What to do about Poor Thread Quality

Often taps get the blame for poor thread quality or rejected threads and it is natural to look to the tap itself as the culprit. Actually, the tap is often the victim of a badly drilled hole. You can't produce a great thread out of a bad hole! Following are some issues and possible resolutions.

1. A dull drill will create a very rough torn hole. Expect poor or incomplete threads.

2. A reground drill must be perfectly concentric. The cutting lips must be of equal length and be ground to the same angles. Failure to create a concentric point will cause the drill to cut on one side more than the other and a crooked, bent hole will result making an attempt to tap that hole very difficult. This can also produce an oval egg shaped hole.

3. Castings sometimes have a tapered hole so the part will release easily. Threading requires straight walls and tapered walls are impossible to thread correctly.

4. Undersized holes are difficult or impossible to thread.

5. Holes that have had the surface work hardened by too high a temperature in the drilling process can become too hard to thread effectively.

6. Materials that shrink or close-in after drilling are undersized for tapping.

7. Holes too near welding or flame cut areas can become hardened and difficult to thread.
Bottom line, consider good hole quality as essential in producing quality holes and if you are having difficulty, dont forget to investigate the drilling process in addition to the tap.

Cnc Milling: a Versatile Process

Author: George Ure

Computer Numerical Control (CNC) Milling is a common type of automated machining process. These machines are specially used for drilling, facing, and turning functions. Their classification is based on the number of axes they have. These axes are labeled as x and y for the two horizontal directions while z is for vertical movement. CNC milling is a cutting process that is used to remove metal or plastic from a block of stock material by the rotating action of the tool. The tool is moved in three (or more) directions to get the desired cut of the material.

CNC Milling machines have been programmed with the help of a set of commands called G-codes. These codes are special CNC functions in alphanumeric format.

The cutting tool is usually rotated along the axis, which is perpendicular to the table where the material to be cut is placed. There are different cutter shapes (called milling bits) such as round (ball end), square, and angled.

Advantages of CNC Milling

A large variety of 2D and 3D shapes are possible. Complex shapes from rod, block, or sheet material can be created and is cost effective for short runs.

Specifications for CNC Milling

• Rigid materials such as metals and hard plastics are used.

• Alternative machines for 2D sheet shapes that include Laser Cut, Turret Punch and fixed punch are used.

• CNC Milling requires software program tooling or work holding jigs.

• To contain costs avoid large variations in work piece height and avoid thin walls.


The CNC Machining centers are computer controlled vertical mills which can move the spindle along the Z-axis. When the machine is used in combination with conical tools or a ball nose cutter it improves the milling precision without affecting the speed thus providing an economical substitute to flat surface job that requires hand engraving.

During the milling process pressure is applied to the material therefore it is better to avoid weak shapes, long thin shapes, or ones with thin walls. CNC milling offers a cut surface that has a visible pattern due to the rotation and movement of the cutter.

eMachineShop offers you information about a vast number of products and machines and CNC Milling machine is one of them. A unique online CMC provider allows you to design and even order custom CNC machined parts. Visit the site www.eMachineShop.com to get details about these and other services. While you’re there, don’t forget to download the company’s free 3D CAD software which makes designing CNC milled parts a snap!

Article Source: http://www.articlesbase.com/business-articles/cnc-milling-a-versatile-process-320816.html

About the Author:
George is a well known author who writes on the topics related with CNC Milling , waterjet cutting and Free CAD Software for the site www.emachineshop.com.

Technical Tips for Drills

Here are links for technical information on drills.

The links cover the following:

Speeds and Feeds for Drilling
Speeds and Feeds for Deep Hole Drilling
Feed Rate per Revolution for drills
Troubleshooting drills

For more information please visit www.toolinghouse.com for drills, taps, and carbide endmills

Types of End Mills

Flutes - Spiral cutting edge on the end mill. 2 and 4 flute end mills are the most commonly used.

• 2-Flute - Allows maximum space for chip ejection. Used for general milling operations.
• 3-Flute - Excellent for slotting. Used for general milling operations.
• 4, 5, 6, and 8 Flute - A greater number of flutes reduces chip load and can improve surface finish, if feed rate remains the same.

Ball End - Used to mill die cavities and fillets, round bottom holes and slots.

Carbide End Mills - This tool material combines increased stiffness with the ability to operate at higher SFPM. Carbide tools are best suited for shops operating newer milling machines or machines with minimal spindle wear. Rigidity is critical when using carbide tools. Carbide End Mills may require a premium price over the cobalt end mills, but they can also be run at speeds 2 1/2 faster than HSS end mills. For best results mount in a hydraulic type holder.

Coatings - The use of Titanium coated tools will increase the surface hardness of the tool to near 85 Rc. This will allow for greater tool life at increased cutting speeds & feeds (15 - 25%). Melin offers Titanium Nitride (TiN), Aluminum Titanium Nitride (AlTiN), and Titanium Carbonitride (TiCN).

Cobalt - Type of high speed steel tool which has a 8% cobalt content (M42). This material has excellent abrasion resistance for improved tool life over standard high speed steel (M7).

