Pipes made of corrugated flex copper were popular about 30+ years ago, in particular they were used to connect stop valves and bathroom/kitchen faucets, as shown in the photo. Typically, one end was permanently attached to the valve outlet while the other had a standard threaded fitting. Due to their replacement by more modern types of connection, no much information is available online on the techniques that were used to cut such pipes to the needed length and to place the fitting right at the shortened end.
Additionally, all the DIY-friendly connection methods for copper pipes (e.g., compression, Sharkbite) work only for rigid pipes and not for corrugated flex pipes.
One potential connection method could be to solder a piece of rigid copper pipe to the shortened end of the flex pipe and then use one of the above-mentioned methods for connection to the braided line. However, soldering copper pipes is not a very DIY-friendly method and surely one that I am not anxious to try, especially in a small confined space.
The two methods that I found in my quick research are:
the use of a press tool that crimps the cut end of the corrugated pipe, creating a stop that allows the insertion of a connector like the one that was present at its original end. The use of such a tool is demonstrated in a Youtube video for a stainless steel flex pipe, but I would think that it should work as well for a copper one. Albeit the crimping tool is rather inexpensive, it only works only one fixed pipe size and I have not been able to find one for the 3/8" size that I am interested in.
Connect a piece of solid copper tubing using an epoxy putty or a fiberglass wrap specifically developed for solderless plumbing connections, which claim to be resistant up to pressures two orders of magnitude larger than that of residential water supply. Then proceed as described in the soldered case.
I am not sure whether this is a code-compliant solution and whether the chemicals released by the epoxy could be harmful in water that, even if not for drinking, is used for personal washing and hygiene.
A succinct description of what seems to be the method that was used back then by the plumbers who worked with this type of pipes is given in an older post in this forum, which mentions the use of
either a top-hat shaped Step Washer that grabs the pipe and has a flat face for the fitting, or a Threaded Cone Washer that screws onto the pipe to make contact and mates with the fitting in a wedge shape
but is lacking in details and explanations necessary for me to understand it operatively, I guess mostly because their author explicitly stated his preference for dissuading DIYers from performing rather than promoting it.
I would appreciate if someone who has familiarity and experience working with this kind of pipes could share some knowledge and wisdom on the matter.
NOTE: As an act of respect for everyone's time, I feel compelled to clarify that my intent is not to open a debate about my choices. I am fully aware that replacing the old multiple turns stop valve and the old corrugated copper line with a modern quarter turn valve and a braided or a PEX riser is a much better solution. However, such a solution has an additional cost that goes beyond the scope of this question, which is simply an attempt to gather some information that is not easily available online about an old technology from those who might have some hands on experience from the old days.
