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more about each step in the process!
The process of selecting the correct drill could be described as follows (in a simplified way):
1. Drill diameter
2. L/D
3. Type of drill
- Work with piece material
- Machine
- Hole accuracy
- Coolant
Type of drill
The type of drill (solid, indexable or brazed) plays an important role in the selection process.
The type of drill will determine the hole accuracy and the cost per hole.
Large
L/D
HSS
Solid
carbide
Brazed
carbide
Indexable
Large
Small
Drill diameter
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Type of drill
The type of drill (solid, indexable or brazed) plays an important role in the selection process.
The type of drill will determine the hole accuracy and the cost per hole.
Solid carbide
Large
Brazed carbide
Hole
accuracy
Indexable (2 edges)
Indexable (1 edge)
HSS
Large
Small
Drill diameter
- Click on the buttons below
Type of drill
The type of drill (solid, indexable or brazed) plays an important role in the selection process.
The type of drill will determine the hole accuracy and the cost per hole.
HSS
Indexable (1 edge)
Cast iron
Mild steel
Steel
Hardened Steel
Stainless Steel
Aluminium
= Strongly recommended
= Not recommended
= OK
= Don´t even think about it
Solid carbide
Brazed carbide
Work piece:
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Type of drill
The type of drill (solid, indexable or brazed) plays an important role in the selection process.
The type of drill will determine the hole accuracy and the cost per hole.
HSS
= Vertical
Solid carbide
= Horizontal
Brazed carbide
Machine:
Indexable (1 edge)
Bench drilling machine
Generel milling machine
Machining centre
General lathe
NC Lathe
General milling machine
Machining centre
= Strongly recomended
= Not recomended
= OK
= Don´t even think about it
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Double angle collet
Hole
diameter
(ø8)
Drill diameter
Thread (ø8)
- pitch 1,25
+ (0,05~0,1)
Finish diameter
(ø8) - (0,5~0,1)
To determine the drill diameter it is necessary to know what the hole is to be used for and the required tolerances.
For an M8 tap hole for a P1.25, the drill diameter of 6.75 should be selected. (M8 – pitch = 6.75)
When using a solid carbide drill there is little over size so increase the diameter by ＋0.05~0.1mm. (6.75 changes to 6.80~6.85mm)
If the hole is to be finished by either a reamer or fine boring then you need to leave at least 0.5~1.0mm for the finishing operation.
LD
Flute
length
2D for chips
to evacuate
1D for regrinding
Depth of hole
For exit= about 3~5 mm
Selecting the L/D (length of the flute)
The method to select the most appropriate L/D length is as shown above.
Selecting the L/D (drill type)
In most catalogs you see that most of the drills are shown as L/D=2, or L/D=3 etc. They are already designated for the depth of the hole to be drilled.
It is recommended to select the shortest drill possible. If the drill is too long then the rigidity will be reduced leading to a reduction in hole accuracy and machining efficiency.
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