Harold Hall

Workshop Processes

Finally, in terms of sharpening the cutter, the cutting edges should be honed to achieve the best possible cutting edge. This is particularly important in the case of small boring tools as the sharp cutting edges will cut more freely  limiting the load placed onto it and therefore the amount that the tool deflects. Also, a small radius (say around 0.2mm) should be honed onto the cutters tip making it stronger and able to produce a better finish.      


If the viewer is interested in the grinding rest I am using this enables the angles to be precisely set and includes facilities for controlling the feed in two directions so that the depth of cut can be increased gradually as the tool is ground.For more detail see below, right.


An Alternative Form

The shape of the boring tool discussed so far is essential where the end of the bore, or a step within it have to be faced so that they are at 90° to the bore's axis. An alternative form though can be considered that will more easily produce a superior finish when a through hole is being made. In this case the side rake (1) is replaced with top rake (2) as is illustrated by Sk. 3. The tool also includes a larger radius on the tip than that suggested above for the blind hole tool. Being larger, say 0.5 to 1mm radius depending on the cutter size. Shaping this form of tool follows almost exactly the sequence above with only the angles changed for the operation shown in photograph 2.


Other tools

I mentioned at the commencement that I also use the method to produce other tool shapes some of the most useful of which are seen in Photograph 11. On the left is a very small parting tool (0.8mm), very useful when parting off workpieces of say 3mm diameter and less. Being so small it can be used on the top slide rather than the rear tool post. The next two are grooving tools, such as used for making a groove to accept a Circlip. The pointed one is used to make lines on a dial, such as one for a machine tool lead screw. The final one is a very small bull nose tool for finishing outside diameters.


It is obvious from the photograph that only small tool bits are required  

and very little grinding is  necessary  making it economical in terms of both time and money. It can also be seen that I produced many of my earlier cutters from broken centre drills, not that I am vary careless and break a large number, they were obtained from a firm having a large number of capstan lathes.


I hope the viewer has found this interesting and been prompted to consider the method described for producing boring tools.



For more details showing how to use either of  my grinding rests see the pages on Tool and Cutter Sharpening