jointer blades - how sharp is sharp?

[Jesse Tutterrow]

It was (past) time to replace the 6" jointer blades on my Delta. So, after checking with here, I purchased a set from Global Tooling. They arrived last night (UPS delivered them about 6:30pm).

Opened the package this morning. No burr, but I was supprised that they did not feel very sharp. So I tried the paper sharpness test. I took a (used) piece of computer paper and tried to use the knife to cut the edge. I would barely cut! The paper was more willing to bend than be cut by the knife.

So, How sharp should the Jointer Knife be?
Am I expected to sharpen the knives I just bought?

Thanks in Advnace,

Jesse Tutterrow

[glenn bradley]

I don't run a knifed jointer anymore but when I did, the knives were like a razor blade. One casual mis-handle and you were bleeding.

[Brendan Plavis]

I always learned the shaving technique, to test a knife's sharpness..

I generally Ill try to shave either a knuckle, or a spot on my arm, to see if its sharp(I have a couple jack knives that I am constantly sharpening for work(opening up boxes upon boxes...)

They always told us in Boy Scouts to rub your finger across the blade, but, I found rubbing it along works just as well(you get a small nick if its sharp...) But I dont recommend this...


I would try to fire it up in the jointer to see if it works... thats a sure fire way...

[Dan Friedrichs]

I'd be interested in the replies to this, too. I did basically exactly what you did (bought a set of knives from Global tooling, tried to cut paper, didn't work, posted here. Here's my old thread: http://www.sawmillcreek.org/showthread.php?t=106475)

At the time, I accepted the wisdom of the Creek and used them as-is, but I'm beginning to think they could be much sharper. I used a different jointer that had razor-sharp knives in it, and it was much easier to use, and the edge did not immediately dull like some suggested would happen.

I'm planning to take mine out and send them out for sharpening...

[Pat Germain]

I've never tried the paper cutting test with my jointer knives. But when I first got my 8" Shop Fox jointer, the blades were very sharp. I accidentally cut myself putting it together. (Ouch!). And I just barely touched the blade.

When I had the blades sharpended a few months ago, they came back even more sharp than from the factory. (I swear, my sharpener can create a one-molecule edge!)

[Dan Friedrichs]

I've never tried the paper cutting test with my jointer knives. But when I first got my 8" Shop Fox jointer, the blades were very sharp. I accidentally cut myself putting it together. (Ouch!). And I just barely touched the blade.

When I had the blades sharpended a few months ago, they came back even more sharp than from the factory. (I swear, my sharpener can create a one-molecule edge!)

That's how I thought they were supposed to be. With the ones I got from Global, I think I could squeeze the blade as hard as I could in my hand and not cut myself.

[Pat Germain]

That's how I thought they were supposed to be. With the ones I got from Global, I think I could squeeze the blade as hard as I could in my hand and not cut myself.

Sounds like those would need sharpening. I'm no expert, but in my experience, sharp jointer blades work much better than dull blades. It's like shaving. :) Find a good sharpener and treat him well. (I think that's good advice for any woodworker.)

EDIT: Oh, dude! I just noticed you're in Colorado. If you're anywhere near Colorado Springs, I highly recommend taking your jointer blades, and anything else requiring an edge (to include kitchen knives) to Rick at Rick's Edge. He's in the phone book and has a little, privately owned shop.

[Brendan Plavis]

That's how I thought they were supposed to be. With the ones I got from Global, I think I could squeeze the blade as hard as I could in my hand and not cut myself.

You can also squeeze a razor all you want, and not get cut... Inorder to be cut by something sharp, you friction must occur, such as rubbing your finger over the blade... :p

Ever see sword walkers? Its not that their feet are of iron, but rather they dont let themselves move, so they dont get cut....

[John M Wilson]

You can also squeeze a razor all you want, and not get cut...

Have you ever actually tried this? Well DON'T! A very sharp knife (like a razor) will cut through material without any lateral motion at all. The "sawing" motion uses imperfections along the blade face to make a cut with less resistance, but a sharp enough blade will cut human flesh very easily with no sawing motion whatsoever.

Remember, Safety First!!!!

