Retraction and Deretraction Guide
Printing flexible filament through a Bowden cable on your desk top printer need not be an impossible task.
Regardless of your preferred filament choice whether it be 1.75 or 3 mm
Not just semi flex material (i.e. polymer with a shore A hardness above 90) but fully flexible material – right down to 60A in 1.75 mm if you desire.
Not at ridiculously slow speeds but the full speed that you would print with a direct drive extruder – and probably even better than what you are achieving already.
Plus with full retraction capabilities.
The following steps will help you achieve this with your Flex Wheel extruder.
Note steps 1 – 3 deal with the elimination of cavities along the extrusion path – A lot has been discussed about this topic but there are a few tips that are likely to help a lot.
Step 1: Choice of Couplings for PTFE and Tube.
Firstly chose the type of coupling that will allow the PTFE tube to be pushed all the way through. Being able to push the tube through the coupling is a very simple way to eliminate the small cavities that exist in the crucial areas at either end of the tube – i.e. where it leaves your drive system and where it terminates within your hot end.
Ideally a good quality coupling with a collet that when pressed easily releases the grip on the tube. This will allow you to easily adjust the length of the tube making sure you eliminate all gaps.
Tube dimensions have been discussed numerous times else where and is pretty well standard and easily sourced
Length – The shorter the better, however I have tested lengths up to 800 mm.
Step 2: Attaching PTFE Tube to the Hotend.
Hotends which allow the PTFE tube to go down the barrel so that they terminate closer to the tip of the hotend are preferred. The maximum temperature design limit of this type of hotend should not be a problem when printing flex as most flexible filaments are printed between 200 and 230 degrees c. If you have an all metal hotend these still work well, I have just found the PTFE lined model seem to preform better on a larger range of flexible polymers.
Attaching the tube to your hot end –
If your hot end is not Bowden compatible a quick design and print of a coupling holder to suit your set up is quick to achieve, a simple coupling holder for the Flex Wheel extruder is included on printable accessories page.
If your hotend is Bowden compatible you may find that the collet to hold the tube is a bit sloppy and even using a collet clip does not always eliminate the movement or that access to fit the collett clip is impossible, in this case you may simply double up by installing a second coupling holder before the hot end as well. Here is a link to a quick vid demonstrating this.
Step 3: Attaching PTFE Tube to the Extruder Drive System.
Aim: To make a seamless transition for the filament from your drive system into the PTFE tube with zero cavities and no resistance.
Fit the PTFE tube ‘snuggly’ over the stainless filament outlet tube of the Flex Wheel. As the ID of the tube will be different from the OD of the stainless steel tube preform the following steps.
- Very carefully using a 3 mm bit (1.75mm) or a 4 mm bit (3mm) drill approximately 5mm into one end of the tube.
- By hand use a drill bit corresponding to the ID of your tube and twist it inside drilled portion to remove any burrs created.
- For really great results remove the filament guide from the flex wheel slide the PTFE tube over the outlet and using a length of rigid filament run through system and feel for any resistance, if some is present repeat the above step a couple of times to create a seamless transition.
- Finally clean and blow the tube to remove any debris.
Attach the coupling holder and the slide through coupling to the body of the Flex Wheel. The coupling holder for the flex wheel can be downloaded and printed from printable accessories page.
Step 4: Reduce Micro Steps on Your Extruder Driver
The Flex Wheel is powered by an awesome little geared nema 17 stepper with a 30:1 High Precision Planetary Gearbox. This motor coupled with the larger diameter gear box means that the E steps need to re calibrated. The new steps for your extruder will be a high number. Check out Users Guide for more information.
To reduce this number of steps to a realistic level I have cut back the micro stepping function to 1/8 th step, this will give your motor more torque – which is great for pushing flex through a Bowden tube.
Step 5: Setting Retraction
Flexible filament experiences a great deal of hysteresis, much more so with Bowden cable, however from experience the amount required to ‘unwind’ and ‘re tension’ during retraction and deretraction movements is definable and constant.
The Flex Wheel makes these movements possible due to different mechanism used to generate force upon your printing filament .
How much to retract – this will be material and length of tube dependent, a good starting point to determine the minimum amount is by the following experiment –
- Heat your hotend to about 15 degrees below what you would print with.
- Slowly extrude filament by small increments until the filament just starts to form at the tip of the hotend.
- Unscrew the Bowden coupling at the flex wheel side – it should spring up as the tension is released.
- Measure this amount and that will give a figure on how much needs to be retracted just to overcome the hysterias – then add 2 mm to this length, check printing quality then fine adjust if required.
How quick to make retraction movements –
Flexible filament by its nature is very stringy and while the above settings will reduce the majority of ‘blobs’ and reduce stringing to an acceptable level, even better results can be achieved with the following.
- The standard 4988 chips are sufficient however the power of the Flex Wheel requires everything they have and acceleration and speed are limited by them.
- If you want to get the most out of retraction I would suggest upgrading to the higher power driver which is compatible with desk top electronics we all use for example our affiliate stocks link to come.
Step 6: Final Point: Changing Filament / Bowden Cable.
A common problem when you change flexible filament is when you withdraw the filament from the hot end a thin tail can be created, this may sometimes have blobs.
This tail and blob can easily break off when travelling through any extrusion mecahanism.
A quick simple way to avoid this problem is to unscrew the coupling at the point were the tube meets the Flex Wheel withdraw the filament from the tube snip off the deformed tail, good practice is to make the cut at a 45 degree angle so ready to feed next time.