Slotting on the

Slotting toolsstandard tools

The ones in photo 12 were obtained second hand These tools are usually too big as the ISO standard for shaft minimum diameter relative to key dimensions is given in table 3

Slotting toolsshort

tools

See photos 13 and 14 . As most of the keyway slotting is for a short length, I've used standard HSS square bits of the right width, set in a bit holder giving the 3 degree clearance angle The bit protrusion is adjusted to just slightly more than the slot depth, see fig 38 The problem is to find the good width for the HSS bits as they are usually slightly undersize (by 0 05mm) I was fortunate enough to find some just 0 .01 mm undersize that could be used The 3mm width tool was cut from a HSS wood planer blade Even a too small tool can be used as a second cut can be done

Too/ for slotting hexagon holes

Special tools to widen the slot, or some file strokes can do the job, as these short tools are so easily and quickly made

A 120 degree angle bit is used for slotting hexagon holes, see photo 15 and fig 39 Note that the dihedral angle

Square hole made with special too/ must be 120 75 degrees for machining a true 120 degree angle (for 3 degree clearance and 15 degree rake angles)

For a good symmetry, the Di dimensions must be equal (be careful when sharpening) to ease the tool height adjustment (see later)

A special 90 degree bit is used for slotting square holes, see photo 14, and note that the dihedral angle must be 90 9 degrees to machine a true 90 degree angle (for 3 degree clearance and 15 degree rake angles)

For machining small square holes (4 and 5mm) I've made special tools from small round HSS bits stuck with epoxy glue on a square body before grinding The 3 degree clearance angle is given by the 10mm short square tool guide, see photo 16, 17 and fig 40,very convenient for machining square holes in boring bars and the like

A plain 4mm square HSS bit can be used to slot a 6mm square hole Of course the machined square angles will be a few tenths of a degree less than 90 degrees but this won't worry us very much for an HSS tip sitting in a boring bar. It's also possible with this tool to machine smaller squares by grinding the back, as I was unable to find 3mm square HSS bits

For these machining operations, it is of course necessary to index the lathe chuck

Slotting toolslong tools

See photo 18 and fig 41.

These tools were made with a 6mm HSS square tip silver soldered on a steel body, so no problem with the tip thickness and maximum stiffness as the protrusion of the bit can be adjusted to the minimum value Photograph 19 shows how to hold the HSS tip on the body for silver soldering using a 'C' clamp made with a 3mm diameter iron wire

Tools dimensions (for fig 41) are given in table 4 e To be co ntinued

Next Time

We finish off by slotting some polygonal holes.