TAKAMAZRYU-GI

Our special conical round hole bushings are effective in solving the problemsof chatter and poor chip discharge during deep hole drilling.

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Efficacy of Special Conical Round Hole Bushingsin Deep Hole Drilling
Addressing Chatter and Chip Discharge
Failures that Occur During Deep HoleDrilling

Machining load

Load point(cutting point)

Deflection
Support point(Figure 1)

D = Shank diameter

One of the most important factors in ID cutting is that theshank diameter of the applicable ID holder (hereafter referred toas the “holder”) should be made as large as possible considering
the machining diameter and shape.
The reason for this is that the larger the overhang ratio,
which is obtained as “holder overhang (hereafter L)/shankdiameter (hereafter D)”, the lower the static rigidity of theholder and the greater the deflection of the shank due to the
cutting load, which may cause chatter. (Figure 1)

Cutting with conical round hole bushings
If chips are not discharged out of the hole, various problems
will occur. In some cases, this can be solved by enlarging thedischarge path for chips by, for example, increasing the overhangor reducing the shank size, but in most cases, the overhang ratio
is increased and the static rigidity decreased, causing chatterand worsening the problem. This most commonly happens when “L/D >5”.
A solution to this problem is to use a conical round holebushing. (Figure 3)
WideSpecial conical round hole bushing(Figure 3)

Features of conical round hole bushings

L = Overhang

Chatter has various causes, but if we focus on overhang ratio,
chatter tends to occur when the shank exceeds “L/D = 3” forsteel and “L/D = 5” for cemented carbide.
For this reason, in most cases where deep hole drilling exceeds“L/D = 3” the holder is mounted at the machining depth + α(where α = about 5 to 10 mm) to minimize the overhang.
This means that when a standard round hole bushing is used, thegap between the workpiece and the holder is too small to allow anadequate chip discharge path, and depending on the form and sizeof the chips, they may not be discharged. (Figure 2)
Narrow

1. The length of the bushing is extended while maintaining its
rigidity by making the end of the bushing into a cone, thereby
securing the chip discharge path.
2. The overhang of the holder can be minimized because the holder
can be mounted with approximately the same length as the cutting
depth.
3. By providing a coolant path on the inner surface of the bushingand using it in combination with a U-drill turret holder and an
ordinary holder, coolant supply comparable to that when using aninternally lubricated holder can be achieved with higher rigidity.
Usage in combination with a coolant pump with a supply capacity ofl.5 MPa or higher is effective in also preventing chips fromwrapping around the shank.
4. For through holes, a rear coolant unit (through-spindle coolantunit) can be used in combination for better results.
5. Effective for deep hole drilling at “L/D = 3” and higher.
WideNarrow

Standard type round hole bushing(Figure 2)
Standard type round hole bushingSpecial conical round hole bushing(Figure 4)

CautionThis product is not effective for all ID cutting.
Since the form of chips varies depending on theworkpiece material and cutting conditions (includinginserts), the effects may not be seen in some cases.

Figure 4 shows a comparison of the chip discharge ranges withthe same overhang. It can be seen that the conical round holebushing provides a larger discharge zone even with the sameoverhang.
The special conical round hole bushing has been well received
by many customers as a means of solving the problems with chips
and chatter in deep hole drilling because it can improve chipdischarge while maintaining rigidity.