Drilling Holes: Using a Brace and Bit
A swing brace bores holes fast and accurately, and can be used with bits which drill bigger holes than you can get with a.
The vital measurement on a brace is its `sweep’ — the radius of the circle described by the grip. A wide sweep gives more power, but makes the brace harder to handle in confined places. A 250 mm (10 in) sweep is the best compromise.
A ratchet brace is better than a fixed one, as it allows drilling in confined places by working the grip to and fro through an arc instead of through a full circle.
When drilling, avoid splitting the wood as you near the end of the hole in this way: drill until the point of the bit just breaks through on the other side, turn the wood round and resume drilling with the point in the hole it made from the other side.
If you cannot drill from both sides, take the last few turns gently to minimise splitting, or place a block behind the hole and drill through into it.
Fit the bit with a depth-stop if you are drilling to a fixed depth. A depth-stop can be bought or made from a piece of drilled-out scrap wood or rubber tubing which fits over the bit and stops it from going deeper than you want. Insulating tape stuck round the bit also provides a guide.
Only square-ended bits can be used with a brace. They are fitted by inserting them into the jaws of the chuck, which is held in one hand while the brace is turned clockwise to tighten the jaws.
If jaws start failing to grip after long use, you can buy a replaceable set: fit them by unscrewing the chuck to its fullest extent, easing out the old ones and putting the new set in with the open (wider apart) end facing out of the chuck.
Bits suitable for brace use include:
Jennings pattern — the commonest type, whose spiral keeps the hole straight during deep drilling.
Solid centre pattern — fast but slightly less accurate.
Expansive bit — has adjustable cutter for holes of different sizes. May wander on deep holes: unsuitable for material less than 9 mm in) thick, and.
Forstner bit — extremely accurate but requires a lot of pressure to keep going; drills flat-bottomed holes.
Centre bit — first class for cutting; wanders on long holes.
Using a 100 mm (4 in) needle file with a medium cut, you can sharpen Jennings pattern, expansive and centre bits yourself. The procedure is to restore the cutting angle, filing off as little metal as possible.
Send Forstner bits back to the tool shop or manufacturer for resharpening. Masonry bits need special resharpening equipment and it is easiest to replace them, though some manufacturers provide a sharpening service. Screwdriver bits can be reground. Countersink bits must be replaced when worn.
The wheelbrace, used with twist drills, is for cutting holes up to 8 mm (5/16 in) diameter in wood, metal and plastic. It is obviously much slower than the electric drill, but it is more easily controlled and can get into places where an electric drill cannot.
It is usually sold with an additional, removable side handle, which is used only when more pressure and control are needed.
In such situations, press the main handle into the stomach, to give pressure, and use the side handle to prevent the brace from twisting as you use the turning handle.
If drilling upright, grip the main handle in the fist and press down on that with the chest to get more pressure.
Chucks fitted to wheelbraces contain three self-centring jaws to take round-shanked bits or countersinks.
After a great deal of use, the jaws may become worn and fail to grip, but replacements can be bought and are easily fitted in a few minutes: remove the chuck from the brace by unscrewing as if opening the chuck jaws, hold the knurled body of the chuck in a vice and unscrew the back cap; remove the chuck body from the vice and tap it so that the old jaws fall out.
Drop in the new set with the points first and squeezed together. Push them home; refit the back cap to the chuck body andit back on to the brace.
Wheelbraces need little maintenance. Apply a little oil occasionally to the gears, the chuck and the oil hole in the casting just above the chuck. Should the main drive-wheel need cleaning, remove theholding the turning handle, lift the handle from the centre shaft, and take the wheel off.
When reversing the procedure to refit the wheel, you must ensure that the pinions mesh with it before you finally fit the handle.