[HELP] First thread turning.

[TomG]

Your question is actually rather timely. I was just planning a YouTube video of my own on single point threading because the techniques I see on YouTube are generally overly complex and confusing. I tend to be contrary and do it a bit differently. I’ve been bouncing ideas around in my head for a few weeks and now seems to be as good a time as any to put them to “paper”. Here’s a basic rundown of what I plan to pattern the video after. It's a work in progress, so ignore any typos and be patient because my typing sucks. I'll post it as I it develops, starting with the tool:

The first step if you haven’t cut a single point thread before is to grind the tool. A threading tool is actually easier to grind than a turning or facing tool, but care must be taken to get the 60º angle as close as possible since you are making a form tool and the thread form will only be as accurate as the form of the tool. Since you are making a form tool, the top of the tool must be flat, no back rake is allowed. Therefore, if you are using a lantern type tool holder, the top of the tool must be angle so when it is held in the holder, the top is flat, not angled back. If you use a quick change tool post, just ignore this step. I usually start by grinding the left flank 30º to the side of the tool, adding about 12º of clearance so the cutting edge doesn’t rub, a few degrees more for aluminum or brass. When you grind tools with flat sides, use the entire face of the grinding wheel, moving the tool back and forth to generate the straight edge. And don’t forget to dress the wheel before starting.

Something that needs to be addressed with a threading tool is the helix angle of the thread. If you look at the side of a thread, you’ll see that the thread angles, to the left for a right hand thread and to the right for a left hand thread. This is the helix angle and it must be accounted for in the clearance angles of the tool. In other words, the leading edge of the tool requires slightly more clearance than the trailing edge. This helix angle business is not that important when cutting a 60º V thread, but is critical when cutting an Acme or square thread, so it’s good to understand the concept now. I’ll go into more detail on how to calculate the helix angle for various threads in the video.

Once the left flank of the tool is ground, it’s time to grind the right flank. This angle forms the V shape of the thread and as already mentioned, needs to be as close to 60º as possible. Use an arrow head thread gauge to dial this angle in, holding it up to the light to see. This side of the tool, the trailing side requires slightly less clearance than the leading side to allow for the helix of the thread, about three degrees for common threads.

Now that the right side is complete, it’s time to add the flat. A flat is not a necessity for 60º V threads, but it makes a nicer looking thread and one that is slightly stronger than a sharp V. The flat is ground or stoned (it’s very small) square to the shank and the width should be 1/8 the pitch of the thread, or less. For instance, the flat for a thread that is 16 threads per inch is (1/16)8=.008”.