GRINDING LATHE BITS

In this exercise we'll explore grinding lathe bits.  We'll first go over using the bench grinder then proceed to grinding six lathe bits that will cover a wide variety of lathe turning tasks.  This is meant not just as reading material but as a set of exercises – you will get vastly more benefit from it if you play along grinding all of the tools described.  When you are finished you should never have reason to hesitate to grind a cutter again.

Tools needed:Bench Grinder with course and fine wheelsA wheel dresser (star wheel, abrasive stick, or diamond)Sharpening stoneOxy/Acetylene or MAPP torch

Materials needed:five (5) pieces of high speed steel tool bit 1/4” to 3/8” square.One (1) piece of W-1 drill rod, 3/8” dia is good.

The two-wheel bench grinder exists in most shops and garages and is frequently misused.  The purpose of this section is to make you see that it is really a fine tool, deserving of the respect and care in operation that you would give any other machine tool, such as a lathe or milling machine.

There are numerous types of abrasive wheels available for the bench grinder, but we'll focus on the 'standard' aluminum oxide wheels.  Other wheels may receive mention in passing.

A wheel should be selected to fit the grinder, the external diameter should match and is probably 6”, 8”, or 10” for most home shops.  Larger wheels exist, but those machines are rare in the home shop.  The width of the wheel should be 3/4” or wider and the wheel must be selected to fit the grinder shaft.  Many wheels come with adapters to fit various shaft sizes, but if you have a largish grinder you may find that even the biggest hole isn't big enough.

A new wheel should 'ring' when tapped lightly with a piece of metal.  This is a quick check of the integrity of the wheel.  If a wheel makes a dull 'thud' when tapped, it should be discarded.   Modern manufacturing methods have all but eliminated bad wheels, but it never hurts to check.  To test, grasp a rod in one hand and place the wheel on the rod.  Without touching the wheel with your hands, tap the side lightly with a piece of metal, such as the end of a wrench.  You should hear a ring.

The wheel is installed on the grinder between two flanges – these may be separate flange pieces, or a flanged nut.  Never tighten a flange-less nut directly against the grinding wheel.

With the wheel installed, stand aside and turn the grinder on.  The wheel should spin smoothly.  If the wheel is new, clogged, or worn, it should be trued.  Truing the wheel is a process called “dressing”.  Dressing the wheel is done by holding a tool against the face of the wheel, and square to the tool rest and running it back and forth to break off some of the surface grit and expose new, sharp grit.  In doing so any metal that has been stuck in the wheel from previous grinding is also removed.  Wheels get dull with use, dressing is also the means of sharpening them (by exposing new grit).  Wheel dressers come in three basic types:

1.The abrasive stick.  Abrasive stick dressers are the most inexpensive and usually do not use a guide. They are composed of a stick of abrasive sleeved inside a disposable plastic sheath to keep them from breaking. 2.The 'star wheel' dresser is perhaps the most common and is composed of a handle to which small, hardened wheels are attached.  The head frequently has hooks that are hooked around the front of the tool rest (between the tool and the wheel) so the rest can act as a guide.  The cutting wheels are pressed (lightly) into the grinding wheel by raising the back of the handle.  Make contact and move side to side. 3.The diamond dresser is a single piece of industrial diamond.  It is very effective, but must be moved side-to-side more slowly because of it's narrow contact surface.  Diamond dressing tools usually come with a plain shank to which a holder or guide is affixed.

When dressing a wheel move smoothly and slowly across the face of the wheel until the face is flat, the corners are reasonably square and there is no metal stuck in the wheel.   The following pictures show using the different dressing tools:

Dressing with the abrasive stick relies on the accuracy of the person doing the dressing:

Dressing with a diamond is quicker and with a fixture more accurate, but requires a finer touch.

The star wheel is the safest and easiest bet, IMO.  It does a good job and relies on the tool rest for squareness.  If you have only one dressing tool, this is the one I recommend.

