CTC Dual / Bizer filament sensor bracket
Description
A replacement cable bracket for the CTC Dual printer to sense filament end-of-reel. It uses optical sensors rather than microswitches. Search eBay or similar for "Arduino slot optocoupler'. As a sample advert (not a recommendation) https://www.ebay.co.uk/itm/161817129903 The sensors slot in to the bracket from the back and are held in place by being clamped to the back of the machine. The idea is that they would be used in conjunction with an Octoprint Plug-in to pause when a reel is expended, or even to automatically switch extruders. The trick to using these sensors is to fill most of the gap with something opaque, leaving only a narrow path for the light to pass through that can be blocked by the filament. The cross-hole between the two arms of the sensor needs to be smaller than the filament to enable the filament to block all light. I used a 1.5mm drill to finish out the sensor tunnel after printing. Sensors from a different vendor might require smaller or larger holes. Alternatively the analogue output pin of the sensor board could be used. The filament path hole was finished out to 2mm. The bracket includes provision for a set of PTFE guide tubes, lower ones to help keep the filament on the spools (and not wrapped round the spool support pegs) and upper ones to guide the filament in to the extruder. It is not yet clear if either offer an improvement. The guide tubes are a simple push-fit in to 4mm holes in the part. The forces on both tubes are such as to push them in to the part rather than pull them out, so proper pipe fittings are unnecessary. These will probably need cleaning out with a 4mm drill after printing too. Print the part as-uploaded with support set to "touching bed" for best results.
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