Setting tool heights on a lathe
It is important that the tip of a lathe tool is in vertical alignment with the centre of rotation of the lathe – too low and a parting-off tool (say) will not cut all of the way through the piece or a facing operation will result in a ‘pimple’ remaining, too high and no tool will cut correctly as the top of the tip on the tool will not be in contact with the material.
Fortunately, there is a simple way to do this, with the aid of a humble steel rule. This can be done on the lathe chuck (recommended if the unmachined workpiece is not circular) or the workpiece itself (acceptable if the workpiece is already round and merely needs reducing in
diameter on the lathe). Photos A to D show the first method.
The tool height needs to be set such that when the ruler is lightly ‘nipped’ onto the workpiece or chuck by the tool (Photo A), it is exactly vertical. This is a near-magical technique – it is very simple to do, but very accurate.
The height of the tool can either be adjusted using the adjustments available on the toolholder itself (for example if you are fortunate to have a Dickson-style toolholder, as is fitted to the Harrison shown in Photo B) or it can be adjusted by adding ‘shim’ (thin pieces of metal) underneath the tool, as needed, when
mounting it in the toolholder (which is what I had to do on the Myford shown in Photo 6).
The great benefit of the Dickson style of toolholder is that once the tool-height has been set, it should never need re-adjusting (at least with an indexed tool – a ground tool may require minor re-adjustment after it has been re-ground/sharpened).
Note that in Photo A, the toolholder is (deliberately) not seated correctly – in this case it has been made ‘too high’, for illustrative purposes, simply by placing the adjustment collar on top of the clamp it is supposed to slot into. Needless to say, it should never be used in this position!