Over the next few weeks I’m going to be publishing a a series of how-to videos on grinding High Speed Steel (HSS) lathe tools by hand. The three part series covers the following:
- Part 1: Grinding a Right Hand (RH) Tool
- Part 2: Grinding a Left Hand (LH) Tool
- Part 3: Grinding a Threading Tool
These videos were produced in cooperation with Bates Technical College in Tacoma, WA where you can earn a degree in both CNC and manual machining. Instruction in these videos is given by Barry Young who is an accomplished machinist, a CNC machining instructor at Bates, and a personal friend and mentor to me.
Thank you Barry, for being willing to share your knowledge with this site and our members once again!
Barry is the author of the “Norman Newguy” column on getting started in machining. He’s also shared his expertise before in other videos that have been featured on this site. If you haven’t seen Barry’s previous videos, here’s a quick list:
So without further ado, here’s Part 1: Grinding a RH Tool
In the video Barry recommends EZE-Lap diamond hones to remove burrs and put the final edge on a newly ground tool. These hones can also be used to renew a dull edge several times before the tool will need to be reground. EZE-Lap hones are inexpensive, and excellent. Here’s a picture of the 5 piece set I have in my toolbox.
They are available from numerous retailers online, including Amazon.
Hi, Barry Young here and today we are going to grind some tool bits for your lathe out of high-speed blanks. This is actually a high-speed tool bit. It’s 1″ square. You probably won’t be using anything this big but it really makes it easy for you to see what I’m doing. I’m actually going to grind a smaller one because this takes forever to grind and I know your time is valuable.
So, I’ve labeled the faces of this tool: face 1; face 2; and face 3. Face 1 is the end of the tool bit and it’s a compound angle. Face 2 is a regular angle, that’s the side rake. The top rake, face 3, is also a regular angle. So let’s knock that compound angle out first.
Step to the side and start the grinder, because it’s dangerous. Just in case.
Now, first thing I’m going to do is turn the tool flat on the tool rest and just grind this away. Now, I’m going to turn this blue because I’m grinding it way to fast. When you do this in your workshop you’re going to want to grind with less pressure and more dunking.
Ok, we’ve got a 5 to 7 degree angle on the end of this tool bit. Now this is mild steel so it ground a little easier than what you’re going to grind. And I’m also using the fine wheel on my grinder which is on the left side. Course are almost always on the right. And I’m using this mild steel so it will go quicker.
Now, we’ve got the end angle, but it’s not a compound angle. It’s just flat right now. I’m going to lower the shank, the end in my right hand, and raise the tip a little bit, like this, to grind that compound angle. No you’ll notice how I went straight into the wheel to match the angle that I had ground before, and then raised the tip.
So, again this is turning colors because I’m grinding it way to fast to save some time on this video so that you can get back to the football game …
As soon as the sparks start coming of the top of the tool instead of going underneath it I know I’ve reached the top. And sure enough ,I have. Right here this grind has gone all the way to the top of the tool. And it got rather warm!
For the second face, face 2, the side rake, I’m going to turn the tool 90 degrees and then I’m going to rotate it back towards me about 3 degrees, which is in the beginning pretty tough to accomplish. But you’ll get used to it the more tools you grind. I like to grind back just about 1.5 times as far as the thickness of the tool.
Just go straight in. Don’t forget to dunk!
Now, if you look right here, one of your goals is to make that grind parallel, the top of that grind should be parallel with the top of the tool. Easier said than done. Practice practice practice!
Once again, we are going to grind until sparks come off the top of the tool. Which means the angle we are grinding has reached the top of the tool. Some of these tool bits have a slight radius on them, the older ones. The newer ones tend to be ground all over and don’t, so they are easier to grind.
I’m starting to see sparks, so I am all the way.
Now, one thing we want to do is try to make one solid continuous grind from top to bottom. This particular one has got two facets. We are going to keep grinding until those facets go away. Try and hold the bit steady as long as you can without burning yourself and that will make it one continous grind.
You can feel when the tool flattens itself on the wheel. That means that you’ve matched all the cuts you’ve made before.
And now we have one continuous grind from top to bottom. Beautiful!
The last grind that we need to do is on the top of the tool, called the top rake. To do that we go on the other side of the wheel. Ninety degrees, tilt it back, and plunge. This is going to be a 2 to 4 degree angle because I’m cutting a really hard material today, 4140, and I need as much cutter left as I can get.
Once again, let’s take a peek right here. Notice how the distance from my grind to the side of the tool is greater at the root than it is at the tip. That means that I had this end elevated a bit and I need to straighten it back out and get it truly horizontal. Which I will do right now.
And, there we are. One continuous grind all the way without digging into the tool. This leading edge is the cutting edge and we now have a good tool except for a few little touch-ups, burrs that I have to get off. And the radius. How in the heck do we get a radius on there?
What I do is I look at the side and I match the angle on the front of the tool to the angle of the wheel and then I walk it around the corner of the wheel. Just like that. And the goal is to get the width of this radius equal on the top and the bottom. You’ll notice that mine is just a little bit narrow at the bottom. So I’m going to go back in untill it hits flat and then I’m going to lower the shank just a little bit. And that should make my radius equal in width from top to bottom.
And that’s definitely good enough. This tool will cut after I get the burrs removed. Which I can do very easily by a super light grind on each face that I did before.
Now, before I use this I would hit it with an EZE-Lap diamond hone to remove any little tiny burrs that I can’t see.
And that’s how we make a right hand turning tool. Just change the angles exactly opposite of these angles to make a left hand turning tool.