Copper whilst easily worked is not as ideal material in some other ways, it seems it can act as a catalyst and promote the formation of gummy deposits, not to be welcomed! Copper is also prone to fatigue failure due to vibration. Although the risk is pretty low, I have only seen two examples 40 years, it is worth noting.
One alternate choice would be flexible armoured tube available these days with stainless braid which looks neat and tidy.
Another possibility is thin wall stainless steel tube which is readily available and while a little less easy to work than copper it is also less prone to kinking. Again, cosmetically it will remain bright and clean. Nipples, etc would best be silver soldered, there are special solders and fluxes for stainless steel but “EasyFlo” has always worked for me.
With regard to making tight bends there is an alloy called “Cerrobend” made by Fry’s and sold in the form of ingots. The formulation is a trade secret but is probably an alloy of tin, bismuth, lead and antinomy. It melts at a very low temperature and has an almost zero shrinkage, I suspect it may even expand slightly as it solidifies. The tube to be bent is filled with the alloy which forms a sufficiently strong core to prevent collapsed walls but still allow bending. It is easily melted out when the bend is finished. It has the added advantage that it will not adhere to the inner wall of the tube making cleaning the bore a breeze. When a very tight bend is required work hardening of the copper becomes an issue. If this is the case make an inital bend at a larger radius, melt out the Cerrobend, re-anneal the copper, refill and finish the bend.
As stated in an earlier post small tube benders are cheaply available and very useful but to be effective the formers need to be an exact match for the O.D. of the tube if deformation is to be avoided for as long as possible. They also restrict the radii that may be made. A special bender is easily and cheaply made if you have access to a drilling machine and a lathe when any desired bending radius can be chosen.
Another interesting source for all sorts of neat copper fittings, bends, “Tees”, “Y’s” all sorts and sizes, (solder type), including 180 degree return bends, is the refigeration industry. Be warned though they have their own thread system for compression fittings and as is to be expected it is incompatible with BSP.
