FUNDAMENTALS OF TAPPING

Designed for PRECISION PROCESS EQUIPMENT

Written by Mike Whitney and OSG Tap & Die

Use the correct style of tap for the job

1.  Hand style straight flute                                     Chips stay in flute

2.  Spiral point tap                                                   Pushes chip forward

3.  Spiral flute (old style)                                         Draws chips out

4.  Spiral flute (new style) necked or din style       Draws chips out

5.  Spiral flute for aluminum                                    Flute design draws chips out

6.  Slow spiral for hard materials                           Draws chips out

7.  Form tap                                                             No chips

   Illustration of tap Terms

Pitch Diameter Limits

Size                            4-40            Tolerance     .0958-.0991            (.0033)

2B fit GH2                  3B fit GH2

Size                            10-32           Tolerance    .1697-.1736            (.0039)

2B fit GH3                 3B fit GH2

Size                            1/4-20          Tolerance    .2175-.2224            (.0049)

2B fit GH5                 3B fit GH3

Size                            1/2-13          Tolerance    .4565-.4500            (.0065)

2B fit GH5                3B fit GH5

Size                            5/8-11          Tolerance     .5660-5732            (.0072)

                                Each H limit increases pitch diameter .0005

Example: for 1/4-20 tap using a GH5 limit the actual tap P.D. would be .220, right in the middle of the tolerance. A GH3 limit would be .219, only .0015 over low limit.

Surface Treatments

1.  Black Oxide/ Steam Oxide.    A porous surface that retains cutting fluids to help add lubricity, reducing heat and friction.

2.  Titanium Nitride (TiN).     A hard (2000 vickers) durable surface coating (5 microns) that offers high lubricity  (coef, of friction 0.4) increases tool life and also utilizes higher speeds and feeds than uncoated tools.

3.  Titanium Carbonitride (TiCN).   Harder than TiN (2,700 vickers) better for hard steels. Can also be used for aluminum and cast iron with good results.

4.  Titanium Aluminum Nitride (TiALN).    One of the hardest (2,800 vickers) with good lubricity (0.3 coef. of friction) of the standard coating. It also has the highest oxidation temperature (800 c) primarily used on carbide drills and end mills. Dry machining in the high speed applications is possible.

5.  Diamond.    The hardest of all coatings, (8,000 vickers) used in non ferrous applications, aluminum, copper, graphite, etc. There are usually two processes, pvd a lower cost coating and cvd which provides better grain structure, harder surfaces and up to four times longer tool life.

Use the right OSG tap and coating for the material and application.

                        Material                                             Coating                           

Low 1010 - High Carbon 1080, A36 Hot Roll.     S/O, TIN, TICN

     Spiral Point, High Helix, Form tap*

     Cut 50 SFM    Form 50 SFM                                                                                                        

Alloy Steels 41 - 4340, 8620, 1117 Etc.                 S/O, TiCN

       Spiral Point, High Helix, form Tap*

        Cut 25 SFM      Form 20 SFM

Tool Steels A2, D2, S7, H13 etc up to 35 HrC    S/O, TICN                          

        Spiral Point and High Helix

         Cut 25 SFM

Stainless Steels 300, 400 Series                          S/O, TiN, TICN                

      Spiral Point, High Helix, Form Tap*

        Cut 25 SFM    Form 25 SFM                                                                                               

Nickel Alloys, Titanium, Inconel, PH Series           S/O, TICN                    

        Spiral Point and Slow Spiral Flute

        35 - 45 HrC 8 - 15 SFM cut only                          *FORM TAPS USUALLY 3/8 AND UNDER          

If you don't remember anything else..........

You have to know this

RPM = (3.82 x SFM)

* SFM = 0.263 x RPM

* IPM -= RPM X IPR

* To calculate metric threads divide the pitch by 25.4  and multiply by RPM to give you IPM.

Example:  M8 x 1.25 @ 500 RPM  1.25/25.4=0.049x500=24.60

Tap Troubleshooting Tips

  1.  Use the correct style of tap for the job.

  2.  Use the largest minor diameter possible. Make sure the hole is clean,

       Do not over peck especially in stainless and nickel based materials.

       For best results use OSG cobalt and carbide drills for the best hole

       conditions.   

  3.  Make sure you are using the correct GH Limit.

  4.  Surface treatments reduce friction and help prevent galling and

        tearing.

  5.  Be aware of the correct RPM range for the material you are 

        tapping, too slow can cause as many problems as running too fast.

  6.  Chipping of spiral point taps is generally caused by RPM that is 

        too slow.

  7.  Spiral flute taps are designed to eject the chip. RPM's that are too

        slow will cause chip packing and premature breakage.

  8.  Unless specifically required, 65% or less thread height is sufficient in

        most applications. A 65% thread is only 3% stronger than a 55%

        engagement.

  9.  Excessive depth does not equal extra strength. 2x dia. is a

        sufficient safety factor.

10.  If none of the above works, Call us. 724-789-7853

 Carbide Taps for all of your tapping needs.