Sandvik Coromant Threading - Manual (Page 24)

24
2-3 x dm
m
5 x dm
m
5-7 x dm
m
2. Applications – Thread turning
Boring bar type Max. overhang
Steel
Steel dampened
Carbide
Internal thread turning
Internal threading is more demanding than external threading, due
to the increased need to evacuate chips effectively.
Chip evacuation, especially in blind holes, is helped by using left-
hand tools for right-hand threads and vice versa (pull-threading).
However, this also creates the greatest risk of insert movement.
Modifi ed fl ank infeed should always be used to generate a spiral
chip, which is easy to guide towards the entry of the bore
Boring bar selection also has a strong infl uence on the effective-
ness of internal threading. Three main bar types can be used for
internal threading, depending on the length of overhang and level of
stability required.
• Steel boring bars - maximum 2-3 x bore diameter overhang
• Steel dampened boring bars - maximum 5 x bore diameter over-
hang
• Carbide boring bars - maximum 5-7 x bore diameter overhang
Boring bar defl ection is infl uenced by the boring bar material,
diameter, overhang and cutting forces. The recommended clamping
length in a boring bar holder with a sleeve is 4 x bar diameter dm
m
.