Materials

The materials you grind will greatly impact the life and effectiveness of the grinding wheel.  Soft steel will load up the wheel (leave metal in it) reducing the ability to cut and marring the workpiece.   To keep the wheel working well the wheel will need to be dressed frequently.  Aluminum should never be ground on an aluminum oxide wheel as it will load profusely.  If aluminum is to be ground a rubberized abrasive wheel or belt grinder should be used.  If you have the luxury of multiple grinders, reserve one just for grinding hardened steel – this will preserve the wheels.  Hardened steel, like the HSS tool bits we will be grinding load the wheel very little.  If you grind enough you will eventually have the experience where you dress the wheel and the cutting seems to be improved tenfold – grinding is time consuming enough without trying to use a loaded or dull wheel – keep your wheels dressed!

With the wheels installed and dressed it's time to get ready to grind.  Get a cup or can and fill it two-thirds full of water.  The water will be used to quench the tool to keep it from overheating while we grind.  You will be quenching periodically, so place the can somewhere convenient, but make sure it won't vibrate off if it's on the same surface as the grinder.  A nice arrangement is to hang the can, using a piece of wire, so it's directly below the wheel – this keeps it handy and minimizes wasted motion between grinding and quenching.  When quenching, perform a meaningful quench – it is not enough to get the tip of the tool wet, you want to transfer its heat to the water.  Dip the tool and swirl it.  Spend a full 3-5 seconds in the water or you'll find yourself quenching much more frequently than you need to.

As you grind, apply only light pressure to the workpiece to hold it against the wheel.  Heavy pressure will

not speed up grinding but will dull the wheel, load it with metal, burn your fingers and ruin the temper of the workpiece.  Light pressure allows you to feel the face you are grinding and repeatably place the face in full contact with the wheel.  Heavy pressure results in a loss of feel and your piece will come out faceted, like a diamond, because you could  not repeatably hold the part in the same place.

If you burn your fingers, or the tool bit becomes discolored, you are pressing TOO HARD!  Get comfortable and reconcile yourself to the fact that grinding will not be fast.  Later on in this tutorial we'll grind a boring bar from oil-hardening rod – this allows us to use machining tools to cut the rough shape desired and grind only for final shaping.

We'll grind tools for general home use on steel and aluminum.  Before we're done I'll give you angles appropriate for use in other materials.

Procedure

I've tried to generalize grinding lathe tools into a generic procedure.  In general we will grind bits as follows:

1.With the tool rest set between 5* and 10* grind the leading (dominant cutting) side.  The tool rest angle creating side clearance as we grind.2.Grind the opposite side with the same clearance3.Shape the 'point' if necessary4.Grind the rake.  Rake is the angle of the top and there are two such angles: top or back rake, which is the angle the surface slopes front to back and side rake which is the angle side to side. That's two angles of one face, so they're ground in one step.5.Honing the important edges, where necessary.

The standard right-hand cutting tool

We'll start by grinding a standard right-hand cutting tool.  The tool is useful for turning toward the headstock and facing.  It will likely be the most frequently used tool in your arsenal.

Note: I have no idea why this is called a right-hand tool – but it is.  I always want to get this backwards.  My best guess is because it cuts from the right even though it cuts to the left (toward the headstock).

I'll describe this first process in pain-staking detail, after which the other cutters should seem like more of the same.

Start by setting the tool rest on the grinder between 5* and 10*.  You can measure this angle with a protractor, angle gage, or just eyeball it.  The good news is for the vast majority of your work these angles do not have to be exact.  For hobby use, err on the side of too much angle.  The cutter will still work, it will just be less strong than a cutter with a shallower angle.   (Unless you go to extremes, strength is mostly important in a production environment where the cutter is asked to remove as much metal as possible, as quickly as possible.  In the home shop most cutters are treated rather gently by those standards.)  

Any time you are grinding with a rest the rest should be as close to the wheel as possible without touching it.  Any gap is an invitation for something (clothing, a finger) to get caught between the wheel and the rest and get sucked in.  

