8.10 Drilling
Micky R. Jennings
Drillingis the primary machining process of creating a hole by using a twist drill. The twist drill can be turned by many different machines to create holes. The drill press is a basic machine used in a machine shop to create semi precision hole positions that are square to a surface. The main design feature of the drill press is to spin tools and apply pressure perpendicular to a workpiece; these features are essential for an accurately drilled hole.
Step by step process for drilling:
- Lay out holes to be drilled on material.
- Center punch hole locations.
- Clamp part securely in drill vise.
- Do not clamp the vise to the table.
- Select a center drill with a pilot slightly larger than the chisel point, or a spot drill with the body larger than the chisel point.
- Mount the tool in a drill chuck.
- Adjust the table height or position.
- Calculate and select the spindle speed for the tool that will be used to spot the hole. The spindle speed is based on the largest diameter where the tool and the workpiece meet.
- Apply a drop of oil to the center punch mark.
- Gently bring the spotting tool down to the center punched mark on the part with the right hand, while precisely positioning the vise with the left hand. Leaving the vise unclamped will allow the vise to float on the table and more precisely align with the center punch mark.
- If using a center drill, drill down to where the countersink just starts to enter the work. Be careful with the pilot; it is somewhat delicate and can be easily broken off in the part. If using a spot drill, drill down to where the diameter the tip of the spot drill makes is slightly larger than the chisel point of the drill.
- A general rule for drill press operations is to clamp work to the table or use a vise rotation stop if the cutting tool is over 1/2 inch. Above 1/2 inch, the tool’s grip on the part can become stronger than the operator’s grip on the vise. Use the spotting tool to align the vise and part during the clamping process if necessary.
- Calculate the spindle speed for the drilled hole required for the part.
- Mount the appropriate twist drill in the drill chuck.
- Add a drop of oil to the marked spot.
- Turn on the spindle and advance the twist drill into the marked spot.
- Push with light force to initiate the cut. Increase the force until a curling chip is formed by the cutting edge.
- Chattering may occur until the entire tool tip is in the formed hole and the bit becomes stabilized by the margins.
- Continue cutting with moderate pressure.
- Occasionally break the chips by backing the drill quickly out of the hole as they reach 3-6 inches in length, or if the chips quit coming out of the flutes.
- Ease up on the pressure as the tool begins to break through the backside of the part.
- Examine the drilled hole.
Step 1: Lay out holes to be drilled on material.
Step 1: Lay out holes to be drilled on material.
Step 1: Lay out holes to be drilled on material.
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