[Jeff Willard]

You can also squeeze a razor all you want, and not get cut... Inorder to be cut by something sharp, you friction must occur, such as rubbing your finger over the blade... :p

Ever see sword walkers? Its not that their feet are of iron, but rather they dont let themselves move, so they dont get cut....

Don't try this at home. I've been cutting meat for 30+ yrs., and the first thing I heard as an apprentice was, "knife pressure, don't saw the meat". If anybody needs this confirmed, I will gladly demonstrate.

[James Williams 007]

I have ordered jointer and planer knives from global and they are always sharp and ready to use. Now they are not as sharp as my chisels and plane blades but I spend some time doing those myself and I could shave with them.

[Nathan Palenski]

You can also squeeze a razor all you want, and not get cut... Inorder to be cut by something sharp, you friction must occur, such as rubbing your finger over the blade... :p

Ever see sword walkers? Its not that their feet are of iron, but rather they dont let themselves move, so they dont get cut....

Not all edges are the same. Frequently laminated blades require you to slice but its not the rule.

A meat cleaver wouldn't work if blades only worked by slicing.

[Brendan Plavis]

I could be wrong, but I think those create the friction, due to the weight, when it breaks the bone...(bone moves when broken, causing the friction.) But I could be wrong...

[Nathan Palenski]

I could be wrong, but I think those create the friction, due to the weight, when it breaks the bone...(bone moves when broken, causing the friction.) But I could be wrong...

Go to the hardware store and buy a sleeve of single sided razor blades. Fool around with one for about 10 minutes and get back to me.

[Brendan Plavis]

Go to the hardware store and buy a sleeve of single sided razor blades. Fool around with one for about 10 minutes and get back to me.

I have an Xacto right here... can squeeze all I want... no injuries...

Have any more half baked comments you would like to add?

Please dont go off half-cocked...... it only wastes my precious time...

[Van Huskey]

Most everyone is half right regarding blades cutting. There are two parts to cutting pinching or cleaving and sawing. In simple terms the latter is what Brendan is describing and the former is what the others are talking about.

To the OP JP knives should be REALLY sharp but everyone sees REALLY as a different thing. Although I don't fool with knives anymore I always got a few nicks setting blades and never thought of them as being anything but "razor sharp" when I installed them. I never tested them by cutting paper but I will point out cutting paper is far from a universal constant since there is a technique to it and the "better" you are the duller the blade one can get to cut paper, even if we assume all "printer" paper is the same. Since there is no easy way for the average woodworker to quantify sharpness you just have to do your best to subjectively or objectively rate the results and longevity of the edge.

Now if someone wants to build a sharpness jig it seems possible and rather easy, you would need a consistent substance that could be consistently dimensioned and could cut by the blade in question relatively easily then a way to bring the blade in contact with, and guide it through, the material along with a force gauge for the imperical measurement...

[Dan Friedrichs]

I have an Xacto right here... can squeeze all I want... no injuries...



Your knife is dull. Think about how chisels and planes work - there is no "sawing" or "friction" motion.

[Ron Jones near Indy]

Have you contacted Global? I'd like to hear their side of this.

[Leo Graywacz]

It doesn't really matter all that much. That razor sharp edge goes away pretty quick. I mean in about 8' of wood quick. Then you are left with sharp.

[Brendan Plavis]

Your knife is dull. Think about how chisels and planes work - there is no "sawing" or "friction" motion.

Oh contrare.... your pushing the block along causes friction.....

[Dan Friedrichs]

Oh contrare.... your pushing the block along causes friction.....

How is that any different from pushing a knife into your finger?

[Chip Lindley]

Yes, back to the OP's question! Freshly sharpened planer/jointer blades should shave you! They are ground commercially on a grinding jig with round wheel, which leaves a slight hollow grind. After grinding they are stropped to remove the wire edge. Knives will then easily shave you! They will also cut flesh at the slightest provocation. A brand new knife duller than this is unacceptable IMO! You didn't get your $$$'s worth.

I grind planer/jointer blades in the shop with a holding fixture slid back and forth beneath a hollow cup wheel. This does not leave a hollow grind but a flat surface with minute crisscrossing swirl marks. The wire edge is still removed by honing on an oil stone. These edges will shave.

Any presumably sharp blade that will not bring blood by pressing down on it, is not very sharp at all. A dull blade will show a glint of light (especially nicks) when the edge is viewed straight on.

