My typical wipe purge setup is to purge behind a bungee cord which knocks the string off when the tool moves to the brush. The brush is the silicon basting type and meant to be a secondary attempt to knock off a string which may still hang on. This worked about 95% of the time for a large print. However, I would really prefer to have the entire tip of the nozzle wiped clean. My cohost suggested using silicon foam. Same 600C spec as the brush. They sell sheets of the stuff for T-shirt machines. https://www.amazon.com/gp/product/B07D1CFM9F/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 I made a shoe holder that slides into the brush holder. The foam is held by the sides of the shoe and it's positioned right at the point of the nozzle with just a bit of pressure. The pressure is enough to get the nozzle to etch a path into the foam and with my zig zag wipe I get a nice wipe around the entire nozzle tip. Now I not only get 100% of every string, I also get a very nice clean initial extrusion on the start of the tool path. Great stuff!
Those bits were only from the initial use. Initially after the nozzle tip cut it's path through the unused foam, the foam did pile into the orifice of the nozzle and the first extrusion spat out the foam with the PLA. Once the path is cut I probably do not want to move the foam at all so that the nozzle uses the same cut channel every time. The channel seems to do a wipe around the entire tip. After the print is done all the nozzle tips are nice and clean. I ran two 8 hour long 4 color tests and neither saw and strings or foam bits in the print. So far this stuff made an enormous improvement. Next I'm going to cut way back on the amount of prime. For sure the stuff needs replacement after awhile. However, for $20 you get a LOT of it. I'll include the shoe here. I cut a rectangle of foam and then I either slide it into the shoe or I put in one side then compress the foam to insert it into the other side. I also cut the ends at an angle so that the nozzle hits the foam on a ramp which makes the contact way less abrupt. I've held off posting my modified brush holder bracket since it is still a work in progress, but the left side bracket that E3D has in the TC GitHub is the same position and shape.
