Replies

1. 
   gb93433 | Apr 22, 2006 08:26am | #1

   What you are describing is jointing the knives. It has been done for years since knives for machinery have been made. The only difference is that the cutterhead spins the regular direction.

   To joint the knives you must make the stone just very very lightly touch the tips of the knives. It must be done in such a way that the tick of the knife can hardly be felt on the stone you are using.

   It produces a very slight round land on top and makes each knife exactly the same height giving great glass smoot cuts. It will do this about three times before I send the knives in to have them sharpened.

   It is also commonly done on a planer.

1. 
   philip | Apr 22, 2006 11:21am | #2

   I think you forgot to say that the stone is pplaced on the out table?(which may have been lowered a micron or two)
   Actually I think it is a poor practice and not a good substitute for proper knife setting and grinding . One can back-bevel the knives by hand in the block and get the effect you mention without the potential drama of stones and spinning cutter blocks.Philip Marcou

1. 
   gb93433 | Apr 22, 2006 06:35pm | #4

   Jointing it is not a replacement for proper knife setting. There is not a machine made that will set each knife exactly the same height. Not even a Weinig is that good. When my knives get dull I back bevel them and then joint them to ensure they are the same height when they are running. If you do the work by hand it will take you a long time. I suppose it can be done but I do know from experience it is still not the same.When I do mine I use a diamond stone and place it on top of a piece of paper on the outfeed table. This allows me to slide the stone freely. Once I am done I do not need to adjust the outfeed table because it is about .003" below the top of the knives. It will produce glass smooth cuts without any detectable scallops. In fact it is so smooth that there is a suction between the table and board of the outfeed table. If you take a look at the web page http://www.olivermachinery.com/ReferencePhotos/MachinePics/166.jpg and notice the picture to the right in the middle of the pictures you will notice a machine which is jointing the knives.“If you detect a flat on the tip of each knife about the width of a human hair, you've done a great job. As the knives wear, several rejoints are possible for sharpening purposes. Stop when the flat area reaches about 1/32" wide, because the wood will burn from too much contact by the "heel" (flat spot) and the noise will disturb all the cats for miles.” (http://www.woodweb.com/knowledge_base/Using_jointing_attachment_on_moulder.html)There is also another explanation at http://www.weinigusa.com/weinig/jointing.htmAnother page to look at is page 14 of the owner’s manual at http://www.wmhtoolgroup.com/partfiles/Powermatic%20Model%2054A%20Jointer.pdf

   Edited 4/22/2006 11:36 am by gb93433

1. 
   philip | Apr 23, 2006 12:43am | #6

   Thanks. I will re-visit the technique. I suspect though that it may not be good for all machines-the angle at which the knives are set in the block would affect things?Philip Marcou

2. 
   jes | Apr 23, 2006 05:19am | #11

   Well, it's done, and it worked beautifully. I did do it with the blades spinning backwards, which felt quite a bit safer to me, for it eliminated the chance of the blades grabbing and hurling the stone across the shop, as well as seriously reducing the risk of losing a finger if in a moment of utter thoughlessness one of them came in contact with the spinning cutterhead. My test board was a piece of wild-grained walnut, and sure enough, it came out silky smooth. No matter how straight and true I might have eventually been able to sharpen the blades by hand, there's no way I would have been able to set them so accurately. I wonder why this method isn't more common? It seems so perfectly logical, and so much quicker. Or maybe it's more common than I think. Certainly when looking for jointer sharpening advice on the web, most of what I came across seemed much more time consuming, and probably not as effective. Am I missing something?
   Jesse David

1. 
   philip | Apr 23, 2006 08:25am | #12

   Missing something? Yes, I think you are missing the fact that jointing is not sharpening. What you have achieved is to get all knives cutting in the same circle, but the more you joint as you have done the closer you get to a negative cutting angle -good for hard woods, no good for softer woods. More noise and greater hold down and through put forces required.It depends to some extent on what timbers you are working with. See how many times you can joint before the process becomes counter-productive.
   T Frids method, even though referred to as jointing , is actually not -he is grinding/sharpening the bevel , and since the router is referenced off the out table the grind will be in the same plane, and the knives all the same height. The method works well when each knife can be stopped in the right position -not always possible on a lot of machines.Philip Marcou

2. 
   jes | Apr 23, 2006 09:32am | #13

   In the process am I not sharpening as well as jointing? Also, I'm not sure what you mean by coming closer to a negative cutting angle - whatever the degree of back bevel, doesn't the cutting angle remain the same? I do appreciate your input, but I'm not sure I understand all of your points.
   As for how many times I could joint before it becomes counter productive, I figure I would just do as I've done and back bevel before jointing, so that only the very tips of the blades are jointed (as it is now, only about 1/64th of an inch). That way it wouldn't really make a difference how many times I repeated the process.
   I must say they certainly seem to be cutting exeptionally smoothly now, though I've only been working with walnut since jointing them.
   I would like to check that Tage Frid method out - do you recall which book that is in?Jesse David

