Sharpening Planer knives

Bridgeport Bill · Mar 4, 2009

Trying something new to me and had poor results. As a matter of fact horrible results. I made this jig to sharpen my planer knives and and they warped. :angry:

I was using a 24" surface grinder with a 48 grit wheel. Taking around .0005 in a pass and making 7 to 8 passes to remove the nicks in blades. After what I felt was a sucessfull rough in pass on all three blades I noticed on reinstallation of the blades for a finish pass, they were warped. Was it heat or something else?

Dave RI · Mar 4, 2009

Bill ,

I would say it definatly heat related , are the bades supported i the fixture throughout the length of the blade ? you may need a wet grinder to do those blades , also try taking a .0005 cut but climb grinding into the piece the heat will be less . just my.02

Dave M
Dm Precision

atty · Mar 4, 2009

Bill,

We do industrial knife sharpening with a 46 grit resin bond stone with lots and lots of flood cooling. I cannot imagine hitting those blades dry. Too much heat, and in a hurry.

Konrad · Mar 5, 2009

wet wet wet, slow slow slow, ....0005" is way too much in one pass.

9100 · Mar 5, 2009

A hardened blade will likely have a lot of internal stress and when you grind away one side, you remove part of the stressed area so the rest pulls its way. The last time I sharpened blades like that, I left them on the rotor and ground them in place with the rotor shaft supported on vee blocks and a stop against one of the blades for alignment.

Bill

Jim Moser · Mar 5, 2009

Don't know how you laid out your jig but it helps to skew it on the vice so wheel contact is staggered thus creating less heat and coolant.

Woodymyster · Mar 5, 2009

I had the same problem as you. I ended up not using my surface grinder and had to make a jig to fit on my water wheel for the planer knives. Using the wet stone ended the warping problem, but now I couldn't sharpen all three blades at once. Planer knives aren't much different from the metal in some woodworking chisels or planes. You can overheat a chisel in a matter of seconds on a fine grinding wheel, the planer knives shouldn't be any different.
Jon

Bridgeport Bill · Mar 5, 2009

Thanks for the input, I suspected it was a heat issue. I will look for a way to flood coolant.

D Rennie · Mar 5, 2009

Woodymyster said:
Planer knives aren't much different from the metal in some woodworking chisels or planes. You can overheat a chisel in a matter of seconds on a fine grinding wheel, the planer knives shouldn't be any different.
Jon

All of the planer knives that I have are HSS, and I imagine all but Chinese junk would be as well. So very different steel from most chisels, they will take a lot of heat without hurting them.

Still, heat will easily warp them. They guy that I just had sharpen my knives did them dry but he is careful to take very light passes and gives them time to cool down. He did a nice job.

Doug

adama · Mar 5, 2009

As some one with a orfully large pile of some what sandy wood to be planed in the near future it sounds like i need to get my wetsone out the back of the garage! Think i will leave the surface grinder out of it.

cmjohnson · Mar 5, 2009

I use one of these: A Makita planer blade sharpening system. It's application-specific and does a fantastic job. It's also not very expensive.

It also does a fantastic job on any and every other edged tool that can be
brought into contact with the stone. My wood chisels are so sharp they will
cut you if you just look at them the wrong way from across the room.

CJ

aboard_epsilon · Mar 5, 2009

here's mine ...as you can see it's quite substantial ...ans when the blade is in it ..it don't stick out as much as yours ..most of the blade is buried in the device .

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Sharpening Planer knives

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