Step 1: Grind the first (long) side.  This side is ground at roughly 30* - again, don't get too hung up on the angle.   Look at the pictures and drawing and make sure you start on the correct side, or you will end up with a tool for cutting away from the headstock – useful, but not what we're after. The angle of the tool rest imparts side clearance as we grind.  This step is the slowest as it involves the most metal removal.  Take your time, quench often, don't press too hard.

Here's the side we just ground.

And here's the front.  Notice the clearance angle provided by the tool rest.

That last picture should have been this one...

Take a minute and compare your first surface with the pictures and drawings.  You should have side clearance as shown in the end view and an edge that is ~1.5 times as long as your bit is wide.  The ground surface should be a single surface rather than a collection of facets.  Correct any problem areas before continuing.

Step 2: Grind the opposing side.  The angle here is sharper, roughly 45*.  It now becomes extra important that you not press too hard.  As the material forms a point that area is more susceptible to heat damage than the thick sections.  Quench often and don't let the piece discolor.  (If it does, it's not the end of the world – it'll probably still work fine as long as it wasn't bad, but strive for perfection).

And the front view of same...

Now we have the basic shape.  There are a number of cutters we could make with just those two steps – threading tools come to mind – we'll cover them shortly.  

Step 3: Put a small (~1/32”) radius on the tip.  Continue using the tool rest for this step to get a nice looking radius all the way down the front edge.  Just touch the tip very lightly to the grinder and rotate the bit to 'touch in' a small radius.  This needs to be done smoothly and in one shot – if you try to touch it up too much you'll end up with a large radius. This radius is what will enable a smooth finish.  If we left it sharp, the cut would look like threads up close.  The combination of some radius and a slow feed are what give a smooth appearance and texture to the work.

Step 4: Grind the top and side rake.  The rake is put in free hand.  Look at your cutter.  We want a slope that goes from the first edge we ground back to the square (unground) edge.  At the same time, we want a slope that goes from the tip back toward the shank.  That means we need to start grinding not at the tip and the long edge, but at the back and the 'far' edge – where the grind will be deepest.  You'll have to hold those angles while pressing (lightly) against the wheel.

Here's the general position you'll use:

And here's the started surface.

As you grind, hold the long edge horizontal to the cutting wheel.  When you get close to the edge, switch to your fine wheel and continue grinding until the grind reaches the long edge.  That's it – you should now have a nicely formed cutter.

You may use the cutter as-is, or hone the sides for fine work.  (When honing be careful not to round your cutting edges!)

Take it to the lathe and give it a try.  You should be able to face and turn (toward the headstock) and with a slow feed you should be able to achieve a nice finish in aluminum or steel.

Grinding that one cutter should have given you the process and technique to grind three  more useful cutters to follow.  None of them introduce new concepts, so let's describe them and grind them.

Now for practice you'll grind the next tool (almost) on your own.  (Referring to the directions above as necessary)

The right hand cornering tool

The right hand cornering tool is almost the same as the right hand turning tool, with two differences1.The tip is kept sharp, allowing you to cut a sharp shoulder.2.The tip angle must be less than 90* (75* is 'ideal') allowing you to cut into a corner and leave a nice 90* angle using the motion of your lathe apron and cross-slide.

Give it a try – same steps as before, just don't put the radius on the tip and watch your side angles a little more closely.

Two more!  Now grind the left hand tools.  Same as before, but the side angles are reversed.

At this point you should have a nice complement of general turning tools.

Threading tool

The threading tool is easier to grind because there's no rake – the top is just flat.  A flat top is very common with form tools.  Form tools are those that rely on the shape of the cutter to impart a particular shape of cut. In the case of the (standard) threading tool the shape is the precise 60* angle of the thread.  It's important that the shape be perfect, so this time your side angles are critical, but it's still easy to achieve them.

Grind the first edge at 30* as before.  I like to grind this side extra long – it will provide more clearance when threading to a shoulder.  Then as you grind the other edge, you'll want to check your angle frequently and get a perfect 60*.  You could do this with a protractor or angle gage, but for  60* cutters every machinist should have a 'fishtail gage' made for precisely this task (and some other threading tasks).