3. 
   QCInspector | Apr 23, 2006 10:46am | #14

   "In the process am I not sharpening as well as jointing?"You are not leaving a clearance angle behind the cutting edge. To exaggerate, think of how it would cut if all you had was a cylinder with just a tiny slot across. The edge at the slot might cut your finger but the cylinder would rub the rest of the way around.You can extend the interval between sharpening with a stone and the blades in the cutter head and still have a clearance angle.
   Take a bench stone and put it on the cutterhead and the beveled edge of the blade. It will touch the tips of the blade and a point on the cutterhead behind the blade slot/wedges.
   Rub it in circles or any pattern you chose until you have removed just enough to sharpen the edge.
   It will only take a moment or two per blade and the tiny flat that is also made on the cutterhead will do no harm but the blades will cut for a while longer with their new micro-bevel.

4. 
   philip | Apr 23, 2006 12:40pm | #15

   Jes, the book is "Tage Frid Teaches Woodworking:Joinery, Tools and Techniques, page 45.
   The process of back bevelling reduces the cutting angle: take a typical block where the knives are at a 30 degree cutting angle-you put a 20degree back bevel on, the result is a 10Degree net cutting angle. If you had put a 31 degree back bevel on you would have a negative cutting angle. The more you joint the more you are going to back bevel-can you see where this is going? I think that you can only get two or three jointings before it becomes counter productive.
   If you draw a cross section of a block , with the knives ata machine cutting angle of say 30 degrees it will be clearer-sorry I can't do drawings by computer yet....
   So I don't feel that the jointing constitutes actual sharpening , but the back bevelling is more on that track.
   It will be interesting to know how many times you can repeat the process.Philip Marcou

5. 
   gb93433 | Apr 23, 2006 04:28pm | #16

   Jointing is also sharpening to a degree. If the leading edge is rounded and you are creating a crisp edge by jointing, then the knife will effectively be sharp. For example, a square edge on a piece of steel can be sharp but if it is rounded it will not cut. It works extremely well. People wonder why they have not heard of it before. I doubt very many people have read the owners manual or have ever seen a set of knives being installed and jointed.When I taught high school my students would see me do things like that. My students learned how to cut hand cut dovetails and sharpen all of their hand tools. In my years of college studying to be a teacher jointing was mentioned as not necessary and definitely not safe. The one day I saw my employer where I worked do it. I saw the results. When you joint a set of knives the objective is to create a land as small as possible such as about one hair in width.

2. 
   jes | Apr 23, 2006 02:17am | #9

   Thanks for your thoughtful replies, and the informative links. I began to set up the process, but I found that the blades didn't have enough of a back bevel on them for only the very tips to touch, so I'm going to remedy that and begin again. I'll let you know how it turns out.
   Jesse David

2. 
   SawdustSteve | Apr 22, 2006 03:25pm | #3

   Hi Jes... on some of the OLD rockwell jointers, there are three 1/4" index holes drilled into the outboard end of the cutter head. A 1/4" pin is placed in a hole and the head rotated until it hits a stop (the rabbit support). If you have these holes, use them to 'lock' the head so it won't rotate and then use a stone to skim over the edge of the blade to put a micro-bevil on the blade. I 'd place a piece of index card BETWEEN the stone and the bed so you don't grind away at the outfeed table. At one time there was a jig that went over the jointer. It had a high speed motor with a cup wheel mounted on it. One or two passes and the blade was re-ground, absolutely in plane with the tables. SawdustSteve

3. 
   sapwood | Apr 22, 2006 08:52pm | #5

   Tage Frid in one of his early books on basic woodworking shows how to sharpen jointer knives using a router and a cup wheel. His technique can be adapted to any machine. It works. I surfaced a small machine for years doing this, never having to remove the knives and suffer the tedium of accurate alignment.

1. 
   philip | Apr 23, 2006 12:50am | #7

   That is a good technique-I tried it on my machines-but it does not work on all- the problem for me was to be able to stop the block at the right position for each of the four knives-I'm talking about a Griggio.
   The other problem I had at the time was to find suitable cup wheels mounted on 1/4" shaft-they were not cutting the HSS nicely. I think I'll re-vist that one too.Philip Marcou

4. 
   jimmy | Apr 23, 2006 01:01am | #8

   The process is sound, but I would not , repeat not, do this unless you have someone familiar with the process to give you hands on experience.  Could be an accident waiting to happen just to save a few bucks...JImmy

1. 
   jes | Apr 23, 2006 02:24am | #10

   Thank you for your concern, but I believe I can approach this with enough prudence to keep myself from injury. I've learned through some very direct experiences not to take safety lightly, so I do genuinely appreciate what you're saying.Jesse David