Tuesday, October 18, 2011
While it is obvious that wood lathes spin wood around, it is not always obvious to the first time buyer that spinning wood, if out of balance, vibrates tremendously. In addition, wood lathes may be asked to spin very heavy sections of wood and need to be able to withstand considerable force. There are a couple of simple things to look for to ensure that a lathe is sturdy enough for the work at hand.
If you have a small shop and intend to turn small objects, it may seem as if sturdiness will not be a factor, but this is simply not so. Most small lathes turn at high speeds and have a very high minimum speed. Just as on a car, an unbalanced wheel does not seem a problem at low speeds but vibrates at high ones, the same thing happens on a lathe with unbalanced wood or with unbalanced lathe parts. While a small piece on a small lathe may not try to walk across the floor, vibration encourages poor cuts and difficulty in a good finish.
Larger lathes tend to have lower minimum speeds and thus allow for less vibration in unbalanced pieces. However they also are generally bought with the purpose of handling larger pieces of wood and thus more weight. A bowl blank of forty pounds is not unusual on a lathe with a twelve to sixteen inch swing and can literally walk a light lathe across the floor of the shop.
The solution to the problem is to have a lathe sturdy enough to handle the work. It starts with a good foundation such as a stand that is well made and heavy enough to not move under the forces of turning. Sand is a good vibration absorber and many turners design their lathe stands to hold hundred of pounds of sand.
The lathe itself should have lots of cast iron and steel in its construction. Stamped metal parts tend to give little support. Good welds should be looked for. Check with your woodturning friends and find out what lathes they use for the type of turning you intend to do and then find out if they are satisfied. Good bearings are a must and even more important are the bearing housings. Bearings are easily replaced but not where they live in the lathe.
One of the best tests of sturdiness is common sense when looking at the lathe. If it looks solid it likely is. This would not be just a catalogue look but rather a chance to stand at it and see if the steel is substantial and the iron castings are solid and well finished. The mechanisms to hold the headstock, tailstock and tool rest should be strong and lock firmly. Speed controls should move easily and switches readily accessible.
The final test of the lathe will happen as you turn on it. Many turners will push the envelope of size and speed and safety is each individual's responsibility but much of it can be ensured with good planning and a little foresight.
Friday, October 07, 2011
One of the best and worst things to happen to modern woodturning is the invention of the four jaw chuck for holding wood. While it is a great addition to the woodturner's asenal, it is also an expensive tool and many beginners find that it costs more than their wood lathe. Also, like many tools a cheaper version is aggravating and in some cases simply dangerous to use. One thing to remember is woodturning has been around for thousands of years and there are many ways to mount the wood without the newest fashions. The Jacob's chuck is a great tool for all turners.
A Jacob's chuck is designed for holding drill bits. It is the chuck on the end of the drill press or the electric hand drill. As such it is often used held in the tail stock of the lathe to hold a drill bit for putting a hole in a piece of wood in the head stock or vice versa. However, it may also be used to hold a piece of wood for turning.
The difficulties in using a Jacob's chuck for holding wood are
- its size which is generally limited to one half inch although slightly smaller or larger ones are available for some lathes
- its having three jaws which make it awkward to hold onto a square piece of wood
- it is made for holding metal and may well crush the wood in its jaws
These limitations are easily dealt with.
The time to use a Jacob's chuck is generally to turn a spindle that needs to be held on one end only. This means that the stronger grain orientation of long grain is being used as opposed to face grain. In such circumstances a piece of one half inch wood such as maple is easily strong enough to support a three inch spindle of reasonable length. It remains to mount the spindle first between centers and turn it round, allowing for a short length at one end to be turned down to one half inch so as to fit in the chuck. Now it can be remounted in the chuck, trued up and finish turned.
Note that this also removes the second difficulty of trying to fit a square piece of wood into a three jaw structure. The tenon to fit the chuck is now round. It also deals with the third problem of crushing the wood. This would serve to mar the wood and also to move the piece off center for turning. A truing cut will put it back on center and the tenon is considered waste wood and removed from the finished piece.
The old and established technology of the Jacob's chuck is not as versatile as the newer four jaw chuck but it is reliable at a much lower cost and opens new avenues of wood turning to the beginner without a lot of expenditure. Besides which, a Jacob's chuck is a welcome addition to every turner's arsenal.