Turning with Sharp Tools - Bowl Gouges, Part 1
When we last left off with our tutorials, we covered the correct sharpening of roughing gouges. This month, we are continuing this series, where we will be covering the different types of grinds which can be used with bowl gouges. This will be a multi-part tutorial due to the complexity involved in sharpening and modifying the bowl gouges that we use.
This tutorial is going to begin by explaining the bevel angle at the cutting edge of the tool. Most tools will usually come standard from the factory pre-ground at about a 45 degree angle. What's the reason for this? It's a good all-around angle suited for most projects. So why make modifications? Let's take a closer look at what different angles can do for your tool...
30 degree angle
- The tool will require less pressure to make cuts. This works very well when cutting thin-walled pieces.
- Softer woods can be cut more cleanly, with less end grain tearout.
- The tool will be easier to control when making flatter cuts, such as when cutting platters and shallow bowls.
- Harder woods can be more difficult to cut
- Most standard bowls (such as a half-hemisphere shape) or deep bowls will be very difficult to cut, as the bevel cannot remain in contact with the wood when getting closer to the bottom of the bowl. If the bevel of the tool does not remain in contact when cutting, tool control becomes difficult, and catches become much more likely.
40 degree angle
- The tool requires only moderate pressure in cutting, and will still work well with thin-walled pieces.
- Soft woods will still cut fairly well, with minor end grain tearout.
- The tool will still make flat cuts well, and will also be able to cut medium depth bowls, so long as the rim is fairly wide, and the piece is of moderate depth.
- Harder woods will still be somewhat difficult to cut.
- Deep bowls will be difficult to cut, as the bevel won't be able to remain in contact with the wood near the bottom of the bowl.
50 degree angle
- Provides a good balance between cutting hard and soft woods. Good general purpose grinding angle.
- Will make flat cuts fairly well, and is able to cut deeper bowls and pieces with narrower rims.
- Although this is a good general purpose grinding angle, it does not excel at cutting either extremely hard or extremely soft woods.
60 degree angle
- Cuts harder woods more slowly, but with greater ease.
- Works well for cutting deep bowls and bowls with rims that are narrower than the overall diameter, as the tool's bevel can remain in contact with the wood at all times.
- Does not perform well when cutting softer woods. End grain tearout is more prevalent.
- Flat cuts, such as those in platters and shallow bowls, become more difficult
70 degree angle
- Aids in cutting extremely hard woods.
- Is necessary for performing clean cuts in very deep bowls and forms, as the bevel can more easily stay in contact with the wood.
- Performs very poorly when cutting softer woods
- Can be very difficult to control when making flat cuts, such as in platters and shallow bowls.
So, to summarize everything more briefly, here's what you need to factor in when deciding on the angle to grind your gouge at:
What's the hardness of the wood(s) you're cutting?
Shallower angles cut softer woods better. Steeper angles cut hard woods better. If you turn a lot of both woods with one gouge, you may want to find a good compromise that will perform fairly well in either situation.
What's the depth of the piece(s) you're cutting?
Shallower angles cut shallow, wide-rimmed pieces better. Steeper angles are essential for getting good cuts in deep, narrow-rimmed pieces. If you are doing a bit of both, then you will want to find a good compromise here as well.
Remember to take both of these into account when deciding what is best for your bevel grinding angle. If you're fortunate enough to have multiple gouges, then consider trying different angles on different tools to cover a wider variety of situations!
That's all for this month's tutorial. Next month, we will go into more detail about the "wings" of a bowl gouge, and how different grinding methods affect performance of the tool.