Tersa Knife Questions

[Derek Arita]

I have a couple of chips in my knives that show up in 3 raised lines. Somewhere, I remember all you have to do is shift one of the knives right or left. Is that true and if so, how do I loosen a knife/knives to move it?

[Robert LaPlaca]

Derek, the Tersa knife are held in place with multiple “gib wedges”, centrifugal force locks the knifes when the cutterhead is powered up. I use a piece of cedar shim and a dead blow hammer to tap each of the cutterhead wedges down,they will make a snapping noise when they release, after the gib wedges are released on a knife, you can move the Tersa knife or remove it if you like. Remember each knife is two sided…

[David Zaret]

robert called it. i use a brass "wedge" that came with the Martin jointer to tap the gibs loose, and just slide one or two of the knives over a quarter inch or so. when you change the knives, give the pocket a good hit with compressed air to ensure nothing gets snagged when you slide the knives in.

[Derek Arita]

Thanks you guys. I've had the J/P for years and never had to mess with the knives. I guess after about 20 years, I have no complaints.

[Jim Becker]

This is one of the reasons that I happen to love Tersa knives..."stuff happens" and being able to slightly shift one knife to eliminate a visible ridge on the material being milled is wonderful. And...you can do it multiple times given you have multiple knives and can move in both directions. (there's a limit to how far you can go, obviously)

[Frank Martin]

Thanks you guys. I've had the J/P for years and never had to mess with the knives. I guess after about 20 years, I have no complaints.
Now I am really curious. Do you mean you have been using the same knives (same side) for 20 years? At least the knives I use (M42) definitely don’t last that long…. What kind are yours?

[mreza Salav]

I am surprised to read that too. Unless they are carbide and only used occasionally.

[Derek Arita]

Better if I said 15 to 20 year old, I can't recall exactly. They still cut very well planing and jointing. I purchased a spare set when I purchased the machine and have never had to use them. I haven't even used used the flip side of the knives yet. I'm just hobbyist and earlier on used a lot of oak and maple, however these days I use a lot of pine, birch and poplar.

[David Zaret]

I am surprised to read that too. Unless they are carbide and only used occasionally.

i guess it's all relative. i have carbides in my planer, and i still have them sharpened after a few thousand feet or so. i have a drawer full of spare knives - nothing cuts better than sharp tersas.

[Jim Becker]

Better if I said 15 to 20 year old, I can't recall exactly. They still cut very well planing and jointing. I purchased a spare set when I purchased the machine and have never had to use them. I haven't even used used the flip side of the knives yet. I'm just hobbyist and earlier on used a lot of oak and maple, however these days I use a lot of pine, birch and poplar.
Derek, I suspect that if you flip the knives, it will become very clear about how "not sharp" the sides you have been using for so long are at this point. Even with low volume hobby use, they do dull.

[Derek Arita]

Derek, I suspect that if you flip the knives, it will become very clear about how "not sharp" the sides you have been using for so long are at this point. Even with low volume hobby use, they do dull.

You're probably right. I should flip them soon and I'll likely notice the difference. Good advice.

[Robert LaPlaca]

Usually, your ears can tell when the knifes need to be changed. As Tersa get duller, they get much louder.

[Robert Hayward]

Derek, I suspect that if you flip the knives, it will become very clear about how "not sharp" the sides you have been using for so long are at this point.
I had this experience with my DW735. The knives had not been flipped longer than I could remember. I thought they were cutting good then I hit a knot and chipped all three knives. Flipped them to get rid of the ridge left by the chip. Was amazed at the difference in cut quality. The machine was quieter and the motor now barely slowed down when doing a wide cut.

[Chris Pyle]

Someone suggested to me that I should get two knives for each slot on the cutterhead so they can be knocked down and put back in and swapped to remove any nicks that develop.

For instance, if you have a 16" jointer, you could order 4" and 12" knives and alternate the 4 and 12" knives back and forth as you turn and install the head. This way, if a nick/chip develops, you could knock 2 rows down and swap the knives in relation to one another for a little more life out of the knives. TIFWIW.

[Jim Becker]

Chris, you can do combinations of shorter knives with Tersa, but you'll want them all to be installed in different orders so none of the places they meet are lined up with another row. But...this is a bit complicated to keep track and honestly, you can move one of the long knives just a skosh to get the same effect.

[Chris Pyle]

Thanks Jim. I tried to say as much above but I appreciate you putting it out there for anyone wondering how that would work.

I was trying to say for a 4 knife head, you should have:

4" 12"
12" 4"
4" 12"
12" 4"

and then when the dreaded raised bumps show up on stock from nicks/, you can knock them down and swap their relative positions.

But I trust your experience over mine, just something a cabinetmaker told me about a while back. I'll be following his suggestion as I develop wear on my current set of knives to see if it's worth the effort.

[Jim Becker]

I'll raise you a complication, Chris... :). My Tersa head is three knife. :D Seriously, one of the beautiful things about the Tersa system is to be able to shift even just one knife laterally a hair to eliminate "the bump" from a small damaged place on the knives...a few quick whacks with a mallet and wide flathead screwdriver to unseat the gibs for that knife, a touch to either end of the knife to move it a hair and the next time you turn it on, it seats the gibs and you're good to go with no visible "hump/bump" in the wood you're working.

[J.R. Rutter]

Thanks Jim. I tried to say as much above but I appreciate you putting it out there for anyone wondering how that would work.

I was trying to say for a 4 knife head, you should have:

4" 12"
12" 4"
4" 12"
12" 4"

and then when the dreaded raised bumps show up on stock from nicks/, you can knock them down and swap their relative positions.

But I trust your experience over mine, just something a cabinetmaker told me about a while back. I'll be following his suggestion as I develop wear on my current set of knives to see if it's worth the effort.

I do this with my moulder heads. One other advantage is that if you typically work towards one side of the cutterhead, the knives can get worn on that half, but still be sharp at the other side of the head. By having split knives, you can swap positions in each knife slot and get a fresh edge where you need it. For my moulder, most of what i run is under 4" wide on a 9" cutterhead. Similarly, on a jointer, if you tend to keep the fence towards the far side, then you would benefit from this setup.