Use the gage to check your angle as you grind the second edge and when it's perfect (and the tip of the tool is pointed) it's done.  Polish the top on a sharpening stone and you're ready to cut threads!

There are a huge number of other form tools you could grind, just let your imagination do the work.  Note that form cutting involves large forces so you shouldn't expect to cut large forms on a small lathe.  I've seen it recommended that a tool for steel never exceed 1/8” in contact with the work at one time.

Here's another form tool for radiusing the corner of a workpiece – remember your clearance and I'll bet you can grind one without further instruction.

And here's the side view, so you know I wasn't cheating...

Finally, let's make a boring tool.  The straightforward way to make a boring tool is to grind one section thinner than the rest, but for best strength we can avoid that.  Using a piece of drill rod you can form a cutting edge in soft steel, then harden it.

Start by taking a piece of drill rod (I used W-1) and bending it to about 30* by heating it with a torch and lightly hammering the end.

Allow the bend to air cool – this will keep the metal soft.  

Now grind a tip on it as shown.  Keep in mind the tools you have just ground and work to make the cutting angles similar.  Remember how the tool will be held, and make sure you have front and side clearance.   Since the cutter is annealed at this point, you can actually machine these surfaces in, if you like.

Here the top and 'front' are ground...

And here's the end view - nothing new - same angles we've been working with all day...

Our previous cutters were ground from High Speed Steel, but this drill rod is softer, so when you reach a shape that looks right, you must harden the bit.  Hardening is a skill, and like any other skill requires some practice, but a careful first attempt should still result in a usable cutter.  To harden the piece you will need a magnet, a cup or bucket of water, some bar soap, and a torch.   Rub the soap against the cutter, getting as complete a coat as possible.  Fire up the torch and holding the cutter in pliers, heat the business end in the flame – strive to heat it slowly and evenly.  As it gets dull red check it with the magnet – keeping the piece in the flame as much as possible.  When the piece shows no attraction to the magnet, plunge it quickly into the water.  The piece is now hard, but it is 'glass hard' – it would chip under use, so you need to temper it back to some degree of toughness.  This is easiest in low light (like only the torch).  Run the piece under a wire wheel or sand it with some emery cloth to get a clean surface – this will help you see the colors.  Heat the piece again concentrating on a slow even heat.  Watch for colors to appear on the steel – like oil on water, but not as pronounced.  You are particularly watching for a yellow or 'straw' color.  As you see the cutting edge turn yellow, quench the piece again.

The piece is now hardened.  Using a stone, or a light touch on a fine wheel sharpen the piece as you might if it were dull.  You can also radius the tip as on the turning tools if you'd like.  It is now ready to use.

There's no such thing as a 'complete' set of lathe tools, but if you've followed these instructions you now have a set that will serve you for a great many tasks.

Refinements

A 'real' machinist is quite likely to grind his tools without the aid of a tool rest.  Once you have seen the angles necessary, it's fairly simple to do, but takes practice.  I encourage you to work on this aspect of grinding AFTER you have ground the six tools shown here, in the manner described.  Using the rest, in my opinion, helps teach what it is that we're after.  Learning to grind freehand is a convenience (it's faster) but a luxury (it's unnecessary).  In the end results are all that matters and you can get results with a tool rest that are in no way inferior to free hand ground cutters.  In fact, the greatest complement I can think of for a free hand cutter is “it looks like it was ground in a fixture”.

Not mentioned in this work are 'chip breakers' which are essentially any mess you may choose to make on the top of the cutter to encourage chips to break rather than form long curls.  I consider chip breakers completely optional in the home shop and leave further discussion to the many books that cover cutter grinding.

Finally, here is a table of angles for use in various metals.  I'm sure the posting will botch any formatting I attempt, so the table reads as follows:

Material, Top rake, side rake, front clearance, side clearance.

