Tersa Knives - observation

[Doug Mason]

I have a MM FS 35 Smart Jointer/Planer that uses the Tersa knives. In the almost 4 years that I have had the machine, the HSS knives have worked well for me ( a hobbiest)--untill last week.

It was then that I was running some 30/40 year old doug fir (from a collapsed roof), with rough painted surfaces, on the jointer. Well after not more than 5 minutes I noticed that the knives weren't cutting anymore. I assumed that my outfeed table had become out of parrellel with the top of the knifes--so I reset my outfeed table accordingly. The same thing happened again, and again, and I eventually left the shop in frustration.

Upon returning today, I pulled out the 4 knives and looked closely at them; and observed that their hieght in the center (where I had been jointing the doug fir) was lower than on the sides. I could just barely detect this with my eye--but the center area had definately worn away. The wood was rough--but not overly so. Maybe there were small roofing particles embeded in the wood? What else could it be?

So I guess I'll get the more tough M42 blades from Simantech--and use these heaeafter. I handplane most surfaces--so that is not an issue. Does anyone get the carbide blades (at $126 each)--I'm wondering if this would be the best value?

On a sidenote--I decided to go straight to the jointer (as opposed to the bandsaw) because the boards are 7 feet long and hefty--very difficult for one person on my bandsaw.

[Tom Rick]

It is my understanding that old painted boards are about the toughest service you can ask of the cutters.
Someone was just telling me that the pigments contain silica and various metals which wreck knives like nothing else.

[John Harden]

You say the knives "weren't cutting any more". What exactly were the symptoms? Regardless, my guess is that the culprit is that you were planing off paint. This will bugger up jointer knives pretty darn quickly.

I've used the Tersa knives and they cut like there's no tomorrow, even in highly figured woods. I own a Felder and they use a very similiar blade system, which works just as well as the Tersa.

Carbide would definitely hold an edge longer than HSS, but my guess is they won't perform as well in highly figured woods, due to the fact that carbide can not be sharpened to the same degree that HSS can be.

I'd also be interested in hearing from someone who uses the carbide tipped blades in their Tersa head.

Regards,

John

[Doug Mason]

"You say the knives "weren't cutting any more". What exactly were the symptoms"

The symptoms were that there was no cutting--as if the outfeed table were higher than the blades (which is what I initially thought was the problem); the center of the knives had been worn away. And yes--I was just jointing away the paint (too lazy to use a scrub plane!!)

[John Harden]

I understand. I think you just learned a valuable lesson about not planing paint. Nasty stuff. I've planed a lot of MDF and while it is tough on HSS, it is still not in the same league as paint.

Regards,

John

[Peter Quinn]

We use terminus heads at work in jointers and planers, and have to switch to carbide for running teak. Teak will just grind them down, and they don't project by much. I know the white primer I use has silica in its base, and teak has silica in it. Maybe the paint just ground the knives down like a grinding stone? I have seen the knots in old fir wreck new knives, they get so hard, but that usually involves localized knicks. It seems plausible that the paint actually ground the knives down?

[Larry Edgerton]

Its the paint, not the knives. I keep a portable electric hand planer with carbides around just for that circumstance, getting rid of the paint with the relitively inexpensive carbides in the portable. Even M42 will not stand up to paint.

As a side note I have tried the Tersa clones, not made by Tersa, and they are not worth the price difference. I get more value out of the authentic Tersa knives. I wish there was a viable alternative that was less costly, but I have not found it. I have not invested in Carbide because there are ocassionally stones embedded in woods, and then you have a very expensive piece of junk as they chip. I tried them in my jointer when working Teak and the cut was not as clean, although acceptable and then I hit a rock in some figured walnut, and they were toast. I didn't get my moneys worth, so I switched to the ESTA system in that machine.

[Robert LaPlaca]

I have a MM FS 35 Smart Jointer/Planer that uses the Tersa knives. In the almost 4 years that I have had the machine, the HSS knives have worked well for me ( a hobbiest)--untill last week.

It was then that I was running some 30/40 year old doug fir (from a collapsed roof), with rough painted surfaces, on the jointer. Well after not more than 5 minutes I noticed that the knives weren't cutting anymore. I assumed that my outfeed table had become out of parrellel with the top of the knifes--so I reset my outfeed table accordingly. The same thing happened again, and again, and I eventually left the shop in frustration.

Upon returning today, I pulled out the 4 knives and looked closely at them; and observed that their hieght in the center (where I had been jointing the doug fir) was lower than on the sides. I could just barely detect this with my eye--but the center area had definately worn away. The wood was rough--but not overly so. Maybe there were small roofing particles embeded in the wood? What else could it be?

So I guess I'll get the more tough M42 blades from Simantech--and use these heaeafter. I handplane most surfaces--so that is not an issue. Does anyone get the carbide blades (at $126 each)--I'm wondering if this would be the best value?

On a sidenote--I decided to go straight to the jointer (as opposed to the bandsaw) because the boards are 7 feet long and hefty--very difficult for one person on my bandsaw.




Paint is very very abrasive, the life of a paint scraper is very tough... I would bet the paint is what finally toasted your HSS knives..

Having said that, I haven't had much luck with the HSS Tersa knives, I find the M42 last much longer for the upgrade in cost over HSS..