Bill Grumbine
03-01-2004, 9:57 AM
Good morning all
Recently I posted another short photo essay on a cut that I call the tangent cut. Here is it slightly modified for John Miliunas (and anyone else interested) regarding bowl gouge profiles and how to get the most out of one sharpening. I use a progression of cutting techniques that utilize different parts of the gouge, which allow me to cut longer with less trips to the grinder. The first picture below is from an article I posted last week.
<img src= "http://www.enter.net/~ultradad/roughbowl04.jpg">
The initial cut I use to rough the bowl is what I call the 45, 45, 45 cut. The flute is 45 degrees off vertical, and the handle is 45 degrees from level as well as trailing the cutting edge by 45 degrees. Please note that these angles are approximate, and not set in stone. This gives a very aggressive cut which will remove a lot of wood fast. The shavings are coming off the tool just past the tip. It does not always yield a smooth cut, especially on endgrain. This picture is from the article I did on roughing a bowl last week. Then I move on to what I call the tangent cut. This cut uses a different part of the edge, as well as a different presentation to the wood.
<img src= "http://www.enter.net/~ultradad/tangentcut01.jpg">
Here is an overview of the way the gouge is held. Keep in mind that I am standing back so that my turning muscle will not occlude the photo of the gouge. This is a trumpet shaped bowl, but the principle is the same regardless of the shape. The gouge is held at a very low angle, and is presented in such a way so that the long axis of the gouge is in line that contacts the wood at a tangent point of its surface. What that means in plain ole English is the force of the rotating wood is all directed down along the handle of the tool. This works very well for minimizing the dreaded catch. This is quite a different presentation than the initial cut, and allows a part of the edge further back from the tip to be used.
<img src= "http://www.enter.net/~ultradad/tangentcut02.jpg">
Here is a closeup of the tip of the gouge so you can see its presentation clearly. The bevel is rubbing, but the tool has not yet begun to cut. You can all see that I like a looong bevel.
<img src= "http://www.enter.net/~ultradad/tangentcut03.jpg">
Here is another closeup of the same presentation. You can see the bevel rubbing. This is how you start the cut, with the bevel rubbing, but not actually cutting the wood. The shaving will come off of the edge just past the tip. To begin cutting, the gouge is rotated about its long axis by a flick of the wrist until the bevel starts to cut. Within a certain arc you can vary the depth of cut by varying the rotation of the tool. If you turn it too far, the edge will dig in a bit and cause a groove, but usually not a drastic catch. To make the cut then, the tool is pulled along the surface in the direction the flute is pointing, keeping the entire tool in its current orientation! Failure to do so often results in large scary catches. The most frequent departure from the proper cut is to pull faster with the hand that is holding the handle of the gouge, causing it to pivot the tool so that the same edge is still cutting, but the tool has swung through almost 90 degrees, so that it is close to flat. At that point there is no support for the edge and the tool rolls into the wood biting off way more than it can chew, and you have a catch - a BIG one.
<img src= "http://www.enter.net/~ultradad/tangentcut04.jpg">
Here is a closeup testifying to the effectiveness of this cut.The surface to the right of the sharp corner has been cut with this cut. The other surface to the left has only been cut with the beginning roughing cut. This is a very effective cut that works well on removing tearout, smooths over wild grain, and generally saves money on sandpaper and blood pressure medication.
There are yet two more cuts that can be used before a trip to the grinder, and they will often come in succession to the cuts described above.
<img src= "http://www.enter.net/~ultradad/shearscrape01.jpg">
This cut is called the shear scrape, and can use the long edge on the right side of the tool as well as the left, which has been used to this point. This cut is a light leveling cut designed to remove a very small amount of wood. It is good for getting rid of ridges that are left by other cuts, and sometimes will do a good job of removing tearout. In this picture, the tool is being used on the left edge. If the bowl were still attached to a faceplate at the top, the proper cutting direction would use the right edge. If the bowl is in the orientation shown above, it is usually because it has already been roughed, so the previous cuts would not have taken quite a toll on the tool yet. The cut is made with the tool flat, or parallel to the floor. Both edges touch, and then the top edge is rooled away just enough to get it away from the surface of the wood. If it rolls away too far, you will get a big catch and have to change your shorts. :eek:
<img src= "http://www.enter.net/~ultradad/shearscrape03.jpg">
Finally, there is what I call the vertical shear scrape. This is a tricky cut, but it is worth learning. It is the final reserve cut that is designed to remove tearout in the most contrary of blanks. It can also use either edge, again depending on which way the bowl is facing. The gouge is placed in a position similar to the tangent cut, but rolled over so that both sharp edges are touching the wood. The lead edge is then lifted just slightly to allow the trailing edge to start cutting. When used properly, the cut produces fine wispy shavings that many turners refer to as angelhair.
By using these four cuts, just about any kind of wood can be smoothed to the point where it is ready for sanding without too much effort. Used in succession, they also allow for maximum use of a sharpened edge, and will prolong the life of the gouge as well as maximizing turning time over sharpening time. Good luck with it, and John, this may be more than you ever bargained for when you asked about steel!
