Benchwork IV –Hand Taps and Hand Reamers

On a blueprint you may find the following thread designations:

You may then choose to tap the hole by machine or by hand, depending on the availability of taps and the workpiece contours.

Taps are used to cut internal threads in holes Taps are used to cut internal threads in holes. The active cutting part of the tap is the chamfer.

Taps are available with two, three or four flutes which provides space for chips to accumulate and allows cutting fluid to flow to where the cutting takes place.

A set of standard hand taps (1/4ӯ+) consists of three taps: taper, plug and bottoming

The taper tap has the first 8-10 threads ground at an angle The taper tap has the first 8-10 threads ground at an angle. The taper begins with the tap drill diameter at the point end. It extends until the full outside diameter is reached. These angled threads do the rough cutting. Due to the angled teeth less force is required and it is easier to align this tap.

The plug tap has the first 3-5 threads tapered and may be used for tapping through a part or for tapping a specific distance. You could tap a blind hole, provided the threads did not need to be cut to the bottom.

The bottoming tap is backed off or tapered at the point end from 1-1 ½ threads and is ideal for cutting threads to the bottom of a blind hole. Extra care must be taken to ensure the tap doesn’t jam at the bottom of the hole. Since so much force is applied on the first few teeth it is important to use a complete set of taps.

Machine screw taps cut threaded holes smaller than ¼”Ø Machine screw taps cut threaded holes smaller than ¼”Ø. For example, a designation of 10-32 means that the outside diameter (OD) of a machine screw tap is equal to the number of the tap (#10) times .013 plus .060 (10 x .013) + .060 = .190

Serial set taps are used when deep thread must be cut by hand in tough materials. Taps that cut deep threads have a different design. The third tap is the only tap that cuts to the full diameter.

The final type of tap generally cut by hand is the taper pipe tap The final type of tap generally cut by hand is the taper pipe tap. It is used to tap holes with a taper of ¾ in. per foot.

Parts cut with a tapered pipe thread may be drawn together to produce a rigid joint. When a pipe compound seal is used on threads, the line is made gas or liquid proof. Dry seal pipe threads can also be cut to ensure a pressure-tight seal.

Wrenches:

Dies are used to cut external threads on round metal bars Dies are used to cut external threads on round metal bars. Split dies have a set screw on the side which can be used to expand the die to allow easier cutting on the first pass.

Solid dies are used to cut damaged threads (chasing) and some shops have screw plate dies, which are best for cutting harder materials.

A Die Stock is generally used to hold a die when cutting external threads.

Reaming is the operation of finishing a drilled hole Reaming is the operation of finishing a drilled hole. A finished hole has the specified diameter size, is perfectly round, the diameter is the same from end to end and it has a smoothly finished surface. A drilled hole is seldom accurate enough in size or sufficiently smooth to be called a precision hole.

The cutting on many hand reamers is done along a tapered starting end The cutting on many hand reamers is done along a tapered starting end. The amount of material removed in hand reaming ranges from .001 to .003 and occasionally .005 in soft materials.

Types of hand reamers: Solid or fixed Adjustable Expansion Taper Socket Taper Pin

Solid or fixed

Adjustable

Expansion hand reamer

Taper Socket

Taper Pin

Using the chart in the Machinery Handbook will help you determine the step drill diameters and their depths.

Example question: List the drill diameters and depths to use before reaming for a #9 taper .4688 at 6 inches .508 at 4 inches .548 at 2 inches Top drill diameter not necessary as it is the diameter at the top of the hole that the reamer will cut, which is .591