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Harold Hall

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Manufacture

The essential thing about their manufacture is that they should all be the same diameter within close limits, say +/- 0.005mm, and their base square to the outer diameter. This latter point can easily be achieved by machining both the outer diameter and end face without removing the part from the chuck. The drawing gives some suggested dimensions and would suggest that you work to these unless you expect to work with bores closely spaced in which case they may need to be made to a smaller diameter, or make a second set. A small chamfer could also be added to the top so as to make it doubly obvious which is the working end. Commercially, buttons are made in sets of four with one longer than the others permitting close hole centres to be set up.

 

To make the outside diameters that accurate set the top slide to nominally 6° when 0.01mm feed of the top slide will feed the tool 0.001mm radially. When attempting to take such minute amounts off the diameter the tool will have to be honed to a very precise edge and a round nose tool is a good choice in this case as it is not required to machine up to a shoulder. It is also absolutely essential that the cutting edge is not above centre and to be sure regarding this it is best to set the tool very slightly below centre.

Not required for these toolmakers buttons but if you are into even higher levels of precision 0.6° will give an axial to radial ratio of 100:1. See my pages on turning precision diameters and lengths for explanations as to how the top slide can be set to 0.6 degrees.

Metalworking

Workshop Processes

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Drawings