Can I modify Shimano 12 speed cassettes and custom my own cassette?

[lidation]

Shimano cassettes are separated into multiple pieces and the 11 speed and 12 speed are essentially using the same spacing between cogs. I have so many old Shimano cassettes lying around, and we have AliExpress. I'm wondering maybe I can just mix and match and make my own cassette? Like I would like to make a 12 speed 11-46T with very close spacing at the 11-17T.  Any problems by mixing things like this?

[Super_davo]

The width of the cogs between 11 and 12 speed is very slightly different, and if you've making custom ratios the ramping will likely be out. On the 12 speed cassettes I have at least one of the cogs is dished slightly and has a thinner spacer than the rest.
You might change some cogs and get it to work - e.g if you had a worn / damaged 14 and changed it for an 11 speed cassette 14 (where the next cog was a 13 /15 in both cases) - but if you're attempting to make custom ratios and changing significant numbers of cogs you either won't get it them all on the freehub and the lockring to engage or the shifting will be atrocious or both. .

[Daviddavieboy]

 Cassettes used to be built this way but I am sure to avoid consumers screwing things up it's just easier to pin them together.