Models for grinding HSS Lathe Tools

[mikey]

Hey mikey, can I have a picture of what your jig setup looks like to grind these?

I don't use any jigs. I don't need them and neither do you. I'll show you exactly how these are ground and you'll see why I say that. In fact, if you can draw a line and grind to that line then you'll be fine.

These tools are simple turning tools that are very, very easy to grind. Don't worry, you can do this.

 

[mikey]

The models are done and will be on their way to the first three recipients shortly. I just wanted to give a preliminary explanation of what each tool is and does. We will go into each tool in much more depth very shortly.

They are made of mild steel keystock and I was reminded how soft this stuff is when I tried to hone the faces of the square tool. I was able to remove all the grind marks but I totally changed the geometry of the tool in the process! So, out those went and I ground new square tools. This time, I merely deburred each tool and put a nose radius on them so expect to see grind marks and bare keystock surfaces but at least the geometry will be accurate. When you grind one of these tools from HSS you can hone the faces without altering the geometry much at all. Please note that while the models are not honed, the edges are quite sharp so handle them carefully.

NOTE: Tool grinding can be dangerous and I encourage you to use eye, lung and hearing protection. Grinders, both wheel and belt, can eat your hands in an instant so stay focused and know where your hands are at all times. Inspect your grinding tools and be sure they are in good and safe working order. Do this at your own risk and please don’t blame me if you get hurt in the process.

Okay, let me tell you about the model tools in the set. There are four basic lathe operations: turning, facing, threading, and making holes (drilling/boring). Of course, there are many variations of these basic tasks but the point is that your tools will allow you to do most basic lathe work.

From left to right we have a general purpose right hand Square Tool, a general purpose RH Knife Tool and a 60° threading tool. All these tools are proven to work as intended and all are simple to grind. We’ll discuss each of these tools in more detail as we go along.



· Square Tool: I call it “square” because the two relief and two rake angles are the same - 15°. You can just call it a right hand turning tool, meaning it cuts toward the chuck. A left hand tool will be a mirror image of this tool and will cut toward the tailstock.

I made this model tool with a 2° smaller angle at the side cutting edge than my usual square tool has (ie; 7° on the model vs 9° on my usual tool). Below is my tool on the left, your tool on the right.




This is because many of you will use this tool to rough with and this smaller angle provides more mass at the tip to handle higher cutting loads. This does not alter the performance of the tool. You simply need to alter your lead angle a bit more in use and it will work exactly the same as my tool. If you insist on making yours the same as mine, I will tell you how to do it when we discuss grinding it.

I put a ~1/64” nose radius on this model. That is usually sufficient for most work but if you prefer, you can enlarge your nose radius to whatever you like. For roughing, however, a smaller nose radius is preferred. Besides, this thing has 15 degrees of back rake and that helps produce a nicer finish so don’t go overboard with large nose radii. Large nose radii increase radial cutting forces (we'll go into cutting forces superficially at a later date) and increase deflection. On a 3/8" turning tool, Machinery Handbook recommends a 1/64" radius Max. I listen to that, mostly, but do go up to 1/32" when I feel I need it.

This tool will turn, face and chamfer. The 80° angle at the tip will allow the tool to turn into a shoulder without rubbing and then face out without rubbing, all without changing the lead angle of the tool.

o When facing the end of a work piece, the tool is angled so the cutting point of contact is just aft of the tip, at the forward area of the side cutting edge.

o When turning, the angle of the tool will vary with the operation; more perpendicular to the work for roughing and slightly angled toward the tailstock for finishing. This is called changing the lead angle of the tool and has been discussed elsewhere. If we need to clarify it further, please comment so we can do that. You need to try different angles until you find what works for you; there is a sweet spot for turning but it depends on the operation – roughing, sizing or finishing.

o When chamfering, use the edges near the tip of the tool to chamfer outside corners or inside a bore; just angle the tool to cut with the side or end and slow your speed a little because you’re using it as a form tool so cutting forces are higher. Bring the tool into contact and gently feed it into the work with your cross slide and it will chamfer as well as a purpose ground chamfering tool.

The relief and rake angles on the tool are a compromise that allows it to work with multiple materials; mild and medium carbon steels, stainless steel, aluminum, brass and most plastics. While the tool is not optimized for these materials it will cut all of them rather well. This tool will also cut harder materials like tool steels (O-1, etc.) and harder steels (1144, 4140, etc.) but it is better to alter the tool angles to optimize the tool for these materials and use a cobalt or tungsten bit, or use carbide if that is available. Don’t worry; I’ll tell you how to alter the angles.

