Degrafting: what would you do?

[mmcavall]

This will be my first attempt to degraft a cactus.
What is the right thing to do? Where do I have to cut? Can I keep part of the stock? How much of it?
Thanks in advance for any advice!

[Hanazono]

How big is the scion in diameter?

[mmcavall]

thanks Hanazono for replying.
It's between 3.0 and 3.5 cm

[Hanazono]

I think the scion is "hakuun".
You can go to a normal degrafting for a myriostigam related species.
The size of scion should be more than 3 cm in diameter for the rooting and so it is alright to go.

The actual Joint between scion and stock is penetrated deeply into the scion which is the disadvantage of Hylocereus stock.

Cut the scion at the visual joint at first.
The vascular bundle of the stock remains in the scion.
Slice off the scion from bottom until disappearing the vascular bundle of the stock completely.

Now you can go to a normal rooting process.

[mmcavall]

Thanks Hanazono, I'll try to do as you suggested. Maybe I'll have to ask more questions. Thank you very much.
Here is another picture of the plant: