TAKAMAZRYU-GI
vol.17

Are you having problems with deep hole boring? There is a groundbreaking tool,the "Hydro-bush for Lathe Holders" that can solve the hole boring problems
you have been having up to now.

Hydro-bush for Lathe Holders

The Evolution of Deep Hole Boring
The Occurrence of Waviness and the Its Causes

Solving the Gaps Problem

In deep hole boring using a boring bar, there are cases
where turning is abandoned completely, or cutting have tobe performed at lower rpm speed due to the generation ofwaviness, reduced tool life, or cutting chips and others.
The generation of waviness in particular may be tied tomechanical rigidity, or machine performance may also besuspected.However, the main reasons for the generationof waviness are the rigidity of the workpiece itself,chucking rigidity, tool rigidity, tool grip rigidity,
and others. The gripping rigidity of the tool is ofparticular significance in machining with boring bar
with long projection.The "Bushing method", a boring bar
fixing method where a bushing prepared on a per-sizebasis is inserted into the turret holder and then fixedwith two bolts after inserting the bar into the bushing,is mainstream, and not limited to TAKAMAZ. It has been
adopted for such reasons as easy modification of freeprojection, ease of use, and low cost of mounting.

To solve this problem, we have fabricated a hydro-bushing forlathe holders using the hydro-fixing method used in machining
center holders. Using this product makes gap-free fixing
possible by expanding the elastic film into a cylinder relative
to the turret holder inner diameter and the tool outer diameter,
and making it uniform. (See Fig. 2)

Boring Gap Problems
However, the fact of being able to insert the bushingand boring bar into the holder shows that a clearance
exists, resulting in tolerance ranges of outer diameter+0.013~0mm and inner diameter 0~-0.013mm in the H6
tolerances for φ20, generating a maximum clearance of
0.026mm. This exists between the bushing outer contour
and the turret holder inner diameter, as well as between
the bar outer diameter and the bushing inner diameter;
meaning that a maximum clearance of 0.052mm is generated.
In fact, because machining is performed in pursuit of
the tolerance median, this mostly does not result in
leading-edge values, and gaps will surely occur. Even
if the bar is securely fixed with bolts, it is still
fixed only in the vertical directions, and gaps will
occur in the horizontal directions. (See Fig. 1)

Figure 2

In addition, bolt fixing the hydro-bushing at the end of theturret holder makes it possible to realize 2-surface binding,affixed as one unit, as well as making shapes possible. (See Fig. 3)
As a result of testing, it was confirmed that the dramaticincrease in tool gripping rigidity increased spindle speed andeliminating waviness that blur patterns on continuously-machinedparts were eliminated,and that tool life increased.Beyond these,
it is also thought that the wider selection range of cutting
conditions and chip breakers can also contribute to improved
cutting process.
However, during application of this method, it will be necessary
to fabricate round shank tools without flat surfaces, as well as
the special fabrication of the hydro-bushing, dedicated turretholder, and all parts.
The effects such as:• Shortened cycle times through increased speeds• Improvement on the freedom of tip and cutting condition selection• Stable machining due to increased tool life, etc.,
can be obtained, making it possible to realize higher-efficiency
machining.

Figure 1
Figure 3

Bolt Fixing