Havin problems executing the knife drill Custom combo in a-groove

Yep It seems that I can’t get yamazaki’s Knife drill custom combo down. You know the one where he punches then knife attack and repeat intill you get to the corner then do a yondon drill on them. I’ve tried thousands of times but for some reason can’t get it executed well at all. Shit I can’t even connect the drill at the end. Probally cause I’m on pad but How long did it take you to get that shit down?