What would be the considerations in converting a long-sleeved cardigan into a cardigan vest? Obviously, I’d leave off the sleeves and knit an armhole band instead, but I’m sure it couldn’t possibly be that simple.
Wouldn’t I need to make the armhole larger/longer…? If anyone could direct me I would appreciate it. 
Are you talking about changing an already-knitted cardigan to a vest, or modifying the pattern for a cardigan to a pattern for a vest?
There should be enough ease in the armhole of a cardigan to allow that kind of change. If it was a pullover patter you wanted to change, you’d need to make the armholes a bit larger, but not with a cardi.
Yes, it is that easy.
Quick story: One summer I was knitting my father an Irish Fisherman sweater. Came County Fair time, and all I’d done was the body. So I sewed it together, threw on a quick neck band and two arm bands - and entered it as a vest. Got a blue ribbon!
Next year, I’d finished the whole thing. So… I entered it again in the County Fair as a sweater. Got another blue ribbon! :teehee:
So yes. That really is all you need to do. I have the blue ribbons to prove it.
Dot
MrsDavis, I was talking about changing a pattern! I didn’t think to specify that! :doh:
Suzeeq and DorothyDot, thank you! For some reason I’ve had an awful time finding a pattern for a V-neck cardigan vest that’s knit flat, but found several nice long-sleeve cardigans I wished were sleeveless! Now to read up on how to knit an arm band! :mrgreen:
Hope I’m not getting in over my head here! 
But it’s a gift and I want it to be just right.
Well, I’d love to see a picture of the prize-winning vest, if you have one!! 
Uh, I’d love to post a picture… but this was 30+ years ago.
So, sorry. No picts.
And it’s a sweater now anyway… 