Iron  5*, 12*, 8*, 10*Stainless 16*, 10*, 10*, 12*

Copper 16*, 20*, 12*, 14*Brass and other Cuprous alloys 0*, 0*, 8*, 10*Hard cuprous alloys 10*, 0*, 12*, 10*Aluminum 35*, 15*, 8*, 12*Plastics 3*, 0, 10*, 14*

Don't get hung up in these angles – they are formulated for maximum tool life at maximum cutting depths and speeds.  The 'generic' cutters you have just made are adequate for many materials at non-production feeds and speeds – this table is presented only to help you optimize your cutters if you find yourself cutting a lot of a particular material.

If you enjoyed and benefited from this tutorial, please post pictures of your bits and a brief history of your tool-grinding experience.

Thanks!

GsT

Firstly, thanks to GeneT for his "How to" series. Very informative!

I hope that this adds a little to the knowledge:

Hi Gene

I downloaded it from the net a few months back as a one page PDF file that I converted to JPG to post here. I can't remember where I came accross the file.

I came across these as well...

And I found this also: Grinding Your Own Lathe Tools

Grinding Your Own Lathe ToolsTools shown above, left to right: A right hand cutting tool, a left hand cutting tool and a boring tool.

As with any machining operation, grinding requires the utmost attention to "Eye Protection". Be sure to use it when attempting the following instructions.

My first experience in metal cutting was in high school. The teacher gave us a 1/4" square tool blank and then showed us how to make a right hand cutting tool bit out of it in a couple of minutes. I watched closely, made mine in ten minutes or so, and went on to learn enough in one year to always make what I needed. I wasn't the best in the class, just a little above average, but it seemed the below average students were still grinding on a tool bit three months into the course. I believe these students didn't have the confidence in themselves to work with their hands. Grinding lathe tools is easy, and the only reason we sell them is to help a beginner get started. If you are to be successful in making metal parts on a lathe, you have to teach yourself to grind tool bits.

Consider a Carpenter who didn't have the confidence to drive a nail because he was worried about missing the nail and hitting his thumb. He/she wouldn't be in the trade very long! Some things you do in trades require a positive approach and tool grinding is one of them. If you keep stopping to see if you're grinding it correctly you'll not only waste a lot of time, but will end up with a less than perfect cutting edge. Set up the grinder correctly and do it! It shouldn't take but a few minutes to make simple cutting tools and only a few seconds to resharpen them.

A bench grinder doesn't have to be expensive to work well, but it does require good "wheels" for high speed steels. Try to find a source for grinding wheels from an industrial supplier. Some of the wheels that come with inexpensive grinders wouldn't sharpen a butter knife. Sixty grit is a good place to start. A wheel dresser is also a necessity. They cost less than $10 and are readily available from good hardware stores.

FIGURE 1--A wheel dressing tool and spare "star wheel" sharpening insert.

Grinding wheels should be considered cutting tools and have to be sharpened. A wheel dresser sharpens by "breaking off" the outer layer of abrasive grit from the wheel with star shaped rotating cutters which also have to be replaced from time to time. This leaves the cutting edges of the grit sharp and clean.

A sharp wheel will cut quickly with a "hissing" sound and with very little heat by comparison to a dull wheel. A dull wheel produces a "rapping" sound created by a "loaded up" area on the cutting surface. In a way, you can compare what happens to grinding wheels to a piece of sandpaper that is being used to sand a painted surface; the paper loads up, stops cutting, and has to be replaced.

For safety, a bench grinder should be mounted to something heavy enough so it will not move while being used. The tool support must be used and should be set at approximately 7°. Few people have the skill to make tools without a tool support and in essence it's wasted effort. Tool supports are usually made up of two pieces that allow you to set your tool rest above or below center. It really doesn't matter whether its above or below as long as the support is at 7°.

FIGURE 2--Set tool rest at any height, but at 7° angle from centerline of wheel.

The reason tool supports are designed like this is so they can be used for a variety of uses, not just tool bits. What this means is that if the tool support is above or below center it must be adjusted as the wheel diameter changes.

Now it's time to make a tool, and whether you turn this job into a major project is up to you!

When working around grinders it is an absolute necessity to wear EYE PROTECTION. Grinding debris is thrown out at high velocities and can damage not only eyes, but also expensive glasses. Wear safety glasses or a full face shield.