One night while waiting and waiting for our freight train to arrive, (what railroad crews get paid to do most) an office worker complained about his dull pocket knife. I spent fully a half hour sharpening his knife with a small diamond grit pocket sharpener. When I finished, that blade would slice paper with little effort! I handed it back to him, saying, "Be care.....ful" He pressed his thumb into the blade and sliced himself to the bone. He said that knife NEVER cut like that before; even when it was new! Oh, well, I tried to warn him!

[george wilson]

Maybe I'm another misinformed idiot,too,Brendan. I'm NOT going to squeeze razor blades in my hand either. I am well known for making a sharp edge,and I can guarantee you that I've pressed a sharp edge into my fingers more than once.

And,I think you are very arrogant. If your time is so precious,why are you hanging out on a forum???

[Brendan Plavis]

Maybe I'm another misinformed idiot,too,Brendan. I'm NOT going to squeeze razor blades in my hand either. I am well known for making a sharp edge,and I can guarantee you that I've pressed a sharp edge into my fingers more than once.

And,I think you are very arrogant. If your time is so precious,why are you hanging out on a forum???

Is this comment needed?

[Andy Sowers]

Well you can add me to the list of not super sharp jointer knives from Global... I went with them a year or so ago after reading some positive reviews here on the creek.

Granted, they were MUCH better than the dull OEM ones I took out, but they were no where near razor blade sharpness, and they would barely cut paper.

I guess the next time, I'll think about getting these resharpened vs buying new ones. Last time I priced it, the cost to get them sharpened is about the same as buying new ones for my little 6" jointer.

Andy

[george wilson]

It was just as needed as your arrogant comment about wasting your precious time. I see your precious time is still on the forum.

[Gary Click]

I don't use knives in my jointer and planer any longer but when I did I made sure that they were very sharp weather I had them sharpened or sharpened them myself.

I used my 6X18 surface grinder with a bevel jig to grind blades for a 6" jointer and a 15" planer. I also resharpened the blades for my DW735 even though they are "disposable" by lighty grinding the back flat side before switching to a Byrd head. If they were not run until the edge was turned taking .002" to .004" off the back would restore the edge.

I agree with the sharpness needing to be extreme and without getting into the mechanics of the cutting action, I will say that if you touch the edge of one of my blades when fresh you get a cut that starts off feeling like a burn and after a second or so starts to bleed.

I was taught what a sharp edge was by my father who ran a book trimming machine in a bindery for 40 years. He could hone an edge sharp faster than anyone else I have ever met.

gary

BTW - Chip what RR are you with? My day job is designing and building turnouts and diamonds for the Class 1's.

[george wilson]

When I was in college there was a veneer factory nearby. We went on a field trip to it. There was an old guy who sharpened the 10' long veneer slicing blades. He went up and down the blade VERY FAST. He had a stone in each hand. One was for the bevel,and one held on the flat to take the burr off. Both were manipulated in circles very rapidly. I must say,the guy made me nervous!! I had long been making razor sharp edges,but the size of that blade,and his quick motions did make me nervous,because one false move at that speed would certainly gone to the bone!!! He claimed he never cut himself.

[Nathan Palenski]

I have an Xacto right here... can squeeze all I want... no injuries...

Have any more half baked comments you would like to add?

Please dont go off half-cocked...... it only wastes my precious time...

Your blade is dull.

If you'd like to be educated on the subject go register on bladeforums and talk to cliff stamp. He's an expert on the subject. I'd ask him about his "worlds best sharpener" test.



Now if someone wants to build a sharpness jig it seems possible and rather easy, you would need a consistent substance that could be consistently dimensioned and could cut by the blade in question relatively easily then a way to bring the blade in contact with, and guide it through, the material along with a force gauge for the imperical measurement...

Cliff stamp has system he uses for testing sharpness. He's gone into excruciating detail on the subject on bladeforums.



Any presumably sharp blade that will not bring blood by pressing down on it, is not very sharp at all. A dull blade will show a glint of light (especially nicks) when the edge is viewed straight on.


