Maintaining Your Chuck archive
Wednesday 1 December 2010
Nick Arnull looks at some of the basic presentations for the 10mm (3/8in) bowl gouge
The modern bowl gouge is manufactured to very high standards and is probably the most used tool owned by many turners. In the past, the tools were hand forged from carbon steel and came in all shapes and sizes.
We are fortunate today to have good quality M2 HSS (High Speed) steels giving us a tool that takes and holds its edge for a lot longer. The bowl gouge can be ground to create various tip profiles: square/straight across, fingernail and long grind/swept-back gouges, which all offer great versatility for a vast range of techniques. Today, if you ask turners which type of tool they prefer, many will give different answers, but there seems to be a current preference towards the fingernail profile, more easily mastered than some of the other grinds available. My personal recommendation is a 10mm (3/8in) square-ground traditional gouge. This tool will produce a much superior result than all the others when making finishing cuts.
A typical bowl gouge is manufactured from solid bar with a deep flute milled along two-thirds of the length of the bar. The flute is milled in such a way that the shavings will eject from the tool without clogging whilst making a cut. There are some profiles however, that have quite narrow flute profiles and these unfortunately have a tendency to clog up with shavings created by the tool.
There are three basic cuts: the push cut, the pull cut and the shearing/scraping cut. Within this article I will illustrate these various techniques.
The toolsBowl gouges normally have much longer handles than spindle turning tools to allow the user better control. They also have deeper flutes in relation to the bar size than a spindle gouge. They can be ground in a variety of ways: square across through to a swept-back grind of varying degrees. These are oten referred to as: Celtic/Irish grind, Ellsworth grind and long-grind bowl gouges. There are also many other names for these grinds. Individual turners have their own personal variations on these for various reasons; no grind is right or wrong.
Sharpening (basic square-ground bowl gouge techniqueSharpening the square-grind bowl gouge requires a steady toolrest and positive presentation. The bench grinder needs to be switched off, set at the angle to the toolrest to allow the bevel to fully contact the grinding wheel. Rotate to the left and roll the tool to the right, blending both sides together to create one continuous bevel, which appears at the front of the tool.
Start by setting the tool table at the correct angle. When you are ready, turn on the grinder and start to sharpen the front of the tool. Rotate the tool to the left, and then return to the centre
Next, roll the tool to the right, making sure there is one continuous, flowing movement to create a flowing bevel. Note: the tool remains at a 90° angle to the wheel at all times when you are sharpening the tool using this method
Sharpening the fingernail gougeStep 1:
Set the tool against the grinding wheel to the required bevel angle. With the grinder turned on, rotate the tool to the right and once sharpened…
…roll the tool to the left hand-side. Once the wings of the tool have been ground, grind the front to blend the sides and front together in a smooth flowing bevel. Note: the swing required on the handle to achieve the grind
What is meant by bevel rubbing?Turners often use the term, but I wonder how many truly understand what it means? My understanding is that the tool at its cutting edge requires bevel support to allow the tool to cut in a controlled manner. The amount of support relies upon how heavy the cut is: if it is a light cut then less bevel support is required. As the cut becomes heavier, the amount of bevel support required is increased as the edge cuts deeper into the wood. The edge has to submarine below the surface to achieve a cut. The depth of cut is limited by three elements: bevel length, lathe power and the ability of the turner. The amount of true bevel contact is actually much less than expected; the resin build-up just behind the edge is the actual amount of bevel contact that has occurred. The often referred to catch is a result of insufficient bevel support for the attempted cut. Even a 10mm (3/8in) tool can take a very wide shaving, giving you the opportunity to explore a multitude of different cuts
Basic tool presentation for the square-ground bowl gouge (push cut)Often the beginner will find it difficult to know where to start with this technique. The bevel is ground to 45° which means the tool needs to be presented at this angle at all times: rub the bevel, lift the tool until the dust/shavings start to appear, then rotate the flute of the tool in the direction that the tool is going to travel and begin to move slowly across the blank. Make light cuts to begin with as there is often more air than wood. Heavier cuts can be made once the bevel is in constant contact with the wood to create fluid curves/shapes.
Fluid movements are required throughout the action of turning a curve. This means that the handle has to be constantly on the move. To create a concave shape the handle will need to be pushed towards the back of the lathe. When you are creating convex shapes, pull the handle towards the front or the headstock.
Start with the heel of the bevel rubbing against the blank, lifting it until dust or shavings appear over the edge. At this point rotate the flute in the direction of the cut and travel gently across the face of the blank. As work progresses the bevel will be in full contact, at the cutting edge. The depth of cut will appear as a step ahead of the tool – this is where the cutting is occurring. Bevel contact occurs from the supporting bevel touching the bowl being created
The correct stance that needs to be adopted as work progresses is as follows: keep the handle low to ensure the bevel is in contact with the timber at all times. Also ensure to pull it in against the body while you are doing this. To add stability, the hand should be angled towards the end of the handle at a position that is comfortable to use
As you approach the finished profile of your bowl, change to a smaller section tool. Alternatively, you may choose to sharpen your tool, taking a light controlled cut across the surface of the bowl, this will produce a finer finish off the tool
The pull cutThis is a more advanced cut. As you improve this will produce some amazing results, using a much more powerful grip.
Using a slightly swept-back ground gouge, rotate the flute towards the blank, and using the leading wing of the tool, rub the bevel against the wood until the tool is at the point of cut. At this point, pull the tool towards you, this will then remove the wood you do not require, creating the shape you are aiming for: this is a bevel rubbing cut. It can be used as a powerful cut to remove large amounts of shavings, or with very light presentation to refine the exterior shape, producing feather-like shavings.
Turning the rim of the bowlStep 1:
Line the bevel up with the face and the rim of the bowl, point the flute in the direction of cut, and traverse the face of the timber. Maintain bevel rub throughout as you attempt to make the rim flat
Continue as far onto the face as required for the chosen rim width, but it is important to never go past the centre point
Turning inside a bowlAlways start at the centre and work progressively towards the outside of your bowl. Each cut is a practice cut for the finished bowl.
Point the bevel in the direction of travel and rotate the flute so that the cut occurs on the lower wing. Gently push the tool forward in line with the bevel angle so that the tool enters the wood. Onc