Please can I pick your assembled brains
I am finishing off making a Hemingway fixed steady for my MYFORD 7 and this involves tapping the finger adjustors in the aluminium casting for a quarter whit cap screw.
I am far from happy with the results in that the new taps did not cut cleanly leaving an ill formed thread and a floppy fixing. The metal just seems to tear
I used 3 in 1 oil as a lubricant and firstly tried a taper tap and secondly a second tap which gave a marginally better result. The casting was about 3/8 thick. I had a similar result on a thin piece of alum. plate with a 5 mm tap Last week and had to resort to using mild steel. The results using these taps on steel was fine and as to be expected.
I used the recommended size 20 drill and used thin oil and RTD grease as a lubricant.at different times
I can't believe everybody has these dire results and perhaps someone can suggest what I'm doing wrong please
Mike