why no ply on jointer?

[keith ouellette]

I have read this a few times and would like to know why. I ran some plywood on my jointer and it worked. Does it do something to the blades?

[Tom Kelley]

Keith,
According to Rick Peters in his book "Jointer & Planer Fundamentals" its ok to joint plywood. He does caution to take light cuts as plywoods high glue content dulls the knives. So he advises to do it "sparingly" I hope that helps you.
Tom

[Chris Rosenberger]

The glue in the plywood will eat up steel blades. I have also seen aluminum & steel chips in plywood. I have run plywood over a jointer that had carbide blades on it.

[Jamie Buxton]

The usual explanation is that the glue line dulls the blades. I think that is not right. My jointer/planer has disposable blades. When I had a set that was ready for disposing, I picked a spot that was still sharp, and edge-jointed a bunch of plywood. It only took ten or twenty feet of jointing before I could see the dulling on the cutting edges, using a loupe. The dulling was not on the glue lines, but rather at the end-grain.

[Joe Chritz]

The other fellas hit it.

Other than the glue being hard on blades there isn't a reason not to do plywood. Heavy cuts could be an issue because of alternating grain directions but that is pretty unlikely.

Joe

[Thomas S Stockton]

The only reason is it dulls the blades, but in reality is probably no worse than planing purpleheart and a whole lot better than teak or anigre. The trick is to not run it in the middle of the jointer but do it on the ends, this way you don't totally trash the knives.
Tom

[keith ouellette]

Thanks. Now I know. I'm not going to risk my blades anymore unless its important.

[Jim Becker]

I would say, do it "once in a great while" if you really need to, but in general, avoid it due to the quick and excessive wear it will cause to your cutters as others have already pointed out.

[Cliff Rohrabacher]

When you hit the cross grain it gets dicey

[Michael Schwartz]

I do it when I need a really strait and flat refrence surface on plywood, usually for jigs.

An alternative could be to edge joint a piece of plywood on a router table or shaper, or with a strait edge guide and rotuer.

I use a handplane quite a bit to true plywood or even mdf, often in form or template making.

Using a jointer in general dulls the knives and they aren't going to get any sharper by not using them so if they are allready kind of hammered go ahead and run all the plywood or bent laminations you want on them. If your knifes are new try not to run too much and run it off to the sides so you can shift the fence in.

I am considering keeping a cheap jointer in my shop for the task of edge joinging plywood and bent laminations.

[Mike Heidrick]

I have found hidden material in my box store plywood before - metal pieces etc. in between the laminations (luckily not since my SS). May want to run a metal detector across it before using it on a jointer.

[Scott Banbury]

If you need to joint your plywood, do it--that's why you have the tool.

I do it all the time as I rarely see good machine edges on the plywood sold these days. When I do it, I slide my fence all the way over leaving just enough blade out for the width of the ply and leave the other end of the blades for my solid wood edge jointing.

I believe blades ought to be sharpened regularly. I have 2 sets for each of my machines and swap them out and take them to the sharpener every 2 months or so. Even if I was a light hobbyiest, I would still get them done at least once or twice a year as the edges will be deteriorating just sitting around unless bathed in oil.

Sure, it's a little time and money but I think not needing to scrape off nick ridges and avoiding the burnishing or chip out of glue edges is worth it.

[Mitchell Andrus]

The usual explanation is that the glue line dulls the blades. I think that is not right. My jointer/planer has disposable blades. When I had a set that was ready for disposing, I picked a spot that was still sharp, and edge-jointed a bunch of plywood. It only took ten or twenty feet of jointing before I could see the dulling on the cutting edges, using a loupe. The dulling was not on the glue lines, but rather at the end-grain.

Same here. Extra wear at the end grain. I ruined a set in less than 10 feet. Made the edge of the blade look like a wavy potato chip.

[Tom Cowie]

Keith,
According to Rick Peters in his book "Jointer & Planer Fundamentals" its ok to joint plywood. He does caution to take light cuts as plywoods high glue content dulls the knives. So he advises to do it "sparingly" I hope that helps you.
Tom


Same as the others have said. it will eventually destroy your blades unless you have carbide ones.

Tom