Grinding a thread cutting tool.

[oxford]

I have some questions about grinding a hhs thread cutting tool. First, I have very little knowledge about grinding tools. When I was a machine shop student at the vo-tech many years ago we had to make a nut and bolt and cut the threads for the bolt. We had to grind the blank for the 60 degree angle but we were taught to only grind the blank on one side, not both. If I remember correctly it was said you were only having to deal with grinding and keeping straight one edge not 2. We also did not grind any off of the top of the blank(rake?). We were using these in a lantern tool post.

Over the years I have not seen a thread tool ground like this. They always seem to have both sides ground with the point in the middle and the top ground. Is the way I was taught a long time ago an acceptable way of doing it?

[outback]

Oxford;

We had a debate on this a couple of months ago. Some think the rake angle on top has an effect on the 30 degree angle on the right side of the tool. I still grind the rake angle on the top of the thread.

I grind the 60 degree thread form on both sides of the tool and both have clearance angle. The form I grind is on center.
I use a special fixture actually.




Jim

[doctor demo]

I would say that any way You want to grind a tool that has the proper angle when You are done is o.k. I've even used round pieces of tool steel to make thread cutting inserts in home made boring bar shanks.

Steve

[Juergenwt]

Here is a good way to grind a threading tool. For right hand threads you need to back off the left side of the 60 deg angle.





http://i305.photobucket.com/albums/n...wt/Toolbit.jpg

The good part is, this way of grinding let's yo cut close to a shoulder and keeps the tool holder away from the chuck.

[darryl]

I've done it both ways. Part of the choice of method has to do with how the cutting tool is held, and what effect it might have on clearance. With the tool ground on one edge only (not counting relief angles) you could mount it to allow threading closer to the chuck. If you consider the relief angles and sharpening, it would probably be easier overall if it was ground on both sides. When it comes to having a holding jig to grind the cutter, it helps if most of the shank of the tool is angled away from the grindstone. With the single grind, one edge is easy, but to sharpen the straight side (and grind some relief) the side of the tool would be parallel to the grindstone. I don't think this is as easy to do, and you don't get to pass the cutter across the whole width of the wheel as you grind, unless you grind the whole side. If you did that if might interfere with the way the cutter is held on the tool post.

A compromise I've used is to grind the right side of the tool to say 15 degrees or so, then grind the other edge at 75 degrees- still leaving you with a point with a 60 degree included angle. It might be less intuitive when you go to set the tool at the correct orientation for threading, but it works, and gives you sort of the best of both worlds. I hate it when I'm set up for threading and some part of the holder or whatever gets too close to the chuck jaws.

[Lew Hartswick]

Here is how I "solved" the threading bit grinding problem. :-)
http://home.earthlink.net/~lhartswic...ingFixture.jpg
http://home.earthlink.net/~lhartswic...ingBit%202.jpg
...lew...

[GadgetBuilder]

I copied Martin Cleeve's jig: http://www.gadgetbuilder.com/ThreadingTools.html

It also sharpens some internal threading tools by putting the boring bar in the holder. Plus I've used it to sharpen some non-threading tools for the lathe and shaper by setting angles with a protractor, although there are limits to the angles allowed.

John