps and bad surface finish on the print is basically the printer falling flat on its face. It intentional failure- pushing the limits until you can find it.
Jumping ahead to the resulting print-
https://youtu.be/c5xcAjdjYhI?t=326the author picked the elevation of the best looking part of the calibration object and computed that for the filament and temp, best flow was 3.7 mm^3/s. You might scoff at the final answer but the procedure gives consistent results.
3.7 is a far cry from the theoretical max of 10mm^3/sec for v6. But the truth is that for that printer, under those parameters, that was the authors interpretation of 'best quality'.
As an aside, we calc'd out the extruder filament speed to maintain the throughput of the E3D to yield 10mm^3/sec. It was surprisingly low, like on the order of 2mm/sec for 1.75mm filament.
EDIT: I use KISS and Slic3r PE depending on the print. I use the calibration process in KISS to get printing parameters for Slic3r to get close to the dialing in spots. Doing temp, flow and destring (retraction) takes about an hour of print time total with a couple of iterations.
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@sinned6915 agree with most of that, I'll have a look at the link later. Have they calibrated for linear/non linear extrusion correction and got pressure advance set up before doing that?
I tend to limit my max speeds to either 10mm3/sec, when the extruder stepper skips, or when the plot of the required extrusion corrections takes a sudden jump for the sky!
Yes filament speed at 10mm3/sec is low, 3.6mm/sec. The melt zone on the V6 is little more than 2mm long, but those to figures next to each other elequently demonstrate a reason why I am interested in longer melt zone.
I really want to do destructive pull tests at some point because I don't think dull parts are poor parts. Geometrically they are still good aside from a little more ringing.
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i don't understand your question about linear advance. i don't see how its relevant for this calibration.
if you are skipping steps, then you have found you limit. but is that number reproducible or repeatable? how predictable is it?
i don't use any of the linear advance / pressure advance. i think its folly and band aids over scabs to try and go faster when you are already at the point that the hardware cant keep up.
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He wasn't talking about linear advance / pressure advance but rather non-linear extrusion which makes adjustments to the extrusion speed/rate at different print speeds.
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It's not linear advance. There's Linear & non-linear extrusion correction and pressure advance.
Yes it it a correction but in my opinion far better used than ignored as even with equal melt temp across the processing range back pressure will increase with increasing volumetric throughput leading to a reduction in filament mm per x number of steps.
Without these you will limit speed. Each to their own.
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@DocTrucker said in External perimeter speed?:
Without these you will limit speed. Each to their own.
When I first used my printer I set the slicer max print/move speeds to 60mm/s.
This worked well and I ended up using it for many months at this setting.
Recently I decided to see if I could speed things up. I increased the setting from 60 to 80, to 100 and finally to 120.
At 120 it seemed to be under extruding a bit.
Is this the kind of problem you are talking about?
Thanks.
Frederick
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@fcwilt it's the way this conversation is going at the moment yes, but originally I was canvassing to see how different people were setting external perimeter speed to their standard.
Any how, you can test if you need linear or non linear correction. Get your nozzle up to temp and in free space. Mark up 120mm behing the extruder on the filament, extrude 100mm and then measure back from the extruder to the mark to see how much has been drawn in. Repeat for different filament speeds bearing in mind that filament speed is much lower than head speed.
I find is the steps per mm are accurate for low speeds by the time you are upto about 10mm3/sec the under extrusion is in the 5-10% range. Different hot ends behave very differently. I ran a 3 way diamond breifly and that needed very little correction.
