12 第 3 章：钻床

目标

完成本单元后，您应该能够：

• 识别钻床

• 了解安全规则。

• 描述要使用的工具。

• 描述铰孔。

• 描述钻孔过程。

• 描述动力进给和手动进给攻丝过程。

• 描述修整车轮的程序。

说明

钻床或钻床主要用于在工件或零件上钻孔或扩大圆柱孔。在钻床上进行的主要操作是钻孔，但其他可能的操作包括：铰孔、锪孔、锪孔和攻丝。

学生商店使用的落地式钻床是一种非常常见的机器，在家庭和工业车间都可以找到。该款钻床由头部、工作台、立柱、底座四大总成组成。

头部包含用于驱动主轴的电机和变速机构。主轴安装在套筒内，可通过手动或自动进给上下移动。工作台安装在立柱上，用于支撑工件。根据加工需要，工作台可以在立柱上升高或降低。立柱是钻床的支柱。头部和底座固定在上面，用作桌子的导向装置。铸铁底座是整个结构的支撑构件。

安全

1.熟悉启动和停止开关的位置。2。钻床工作台应清理杂物工具和材料。 3．确保所有钻头均已磨尖且夹头处于工作状态。不应使用任何钝的钻头、破损的柄脚或套筒。 4．切勿尝试用手清除桌子上的碎屑。使用刷子或其他适当的tools.5。切勿尝试在未拔下电源线的情况下对机器进行维护。6。在机器关闭并完全停止之前，切勿将卡盘钥匙插入卡盘。7。应始终保护皮带和滑轮。如有磨损，立即向教官报告更换。 8．所有工件应在开始加工前用虎钳或夹具固定。9．如果工件在台钳或夹具中移动：       • 不要试图用手将工件固定到位。 • 请勿在机器开启时尝试拧紧虎钳或夹钳。 • 关闭电源并等待机器完全停止，然后重新拧紧虎钳或夹具。10。使用适当的速度设置和钻孔类型为要加工的材料。11。安装钻头时，应达到全深度并在夹头中居中。12。通过使用间隙块和调整进给冲程，消除钻头撞到工作台的可能性。13．始终将钻头缓慢送入工件。如果要钻的孔很深，请经常将钻头向后拉以去除刨花。14。在离开钻床任何时间之前，应关闭电源，机器应完全停止。 15．如果在钻床上观察到任何不安全的情况或移动，请立即向教员报告。16。始终保持钻床清洁整洁。

程序

钻床的成功操作需要操作者熟悉机器和所需的操作。以下是钻孔时应遵循的一些良好观察：

1. 在钻孔之前，通过绘制两条交叉线来定位孔。使用中心冲头为钻孔点打一个压痕，以帮助钻头开始钻孔。

2.根据需要选择合适的钻头。

3.选择合适尺寸的中心钻。

4.选择切削液。

5. 将工件正确固定在工作台上。

6. 为钻头选择正确的 RPM。考虑：钻头尺寸、材料和钻孔深度。

7. 使用称为啄钻的间断进给来打碎正在产生的切屑。

8. 导向孔应用于直径大于 3/8” 的孔。孔的扩大幅度不得超过 1/4”。

9、完成后清理钻床及周边区域。

*** 硬性规定和快速规定并不总是适用于钻床中执行的每项操作，因为许多因素会影响材料加工的速度和进给量。以上建议，结合所用工具的知识，将为操作者使用钻床提供一个合理的指导。

工具

麻花钻 - 麻花钻是一种用于在工件上制造圆柱形孔的尖头切削工具。它沿其长度具有螺旋槽，用于清除孔中的切屑。麻花钻是当今最常用的，但还有许多其他风格的不同用途。麻花钻由三个主要部分组成：柄部、主体和尖端。柄是钻头的一部分，固定在钻床的主轴中。钻床的动力通过刀柄传递。柄是两种样式中的一种，直的或锥形的。直柄钻头固定在摩擦卡盘中。钻头和卡盘之间的滑动通常是一个问题，尤其是对于较大的钻头。当使用直径大于 1/2” 的钻头时，通常使用锥形柄钻头。与直柄钻头相比，它们提供更大的扭矩和更少的滑动。如上所述，主体通常有两个排屑槽来清除切屑。 These flutes are not cutting edges and should not be used for side cutting as an end mill. The point of the drill bit does all of the cutting action, which produces the cut chips. The point is ground on the end of the drill bit.

     Holes produced by twist drill bits are generally oversize by as much as up to 1% of the bit’s dia. The accuracy of the hole is dependent on the following factors:size of the bit, accuracy of the bit’s point, accuracy of the chuck, accuracy and rigidity of the spindle, rigidity of the press, and rigidity of the workpiece in its setup. All holes to be drilled should be started with a centerpunch, centerdrill, or both.

Twist Drill Formats

1. Number sizes:#80 (.0135”) to #1 (.228”)

2. Letter sizes:A (.234”) to Z (.413”)

3. Fractional sizes:1/64” (.0156”) upwards by 64ths/inch

Reaming a Hole

     A reamer is a precision cutting tool designed to finish a hole to a specific dia. Since drill bits produce slightly oversized holes, reamers are used where precision tolerances are required, .001”. Reamers have little if no cutting action on their ends, so a pilot hole is required as a preoperation to reaming. Some general guidelines for using reamers are:

• Drill a pilot hole that is a bit smaller

• When starting a hole, drill it a bit undersized.