The angles on this tool allow it to cut with significantly lower cutting forces and temperatures than a standard tool. This means that it will allow a light lathe to rough deeper, size more accurately and finish finer (than it would when using a conventional tool) before running into the power and rigidity limits of your lathe. It also means the tool will deflect less; if you can dial in a 0.0005” deep cut, the tool will usually cut it.

This tool will be used for most work on your lathe. If you choose, you can optimize the angles on the tool to work with a specific material group but the overall shape of the tool can remain the same.

· Right Hand Knife Tool: This is a kick ass facing tool. Like all facing tools, this one cuts at the side cutting edge up close to the tip. Because all the cutting is at the side edge, the nose radius does not participate much at all and can be small; this allows you to go into the corner of a shoulder and face out without leaving a huge radius at the root/corner. The side relief angle is 15° so it takes light or heavy facing cuts easily. The back rake is more conservative and this focuses the cutting forces toward the side cutting edge, which is what we want with a facing tool.

This tool will also work as a thin work finishing tool. All turning tools will deflect thin work pieces and that makes turning a consistent diameter a challenge. This tool is ground to a somewhat delicate tip and is able to take whisper-thin sizing cuts with minimal deflection. I have turned a taper-free piece of brass that was 1” long and only 0.050” OD and cut it without a taper over the full length with this tool. Although the tip seems delicate, this tool is very stiff and will face accurately.

This is also a really good chamfering tool for both inside and outside edges.

Note that due to the conservative rake angles, pointed tip and small nose radius (~1/64”), this tool does not turn well on longer work. It tends to inscribe a spiral pattern in the work surface so don’t use it for general turning unless you enlarge the nose radius.

My personal knife tools are made of cobalt steel because it holds an edge for a very long time. My tool for steels is about 15 years old as of this writing and it is as good as the day it was ground. It is gently honed after each use. Try one; you will like it.

· 60° Threading Tool: This is just a normal threading tool except it is ground with 15° relief angles on each side. The top is flat (zero rake) but is honed. There is a tiny flat stoned into the tip; this prevents breakage of the tip and flattens the root of the thread a tiny bit.

The cutting tip is offset to the left to allow the tool to thread up close to a shoulder. When you grind your threading tools, use a fishtail gauge like a Starrett C391 or similar tool as an angle template. You must have a 60° included angle at the tip, not more, not less; precisely 60°. Then stone a tiny flat at the tip and hone the tool so it is razor sharp.

The model’s shape allows it to cut threads fairly close to a shoulder. If you need to cut even closer, grind the left side tip angle closer to the tip of the tool; this moves the tip further to the left. The tool, as is, will cut a 4-40 thread on up to ¾-16 and any 60° thread in between. It may go smaller or larger but I haven’t done that yet so I cannot say for sure.

I have found that a 15° relief angle cuts really accurate threads because it lowers cutting forces. Standard relief angles are in the 10-12° range or less and when cutting coarse, deep threads I can hear the tool cut. This tool just hisses and produces threads with almost no fuzz or burrs. It works for me; you might give it a try.

So, these are your tools. I will tell you how to grind and modify each tool in sequence as I write them up. Don't worry; all are really simple to grind. The shape of the tool is what you see but the angles of the tool faces are what really matters. I will show you how to grind the shape but what I really want you to understand is the what and why behind the angles on each face. Get that, understand that, and you will be able to make your tool do almost anything you want the tool to do.

Before I forget, each tool is meant to be used at center height. Make yourself a height gauge and use it whenever you use a tool, even if it is already in a quick change tool post holder. If you want your tools to work as they should, get them at center height.

 

[Aukai]

Awesome read, thanks for taking the time.

 

[mikey]

I just realized that the guys who get the model tools first may need to know how they are ground in order to reproduce them. I’m going to cover that as we go along but they will need the grinding info first, so here it is.

Turning Tool

First, align your tool rest to 15°. You can use the angle on the side of the tool to get this angle. If you have one, you can set it more accurately with a digital angle gauge. Measure ¾” down on the left side of the blank and put a mark. Then measure 1/8” across the tip and mark. Now connect the dots with a line. (If you want your model to match my HSS tool, mark it at 3/16” across the tip, mark it and then grind it.)




Now just grind to the line. This produces the side cutting edge angle. If this were a left hand tool, you would do the same on the right side of the bit.

Once the side angle is ground, use a protractor set to 10 degrees and put the base of the protractor on the side cutting edge and mark the angle.



Then grind to the line and you’ll have this.



