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Printing speed, where to start

kevinellisdesign
(@kevinellisdesign)
Significant Member

Much is covered regarding temperature when trying out a new material, but I struggle to find information where to start with speed.  I have struggled for so long with a Taulman flexible material, going through all the temperature settings, only to be told by a fellow enthusiast that the max speed should be 20mm/s.  I was way off and would not have slowed down enough to reach the correct speed if it were not for his comment.  I tried the temp tower where I found the best of fair prints, but never a good print. 

I don't have access yet to all the material, so perhaps its covered later, but I feel this is vital information at the outset, especially with challenging materials.  Is there a guideline on speed available?  Other materials have been fine.   

Quote
Topic starter Posted : 19/07/2021 9:20 am
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Kevin,

Slicer speed settings are introduced in Module 2 Episode 2. First layer speed is touched upon in Module 2 Episode 4, but the main fundamentals of tuning speed are covered in the Optimization course, particularly Module 6 episode 3.

Having said that I can give you some tailored advice. When printing flexible filament, you will have to slow down, for two reasons. The first (minor) reason is that since the print itself is less structurally stiff, it does not hold position as well under the nozzle. In particular perimeters/walls will be flexible so if you go too fast they can suffer from both wobbling due to inertia effects, as well as flexion due to the nozzle dragging them around while printing. The result will be horizontal ridges on the print, a bit like shifted layers but on a much much smaller scale. In addition you will have the usual speed-based quality detractors common to all filaments, like overheating, ghosting and ringing, and (for the first layer only) loss of adhesion if you print the first layer too fast. The first few of these factors will be improved if you use a printer with a stationary bed, such as a Delta or a CoreXY architecture. On a conventional Cartesian architecture you normally have the bed moving forwards and backwards as the Y axis. This naturally causes the print to wobble, and starts to become noticeable once the aspect ratio of the print significantly exceeds 1 (that is, the print gets significantly taller than it is wide).

The second, major reason for speed limits, is that the filament is flexible and has a tendency to buckle in the Bowden tube if you try and force it through the filament path too hard. Intuitively you know that the nozzle has a certain resistance to flow, and the extruder has to push the filament through with some force. The force is proportional to the printing speed and inversely proportional to nozzle diameter and nozzle temperature - that is, the faster you print the more force the extruder puts on the filament, and the hotter and bigger the nozzle is the less force it takes to extrude filament through it. If you try and print too fast, you end up with too much pushing force on the filament, and rather than the extruder skipping or grinding like with conventional stiff filaments, the filament buckles somewhere within the filament path, and stops being extruded altogether. The result is a print failure as the filament stops coming out at that point.

In order to improve that and to enable you to print flexible filaments at higher speeds, the following hardware will help (you might already have some installed):

  1. A printer with direct-drive instead of a Bowden extruder. Although you can print flexible filaments just fine with a Bowden extruder, the longer tube exacerbates the difficulties caused by the flexing of the filament. You have a longer path meaning more resistance to the extrusion force, more chance of buckling, and you'll need much much larger retraction distances since you have to take up the slack in the entire Bowden tube before the filament actually gets retracted out of the melt zone.
  2. Capricorn tubing. This is a replacement for the PTFE tube between the extruder and the hotend (aka the Bowden tube on Bowden printers). Compared to the stock white PTFE fitted as standard to most printers, capricorn tubing is a higher-quality, more expensive tubing (coloured blue for identification). It has a slicker internal surface (meaning less friction, which crucially means less back-pressure working against your extruder), and tighter tolerances, meaning a smaller internal diameter (which is beneficial as it means much less chance of buckling)
  3. An extruder that has motor-driven, toothed gears on both sides - not just a single driven toothed gear acting against an un-driven smooth bearing. One of the best extruders in this regard is the E3D Hemera, which can easily reach 60mm/s printing flexible filaments (more info here - https://www.youtube.com/watch?v=Ws-rDTRzFlI )
  4. A larger nozzle diameter. Switching from a 0.4mm to a 0.5mm or 0.6mm diameter nozzle will reduce back-pressure due to the larger orifice size, which allows you to push more filament through your printer faster. This comes at the expense of reducing the resolution of your prints though, so larger nozzles are really mostly recommended for larger prints where fine resolution is not so critical
  5. Use a flex filament with a higher melt index, such as PolyMaker Polyflex TPU95-HF. This melts and flows more easily at a given temperature, which again reduces back pressure and allows higher printing speeds. Here's an example from the manufacturer demonstrating a print speed of 100mm/s - https://www.youtube.com/watch?v=Ejj5FHuT7Ak

As always, finding the maximum speed your printer is capable of requires trial-and-error. There are no hard and fast rules because all hardware and material combinations behave slightly differently. You should start at a moderate speed like 30mm/s, make sure you have complete reliability and zero failed prints, and then bump the speed up in small increments (say 5mm/s at a time) until either the quality degrades to the point where you're no longer happy with how the prints turn out, or until you start getting speed-related print failures. Then dial it back down to what seems like a reasonable value.

Hope this helps! Let me know what you think 🙂

 

Regards,
Luke

ReplyQuote
Posted : 19/07/2021 9:38 pm
kevinellisdesign
(@kevinellisdesign)
Significant Member

Thank you for the comprehensive response, it helps heaps!

I have the Creatbot F430 which seems to be a good printer with a direct drive.  

 

ReplyQuote
Topic starter Posted : 20/07/2021 8:27 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

@kevinellisdesign Happy to help. That is a very capable machine you have there, you should be able to go pretty fast before the quality starts to degrade 😀 . With flexible filaments though, an extremely well-constrained filament path is key. You'll have to experiment to see how far you can push it before it starts to buckle.

Happy printing, let me know if I can help with anything else! 🙂

Regards,
Luke

ReplyQuote
Posted : 20/07/2021 9:54 pm
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