In one of the engineering lab rooms in Boston University where students can work on building their projects, there are a few Form 2 SLA printers and Flashforge FDM printers. The Flashforge Inventor Dual Extruder printer was used for a lot of the FDM prints that you see on my additive page. Unfortunately, there is a slight issue with feeding the filament through the side of the printer into the extruder head.
Filament is fed into the extruder from an external spool which stands outside the printer. When the spool is full, the filament slips off the edge and unravels due to the stiffness of the material and not enough tension in the filament around the spool. This causes lots of printing issues since the untangled filament can get caught in strange places and ruin a print. For that reason, I thought that if we could add tension to the spool and guide the filament correctly into the printer, we would be able to overcome the unwanted slip of the filament off the spool. This method would also control the torque of the spool to stay more constant and smooth, while being pulled into the printer. The best way to add tension seemed to be to print and attach a part to the side grate of the Flashforge 3D printer, since it would be an easy attachment location, and since the part would work regardless of the type of filament or the spool being used.
On the left is the final print which turned out really well, and solved all the filament feeding issues.
Below I will describe how I got to this point.
1st Iteration Print and Idea
In our first iteration, a small 2mm hook was designed, indicated by the white arrow, to help attach the part to the side of the printer. The initial thought was that gravity could hold the fork shape over the spool and the filament would thread through the slit in the rod, guiding it into the printer. However, gravity was not enough to hold the fork down onto the spool since the print was very light in weight. Instead we realized that the fork could guide the filament from below the spool, in the orientation shown on right sketch. We tested it, but the filament still slipped off the spool. The problem was that the part did not attach to the spool tightly, and it was easy for it to fall off from the grate.
The first iteration had a print time of roughly 40min with a few supports, although the part was designed to not use supports. The printing software just kept adding the supports and at the time I didn’t know how to adjust it. The print would have been around 20min without supports. It was printed at 200C extrusion head, and 50C bed temp. That was just one single print.
From left to right shows the progression of our part. The picture on the left was printed on the Engineering Product Innovation Center (EPIC) printers which have dissolvable supports, so design for print direction didn't really matter there. That print was designed to print standing upright in any case, and it came out great. However, the hooks on the top were not enough to keep the filament from pulling the bottom of the part off the grate-- a second attachment was needed below.
This is why we tried a second design, with another type of press fit attachment into the grate. Also, the shape of the hole for filament threading made printing the part a little challenging, as the bottom plane was not flat. That was also changed to make printing easier. The idea for a small press-fit connection into the grate was great, however it meant that the print direction had to change to print the hooks and attachments in detail (which was important because we are talking about fitting something into a 2mm wide slit).
This is why we designed the ladder-like structure in the frame instead on the sides to act as support material while printing, so that this part could be printed on it's side. This change also gave more flexibility for squeezing upper hooks and lower hooks into different grates. Four tiny cylinders were also extruded at the hooks and attachment positions to act as supports that could be broken off later. This worked well, and the part printed great. Unfortunately the press-fit attachment at the bottom of the part was too fat in the second print (grey PLA), so the design was fixed and the black PLA print worked perfectly.
The part was tried with the spool and it worked with filament fed from above and also from below, as shown in two sketches above. The spool was able rotate in either direction and it still worked. The height placement of the part could also be adjusted on the grate, which was a good design consideration. Several fillets were added to account for weaknesses at sharp corners, so that stresses could be mitigated.