Attn: Drop in liner makers

[venator]

Okay folks who use drop in liners, I'm trying to figure out how to size them. I always seem to be either 1/4" to a 1/2" off either long or short which leaves me with either a weird outcropping of liner or a weird outcropping of bag, how do you get it correct to the mm every time?  Or is there some trick to give yourself a bit of flexibility? 

[RockyAussie]

There are tricks in some cases depending on the construction of the bag design. If you would show us a picture of the design I or others could try and answer.

[ScoobyNewbie]

I just cut out a fabric pattern of bag and take a quarter , or less, of an inch off. Then sew as usual.