• Drive the reamer at a slow, constant speed.

1. The cutting speed for reaming should be about 1/3 of the speed used for drilling operation of the same material.

2. Before reaming, leave about .010” of material on holes up to 1/2”, and about .020” of material on larger holes.

3. Never rotate a reamer in the reverse direction.

4. Use the proper cutting fluid for the material.

5. Remove the reamer from the hole occasionally while cutting to clear chips, which can cause galling on the surface of the precision hole.

6. Never stop the machine with the reamer in the hole.

7. Clean and return the reamer to its proper storage place.

     Countersinks – Countersinking is an operation in which a cone-shaped enlargement is cut at the top of a hole to form a recess below the surface. A conical cutting tool is used to produce this chamfer. When countersinking, the cutter must be properly aligned with the existing hole, and should be rotated about 1/3 the cutting speed of the drilling operation for the hole. Countersinking is useful in removing burrs from edges of holes, as well as providing a flush fit for flat-headed fasteners.

      Counterbores – Counterboring is the process of cylindrically enlarging a hole part way along its length. A counterbore cutter is similar to a drill bit in that it has a shank and fluted body, but instead of a point, it has a smaller diameter pilot portion. The pilot fits into a pre-drilled hole, and guides the counterbore. Therefore the counterbore must be aligned with the original hole, so the pilot will follow the hole properly. Counterbores are used to accommodate studs, bolts, or socket head capscrews where a flush surface application is required.

      Tapping – A tap is a tool used to cut internal threads in a cylindrical hole. A tap is fluted like a drill, but the flutes actually perform the cutting operation. The flutes extend the length of the threaded section and also serve to remove the chips being produced. The most common taps used are:

1.  The starting or tapered tap. This tap is used to start threads. At least the first six threads of this tap are tapered before the full diameter of the thread is reached.

2.  The plug tap. This is the general use tap, and is used to cut threads after the taper tap has been used and removed. Three to five of its first threads are tapered. This is the last tap used if the hole extends all the way through the workpiece.

     Cutting fluids should always be used when tapping holes. It is also recommended

to advance the tap one full turn and the reverse it 1/4 turn to break the chip being formed.

Always use a tap handle, not pliers or a crescent wrench to turn the tap. They can damage

the tap, and the unequal torque provided can cause a thread to be cut poorly.

Drilling a Hole

1. A center drill should be used to aid with the drilling.

2. A center drill has short flutes and a thick shaft. Therefore, it is very stiff and will not wander. Since a center drill doesn’t cut as easily as a drill bit, use cutting oil.

3. The hole is ready to be cut with a drill bit now.

4. It is recommended to use a smaller pilot hole before drilling the final one if the hole is large. This increases the accuracy of the hole and allow the bits to last longer.

5. If the hole is deeper than the diameter of the hole, use cutting liquid and back off occasionally.

6. The spindle speed should be reduced as drill size is increased.

7. When drilling a through hole, make sure the bit will not drill into the table after drilling through the work.

8. Set a depth stop on the quill to reach a desired depth of the hole.

Deburring a Hole

Often times the top edge of a hole will be clean, but the bottom edge will have some burrs. To remove the burrs, run a deburring tool in the hole around the edge with medium pressure. Repeat this process until the edges are no longer sharp.

Power Feed Tapping Procedure

1. Power feed tapping is similar to hand tapping. Instead of tapping by hand, however, use the drill press to tap the workpiece.

2. Before starting the machine, change the drill press to low gear.

3. Release the quill lock and move the quill to the lowest it can go. This ensures that there is sufficient space to tap to the desired depth.

4. Turn the spindle on FORWARD and set the spindle speed to 60 RPM.

5. Feed the tap down. When the tap grabs the stock, it will automatically feed itself into the hole.

6. When the desired depth has been reached, quickly flip the spindle direction switch from forward to reverse. This will reverse the direction of the tap and remove it from the hole. Reversing the direction in one fluid motion will prevent damage to the tapped hole and the tap.

7. Turn off the machine.

8. Clean the tapped hole, tap, and power feed machine before leaving.

Hand Feed Tapping Procedure

1. Ensure correct tap size for the drilled hole. If the size is off, the tap might break in the hole.

2. Place a center finder into the chuck and align the quill over the hole.

3. Fix a tapered guide to the chuck.

4. Position the tap and apply gentle pressure with the quill while turning the tap.

5. For every quarter turn of thread cut, it is wise to back the tap up slightly.

UNIT TEST

1. What is the chief operation performed on the drill press?

2. Please lists other possible operations performed on the drill press?

3. The drill press is composed of four major, Please lists them.

4. Please name three major parts of a twist drill.

5. All holes to be drilled should be started with What?

6. Name three types of twist drill formats.

7. What is the cutting speed for reaming ?

8. Before reaming, How much of material to leave on holes up to 1/2”, and on larger holes?

9. Explain the different between countersinks and counterbores.

10. Explain the Power Feed Tapping vs. Hand Feed Tapping.

Chapter Attribution Information

This chapter was derived from the following sources.

• Drill Press derived from Mechanical Engineering Tools by the Massachusetts Institute of Technology, CC:BY-NC-SA 4.0.
• Reaming derived from Reaming with a Reamer by CORE-Materials, CC:BY-NC-ND.