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Hi, Barry Young here with part 3 of how to grind tool bits. Today we are going to grind
a threading tool. This is used for external threading on round pieces in the lathe. This
is a rather large one. It's 1" square. We use much bigger ones in industry and much
smaller ones at home in our home workshops. Today I'm going to grind this piece of mild
steel to make it look like a threading tool. I use mild steel because it grinds quicker
here and I won't waste your time. So, off we go. You must have a center gage, like this.
Some people call it a "fish tail". Center gage is the correct term. It's not a "thread
gage". Now, in this fish tail, right on the end is a groove, a v-groove. We are going
to make this tool match, fit in that v-groove. When we are done the tool won't go like this,
or like this, it needs to come straight out of that V. Ok. I usually just put the tool
bit right down onto the tool rest and rotate it 30 degrees, and plunge. Now, I'm grinding
this much quicker than you will to try and make the video short. And that's why my tool
bit is changing colors. When I grind a tool bit for use I avoid changing colors. Alright,
now I'm going to just flip it over and do the other side exactly the same way. Grind
grind grind. Well, we're getting close. Now I've got it roughed out. Let's check it with
the center gage and see which direction we have to go here. Well? What do you think?
Let me take a look here. Looks like we've got way to blunt a tip. So, I'm going to find
out where I was, and then I'm going to crank it over some more to make it actually sharper.
Ok, let it cool down here a minute. Let's check it. Is that a little better? Looks like
there's a É now its a little too sharp. It's got some slop in there. So I'm going to have
to grind the tip away. I'm going to find out where I was and just rotate towards the tip.
Same thing on the other side. And lets check again. Now we're fitting. Pretty darn well.
Ah, it's still a little bit too sharp though. Grind away a little bit more of the tip. Notice
I'm leaving it on the wheel long enough to where it makes one solid cut. That's good
enough for this demonstration, but in the home workshop you can go until that's perfect.
The last face I need to grind is the top rake. So, turn 90 degrees to the wheel, and notice
that the shank end is farther than then end being ground. What that will do is give me
an angle like this, or a "top rake". And what I'm doing now is grinding until I see sparks
coming off the tip. Now if you're doing soft materials you'll make this even more pronounced.
Like for plastics you can go as much as this much, 10, 15, 20 degrees even. Teflon, probably
30 degrees. That'll make it extremely sharp. Now I have a tool that's approximately the
correct shape and I've got the top rake in. The problem is that because I've flipped this
tool bit over I don't have the compound angle that I was looking for on each one of these
faces. To get that, now I can't be on the tool rest. I lift the tool, line it up, you
can feel it when it aligns to where it was, and then lower the shank until you get sparks
off the top. Like this. As soon as sparks come off the top you know you're there. Do
the other side the same way. And once we finish these two compound angle cuts you'll find
yourself to be the happy owner of a new threading tool. Now, there's some things people do wrong
with this tool. Let's talk about that. One is too much slop, which means you need to
grind away the tip, as I did earlier. Another thing they do is what you can see here - faceting.
Lets make that one solid grind top to bottom. And another thing, they don't remove these
burrs on the end of the tool. So, I'm going to get rid of that burr and I do that just
by working it back and forth edge to edge, one edge and then the other. Now we have a
tool that will cut threads. That's how you do that. Thank you very much!