How did I do this to my jointer knives?!

[Adam Cavaliere]

I am very confused right now as to how my jointer knives could all three have nicks in them where I was just jointing!

I had a piece of 1/2" birch plywood that did not seem to lay flat next to my fence on the table saw. I decided it would be good to joint it first before starting to cut. The piece was about 24" x 12" and I was jointing the 24" side.

First it did not seem to be jointing correctly, but I think that is because I may have not been feeding it evenly. I made multiple passes though and never had the blades touch the board the whole time - meaning it never was able to fully joint the board.

The final pass I tried seemed very hard to do and I was suprised at how tough it seemed. I stopped the machine and inspected the blades. All three seemed to have the same nick in them. I inspected the board to see if anything was visible that could have affected the knives, but I do not see anything. Has anyone else run into this sort of problem?

[Pete Bradley]

Most likely you hit junk or metal between the plys. I've seen a lot of complaints of metal in the import plywood from Home Depot and the like. Plywood and 2X4s with knots are pretty rough on jointer blades in general. It's surprising how hard a "softwood" knot is.

Pete

[Tom Esh]

Been there. It sucks. Plywood can contain all sorts of junk, and the glue itself is hard enough to accelerate tool wear. A visible nick suggests junk, so maybe have a close look at that edge to see if there's a nail or piece of metal that might cause more problems later. Also because of the way ply is constructed you'll always have at least one layer oriented end-grain, which makes for tough cutting (and feeding). I'll usually whip out an edge guide and the circ saw before subjecting my jointer to plywood.

[Joe Jensen]

I was taught to NEVER joint plywood. Not because of random junk, but because the glue is very abrassive. I've seen pictures online of jointer knives with worn grooves spaced to match the individual plys (groove for every glue line). This wear was not from random abjects, but from abrassive glue...joe

[Steve Kohn]

I can speak from personal experience about ruining a set of blades by edge jointing plywood.

[Cliff Rohrabacher]

If there is anything in the wood it can nick the blades.
This might even include a bit of concrete or sand that got ground in while the lumber was being moved and hauled about.

Happens to me almost within the first 15 minutes of using a new set of blades. I chalk it up to having an unsealed concrete floor and think about how fast my sander will take the little lines out.

[mike holden]

Been there, Done that!
Its the glue that messes up the blades!
If your lucky, all you need to do is shift one of the blades left or right slightly.
If you aren't, then you need to replace/resharpen them.

Its a hard lesson.
Mike

[Bob Vallaster]

I second what Joe Jensen said.
Alternatives for edging plywood:
table saw
router or circular saw guided by straight edge.

BobV

[Rick Thom]

Another thing that will toast a blade in nothing flat is jointing or planning wood that has been stored uncovered or previously used outside where it has been exposed to the elements. Made the mistake of lending my planner to a friend.. LOL.

[Rod Sheridan]

If there is anything in the wood it can nick the blades.
This might even include a bit of concrete or sand that got ground in while the lumber was being moved and hauled about.

.


Bingo, it's so easy to contaminate a piece of wood.

Standing it on end in the dirt at the sawmill for example, you can imbed small pieces of stone/grit in the wood.

Same for shop floors, which is why I always go over my wood with a metal detector, and then a brass brush to sweep any pieces of grit off the surfaces. I also trim the ends off the rough material before processing it.

Plywood can be even worse as embedded grit or metal objects can be burried inside where you cannot see it.

Regards, Rod.

[Adam Cavaliere]

Well it was a hard lesson to learn, but I really appreciate all of the responses.

So, for the future, the table saw will be my friend with plywood! :)

I ordered new knives from amazon yesterday and should have new ones today (gotta love having Amazon Prime!), and I took the nicked knives in to get sharpened. A bit pricey of a lesson, but I needed a second set anyway!

[Howard Acheson]

I was told years ago to never run plywood over a jointer or through a planer. The adhesives used in plywood are very hard when dry and will knick jointer and planer knives.

[glenn bradley]

I'm sorry for your mishap. It is interesting that a post regarding edge jointing ply was going on just yesterday . . . http://www.sawmillcreek.org/showthread.php?referrerid=5960&t=96046

[Eric Roberge]

This just happened to me too. I'll never run plywood on my jointer again. I second the use of the straight edge and router method.
Hard lesson learned. Damn...I know better than that:mad:

[Rick Fisher]

I am in the business of selling plywood. We bring in retail ply, 3/4" poplar, import 3/4" Birch ($29.00) and Import 3/4" Oak.

For retail, the cheaper the better. I can tell you, this plywood is sold all over North America and its really junky. We sell it to compete with the "borgs". They demand price point everything, quality be damned.