Metal Shapers

by Kay Fisher

Shaper Tool Bits

Part 1 of 3

It is with some reluctance that I write this column. I dread controversy. Experts will disagree with what I am about to say. Let me state for the record that this is my answer to the frequently asked question (FAQ) “How do I grind tool bits for a shaper”? I do not claim this to be the correct answer, but this answer has been helpful to me.

Tool Bit Myths

  1. Shaper tools are like lathe tools.
  2. Only an expert can grind tools properly.
  3. Carbide tool bits are the best.
  4. High-speed steel tool bits can not be purchased pre-ground.
  5. It takes special equipment to grind exact angles.
  6. Speeds and feeds are very important.
  7. Blue while grinding and you draw temper.
  8. There is only one angle that you ever have to grind.

Myth 1 – Shaper tools and lathe tools

Tool bits for shapers are similar to those of a lathe. Left and right terminologies are reversed. However since lathe terminology for left and right have always been backwards (in my opinion) the terms fit the shapers use quite accurately.

There are some lathe tool bits for which we will have little use on a shaper – such as the style E the thread cutting bit. By the same token there are a few shaper styles that have little use on a lathe – such as the T-slot cutting bits.

Also the clearance angles required can be much smaller on a shaper as will be described shortly. So basically shaper tools are different than lathe tools but...

Most lathe tools can be used on a shaper with good results. The extra clearance almost never hurts in amateur applications and most shaper owners also have a lathe and many lathe tools just waiting to be used.

Myth 2 - Only an expert can grind tools properly.

Rubbish! Anyone can grind tool bits that will have proper angles for shaper (and lathe) work. In fact, many experts disagree on what exact angles are proper and many experts who can grind tools to exacting specifications fail to regrind as often as they should to maintain a keen cutting tool.

Myth 3 – Carbide tool bits are the best.

Carbide isn't for amateurs and certainly is not for shapers. Carbide tool bits are very fragile. They can be easily broken. The secret to not breaking carbide bits is to maintain constant pressure and constant temperature. On a lathe this is possible by avoiding interrupted cuts and using flood coolant. On a shaper interrupted cuts are all we do and the tool gets hot during the cutting stroke and cools during the retract stroke. In other words on a shaper the tool bit is in constant physical and thermal stress.

Carbide tipped tool bits can be used on a shaper with light cuts but in general you will be happier with high-speed steel tool bits.

Myford High-Speed Steel Tool Bits      Photo by Kay Fisher

Myth 4 – High-speed steel tool bits can not be purchased pre-ground.

They are hard to find – but they are around. One vendor I recommend is Myford in England. I wish every new lathe or shaper owner was issued a nice, new, sharp set of high-speed steel tool bits. They would probably never purchase another bit because it becomes obvious how to sharpen them and create new ones. They would also learn quickly that good high-speed steel survives much more abuse than carbide tool tips. After all, beginners will abuse both their tool bits and their machines.

Myth 5 – It takes special equipment to grind exact angles.

Fortunately for us amateur machinists this just isn’t true. Also, exact angles aren’t nearly as important as repeatable angles. Some very simple techniques can be used to create the required grinding angles on inexpensive department store grinders.

Myth 6 – Speeds and feeds are very important.

Most experts learn the importance of speeds and feeds early on in their training. Many amateur machinists are retired professionals and carry their knowledge of and respect for speeds and feeds on into their retirement. No doubt many will disagree with what I am about to say. Save the letters and hear me out.

Speed and feed charts are misleading. They make too many assumptions. For instance they assume that you are concerned with removing the maximum amount of material in the minimum amount of time. While this is the reality of trying to run a machine shop at a profit, it is not the desire of the amateur. They assume adequate or flood coolant. Many amateurs work with no coolant or simply drip on a few drops of some (perhaps not optimal) liquid. They assume a robustness and sturdiness of machine that is frequently way beyond the means of most amateurs. It is not practical to assume that a speed and feed chart for a 16-horsepower 2-ton lathe can be applied to your ½ horsepower shaper.

Each material has a set of optimal angles for tool bits at a given speed and feed. One set of angles will give the best finish, while another set of angles gives the fastest metal removal. As an amateur machinist you have no production demands and finish quality only has to be good enough to satisfy yourself.

I’m not saying you should pay no attention to speeds and feeds. But understand that things have to be scaled down to reality. Tool-bit angles that are optimal for fast removal of metal from a large machine may not be optimal for more modest equipment and less demanding production schedules. Not all experts disagree on this point. In fact, in his book “The Amateur’s Lathe”, L. H. Sparey talks about this in detail and ends with this quote: “when in doubt, reduce the speed”.

Myth 7 – Blue while grinding and lose temper.

If you have high-carbon steel and you get the edge so hot during grinding that it turns blue, then you will draw the temper and have to grind back beyond the blue. But if your tool bit is high-speed steel (HHS), then you have to get the tip red hot before you will lose temper. The rule of thumb for grinding is to hold the tool in your hand and, if it is too hot to hold, it is time to cool it off. While I don’t advocate that you never cool your tools while grinding, you should not panic if it gets a little hot and turns blue. If it turns blue and will not hold an edge, then it is probably not HHS.

Myth 8 – There is only one angle.

OK – it is not a myth – yet. But I would like to make it one.

A fellow amateur machinist for whom I have a great deal of respect, did some research and experimentation on tool angles and he came to the conclusion that 7 to 8 degrees is the answer to nearly every question. I have followed his advice and believe that indeed, for most cases, grinding every angle to 8 degrees works well.

