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by chowderhead, published
Caulk seems a nice material for printing and I am in need of a sealant for upcoming printed parts, so I figured I'd try this out. Ultimately, I wish to have a dual extrusion 'bot with ABS or PLA for structure and caulk for sealant.
Caulk is ubiquitous, cheap and there are a number of materials available. I'm presently working with latex caulk because it cleans up easily (there's been a lot of cleanup).
This is most definitely a WIP but the results thusfar are promising. Lots to overcome, though.
Caulk tubes are made for periodic loading and when subjected to constant load, the thin walled tube swells, allowing caulk past the piston. The walls are reinforced with a piece of 2" PVC pipe ripped down the length and held tightly against the caulk tube by hose clamps.
The as-supplied piston is also a bit whimpy and was replaced with a printed version having a groove for an o-ring and the ability to be retracted.
Last but certainly not least is the issue of energy storage - lots of potential here. Air is not your friend and any pressure-induced distortion of the hose or caulk tube winds up expressing itself as lots and lots of ooze.
I had a variety of o-rings, so don't really know what sizes they are. Two are required: One for the piston and one for the leadscrew that is screwed into the base of the piston.
The threaded rod is M8, 18-8 SS: one 22" and two 13" (sorry for the mixed units; we're not going for a Mars landing here anyway...)
Two 608 bearings, one in the motor end, one in the large gear. They act as thrust bearings and washers are needed on both sides of the large gear.
The 2" PVC pipe is slightly large and needs to be ripped a few times, removing about 3/8" from it's wall, so it can be clamped around the caulk tube. I carefully held it against a rip fence and cut with a cross cut blade, making three passes.
The adapter for the caulk tube nozzle is copper tubing of various diameters sweated together. I think 3/8", 5/16", 1/4" and finally 5/32". There are a couple small hose clamps securing the adapter in the nozzle.
The extruder nozzle is a pipette tip that I scrounged. It's something on the order of 250 microliter capacity. I'll see if I can figure out what it is if there's interest.
Hose is PE, 4mm x 6mm, and is available from a number of places (I get mine from Freelin-Wade). I think ice maker hose will work fine.
The extruder tip mates to the hose via a short (1.5") piece of 5/32" copper tube that is threaded with a 10-32 die at one end. The tip is screwed onto the threaded end and then pushed through the extruder mount and secured in place.
The motor mount is presently for a NEMA17, but I'm finding it slips, especially after replacing the piston. I'll be evaluating a NEMA23 shortly. Strike that last; I'm going to try a different transmission having a higher gear ratio and so get the E_steps up to a respectable value. The required extrusion rate with a 46mm piston yields an extremely low piston velocity and a NEMA 17 should have adequate torque with a proper transmission. I think...
It's up to you as to how to setup firmware. I opted to scale E_steps so that 3mm diameter filament could be plugged into the slicer. With the supplied gears, E_steps is 19.5 for an equalent 3mm filament and a 200 step/revolution motor (which causes me some worry - maybe a 400 step/revolution motor is a good idea here?)
Assembly is straight forward except for the piston. Assemble the frame, motor end and transmission leaving the nozzle end off of the frame. There is a small o-ring in the base of the nut trap in the piston. I put it in place by putting a nut and washer on the piston rod, putting the piston on next and then the o-ring and finally another nut. Tighten the first nut, forcing the last nut and o-ring to seat into the nut trap and compress the o-ring. Disassemble the whole thing and put the larger o-ring in piston's groove.
The piston was removed from the caulk tube by drilling a small hole in it's center then threading a long sheet metal screw into the hole. Pull on the screw carefully and slowly remove the piston; use a pliers to get it all the way out. Put the printed piston in the tube with the skirt exposed. Press it into the tube until caulk starts to enter the nut. Thread the piston onto the piston rod, which should be assembled with the frame and transmission.
If you followed the 3mm filament equivalent techinique, slice parts accordingly. I'm still printing very slowly (20mm/sec) while ironing out the bugs.