It isn't the glue line that dulls blades

Most people with jointers have discovered that they don't want to edgejoint plywood. The plywood edge dulls the knives very quickly. The usual explanation for this is that the glue line eats the knives; few of us seem to think that wood could be responsible.

I got curious. I had a set of knicked knives, so I ran the obvious experiment. I set the fence in one location and ran plywood until I could clearly see the wear on the knives. The wear was not at the glue lines, but rather at the end-grain plies. That is, it is the end-grain wood which dulls the knives so quickly!

Jamie,

I would tend to go with you. I know that they say do not join/plan plywood; I always thought it was for the safety aspect for joining, the pratical aspect of planing (thin layers) but not directly associated with the glue.

I do know that they say (I think) that glue dulls blades in things like planing edge joints. I do a lot of that and have never seen the glue screwing up any thing except for staining. Besides, they say use a chisel to clean off the glue. I use Titlebond, maybe exopy, CA or the likes would dull the blades.

Does anyone join plywood? If I have to, I usually use the table saw, circular saw and something like that.

Regards, Joe