I understand that the curve of the two drums is different, but the differences in the curve of a 14 and an 18 are going to be very relatively close. I took a picture of a 14(red) next to an 18(wood).. It looks to me that unless you are filling a hole that is large you shouldn't have any problem with curvature. At least not for a patch. Just my opinion. Keep us posted on what you end up doing.... Thanks, Ryan