What Is a Drill Bushing?

Drill sleeves and fixed drill sleeves are mainly used to determine the axial position of fixed-size tools such as drills, reamers, reamers, etc. The structure and size of drill sleeves have been standardized. According to the use characteristics, the drill sleeve has four types: fixed drill sleeve, replaceable drill sleeve, quick-change drill sleeve and special drill sleeve. And the "interference fit" is used to insert the drill sleeve into the drill template.

Drill sleeve

Drill sleeve: The drill sleeve is installed on the drill template or clamp, and its role is to determine the position of the hole to be processed on the workpiece, guide the tool for processing, and improve the rigidity of the tool during processing and prevent vibration during processing. According to its structure and usage, it can be divided into the following four types.

Drill sleeves can be divided into the following types:

Drill sleeve is divided into

Inner hole of drill sleeve

The basic size of the diameter of the inner hole (also called the guide hole) of the drill sleeve should be the maximum limit size of the tool used, and the clearance fit of the base shaft should be adopted. When drilling or reaming, the tolerance is F7 or F8, G7 for thick hinges and G6 for fine hinges. If the drill sleeve guides the guide post part of the tool, it can be selected according to the corresponding fit of the base hole system, such as H7 / f7, H7 / g6 or H6 / g5.

Guide length H

The guide length H of the drill sleeve has a great influence on the guiding effect of the tool. When H is large, the tool is not easy to deflect in the drill sleeve, but it will accelerate the wear of the tool and the drill sleeve. not good. Generally, the ratio of the guide length H to its aperture is: H / d = 1 ~ 2.5. When the machining accuracy is required or the hole diameter is small, the H / d value can be larger due to the poor rigidity of the drill used. For example, if the drilling diameter d <5mm, H / d2.5; When the distance tolerance of the hole is ± 0.05mm, H / d = 2.5 ~ 3.5 can be adopted.

Chip clearance h

As shown in Figure 7-61, the chip clearance h refers to the space between the bottom of the drill sleeve and the surface of the workpiece. If h is too small, the chip discharge is difficult, the machining surface may be damaged, and the drill may even be broken. If h is too large, the deviation of the drill bit will increase, which will affect the position accuracy of the machined hole. When machining cast iron parts in general, h = (0.3 ~ 0.7) d; when machining steel parts, h = (0.7 ~ 1.5) d; where d is the diameter of the drill used. For holes with high position accuracy requirements or when drilling holes on inclined surfaces, the value of h can be made as small as possible, or even zero.

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