It’s not optimal for cast iron and you must eliminate any rake for brass and bronze, but having a favorite angle can make grinding tool bits much easier. For rake, I double the 8-degree angle to 16 degrees.

Tool Bit Shapes

Everything you ever need to know about “tool bit shapes” can be fully described with four parameters:
  1. Style
  2. Rake
  3. Clearance
  4. Relief
I will digress from the standard descriptions of these parameters because I believe they have been presented in overly confusing ways in most publications.

Tool Bit Styles

Below is a drawing of the tool bit styles for carbide tipped tools defined by the American National Standard Institute. There are more tool bit styles than the ones shown below, but these are the most useful and interesting.

Tool Bit Styles defined by ANSI B212.I-1984(R1990)                      Drawing by Kay Fisher

The MSC catalog gives these descriptions for the tool styles shown above:

Style AR – Right Hand for turning to square shoulder. Used for general machining operations such as turning, boring, and chamfering.

Style AL – Left Hand for turning to square shoulder. Used for general machining operations such as turning, boring, and chamfering.

Style BR – Right Hand 15º Lead Angle for turning when no square shoulder is needed. Used for general machining operations such as turning, boring, and chamfering.

Style BL – Left Hand 15º Lead Angle for facing when no square shoulder is needed. Used for general machining operations such as turning, boring, and chamfering.

Style C – Square Nose for chamfering. A perfect general purpose tool of great utility for chamfering, facing, and turning. Tool can also be used to make special form tools.

Style D – Pointed Nose - 80º Included Angle used for undercutting and O.D. and I.D. chamfering.

Style E – Threading Tool. Standard 60º included angle for universal threading, V-Grooving, chamfering, turning, boring, and facing.

Style ER – 60º Offset Threading Tool. Tip is offset from the shank. For threading and V-Grooving to a shoulder.

Style EL – 60º Offset Threading Tool. Tip is offset from the shank. For threading and V-Grooving to a shoulder.

The styles are simply A through E. The R and L suffixes mean left and right. These descriptions are for use on a lathe. In a shaper, a right-hand tool will cut to the right whereas, in a lathe, it will cut from the right.

The drawing below shows a set of more practical styles for shapers. The round nose is the most versatile and you will end up with many versions of it exaggerating the radius in both directions. With a small radius you can cut down into grooves, with a medium radius you have the most practical shaper tool, and with a large radius you have a cutter for that classic shaper mirror finish.

Tool Bit Styles for Shapers                                                             Drawing by Kay Fisher

The Knife styles are used mainly for making vertical cuts. The reason you don’t normally make left or right cuts on the shaper is that it is much easier to reverse the direction of the cross feed than it is to rewind the table back to the other side for the next cut. So we want to cut in both directions (left and right) hence the popularity of the round nose style tool. Unlike lathe tools, on the knife tool we grind in both top and side rake. This gives the tool the ability to cut both sideways and down.

You can’t tell in the simple drawings but the corners on most tools have a small radius. This is usually applied by simply grinding to a point then honing in a small radius. If you don’t put in some radius then nature will add a rough one for you by chipping off your sharp corners.

In general, more relief and rake makes a better cut, but makes a tool that dulls sooner and is at risk of damage.

Tool Bit Rake Angles

The rake of a tool bit is the angle (or angles) ground into the top. In the case of a round nosed tool the angle cut back into the tool is called top rake. Unfortunately this same angle is also called front rake and back rake. It’s all the same. In the case of a left hand tool the angle cut sideways into the top of the tool is called side rake.

Tool Bit Rake  Drawing by Kay Fisher

But no matter what you call it, rake is rake. With no rake the tool will tend to come out of the work and ride on the surface. With too much rake the tool will tend to dig in and pull the holder, and everything it is connected to, towards the work. Although rake is necessary, it is undesirable to grind rake, because this removes metal that would become the cutting edge in future sharpenings.

Armstrong style tool holders hold the tool bits at a 14 to 20 degree angle, eliminating the need to grind top rake. This way, a tool can be re-sharpened indefinitely. Also, the same tool can be used in a conventional tool holder for brass, which cuts best with no top rake.

Rake angles for steel and aluminum should be between 14 to 16 degrees. Rake for cast iron should be 2 degrees and for brass and bronze 0 degrees. My advice is to ignore rake and always use an Armstrong style holder except for brass and cast iron.

Tool Bit Clearance Angles

Clearance is the angle ground into the side of a tool bit as shown in the drawing below. Clearance angles should be 8 degrees for all materials on a lathe to account for the fact that the tool advances into the work during the cut. For a shaper, the tool doesn’t advance during the cut, so clearance angles can be less. The cross table on the shaper is advanced only during the return stroke or on some shapers between strokes, but never during the cutting stroke - unless you set the adjustment for the cross feed pawl wrong. I’ve done that! With shapers, clearance angles of 2 degrees are satisfactory for everything.

Illustrating an 8 Degree Clearance Angle                                        Drawing by Kay Fisher

It is precisely because clearance is not so important on a shaper that you can use the round nose tool to good advantage for cutting in both directions.

Lathe tools with 8-degree clearance angles also work well on the shaper.

Tool Bit Relief Angles

Relief angles are ground on the cutting end of the tool and are actually part of the style as shown below. On some tools, there is a leading area of zero relief to improve finish. When in doubt use 8 degrees.

Relief Angles                  Drawing by Kay Fisher

Next month, in part 2, we will talk about tool posts, tool holders, and grinding repeatable angles.

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