Milling Machines

[steamjohn248]

I used to do quite a lot of work for a local firm who were supplying components for machines, (robotic), to build motor cars. As a non toolroom trained amatuer, I always asked the 'guvnor' for advice if I was'nt sure. Apart from reccomending I invest in a reversible tapping head for anything under M 10, he said it was always O.K. to go up a size on the recommended tapping drill size i.e. table says 6.5 then use 6.6 . The jobs always passed 'inspection'. (and no it was'nt for Longbridge!)

Steamjohn.

[Tim Bayliss]

Hi all,
There is (what I believe) a really excellent book by Tubal Cain titled Drills, Taps & Dies. This book lists the tapping drills for what must be all known threads. In the book he strongly advocates going slightly larger than the recommended tapping drill sizes and goes further and lists the percentage engagement obtainable for each larger size tapping drill (most of the time we do not need 100% engagement to give an adequate fit).
Boy does it take the sweat out of tapping those tiny BA holes when I know I'm not so likely to break the tap off due to a tight tapping hole size. I keep the book on my workbench and consult it constatly.
Regards,
Tim

[SteveW]

Guys,

I noticed a question above... "how do I get it 90 degrees" or similar.

I can recommend a DTI (dial test indicator) on a magnetic stand. This simple tool can be used to set a face parallel to one or other slide axis by simply adjusting the azimuth for zero deflection on the dial as the face is transited past the DTI plunger.

Back on to milling machines: A tilted head/table can be reset using a DTI set on an 'L' shaped rod set in the chuck with the DTI on the other end of the 'L'. The chuck is swung through 180 deg. and the tilted bit adjusted for a zero reading.

I've used the DTI method with an intermediate angle gauge to set the work at a desired angular offset. The gauge offsets the angle of the work to be parallel to the slide axis.

QED. (Quite Easily Done)