One of the main purposes for this accessory is to check the internal bore of a part
to be machined on the lathe. This, so that a bore within the part can be adjusted
to run true. It can of course be used for many applications, another being to set
a channel in a workpiece on the milling machine table so that it runs in line with
the table's movement.
The device can be seen in Photograph 1 which also shows a right angled sensor, useful
where the normal one cannot gain access to the surface needing checking. Photograph
2 shows the device in use.
When fitting the device to the Dial Indicator the readings will invariably be less
accurate unless both arms are exactly the same length, likely to be even more of
a problem with the angled arm. However, as most often the test being undertaken is
comparative, rather than taking a dimension, it will not be a problem. Do though
when measurements are being taken take this into consideration.
I am not going to go into detail for this as the processes are straight forward.
Two points though are worth commenting on.
One. The tapered counter bore is on both sides of the main body so that the clamping
arm can be fitted either side. This may help when working in a confined space.
Also, the taper would be machined while mounted on the lathes faceplate, not that
different to the setup seen in Photograph 2. The top slide would then be set at the
required angle. On completing the process, increase the angle very slightly and then
use it to machine the angle on the Clamp Screw.
Two. If you made the G clamp, one of the other Dial Indicator accessories, you should
also have a suitable piece of scrap steel to make the main body, The G clamp body
is on page 66 of the “Model Engineers' Workshop Projects” book.
For a wide range of accessories for a Dial Indicator, but which have many other uses,
see this page. Also, a video showing them being used