Adding a Ferrule to a Tool Handle
A shiny metal ferrule on a wooden tool handle looks good. In addition to its decorative function, a properly designed ferrule helps keep the wood from splitting when a severe stress is placed on the tool, such as when you get a catch.
The diagram at right shows how the split may occur in a handle that does not have a ferrule. The shank of the tool literally pries the wood apart.
Two factors directly affect the strength of the tool-
The other is the depth to which the tool is inserted into the handle. The farther the shank of the tool is inserted into the handle, the stronger the junction will be.
The most stress is placed on the tool handle when the tool extends considerably beyond the tool rest with the front end of the handle almost touching the rest. On the other hand, when most of the tool shank is behind the rest, the stress on the handle is minimal.
To be effective, a ferrule must be large enough to allow a significant amount of wood between the shank of the tool and the inner diameter of the ferrule. If the diameter of the ferrule is too small, it may actually weaken the join between the tool and the handle.
Options for Metal Ferrules
Turners have used a variety of items to make ferrules, ranging from rings cut from copper pipe to the compression fittings for joining large tubes. And no doubt, most of them served the purpose.
If you wish to make your own metal ferrules, I think the best way is to cut a ring from the end of a metal pipe or coupling (copper, brass, or aluminum). Each of these materials can be cut easily with a hacksaw and cleaned up with a file. However, the pipe is expensive, especially copper.
You can buy metal ferrules in several sizes, ready to install. This is a good option
because the cost is little more than that of the shop-
Wrapped (String) Ferrules
Another way to achieve the same result is to apply a “wrapped ferrule,” which is nothing more than a string wrapped around the end of the handle and then soaked with thin CA glue and/or epoxy. It may not be as strong as the metal variety, but it is strong enough. I’ve made a dozen or so of these and never had one fail. And, they are quick and easy to apply.
Almost any string will work as long as CA glue and epoxy will soak into it and bond
it to the wood underneath. I prefer small-
We can estimate the strength of the wrapped ferrule by considering the breaking strength of the string and the number of turns. Suppose the breaking strength is 10 pounds. Each turn wrapped onto the handle then contributes twice that, or 20 pounds, of strength from top to bottom of the handle. (The string goes from top to bottom or vice versa twice per turn – first on one side and then on the other.)
So if we wind on 10 turns, we achieve a strength of 10 times 20, which is 200 pounds. If we apply 20 turns, we get 400 pounds, 30 turns gives 600 pounds, and so forth. That is a lot, so a wrapped ferrule is quite strong.
Preparing for the Ferrule
Preparing a seat for the ferrule is a part of shaping the handle. It is done after the hole has been drilled and the blank is on the lathe between a scroll chuck and a cone center at the tailstock.
Making the seat for a metal ferrule requires a bit of careful turning to ensure that the sides are straight (not tapered) and the diameter is the proper size. I generally use a diamond parting tool and creep up on the final fit, checking frequently to see if the ferrule will slip over the seat.
How tight should the fit be? This question is subject to varied opinions. Some turners prefer the fit to be tight so the ferrule has to be driven onto the seat. I prefer a loose slip fit because I always use epoxy to glue the ferrule in place. If the fit is too tight, the epoxy will be pushed ahead of the ferrule as it is installed, and this will essentially produce a dry joint.
By comparison, making a seat for a wrapped ferrule is simple. All you have to do is turn a groove for the string to lie in (for a neat job), and that is it. There is no worrying about turning to a specific size or shape.
A wrapped ferrule offers an option that is not possible with metal unless you have a machine shop at your disposal. You can make a tapered ferrule, one that conforms, more or less, to the curvature at the end of the handle. This allows the tool to be inserted deeper into the handle without adding to the length of the junction.
Installing the Ferrule
For a metal ferrule it is simply a matter of applying epoxy, if you are going to use it, and slipping the ferrule over the seat or pressing it into place if the fit is tight. For a wrapped ferrule, it is a bit more involved.
It is convenient to wrap the ferrule right after cutting the groove for the string, while the handle is still on the lathe, between centers. With thin CA glue at hand, loop the string over the blank and tack it in place with the CA. Cut off the loose end. Then turn the lathe with one hand and guide the string with the other until you have applied the desired number of turns. Tack the end with CA and then cut the string.
To coat the string with epoxy, mix the epoxy and start the lathe turning as slowly as it will go. Use a thin, wooden spreader to apply the epoxy, letting the epoxy ooze from the spreader onto the string. This can be done with or without the lathe being under power – whichever works best for you. Then once the epoxy is applied, start the lathe turning slowly. Hopefully the epoxy will flow out and form a nice uniform bead over the string.
Inserts for Wooden Handles
Metal inserts are available from several sources that allow the tool in a wooden handle to be swapped out for a different one or simply be removed from the handle for sharpening. Set screws are typically used to secure the tool in the handle, but some of the fancier inserts may use a collet to grip the shank of the tool.
A disadvantage of some, but not all, of these inserts is that the insert does not function as a ferrule. That is, nothing wraps around the outside of the wooden handle to provide extra strength and make splitting less likely.
Further, because a larger hole must be drilled in the handle to accept the insert, the resulting junction between the tool and the handle may be much weaker than if no insert is used. Turners have reported the development of cracks and splits that begin at the insert and proceed along the length of the handle.
I think a good solution to this problem is to add a wrapped (string) ferrule to the handle. One option for doing this is shown in the diagram below.