Teach me about cartridge 'retipping'

MC cartridges have a wire that extends from the back of the cantilever through the coil. The wire is pulled through a rubber damping ring then through a hole in the rear pole that has a set screw to lock the wire. As the wire is pulled tight the coil compresses the rubber. The tension on the wire is critical as this determines the compliance of the suspension. 

I would only get a factory rebuild. Some companies like Elusive Disc will give you a new cartridge for a rebuild price. They send the used cartridge back to the factory. It costs a little more but you get a new cartridge right away.

Could you explain why do you need a retip of MM cartridge if you can buy NOS Grace stylus, even F14 (RS14) which is huge upgrade over F9 (RS9) of any kind, the RS14 styli from Grace can be Boron/MicroRidge, Sapphire, Ruby and even Ceramic cantilever. Grace made Aluminum with MicroRidge too. This is the best diamond profile you can get, life span can be 2000 hrs! They are rare, but well worth the investment, I collect all Grace styli. Never re-tipped any of my Grace cartridges (I have many of them). SoundSmith actually rebuild Grace, it’s not a re-tip, he can install whole new cantilever with stylus tip. Re-tip is just a tiny diamond replacement on a cantilever using glue. This is original Grace Ruby, try to find any glue (more here). This is SoundSmith Ruby with glue (more here).

The situation with MC cartridges is another story, you’d better read what cartridge designers think about third party re-tip if you want to know the truth, find Jonathan Carr’s comment on this forum.

Re-tippers will always accept any cartridge for re-tip, this is their job and you will pay for it (very high price). On the other had we have people who have no idea what they are doing and always comment that re-tip is better than the original, at the same time you will find tons of re-tipped MC cartridges on ebay with less than 50 hrs on it (why people are selling them? Think about it).

Here is a typical example of SoundSmith glued stylus tip on Boron Rod cantilever (image from his site again).
And this is a factory job, nude diamond on boron rod cantilever (image under my macro lens).

What re-tippers can’t get today is Boron Pipe cantilevers (just one example), they can’t mount their styli like this. Do you see any glue? This is super riggid and super light mass construction (hollow boron pipe and stylus mounted through the laser etched hole). This is how top of the line MM or MC were made in the golden era of analog (not today). I could add more different images I made myself, but I think it’s enough to understand what I mean. Here is the side view on Boron Pipe cantilever with Nude Diamond. Like Grace it is a high compliance MM (SONY). Same Boron Pipe cantilever you can find on the best Grace models. Extremely low moving mass! Another example is Beryllium (Victor X1II), just look at this. 

Remember Technics best cartridges, this is one of mine under macro lens. Technics made the lowest possible moving mass MM cartridge (Boron Pipe cantilever). See why it’s better.

According to this Technics research:

"Somewhere in the high frequencies, every cartridge has an undesirable resonance point. Undesirable because there the frequency response curve climbs a sudden peak. If that peak is in the audible range, your records sound not as intended. That resonance frequency is determined by the total effective moving mass of the vibrating system - the summed masses of the diamond stylus and, most importantly, the cantilever and magnet, etc. To shift that harmful resonance frequency up into the high supersonics, the effective moving mass must be reduced to the lowest possible minimum. Also, too much effective moving mass increases the mechanical impedance, thereby negatively affecting the cartridge’s tracing ability."

Retippers can’t do anything like that, they don’t even have an access to those cantilevers, they are not available today (boron pipe, beryllium). What they can do is to buy what’s available and install it. Or they can glue a new tip on old cantilever, but glue will add mass etc. Re-tip or rebuild is a compromise, most likely degradation of the very special cartridge (if you have a very special one). This is why a very special cartridges must be shipped back to the manufacturer for rebuild or upgrade with a new one.  

fair points and perspectives so far - thank you

i should have been more precise to distinguish a retip from a rebuild... the difference is of course meaningful, thanks for pointing that out chak...

appreciate other comments that more experienced folks than me may have - am sure lewm, raul, mc and many others will chime in before long