Harold Hall

As this was unlikely to be a requirement in my case I made my cutters, Photograph 3, to their nominal diameters, 12 and 16 mm. This enabled silver steel of that size to be used, rather than a larger diameter that would require reducing in diameter. As commented earlier, the outer diameters were though skimmed  to ensure concentricity. In the case of the larger this has been used to cut some 600 mm of slot without any sign of deterioration of the cutting edges.


When turning the head to width using left and right hand knife tools, as a final measure, set them round by a degree or so and skim each side very lightly  with the full width of the cutting edge. This slightly under cuts the two faces ensuring that the cutter is widest at the cutting edge.


With the turning complete, transfer the cutter to the milling machine and mount in a dividing head set up to give six cutting edges. Make sure that the flat (if made) for the driving dog is in a position that will be machined away. Sketch 1 shows how the end mill is set relative to the cutter to create a rake angle on the cutting edge. Set the depth  of cut  to around 1 mm and make six cuts around the cutter. Then,  lower the cut in stages until there is only about 1 mm of the original outer diameter left at each tooth Photograph 4.


The need for the cutter to be made to rotate in the required direction when eventually used results in the cut having to be taken such that travel of the workpiece and rotation of the end mill coincide. To ensure that this does not cause the cutter to snatch and take up the backlash in the table movement, the table locking screw should be slightly tightened to stiffen the movement. If the cutter head being made is appreciably larger than its shank diameter then the end mill can move from the shank end to the outer end  this eliminating the possibility of snatch.


Mark the 1 mm of the outer diameter remaining with marking blue to aid visibility. Then, using a small fine file, add a degree or so of clearance to the outer diameter leaving just the slightest amount of the outer diameter visible, say 0.2 mm maximum, preferably  less, see sketch 1.


Workshop Projects

T Slot Cutters, Shop Made
T Slot cutter, making

Hardening and Tempering

For one who does not carry out the task of hardening and tempering, and I suspect that this is the case for most home workshop owners, completing the task, resulting in a workable tool, was very satisfying. This process alone makes the project worthwhile even discounting any financial savings.


For the viewer who needs guidance regarding this, see my pages on the subject of hardening and tempering in the processes section.