BORING CHARACTERISTICS

The chip evacuation is a permanent concern of the operator during tapping.
The boring form on the tap is one of the most important parameters to consider when choosing the tool type. The boring types are classified in 4 families, each one having its own difficulties :.

• GROUPE I : EMERGING HOLE

• a/ Not very deep emerging hole : the thickness of the material is lower than the tapping diameter (common case in sheet metal manufacture), it does not have a concern with the chip disposal, the only potential problems are lost centers in the case of manual tapping (tapping is not coaxial with boring) and "over-sizing" in semi-automatic tapping (sensitive drill press with manual descent or tapping arm); thrust is too strong and the tap deforms the obtained thread while cutting on its front edge.

• b/ Deep emerging hole : The thickness to be tapped is higher than the diameter, the chip disposal can pose a problem in case of horizo,tal tapping in materials with long chips, the use of an GUN lead then becomes imperative.
• GROUPE II : ONE-EYED HOLE

• a/ Not very deep one-eyed hole : few problems except in the case of small diameter and materials with very long chips, in which the use of taps with helical grooves is necessary.

• b/ Deep one-eyed hole : this is the most delicate case; helical grooves are almost imperative, lubrification must be looked after particularly, in certain cases is necessary to subdivide and "strp" the operation.

Material operating conditions :
The tapping operation can be simply manual, case in which the main difficulty is to ensure the coaxiality between boring and tapping; the cutting speed is very low by nature, the chip formation is always optimal but the evacuation does not really pose any problem : a standard tap will adapt to most the cases.

The operation can also be semi-automatic with an electro-portable machine, a sensitive drill press provided with a tapping device or a tapping arm : the number of revolutions must be adjusted depending on the material, it is possible to benefit from specialized geometries. On a sensitive drill press with manual descent, it is necessary to warm the user over the risks of "oversizing".

Finally, tapping can be carried out on an automatic machine (mechanical or with numerical control); in addition to the choice of geometry adapted to the material and the shape of the hole, it is necessary to draw the user's attention to monitoring the sprinkling device which must ensure a triple role of lubrification, cooling and assisting on the chip disposal. It should be noted that in this case, the DIN standard is generally imposed for the tools.

Note:
More than the diameter ratio or a small tap, the chip evacuation is more critical problem : a M2X040 (ratio of 5) is much more delicate from this point of view than a M36X400 (ratio of 9), likewise, with the same diameter a fine pitch is easier than the same one with a large pitch : a M10X150 (ratio of 6.7) compared to a M10X050 (ratio of 20). This implies that one can work easier in a hole with a large diameter tap with right grooves, whereas this is almost impossible with a tap of small diameter.

Standards:
The European tap market is covered by 2 series of different standards :
The Iso standards are mostly used in France, Great-Britain and the Scandinavian countries, while the DIN standards are used in Gremany, Italy, etc...
These standards only define the outline dimensions and the tools attachment (diameter and tail lenght, driving square) and have nothing to do with the carried-out pitching. CNC machines generally use tools that folllow the DIN standards assuming a "precision grip" which prohibits any change; the manual uses or on devices with standard taps (rubber grips) are not affected by these problems and can accept both standards with no concern.
Each standards family is divided into numbered families : ISO529, ISO2283, DIN371, DIN374, Din5156 etc...

Tolerances :
One cannot speak about mechanics without speaking about tolerances and quantifying tolerances is an integral part of any manufacturing process.
Naturally, each standards family created is numbered Classes 1, 2, 3 for ISO and 4H, 6H and 6G for DIN.
Schematically, these 3 classes correspond to "standardized adjustments" between screw and nuts : "tight" for 4H or classe 1, "normal" for 6H or classe 2 and "gross" for 6G or classe 3.
The American UN dimensions are noted differently : "classe 1" in ISO and "3B" in DIN for tight adjustment, "classe 2" in ISO and "2B" in DIN for normal adjustment and "classe 3" in ISO and "1B" in DIN for gross adjustment.