Next, we need to grind the rake angles. Measure ½” from the tip and mark the side of the tool. Then put a line on your tool rest, up near the belt or wheel, with a 15° angle like this:



Keep the shank of the tool aligned with the line on the rest and the back of the blank flat on the rest at all times. Now bring your push block into contact with the tool and just push the tool straight into the belt/wheel. It will cut the rake angles all at once. Watch the contact point on the tool and as it just reaches the tip, stop. You should have this:




Knife Tool

You are going to grind the side relief angle on the side of the tool first. It is 15° so you don’t need to change your table angle. Mark ¾” down from the tip (you can actually measure ½”; you don’t need so much cutting surface) and place the side of the tool parallel to your belt/wheel. Bring your block into contact with the blank and do a straight steady push into the grinder until the grind reaches the top edge of the tool and stop.



Use your protractor and set it at 60-70°. I set mine to 65° and made a mark from the tip:



Now just grind to the line. The table angle stays the same. You should have this:



Now you need to do the rake angles. On this tool, the side rake remains at 15° so the table angle remains the same but the back rake is reduced to 10° so re-draw the line on your tool rest at 10°. Mark the side of the tool at ½” from the tip and align the tool shank with your mark on the rest and push straight in to cut the rake angles. You should have this:




Threading Tool

Set your protractor to exactly 30°. On my Starrett protractor, exactly 30° means I need to split the 30° line with the side of the moveable arm. Mark the blank somewhere up near the tip and grind it to the line.



Re-set the protractor to exactly 30° the opposite way, align the arm to the tip end of the first cut and mark. Then grind to the line:



This should give you an accurate 60° included angle at the tip of the tool and it should align exactly to your fishtail:



Note: if you wish the point of the threading tool to be closer to the left side, do it by aligning the protractor arm lower than the tip of the tool. When you grind to that lower line, it will produce a pointed tip closer to the left side. You might be able to get 0.050” closer this way so keep it in mind if you need to get up close to a shoulder.

That’s it, you’re done. See? It’s easy! But don’t get cocky. Mild steel keystock grinds like butter; HSS does not, and cobalt and tungsten are worse. Just kidding; tool steel does take more effort to grind accurately but the process is basically the same. Follow these instructions to reproduce the models but you can change the shape in any way you choose, provided you know why you’re changing it and understand what the result will be.

 

[Z2V]

Great write up Mike, this is going to be a great learning experience, thanks for your interest in sharing this with us.

 

[mikey]

Great write up Mike, this is going to be a great learning experience, thanks for your interest in sharing this with us.

Thank you, Jeff. Yeah, I hope this helps. We're going to discuss each tool in detail next. How to grind it in more detail but also why we're grinding it the way we are, and how we can change the angles we grind to achieve the results we want. By the time we're done you should have what you need to make a lathe tool cut just the way you want it to.

By the way, I know I'm making this whole grinding thing look easy and simple. If you follow the instructions above, it is pretty easy but it's going to challenge some of you. Take your time and grind on keystock until you can get every angle exactly the way you want it. Then, when you grind a HSS tool bit, it WILL be easy.

 

[mikey]

I was asked by one of the guys to clarify "lead angle". While this is a really basic thing, I remember being concerned/confused when I started so let's see if we can make it clear.

The lead angle of a tool is an actual physical feature on the tool. When the tool bit is perpendicular to the work piece, the lead angle is equal to the side cutting edge angle. The side cutting edge angle is the first face you grind on a tool, on the left side; it holds the cutting edge. This angle is not random. Old style turning tools had different angles to suit their purpose. Roughers had less angle, finishers had more angle and facing tools were somewhere in the middle. On a newer style general purpose tool like our Square Tool, the side cutting edge angle is greater than a rougher but less than a finishing tool; it can actually be anywhere between these two but it will be closer to a rougher for general use because the tool will be subjected to high cutting loads.

Lead angle is also variable on the general purpose tool because we can easily position it wherever we like. You will find that the tool roughs better when the shank of the tool is perpendicular to the work:



It sizes better (on the left) and finishes better (as on the right) when the side cutting edge is angled toward the tailstock.



So, when roughing you would turn the side edge more towards the chuck and when finishing you would turn it towards the tailstock. When you face, you would angle the tool just like a facing tool would be:



When you cut into a shoulder, the clearance angles ground into the tool allow it to turn into the shoulder and then face out:



Why does lead angle matter? Because it alters cutting forces. As the tool turns toward the chuck, forces decrease. As the tool turns toward the tailstock, forces increase. This happens because more of the side cutting edge comes into contact with the work as you turn the tool toward the tailstock. Turn it enough and the tool can chatter. If this happens, reduce the angle of the tool and chatter will resolve.

