Metal Lathe Tools - Cemented Carbide
  • Angles shown are good for hobbyists; grinds for production shops should consult a specialist.

  • When both a relief and a clearance angle are outlined (e.g., Side Relief and Front Relief), this is done to facilitate easier resharpening.
    • It is analogous to Secondary Bevels on woodworking chisels.
    • Resharpening should be done when the wear land reaches 1.5 mm (1/16 inch) high.

  • Angles shown are the effective angles, not the ground angles. Effective angles are increased or decreased, based on the angle by which the tool is presented against the work. Additionally, the vertical alignment of the tool (vs. the center line of the work) can also change the effective Front Relief Angle.

  • All angles are given the nomenclature designated by the American Standards Association (ASA).
Carbide vs. HSS
Material Compressive Strength Shear Strength Max Usable Temp. *
Cemented Carbide Higher Lower 1,800 ℉
HSS Lower Higher 950 - 1,100 ℉

* Temperature at which the tool material begins to soften appreciably. For HSS, it depends on the level of cobalt in the HSS.


Tool Shape - End View

Side Clearance Angle should be 4º to 6º greater than Side Relief Angle.

In selecting the Side Relief Angle, the sharpener should :

  • carefully chose the correct angle, as a deviation of even 2º (plus or minus) will lower tool life appreciably.
  • chose the lower angle from the table below for heavy cutting
  • chose the higher angle from the table below for finish cutting.
  • decrease the angle by 2º when making high impact cuts (e.g., work with significant gaps or hard inclusions).

Special Notes :

  1. When grinding the Side Clearance Angle, the sharpener should leave the top 1.5 mm (1/16 inch) unground. This is because the rough grinding of the carbide introduces cracks and makes it more brittle. By stopping short of the top, this is minimized. Then, when grinding the Side Relief Angle, a high grit wheel should be used to make the edge smooth with minimal cracks.
  2. When grinding the Side Rake Angle, the sharpener should be sure the top surface is finished with a very high grit. The roughness of this surface affects the chip damage to the tool, and rough surfaces are more susceptible to damage than smother ones.
Material Side Rake Angle Side Relief Angle Side Clearance Angle Comments
Aluminium
10º - 20º
8º - 10º
Side Relief
+ 4º - 6º
Aluminum Bronze
6º - 12º
7º - 9º
Manganese Bronze
4º - 10º
6º - 8º
Bronze Castings
6º - 12º
7º - 9º
Cast Iron - Soft (170 Brinell)
6º - 12º
6º - 8º
Cast Iron - Medium (250 Brinell)
4º - 9º
5º - 7º
Cast Iron - Hard (400 Brinell)
0º - 5º
3º - 5º
Cast Iron - Chilled
-10º - 0º
2º - 4º
Copper
10º - 20º
7º - 9º
Monel
4º - 9º
6º - 8º
Magnesium
15º - 25º
8º - 10º
Maleable Iron
5º - 10º
5º - 7º
Plastics
10º - 25º
9º - 11º
Steel - SAE 1020
8º - 15º
6º - 8º
Steel - SAE 1040
6º - 12º
6º - 8º
Steel - SAE 1095 or 52100
4º - 8º
5º - 7º
Steel - SAE 2340
4º - 8º
5º - 7º
Steel - SAE 6150
3º - 5º
3º - 7º
Steel - Heat Treated to 350 Brinell
4º - 6º
0º - 4º

Tool Shape - Side View

Front Clearance Angle should be 4º to 6º greater than the Front Relief Angle.

The Back Rake Angle, as shown in the picture to the right, is positive.

  • 5º - 8º to simply control chip direction
  • -5º to protect the finishing point of the tool

If a combined Negative Back Rake Angle and a Back Rake Angle is used (as shown in the picture), the width of the land for the Negative Back Rake Angle is 1.5 - 2 x the feed per revolution.

Another reason to introduce a Negative Back Rake Land is to reduce the ability for introducing breaks or cracks on the intersection between the Back Rake and the Front Relief. This is sometimes called "stoning off" or "dubbing" the edge.

Special Notes :

  1. When grinding the Front Clearance Angle, the sharpener should leave the top 1.5 mm (1/16 inch) unground. This is because the rough grinding of the carbide introduces cracks and makes it more brittle. By stopping short of the top, this is minimized. Then, when grinding the Front Relief Angle, a high grit wheel should be used to make the edge smooth with minimal cracks.
  2. When grinding the Side Rake Angle, the sharpener should be sure the top surface is finished with a very high grit. The roughness of this surface affects the chip damage to the tool, and rough surfaces are more susceptible to damage than smother ones.
Use Front Relief Angle Front Clearance Angle Bake Rake Angle Negative Bake Rake Angle Comments
Aluminium
8º - 10º Front Relief
+ 4º - 6º
5º - 8º 90º angle to Front Relief Angle (can be more than 90º)
Aluminum Bronze
7º - 9º
Manganese Bronze
6º - 8º
Bronze Castings
7º - 9º
Cast Iron - Soft (170 Brinell)
6º - 8º
Cast Iron - Medium (250 Brinell)
5º - 7º
Cast Iron - Hard (400 Brinell)
3º - 5º
Cast Iron - Chilled
2º - 4º
Copper
7º - 9º
Monel
6º - 8º
Magnesium
8º - 10º
Maleable Iron
5º - 7º
Plastics
9º - 11º
Steel - SAE 1020
6º - 8º
Steel - SAE 1040
6º - 8º
Steel - SAE 1095 or 52100
5º - 7º
Steel - SAE 2340
5º - 7º
Steel - SAE 6150
5º - 7º
Steel - Heat Treated to 350 Brinell
4º - 6º

Tool Shape - Top View


The shapes on the right show finishing tools with both a Point Angle, and a Nose Radius. For roughing out, the use of a Point Angle over a Nose Radius has been shown by Leo St. Clair to increase the life of the tool by 100 to 300%, and to reduce chatter (chapter 12 of his book; see also, Notes and Comments at the end of this page).
  • Point Angle
    • For carbide, the width of the Point Angle should be :
      • Soft materials : 2 x the feed rate
      • Hard materials : 3 x the feed rate
    • The Point Angle and the Front Cutting Edge Angle should be the same.

  • Nose Radius
    • If the sharpener wishes to use a Nose Radius, the Point Angle values should be ignored.
    • For carbide, the radius of the Nose Radius should be the greater of the following two values :
      • 2 x the feed rate
      • depth of cut / 8

Increases in the Side Cutting Edge Angle will :

  • decrease chip thickness and increase chip width (retaining the same area of the chip)
  • decrease power usage
Use Side Cutting Edge (SCE) Angle Point Angle Front Cutting Edge Angle Comments
Range Recom.
Roughing Out 10º - 60º 30º 5º - 10º It is recommended that the Point and the Front Cutting Edge Angles match.
Finishing - if a square corner is required n/a n/a 5º - 10º If a square edge is not needed, a point angle (or a nose radius) can be used.


Notes & Comments
Information regarding Grindstones



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