Flow stopping mid print: basic checklist

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Robm1989
Technical
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Joined: Tue Mar 02, 2021 5:41 pm

Flow stopping mid print: basic checklist

Post by Robm1989 »

Flow stopping mid print is extremely annoying especially with long prints. Also the cost when printing with exotic polymers can cause heartache when throwing away perfectly good chunks of material, you can just see the money going up in flames. So to help avoid this, just checking a few common causes can save you valuable time, money and effort. Examples of failed prints are pictured below.

Most common causes of this are due to a few relevant slicer settings. Remember that slicing settings almost always differ between not just materials but also brands due to the slight changes in physical properties of the materials or even in their manufacturing process. The settings most likely to cause this are:

Flow rate: Extremely important as in my experience, the expansion of polymers differs greatly. For example I often print both Polymaker PC Max Polycarb and also 3dxtech Carbon Fibre Polcarb. I find PC Max required 98% flow and the 3dxtech requires a whopping 84% flow. This is due to expansion of the filament and believe me they are all different. Test test test get those profiles perfect before committing to large prints.

Print Speed: Essential that you use the print speeds the manufacturer recommends. I have found that regardless of this the first layer should be slow even as low as 5 or 10mms. This ensures first layer bed adhesion reducing the chance of stringing or squishing the filament. Also allows you to adjust bed height whilst printing the first layer to get that perfect layer height. Printing too slow for the filament your using through the whole print will definitely cause clogging mid print. On the other side printing to fast will have the same effect. Too fast you will find the filament skipping without adhering to the previous layer and clogging on the end of the nozzle in a big blob which will eventually stop the flow. Too slow and the flow will be cut off by clogging inside the nozzle that you cant see. This is the filament being heated to long and expanding too much to fit through the hot end.
Always test print filaments and get those slicing profiles speeds set up and saved for the material brand your using. Finding the sweet spot for your printer setup will save you time and money in the long run.

Retraction: Again this is essential and should be tested and tweaked for every different material and brand. Bowden feed printers require more aggressive retraction than direct drive but with both types too much or too little can cause clogging. This can be either the speed or distance of retraction or even both. Too little distance or too slow can cause material to spew during travel moves meaning the printer now has more material than it thinks when It continues to lay down for the print which shows itself as big blobs of plaster building up on the nozzle which again given time will block the extrusion causing a failed partial print. Again the other way too much retraction will pull the filament out of the hot end which due too expansion when it tries to re-prime the nozzle, will no longer fit back inside stopping the filament flow and grinding a notch in the filament where the extruder motor gear feeds the filament. The print will fail at this point and the filament must be taken out and cut off to remove the ground notch and then fed back in.

Extruder Steps Per MM: This is a hardware setting not in the slicer software that must be calibrated on all printers. There is a procedure and mathematical formula to precisely calibrate this. This is so the printer knows exactly how much material it is putting down at any time. Having this too high or too low will show as too much material or too little being extruded again causing a failed print. Calibrations must be done on your printer before anything else is messed with so you have a confirmed starting point to base all other tweaks on. I wont go into calibration in this thread as its off topic but there is plenty of information available. Do calibration whenever you change any hardware on your printer just for piece of mind to avoid complications.

Temperature: Very important!! This is always specified in the technical data sheet provided with most materials usually in pdf format. But also usually stamped on the role of filament itself. It will have a temperature range at which it should be extruded. This is to take into account the varying ambient temperatures that different people place there printers in. Always set temperatures between those ranges specified by the manufacturer. Above the maximum, filament can burn causing dangerous gasses to release that threaten health and even life!!! Be careful!!
Too low and the material will clog as its not hot enough to become molten and flow properly. Both can cause flow to stop resulting in failed print. Do tests prints with each material and brand to find you optimum temperature for your print conditions.

Other users may have more information on this topic due to there own individual experiences, this is just to help those new to 3d printing overcome common issues.

The following pictures show how just tweaking these few settings can make a difference to your printing success rate. All I tweaked here are slicing settings mentioned above. These are Polymax PC hinges....

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