Shop Made Collet
By Al Hanson
The photo shows a shop made collet used to chuck a reamer in a 5/16″ collet in my milling machine.
The reamer’s shank diameter has been reduced to an odd diameter and I didn’t have enough vertical height to use a drill chuck. I did have some 5/16″ OD drill rod available so I bored it out to a slip fit to the reamer, slit it with a cutoff wheel in my Dremel (more than halfway from each side, staggering the cuts), and ended up with an effective shop made collet. Because it is small I only needed four slits, two from each end (90°). It worked great and didn’t slip at all.
Imperial Tap Drill Sizes
By Tom Nicholls
I recently read the tip on selecting metric tap drill sizes. (Click here to view the tip.) Not only does this work for metric threads, but also for SAE threads. All you have to do is find the pitch between the threads.
For example, 1/4-20 is 20 threads per inch. Take 1” and divide it by 20 TPI. You will get a distance of .050” between threads. Then, just like the metric sizes, subtract this number from the major diameter. Your result is a tap drill size of .200”, or a No. 7 drill.
