Is it possible to connect two pieces of 1.75 mm filament end to end, with no change in width? I am asking the question because I am interested in creating a multi-filament feeder to a single extruder, and I am curious about the process of changing filament while the 3-d printer extruder continues uninterrupted. My current best-guess at the optimal solution is to someone 'cut' one end of the filament and 'melt' it to the end of another filament.
You'd have to ensure that the joining portion of the two filaments do not "bloom" or increase in diameter, which would happen if unconstrained at the melting and joining time. Alignment is also critical, otherwise you have a varying diameter from one color to the next at the point of join.
There's an item on ebay which is precision drilled and has precision machined mating surfaces to ensure alignment of the filament. The filament is extended through the two components, heated (in the case of the video, with a match) and the two metal parts are pushed together. The joining of the metal parts also cuts away the excess bulge of the melted filament, ensuring correct diameter.
In the case of the above item, the joining devices have to be threaded with the filament prior to the joining process and then have to be threaded off the filament by pushing them the entire length of the filament.
This would be okay if one were joining short lengths only. Consider how much fun it isn't to have to slide these two pieces over an entire full spool of filament.
A split device which would enable one to un-latch or otherwise open a clamshell to release the filament would require much more challenging machining to achieve the necessary precision, which is probably why we don't see such a product.
There is a device which can do what fred_dot_u describes in his otherwise explanatorily good answer: the easywelder, made by I3D Inno.
It fixes the filament in a separate part so that the faces are adjoined perpendicularly and then heats the joint electrically with a device that at first sight reminds me of a hair straightening iron.
I am not sure about the joint quality this machine produces, but I am skeptical whether the it is good enough for high accuracy 3d printing. Especially if you take the history of the device into account (he wanted to create a custom O-ring from Ninjaflex), which the inventor shortly describes on this instructable: http://www.instructables.com/id/Welding-tool-for-plastic-filaments
Here is a neat method I came up with: - cut both ends diagonally - insert them in a piece of heat-shrink tubing, making sure the diagonal cuts overlap - protect everything but the overlap with Kapton tape - heat the overlap with a heat gun. - you will need to monitor and experiment with the temperature. too much heat will deform and bubble the filament, too less heat will result in a poor join - use a multimiter with temperature probe.
How it works ?
The heat shrink tubing encloses the filament ends and also pushes them together when it shrinks. The diagonal cuts increase the joint area. Results are super strong and seamless joints. You might need to do a little sanding until you establish the right temperature for your setup.
I made a video how to do it : https://youtu.be/eJeU9lXiQPE
I haven't tried this but it is something I have thought about. The simplest way to try this that I could think of was to try cutting the ends flat and then using a soldering iron or just the printers printing nozzle to melt the ends and then quickly press them together, then you could sand the filamelt to try and clean up the join.
I think what would work better than trying to get the width perfect would be to make sure your printer is doing infill when it hits the join so over or under extrusion wont matter as much or have the printer move to the side of the print and extrude in thin air while getting past the join. I have done this when swapping filaments during a print by pausing the printer, and changing the filament.
idea is good and i know for sure many are working on it but if you want this to work smoothly you may need to fix the device (that is joining two filaments) somewhere near your cutter assembly (if any)arranged to cut the filament...this is the another way to perform the task automatically but you can do it separately with devices available to cut and join the two filaments together.