Basket case

I was using two old component spools to hold my feedstock, see all-wound-up, but I don't have any more so now that I have four polymers I decided to give Vik Olliver's design a try. It has the advantage that you don't have to spool all the filament on, you can just drop in an open reel if that is how your filament comes.

This is my take on it: -



The uprights are 15x15mm aluminium angle. The beam across the top is a piece of 20x10mm channel. The bearing is a standard ball bearing and I reduced its internal diameter with a couple of bushes I had lying around. I then used a bolt with holes through the head as an axle. I found it in the road while I was on a walk wondering what to use. That is the third piece of HydraRaptor that I have picked up in the street.



The baskets are £4.21 in B&Q and have a plate in the bottom with a central hole just right for feeding the filament through. As the machine pulls the filament from the centre of the reel, the basket rotates to prevent it becoming twisted.

It works very well and has the advantage I can buy as many baskets as I have plastics and just take them on an off as needed.

It also allows the filament to rotate in the extruder but ironically, since I tweaked my extruder, PLA no longer feels the need to rotate. Presumably it rotates if the friction between the screw and the plastic is higher than between the plastic and the filament guide. I think that gives a clue to which of my tweaks made all the difference in reducing the extruder torque needed. I think it was adding the washers to space the top of the pump apart so that the screw bites in progressively and sharpening the screw thread.

More PLAying

The tweaks I made to my extruder dramatically improved its ability to extrude PLA. I am not sure which one made all the difference or whether they are all needed. I can now extrude at my target 0.5mm filament 16mm/s with about 75% motor PWM duty cycle. That is less than I needed for ABS before the tweaks.

I can also extrude at lower temperatures. I think 180°C is a bit on the hot side as the plastic is very runny at the temperature. It will flow out of the extruder under gravity and has negative die swell. At 140°C it behaves more like the other plastics and swells to 0.6mm, which is very low.

In a previous article I stated that I could not make sparse filled objects because the filament slumped too much. With the reduction in temperature and increase is speed I now can. Here is a 50% filled block: -



It is still very strong. I expected the warping to be less but I have switched from MDF to balsa and I think that increased it. The balsa I have is only 2mm thick and was only stuck down with masking tape. I might try gluing two pieces back to back with the grains at right angles to get it stiffer.



So now with a slightly tweaked extruder I can do PCL, PLA and ABS at 0.5mm @ 16mm/s. I had to slow down for HDPE to prevent thermal damage to the extruder.

To get good definition at high speed I extrude with a fan running. The fan cools the nozzle which causes more heater power so the barrel temperature rises to the point where PTFE goes soft and the JB Weld turns to dust. PCL and PLA are no problem because the temperature is less. ABS does not seem to need the fan.

I plan to make a PTFE cover for the nozzle which will probably insulate it well enough and hopefully stop filament sticking to it and burning.

Fantastic PLAstic

I have managed to get the GM3 to extrude PLA reliably with the following tweaks: -

• I locked the clutch as per Solarbotics instructions.
• I lubricated the GM3 with silicon grease as per Adrian Bowers suggestion.
• I sharpened the thread a bit with a half round file following Vik Olliver's instructions.
• I spaced the top half of the pump slightly further apart with some thicker washers. That gives the thread a gentle lead in.
• Plenty of oil on the filament.
• I throttled back the flow rate to 3/4 of the rate I normally use (π mm³/s).

The motor runs warm, but not alarmingly so. For some reason the filament is no longer rotating in the extruder.

My first attempt curled away from the MDF bed so I used 2mm balsa wood as Adrian has been using for PCL. That worked well so it's good that we can use it for both. I have yet to try it with HDPE and ABS.

I made my standard test block with 0.5mm filament extruded at 180°C (at the nozzle), layer height 0.4mm, pitch 0.6mm, fan on constantly. The results are excellent: very good filament compliance, i.e. sharp corners and flat sides, excellent layer bonding.

It is slightly more warped than my first test. That is probably because balsa is softer than MDF.



No warts on this one!