If you've never sharpened a tool, take a close look at how ours are sharpened. Let's duplicate the right hand tool on the opposite end of the blank. Be careful you don't cut yourself on the blank or the sharpened end while working with it.

First dress the wheel by taking the dresser and setting it on the tool support square with the wheel and while applying a light pressure move the dresser back and forth with the grinder running. Unless the wheel is in bad shape, it should be ready to use in a few passes.

Grinding Side 1 of the Tool

Turn off the grinder and set the tool support for approximately 7° if you haven't done it yet. If you're not good at guessing at angles use a pre-sharpened SHERLINE tool to set the angle. Metal cutting tools are very tolerant on angles. I've always found wood cutting tools more difficult to sharpen. Too little angle and the "heel" of the tool will rub, too much angle will cause the tool to "dig in" and chatter.

FIGURE 3-- Heel of tool

Have a cup of water handy to cool the tool with and set the blank on the tool rest and start grinding side 1.

FIGURE 4--Grinding Side 1.

FIGURE 5--Properly ground side 1.

Move the blank back and forth across the face of the wheel until you have ground a 10° angle on approximately 3/16" (4mm) of side 1.

This is where the "positive approach" comes in. Unless you push the tool into the wheel with enough pressure, the tool will bounce around and you'll never get a good flat cutting surface. It isn't necessary to worry about getting the tool too hot. Modern day tool steels don't anneal and a little discoloration doesn't effect the tool life in tool room use. What you should worry about is not burning yourself or grinding the tips of your fingers off! Concentrate on holding the 10° angle while moving back and forth. We'll give this edge a final sharpening later; it's time for side 2.

Grinding Side 2 of the Tool

FIGURE 6--Grinding side 2.

The reason the tip angle is ground less than 90° is to allow the tool to get into corners.

FIGURE 7--Properly ground tool cutting into a corner.

Side 2 is ground the same way as side 1, moving the tool back and forth until you have a point. After you get side 2 ground, cool the tool in the cup of water.

Now I want you to learn another aspect of tool grinding. It's important to know when you have ground the surface up to the cutting edge, especially when resharpening lathe tools. Take the tool you just ground and bring it up to the wheel at a slightly different angle than you just ground for this experiment. Watch the point that touches the wheel first and you will notice that the sparks will bounce off the cutting edge only where the wheel has ground from top to bottom.

FIGURES 8A--Tip not yet ground flat and 8B, Tool ground flat all the way to the tip.

This tells you when the tool has been sharpened without taking it away to look which allows you to grind flat and true surfaces. If you sharpen a tool for a SHERLINE lathe, use a 1/4" square tool blank and keep the cutting edge up to the top of the blank; the tool will come out on center without shims. You will have to be precise grinding the third side to accomplish this.

Grinding Side 3 of the Tool

FIGURE 9--Grinding the "Hook" into side 3.

Use the skill you have developed grinding the second side now. Set the blank on the support with the 10° (side 1) up. The tool has to be brought up to the grinding wheel with a slight angle so you don't grind the tip below center. With the tool setting on the rest, move the tool in and grind until you see sparks bouncing off the cutting edge where the corner of the wheel is lined up with the back part of the 10° face. When this happens, slowly decrease the angle without pushing the tool in any more until sparks bounce all the way to the tip. Stop as soon as this happens. You may inspect it, and the surface should be entirely ground. The recommended way is to put more "hook" on the tool than I have suggested, but I have found that the slight increase in performance is offset by the problems encountered resharpening these tools.

FIGURE 10A--Normally recommended "hook" ground into tool and 10B, Simpler method suggested for SHERLINE tools.

To put the finishing touches on your tool, you have to "kiss off" sides 1 and 2 again. You must carefully line up side 1 with the wheel and bring it to the wheel in a positive manner with very little pressure; watch for the sparks on the cutting edge. What you're trying to accomplish is to make the tool set against the wheel on the same plane as when you first ground side 1. If the tool is held too rigidly, it will not align itself, too loose and it will bounce around.

