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.

Selecting Thread Mill Diameters

Tips for Selecting Thread Mill Diameters

When producing internal threads, selecting the right thread mill diameter insures it will operate efficiently.

Thread mills are usually offered in several cutting diameters for a given threads per inch. Smaller diameters are used for small thread sizes, such as 3/8-16 NC.

A larger tool diameter could be used for producing a 3/4-16 NF. However, the smaller thread mill could be used to produce the larger 3/4-16 as well.

Generally, for coarser pitches (coarser than 14 TPI), selecting a cutting diameter no larger than 70% of the nominal thread size to be produced is recommended.

For finer pitches, the thread mill can be as large as 75% of the nominal diameter. Although the tool has radial clearances similar to end mills, if the tool diameter is too close to the thread diameter, the tool may rub, producing more heat that could result in excessive wear.

This rubbing may also distort the thread form affecting the thread angle.

The question is, should the largest thread mill that will fit the hole be used? The answer is, not necessarily!

For the greatest efficiency, smaller mills will remove more cubic inch of metal than a larger one, resulting in greater productivity.

There will be more clearance for the tool and more space for coolant and chips.

However, to optimize the tool, it will be rotating much faster, which may exceed the capability of the machine.

Also, the thread length on the tool may be too short for the thread depth required.

On the other hand, the larger diameter thread mill will minimize deflection, particularly on coarse thread series, but is more prone to rubbing and chip congestion.

Tips for Machining Stainless Steel

Video of Teton Creek Mfg turning Stainless Steel

Here are a list of tips for machining stainless steel:

1. Use a tool that has higher thermal-conductivity
Low thermal-conductivity of stainless steels accelerates tool wear resulting from a decline in hardness of the cutting edge of an insert, this is due to heat piling up. It is better to use a tool that has higher thermal conductivity and with enough coolant.

2. Sharper cutting edge-line
It is necessary to utilize larger rake-angles and wider chip-breaker lands to reduce cutting-load pressue and prevent build-up on the edge. This will help provide better chip control to an operator.

3. Optimal cutting condition
Inappropriate machining conditions like extremely low or high speeds or low feeds can cause poor tool life due to work hardening of work pieces.

4. Choose an appropriate tools
Tools for stainless steel should have good toughness attributes, enough strength on their edge line (cutting edge) & a higher film adhesion.

Korloy offers three grades turning stainless steel:

For high speed turning of stainless steel - NC9020

For medium to low speed turning of stainless steel - PC9030

For medium to low speed milling of stainless steel - PC9530

For Korloy carbide inserts for stainless steel, please visit pgsTools.com to order online.

Hardware for Toolholders and Boring Bars

Find Spare Parts for Tool Holders and Boring Bars

Lose a screw, lock pin, or clamp for your boring bar or toolholder? Wondering what the heck a lock pin or clamp is? Use the following guide to help you sort out what you may need in replacement parts for boring bar or tool holders. Find a definition of each component below the picture.

Here is a diagram (click on image to enlarge) of a Multi-Lock Tool Holder courtesy of Dorian Tool:


INSERT
Either conventional type or chipbreaker type may be used.

LOCK PIN
A solid locking pin for permanent locating of the insert.

SHIM SCREW
Reusable shim screw locks carbide shim into toolholder.

CARBIDE SHIM
Forms a firm seat for insert. Fastened to the shank, but easily replaceable. Protects against
damage to toolholder.

CLAMP
Maximum retention clamp is made of high alloy steel, heat treated. Broad clamp nose provides
positive clamping action. Clamp is positioned to allow for maximum insert retention, with or without chipbreaker.

CLAMP SCREW
Rugged Clamp Screw provides maximum clamping strength.

CHIPBREAKER
Solid carbide, for use when chip control is needed. Available in a range of standard chipbreaker
widths.

Most toolholders and boring bars accept generic shim seats, screws, clamps, and pins. This includes tools from Valenite, Sandvik, Kennametal, and Iscar. Check your manufacturers catalog to be sure of the replacement items part number.

PCD Tipped Carbide Boring Bars

PCD Tipped Carbide Boring Bars

PCD Tipped Brazed Boring Tool. For Bore sizes smaller than 8 mm in diameter. PCD is brazed directly to a tungsten carbide shank providing a rigid boring tool capable of remarkable surface finishies and providing a high productive alternative to internal grinding.

For Bore sizes smaller than 8 mm in diameter, it is not possible to use PCD tipped cutting tool inserts. In order to put a PCD tip into the carbide insert, material must be removed. This makes the insert weak and prone to breakage when it is clamped into the boring bar.

