Screw Cutting using Indexable Tips 06

Harold Hall


I do however feel the problem may be over estimated in many readers minds. For me, if I were making one, I would use the holder just to provide the top rake and front and side clearances, that is to just slope the tip seating back to front with it being horizontal left to right. With that done, the helix could be accommodated by adding a tapered packing strip under the holder itself which could easily be made for various helix angles, see Sk. 8.


The reader may still be concerned having to make the recess into which the tip sits. This is understandable, It can though be overcome by filing the required shape into a piece of thin material, say 3mm thick, and drilled with small holes for eventually riveting it to the shank of the holder. Then, with a tip fixed in place and the shaped piece placed against it, the holes can be transferred to the shank and the two parts riveted together. Replacement screws for fixing the tips are available so can be purchases with the tip.


Using the tipped tools

Reference to a suppliers catalogue shows that the three methods mentioned earlier (Sk.'s 4, 5 and 6) are all proposed as possible methods but with no one method coming out totally on top. Typically, the straight in method produces a channel form swarf that is less likely to leave the grove freely. It also mentions feeding the tool in at half the thread form angle to avoid that problem but points out that if the angle is not precise one side may not be produced cleanly. For my part therefore, I would recommend the straight in method as this avoids the need to set the top slide accurately.


A Word of Warning

Photograph 6 shows a thread being cut on a collet chuck body. For the instructions for making this see elsewhere on the site.  


The thread being made in the photograph has a 1.5mm pitch and the tip was ordered specially for the project. Not being able to read the markings on the tip easily, as it was very small, I did not attempt to make sense of them. However, the process did not work out as I had anticipated and decided that I had obviously miscalculated the amount of infeed required. When I had entered the tool sufficient for the mating thread to fit I found that there was noticeably more end ways movement than I would have expected. Whilst I was not happy with the result I realised it would work perfectly adequately so accepted it as one job not

quite up to standard, not the only one I must admit.


It was when preparing to write this item I decided to get out a magnifying glass and attempt to interpret the markings. It was then that I realised that the 175, being part of a longer reference, was actually 1.75, I had obviously been supplied with a 1.75mm cutter in error and had then used it to cut my 1.5mm pitch thread.


What had obviously happened was that when the tool had been feed in by the correct infeed for 1.5mm pitch, the tool for the larger pitch had not started to add the curve on the threads outer diameter. Because of this the nut would not engage and I had to infeed the tool further. The effect  was to widen the thread being cut causing the end float mentioned.


Workshop Processes

Screw cutting using Indexable tips