My Threading bit design

Faced with some threading jobs I had a think about grinding some blank 1/4" HSS to the correct shape. Since I was going to be threading to a shoulder I had to have a relatively thin tool when finished. I came up with a way to do this while minimising grinding and retaining the strength of the tool.

Theatrical Aside

Of course, as soon as my fellow metalworkers on rec.crafts.metalworking saw the pictures here it turned out that this shape has been in use since the 1800's. As least I know I'm on the right track if I can re-invent something independantly. One day I'm sure to invent something new (-:

I did this by deciding to mount the tool offset by 30 degrees (ie it lies in line with the offset topslide), and grind the tip to match. The following images illustrate what I did. I have used this tool for every thread from 32tpi to 2mm pitch and it has always done the job. I keep it sharp (with possibly a too sharp point for some thread specs) by running it carefully on my fine hard Arkansas stone. The angle is somewhere between 55 and 60 degrees, and I use it for Whitworth, UNC and metric threads as is.

The grinding process is simple, esp on the bit blank I used which came with a angled off end. I first marked out and ground off the 60 degree angle to form the cutting edge, then marked and ground off the flat side on the left to allow working to a shoulder.

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Last modified: February 20 2013 07:52:53.