At the same time, clamping of small inserts into small boring bars becomes progressively more difficult as the bore size reduces.Top clamps trap swarf and, in order to fit inside the bore, become too small to exert enough clamping pressure. Screw locked inserts, while leaving space for swarf, require sufficient material under the insert for the thread of the clamping screw.

These problems are overcome by using brazed tools. The PCD tip is brazed directly to a tungsten carbide shank providing a rigid boring tool capable of remarkable surface finishes and providing a highly productive alternative to internal grinding.

Valenite Carbide Inserts for Stainless Steel

VALENITE INTRODUCES NEW TURNING GRADES FOR FINISHING, SEMI-ROUGHING STAINLESS STEELS

Valenite LLC has introduced two new tooling grades—expanding its targeted and application-specific lineup that allows users to better match machining operations and workpiece materials with tooling inserts for optimum production efficiencies, quality and economies. The new cutting technologies are the ValProTM VP8515 and VP8525 MT-CVD series of inserts. Both are being developed to augment the existing VP8535 grade and provide a complete range of turning capabilities for 304 and 316 stainless steels, Inconel and heat resistant alloys. The VP8515 is for finishing operations and the VP8525 is used for general duty semi-roughing/finishing. The existing VP8535 is for heavy metal removal tasks and roughing operations.

The VP8515 grade is set for high cutting speed (>200 m/min) at typical finishing

cut depths and has broad applicability with F5, M4, M6, M8, PM2, PM5 geometries. This grade is ideal for continuous turning of austenitic and duplex stainless steels at higher speeds providing reliable and predictable performance, with extended insert service life. Inserts using VP8515 grade have a thin yellow TiN outer coating for easy visual wear identification, an Al2O3 layer for thermal protection, a fine MT-CVD TiCN coating that helps to prevent flaking and reduces flank wear. Also incorporated in the tooling is a gradient area for added surface toughness, and a hard substrate offering greater resistance to wear and plastic deformation.

The TiCN/Al2O3/TiN coating is formulated specifically for turning of stainless steels and to resist sticking, notch wear and edge build-up, for enhanced hardness when hot.

The VP8525’s performance characteristics deliver high cutting speeds (>150 m/min) with mid- to large cutting depths...inserts have M4, M6, M8, R9, PM4, PM5 geometries to cover a myriad of cutting parameters. This grade is a basic choice for general duty M-class turning—continuous or intermittent cutting of austenitic and duplex stainless steels. These tools reduce the risk of plastic deformation and, like the VP8515, provide reliable performance and extended tool life. The VP8525 grade has similar coating technologies, layering and substrate construction as the finishing grade, including the TiCN/Al2O3/TiN coating for the efficient turning of stainless steels.

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Get carbide inserts or cutting tools for stainless steel machining at www.pgstools.com. PGS sells cutting tools and carbide inserts from Korloy, Taegutec, Valenite, Iscar and generic carbide inserts online at discount prices.

CNC Turning

To produce hubs, rods, bushes, pulleys and shafts, CNC turning is utilized where the lathe generates materials after inserting the single cutter point in to the material turning. The procedure of cutting is executed through a cutting tool which is applied either parallel or at right angle to the axis, of work piece. The tool may also be fitted at an angle relative to the work piece axis for the machining angles and tapers. The work piece may be of any cross section, but the machine surface should be straight and tapered.

There are various shapes available in CNC like pointed, simple, radius with profile added with threaded surface, curve and fillet. CNC machining is more economical than the CNC milling for producing the actual form through CNC turning. The material used for CNC turning possesses various qualities like material of work piece should be firm and can be of solid plastics. For the short running procedure of the mill, arrangements or alternative machine should be kept. CNC turning reduces the cost by minimizing the design elements.

CNC turning procedure is done through applying pressure on the work piece or the weaker material to form the flexible shapes of the material. Sometimes through CNC, the cut surface is formed by applying the helical feed as it results in rotation. The cutting procedure through which the work piece is eliminated from a material block by the help of the rotation of the tool is known as CNC milling. The work piece can rotate in perpendicular or circular way to produce different shapes and sizes. The cutting tool generally rotates in the CNC milling at an axis in a perpendicular form on the podium to generate various structures.

Variety of shapes that can be formed through CNC milling is 3D or 2D and some compound structured material. CNC milling for short procedure is also very economical. It is utilized to make different parts of engine, multifaceted mechanisms, enclosures and mold and custom tooling.

Thus, is a very effective procedure to make various machine parts of various shapes which is very significant for running the machine.

Get carbide inserts or cutting tools for your cnc machines at www.pgstools.com. PGS sells cutting tools and carbide inserts from Korloy, Taegutec, Valenite, Iscar and generic carbide inserts online at discount prices.

Author: George Ure

Article Source: http://www.articlesbase.com/sales-articles/cnc-turning-488912.html