"Breaking" the Point

Use the same method on side 2. The tool should be ready to use except for the point. I always put about a .010 (.2mm) "break" on the point by holding the tool with the point aimed at the wheel face. Because two angles converge at the point, the angle in relation to the sides is greater. Think about it!

FIGURE 11--Putting a .010" "Break" on the tip of the tool.

This means that if you set the tool flat on the tool rest the tool rest angle would have to be increased to get an even flat. This wouldn't be worth the effort, so the easy way is to free hand it. I always start by touching the heel of the tool first, and then change the angle until a slight flat is put on the tip. Of course, the angle you're holding it at has to be close when starting to get desired results.

FIGURE 12--Handholding the tool to "Break" the point saves resetting the angle on the tool rest.

The purpose of this flat is to improve finish and tool life. I don't recommend a large radius on the tip of tools used on small machines. These machines are not rigid enough to get the desired results from this practice and cause "chatter" problems. The finished product should be a right handed tool, have flat cutting surfaces (except for the radius caused by the wheel), have a slight flat on the tip, and a tip angle of less than 90°. Tools used on lathes such as the Sherline will do all their cutting at the tip of the tool because they don't have the horsepower for 1/4" (6mm) cuts.

I don't recommend using oil stones to improve the edges. After a few minutes use with an occasional dab of cutting oil a properly sharpened tool will hone itself in. I always believe the final sharpening to a tool should take place with the wheel cutting the cutting edge of the tool from the top of the tool to the bottom when using bench grinders.

I realize I've given a great deal of information on how to do what I call a simple operation, but these are very complex instructions to write because I'm trying to tell you how to control your hands, not a simple machine. Incidentally, the reason we call a tool a right handed tool when the cutting edge is on the left is because it is designated by which way the chip leaves the cutting tool. Cutting tools such as left or right handed tin snips are also designated in this manner because the cut-off falls to the left or right.

The left hand tools are ground the same as right, in the same order with the angles reversed.

Boring Tools

FIGURE 13--Typical Boring Tool.

Boring tools are the most difficult to grind. They should always be made as rigid as possible. Tool angles around the "tip" can be the same as any cutting tool, but clearances of the tool body have to be considered careful. A tool ground with enough clearance for a finished hole may not have enough clearance to start with when the hole has a smaller diameter. If you have to bore a hole in a part that has a lot of work in it, have a tool ready to use that's been checked out on a piece of scrap.

Form Tools

Form tools are used to create a shape the same as the tool. To grind form tools, a pattern of the finished shape should be at hand and there should be some possibility of success with what you have to work with. You can't grind a 1/8" (3mm) groove into your tool 1/4" (6mm) deep with a 1/2" (12mm) wide wheel.

FIGURES 14A--A Typical Form Tool made by a custom tool making shop and 14B, a home shop method of achieving the same finished shape in two steps with a tool that can be ground on a bench grinder.

This type of tool is usually made by Tool and Cutter specialists that have high shop rates using precision grinders, diamond dressers, and a large variety of wheels available to them.

All is not lost if we have a good pair of hands with a good mind driving them! We can use the grinding wheel corners on our $50 grinder and generate the shape half at a time on each side of the tool and still get our job done.

Form tools don't need any top relief (hook) to work. Use low spindle RPM and steady feed rates to prevent chatter. The width of a form tool should never exceed three times the smallest diameter of the finished part.

Like any skill, tool grinding is one that has to develop with time. It is also the skill that allows you to go one step beyond the average hacker.

Joe Martin, President and OwnerSHERLINE Products

High Speed Steel Tool Bits Available from SHERLINE

PART NO.. DESCRIPTION

11950 H.S. Steel Cutting Tool, Right

11960 H.S. Steel Cutting Tool, Left

11970 H.S. Steel Cutting Tool, Boring

1200* H.S. Steel Internal Threading Tool

3005 H.S. Steel 1/4" Square Tool Blank

3005B H.S. Steel Tool Blanks (5-Bulk)

3007 H.S. Steel Set (Right, Left, boring)