While I don't think this is easily possible I am wondering if it can be done. So my spool of filament had a tangle and got pulled into the printer head. Some got melted together and after cutting I have a few strands. Would it be possible to mend the ends together to make one continuous strand instead of many small strand?
Sure, but you need to be careful not to have wide or narrow spots. A fixture for this is probably better than freehand welding.
See some ideas for a homemade fuser at https://rigid.ink/blogs/news/how-to-join-or-fuse-filament-together
As @davo says in his answer, this can be done rather easily, but the main problem with this kind of approach is reliability of the joint: sure, it must last only a short time, but during that time it will have to survive bending through your bowden tube (if applicable) and withstanding the grinding of the hobbed gear pushing it through the extruder.
I personally only used the PTFE method (plus heat gun), which is substantially identical to the tinfoil one outlined in the link provided by @davo but here's a couple of observations:
- Freshly cut filament seem to work best. I guess this is because there is less chances for contaminants like dust, skin oil etc... to find their way to the surfaces you are trying to bond.
- I had no problem melting together PLAs of different brands.
- You may have to tune the flow "on the fly" via the knob on the printer to accommodate for different diameters between the two spools you spliced (not applicable to your specific case of "plastic surgery" (pun intended!) on the same spool.
- I find the bond works best if the two filaments are cut at an angle (so that the actual bonding surface is larger)
- A light sanding to smooth out any seam and reduce the diameter of melted part a bit is in order