Corner Radius - Conventional end mill with radius ground on the tips of the flutes to help reduce chipping on the tip. For mold applications, radius tools can remove more material faster than ball ends.

Corner Rounders - Cutters having form ground radius with relieved clearance.

Double End - An end mill that has teeth on both ends of the cutter. End mill holders must have sufficient clearance to allow for the use of a double end cutter.

Drill Point - Multipurpose tool which can be used for drilling, milling, or chamfering.

High Helix - Usually a 40 to 60 degree spiral on the tool's flutes. Effective for rapid chip ejection in milling of aluminum and other materials.

HSS - A baseline tool steel. In the past, a majority of end mills were made from standard High Speed Steel (M7). Usually inexpensive, but do not offer the tool life or speed and feed advantages of Cobalt and Carbide end mills.

Left-Hand Spiral - Used for milling multiple layers of thin sheets where chip flow is directed away from work.

Rougher (Hoggers) - End mill with interrupted shape on outside diameter to remove large amounts of material quickly. Typically can remove material up to three times the rate of conventional end mills with different types available to achieve the desired finish on the material. Melin offers roughers in Coarse Pitch, Fine Pitch, Rougher/Finisher, and 3-Flute for Aluminum styles.

Single End - Teeth on one end of the cutter only. This style is the most common available.

Stub Length - Used for milling of shallow slots in all types of materials where heavy feeds are required and tool deflection is minimized.

Drilling Tips

Drilling Tips

Smaller diameter holes

• High speed twist drills
• Peck drill suggested

Larger diameter holes

• Drill pilot hole
• Use slow speed spiral drills or inserted drills

Taps - Dealing with Poor Thread Quality

Video - Introduction to Threading Basics

Often taps get the blame for poor thread quality or rejected threads and it is natural to look to the tap itself as the culprit. Actually, the tap is often the victim of a badly drilled hole. You can't produce a great thread out of a bad hole! Following are some issues and possible resolutions.

1. A dull drill will create a very rough torn hole. Expect poor or incomplete threads.

2. A reground drill must be perfectly concentric. The cutting lips must be of equal length and be ground to the same angles. Failure to create a concentric point will cause the drill to cut on one side more than the other and a crooked, bent hole will result making an attempt to tap that hole very difficult. This can also produce an oval egg shaped hole.

3. Castings sometimes have a tapered hole so the part will release easily. Threading requires straight walls and tapered walls are impossible to thread correctly.

4. Undersized holes are difficult or impossible to thread.

5. Holes that have had the surface work hardened by too high a temperature in the drilling process can become too hard to thread effectively.

6. Materials that shrink or close-in after drilling are undersized for tapping.

7. Holes too near welding or flame cut areas can become hardened and difficult to thread.
Bottom line, consider good hole quality as essential in producing quality holes and if you are having difficulty, dont forget to investigate the drilling process in addition to the tap.

MILLING; ROUGHING END MILLS, COARSE OR FINE PITCH

When should you use a coarse pitch, and when should you use a fine pitch?

Roughing end mills with sinusoidal waveform are designed to reduce side pressure and cut the chips into much smaller segments.

This reduces chatter, vibration, and deflection, allowing much higher material removal rates without increasing horsepower requirements.

Coarse pitch profiles are recommended for deep slotting and heavy side cuts in medium strength materials where heavy metal removal rates are required.

Fine pitch profiles provide a stronger edge, better tool life, and better surface finish.

These work well for shallower cuts in harder steels, and high temperature materials like inconel and hastalloy.

Drilling

Machinists have the choice of four basic types of drills that are made with carbide cutting edges: solid carbide drills, drills with indexable-inserts, drills with brazed carbide tips and drills with exchangeable solid-carbide tips. Each of these drills has advantages for specific applications.

Solid-carbide drills are made to be used on modern machining centers. These drills are manufactured with fine-grain carbide and titanium aluminum nitride (TiAlN) coatings to provide long tool life. As self-centering drills, they have a specially designed edges that help to control chips and chip evacuation in most workpiece materials. The self-centering geometry and fine tolerances of solid-carbide drills ensure quality holes without additional machining.

Indexable-insert drills cover a broad range of diameters with depths two times diameter to five times diameter. They may be used for rotating applications as well as in lathes.

Drills with brazed carbide tips rely on the strong connection of the brazed tips to the drill bodies. These tools use a self-centering geometry for low cutting forces and good chip control in most workpiece materials. Brazed drills produce holes with relatively high surface finish, close diameter tolerances and good positioning accuracy without additional finishing operations. These drills are available with through-the-tool coolant, and can be used in machining centers, CNC lathes or other machines that have sufficient stability and rpm.

Drills that have exchangeable solid-carbide tips incorporate a steel body with the exchangeable tips that are known as crowns. These tools offer the precision of brazed drills, and offer increased productivity at reduced operating costs. The carbide crowns used with this new generation of drilling tools are available in precise size increments and have a self-centering geometry to produce close diameter tolerances.

Drilling tolerances and machine stability

REF: www.cutting-tool.americanmachinist.com