Similarly, when making heavy roughing cuts it helps to reduce the lead angle. Start with the tool shank perpendicular to the work but if it chatters, turn the cutting edge a bit more toward the chuck.

So, why should you even bother turning the tool towards the tailstock if it just increases cutting forces? Because it significantly improves finishes.

Can you use a negative lead angle? Yes, you can, and you will when you turn into a shoulder and face out. You are cutting with the nose radius but the tool will cut fine as long as you go at least 1/2 the nose radius or more for your depth of cut.

The bottom line is that each function - roughing, finishing and facing has it's sweet spot or angle; you need to find it. Play with the angle of your tool and when it cuts easily and smoothly, you've got it. I almost always start roughing with the shank of the tool angled just slightly back toward the tailstock and reduce the angle if it chatters, which it rarely does. When sizing or finishing, I angle it back toward the tailstock and if it chatters, I reduce the angle. I pretty much know which angle I need so I rarely get any chatter; you will get to this point, too.

PS: by the way, the threads on this 1144 Stressproof tool post stud was cut with a threading tool exactly like the model tool you will have.

 

[Aukai]

I was asked by one of the guys to clarify "lead angle". While this is a really basic thing, I remember being concerned/confused when I started so let's see if we can make it clear.

The lead angle of a tool is an actual physical feature on the tool. When the tool bit is perpendicular to the work piece, the lead angle is equal to the side cutting edge angle. The side cutting edge angle is the first face you grind on a tool, on the left side; it holds the cutting edge. This angle is not random. Old style turning tools had different angles to suit their purpose. Roughers had less angle, finishers had more angle and facing tools were somewhere in the middle. On a newer style general purpose tool like our Square Tool, the side cutting edge angle is greater than a rougher but less than a finishing tool; it can actually be anywhere between these two but it will be closer to a rougher for general use because the tool will be subjected to high cutting loads.

Lead angle is also variable on the general purpose tool because we can easily position it wherever we like. You will find that the tool roughs better when the shank of the tool is perpendicular to the work:

View attachment 242223

It sizes better (on the left) and finishes better (as on the right) when the side cutting edge is angled toward the tailstock.

View attachment 242226 View attachment 242227

So, when roughing you would turn the side edge more towards the chuck and when finishing you would turn it towards the tailstock. When you face, you would angle the tool just like a facing tool would be:

View attachment 242224

When you cut into a shoulder, the clearance angles ground into the tool allow it to turn into the shoulder and then face out:

View attachment 242225

Why does lead angle matter? Because it alters cutting forces. As the tool turns toward the chuck, forces decrease. As the tool turns toward the tailstock, forces decrease. This happens because more of the side cutting edge comes into contact with the work as you turn the tool toward the tailstock. Turn it enough and the tool can chatter. If this happens, reduce the angle of the tool and chatter will resolve.

Similarly, when making heavy roughing cuts it helps to reduce the lead angle. Start with the tool shank perpendicular to the work but if it chatters, turn the cutting edge a bit more toward the chuck.

So, why should you even bother turning the tool towards the tailstock if it just increases cutting forces? Because it significantly improves finishes.

Can you use a negative lead angle? Yes, you can, and you will when you turn into a shoulder and face out. You are cutting with the nose radius but the tool will cut fine as long as you go at least 1/2 the nose radius or more for your depth of cut.

The bottom line is that each function - roughing, finishing and facing has it's sweet spot or angle; you need to find it. Play with the angle of your tool and when it cuts easily and smoothly, you've got it. I almost always start roughing with the shank of the tool angled just slightly back toward the tailstock and reduce the angle if it chatters, which it rarely does. When sizing or finishing, I angle it back toward the tailstock and if it chatters, I reduce the angle. I pretty much know which angle I need so I rarely get any chatter; you will get to this point, too.

PS: by the way, the threads on this 1144 Stressproof tool post stud was cut with a threading tool exactly like the model tool you will have.

Just as good as community college, or at least a good prep for it maybe.

 

[Aaron_W]

In some places you use firm measurements, 1/2", 3/4". You are working with 3/8" stock, will these measurements need to be adjusted if I am reproducing these with 1/4" stock?

 

[mikey]

In some places you use firm measurements, 1/2", 3/4". You are working with 3/8" stock, will these measurements need to be adjusted if I am reproducing these with 1/4" stock?

Good question, Aaron. Just scale it down proportionally. The side and end cutting edge angles do not need to be precise. When I grind tools, I don't measure anything or use lines. I used them here so other folks are able to reproduce the models. It isn't that shape is not important; it is. But you do not need to be precise about the shape. The angles are another thing and that you do need to get right.