Very well said. I've always used the thumbnail test. A sharp blade will "grab" a thumbnail at a steep angle. A very sharp edge will shave it a little. An extremely sharp edge will shave hair without being held against the skin. Jointer knives should come extremely sharp even if they dont stay that way very long.

[Keith Weber]

You can also squeeze a razor all you want, and not get cut... Inorder to be cut by something sharp, you friction must occur, such as rubbing your finger over the blade... :p

When I first read this, I thought that that somebody was grossly naive, until I noticed who posted it. Then everything made sense! It was... well... almost expected.

A sharp razor will cut you without drawing it across your hand. To the OP... "Sharp" planer blades should draw blood with ease, or shave the hair from your wrist. It sounds like yours are dull.

Keith

[george wilson]

Oh,I see from another post that Brendan is 15 years old,and describes himself as a novice. So we have a know it all kid challenging experienced men about squeezing razor blades?

Brendan,I really don't know when I've seen so much disrespectful gall out of a kid. You should be here to learn from your elders. If someone's always "throwing stuff into your shop",it's because it isn't your shop. It belongs to whoever is paying for it. You are privileged to use the space if your parents allow you to.

How dare you tell someone that he's wasting your precious time. That was astounding. There are guys here who are light years ahead of you,and I am one of them. Try to remember that you are just a beginner. Learn from those more advanced than you. Change your ways or you will end up being a big nothing.

[Gary Click]

Well said.

This goes back to the observation of why God gave you two ears and only one mouth. You should listen twice as much as you speak.

It also proves that the speed of light is faster than the speed of sound. Most people appear intelligent until they say something.

gary


Oh,I see from another post that Brendan is 15 years old,and describes himself as a novice. So we have a know it all kid challenging experienced men about squeezing razor blades?

Brendan,I really don't know when I've seen so much disrespectful gall out of a kid. You should be here to learn from your elders. If someone's always "throwing stuff into your shop",it's because it isn't your shop. It belongs to whoever is paying for it. You are privileged to use the space if your parents allow you to.

How dare you tell someone that he's wasting your precious time. That was astounding. There are guys here who are light years ahead of you,and I am one of them. Try to remember that you are just a beginner. Learn from those more advanced than you. Change your ways or you will end up being a big nothing.

[Pat Germain]

Sheesh, lighten up, guys. We're sounding like a bunch of old geezers. If I wanted to be one of those guys, I'd join a woodworking club and not bother with SMC. We should be encouraging young people, not telling them to shut up and color.

I had a grouchy, old, criticizing shop teacher in the 7th grade that turned me completely off from woodworking until I was in my 30s. I think we can agree such attitudes are counterproductive to growing our hobby.

[george wilson]

I am not going to encourage any young punk who tells adults that they are wasting his precious time. Are they taking him away from his comic books? If you want to,have at it. Until he learns his place and learns respect,he deserves no help from us.

I'd never have even thought about addressing adults like that when I was his age. Of course,back then,we had no computers to hide behind.

I've trained about 25 younger people during my 39 years in Williamsburg,and many more before that. I can pretty much guarantee you that if you were to help a smart alec like him,you would eventually come out on the short end of the stick. I've tried too many times to help guys like him to improve himself,having wasted a lot of effort on some.

I do not consider myself a geezer. You should be able to tell that from my work. I am pleased that he is interested in woodworking. He will never achieve greatness with his present attitude.

[Pat Germain]

^^ Sorry, George, but that was spoken just like an old geezer. :rolleyes: The kid made a mistake. We can correct him and politely remind him not to be so cocky.

Remember, that's what Han Solo did for Luke Skywalker. "Don't get cocky, kid!"

[george wilson]

Pat,one of my biggest problems was that I was always too soft hearted and too generous. Looking back,I wish I had fired a few that I didn't. The result was only more trouble for me. You don't know me,so you can stop calling me names.

Did you read all of his snotty posts? He not only said don't waste his precious time,but also said "any more half baked comments you'd like to add",and "don't go off half cocked."

That string of arrogant insults took more than a misplaced thought to type out. He has taken quite some time to elevate himself in his own mind to this point,when really,he's a 15 year novice who hasn't been disciplined properly,and has been allowed to get away with stuff like that.

[Zahid Naqvi]

For now I am going to close this thread from any further posts. I might go back and delete some more posts as needed.