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Lathe – drilling deep holes
This page is really about drilling long holes. One way of doing this involves turning the workpiece round. Doing this guarantees the two cuts will not line up.
When it comes to drilling long holes there are two classes of problems. There are those where the workpiece is too wide to fit in the bore of the spindle and there are those where it will fit in the bore of the spindle.
Drilling deep holes where the workpiece will not fit the bore of the spindle
At fist sight it might seem that the longest hole that can be drilled is when is roughly when the workpiece takes up the left half of the lathes bed length. The drill will take up the right half of the lathes bed length.
however it is possible to drill deeper holes than this in two ways.
Suppose the workpiece is 2/3 of the bed length. A drill 1/3 will fit in the space left and will drill 1/3 the depth.
If the workpiece is turned round it is possible to drill the other half of it with the same drill.
If the tailstock is removed it is possible to fit a drill 2/3 long in the existing hole, replace the tailstock, fit the drill in the chuck in the tailstock and drill the rest of the hole.
Drilling deep holes where the workpiece will fit the bore of the spindle
This is similar to the above except that the right hand end of the workpiece will be at the front of the chuck so, if the length of the bed is x then a workpiece can be x long and a drill x long will fit between the tailstock and the workpiece and drill a hole x long.
Having drilled a hole x long then it would be possible to use the trick above to drill a hole 2 * x long.
It is then possible to turn the workpiece round and do the same again.
Using a tailstock to hold the drill is no very convenient. An alternative is to remove the tailstock completely and, instead, hold the drill in the special toolholder designed to take drills with tapered shanks. But instead of using tapers a bush is made to hold the drill. If the bush is long enough and has a outer bush that can be tightened any length of drill can be used.
The next problem is that it is not easy to find very long drills. One way of making a long drill is to use a blacksmith’s drill which has a narrower shank and silver solder this into a steel tube or rod that has been drilled to take this shank.
With very long, thin workpieces there is the problem of them sagging under their own weight. This can be solved along the part above the bed of the lathe by using a fixed steady.
Where the workpiece goes through the spindle it can be supported by a spindle steady.
fig spindle steady
This steady is fitted to the spindle and rotates with the spindle
If this does not reach far enough it is possible to make a steady that is further out consisting of a piece of plastic tube.
(These parts were made for use as part of a bar-feeding system)
fig extra long spindle steady
In this case the steady is fixed to the casing covering the change gears and does not rotate