Bill
Recently I posted another short photo essay on a cut that I call the tangent cut. Here is it slightly modified for John Miliunas (and anyone else interested) regarding bowl gouge profiles and how to get the most out of one sharpening. I use a progression of cutting techniques that utilize different parts of the gouge, which allow me to cut longer with less trips to the grinder. The first picture below is from an article I posted last week.
<img src= "http://www.enter.net/~ultradad/roughbowl04.jpg">
The initial cut I use to rough the bowl is what I call the 45, 45, 45 cut. The flute is 45 degrees off vertical, and the handle is 45 degrees from level as well as trailing the cutting edge by 45 degrees. Please note that these angles are approximate, and not set in stone. This gives a very aggressive cut which will remove a lot of wood fast. The shavings are coming off the tool just past the tip. It does not always yield a smooth cut, especially on endgrain. This picture is from the article I did on roughing a bowl last week. Then I move on to what I call the tangent cut. This cut uses a different part of the edge, as well as a different presentation to the wood.
<img src= "http://www.enter.net/~ultradad/tangentcut01.jpg">
Here is an overview of the way the gouge is held. Keep in mind that I am standing back so that my turning muscle will not occlude the photo of the gouge. This is a trumpet shaped bowl, but the principle is the same regardless of the shape. The gouge is held at a very low angle, and is presented in such a way so that the long axis of the gouge is in line that contacts the wood at a tangent point of its surface. What that means in plain ole English is the force of the rotating wood is all directed down along the handle of the tool. This works very well for minimizing the dreaded catch. This is quite a different presentation than the initial cut, and allows a part of the edge further back from the tip to be used.
<img src= "http://www.enter.net/~ultradad/tangentcut02.jpg">
Here is a closeup of the tip of the gouge so you can see its presentation clearly. The bevel is rubbing, but the tool has not yet begun to cut. You can all see that I like a looong bevel.
<img src= "http://www.enter.net/~ultradad/tangentcut03.jpg">
Here is another closeup of the same presentation. You can see the bevel rubbing. This is how you start the cut, with the bevel rubbing, but not actually cutting the wood. The shaving will come off of the edge just past the tip. To begin cutting, the gouge is rotated about its long axis by a flick of the wrist until the bevel starts to cut. Within a certain arc you can vary the depth of cut by varying the rotation of the tool. If you turn it too far, the edge will dig in a bit and cause a groove, but usually not a drastic catch. To make the cut then, the tool is pulled along the surface in the direction the flute is pointing, keeping the entire tool in its current orientation! Failure to do so often results in large scary catches. The most frequent departure from the proper cut is to pull faster with the hand that is holding the handle of the gouge, causing it to pivot the tool so that the same edge is still cutting, but the tool has swung through almost 90 degrees, so that it is close to flat. At that point there is no support for the edge and the tool rolls into the wood biting off way more than it can chew, and you have a catch - a BIG one.
<img src= "http://www.enter.net/~ultradad/tangentcut04.jpg">
Here is a closeup testifying to the effectiveness of this cut.The surface to the right of the sharp corner has been cut with this cut. The other surface to the left has only been cut with the beginning roughing cut. This is a very effective cut that works well on removing tearout, smooths over wild grain, and generally saves money on sandpaper and blood pressure medication.
There are yet two more cuts that can be used before a trip to the grinder, and they will often come in succession to the cuts described above.
<img src= "http://www.enter.net/~ultradad/shearscrape01.jpg">
This cut is called the shear scrape, and can use the long edge on the right side of the tool as well as the left, which has been used to this point. This cut is a light leveling cut designed to remove a very small amount of wood. It is good for getting rid of ridges that are left by other cuts, and sometimes will do a good job of removing tearout. In this picture, the tool is being used on the left edge. If the bowl were still attached to a faceplate at the top, the proper cutting direction would use the right edge. If the bowl is in the orientation shown above, it is usually because it has already been roughed, so the previous cuts would not have taken quite a toll on the tool yet. The cut is made with the tool flat, or parallel to the floor. Both edges touch, and then the top edge is rooled away just enough to get it away from the surface of the wood. If it rolls away too far, you will get a big catch and have to change your shorts. :eek:
<img src= "http://www.enter.net/~ultradad/shearscrape03.jpg">
Finally, there is what I call the vertical shear scrape. This is a tricky cut, but it is worth learning. It is the final reserve cut that is designed to remove tearout in the most contrary of blanks. It can also use either edge, again depending on which way the bowl is facing. The gouge is placed in a position similar to the tangent cut, but rolled over so that both sharp edges are touching the wood. The lead edge is then lifted just slightly to allow the trailing edge to start cutting. When used properly, the cut produces fine wispy shavings that many turners refer to as angelhair.
By using these four cuts, just about any kind of wood can be smoothed to the point where it is ready for sanding without too much effort. Used in succession, they also allow for maximum use of a sharpened edge, and will prolong the life of the gouge as well as maximizing turning time over sharpening time. Good luck with it, and John, this may be more than you ever bargained for when you asked about steel!
Bill