Carbide Inserts For Screw Machines

There have been recent advances in carbide technology that allow these types of tools to run at the lower cutting speeds often encountered in screw machines. Also, there has been a greater willingness by the major carbide manufacturers to produce designs for this segment of the market. The benefits to the industry can be looked at from several different points. The most important are as follows.

1. Increased cutting speeds and higher production rates
2. Decreased down time
3. Higher quality
4. Lower overall tool costs
5. Operator safety

As in any manufacturing environment, the quantifiable advantages have to outweigh the cost and time to justify considering a switch to different tooling. This is probably even more important within the screw machine industry.

The types of cutting tools in use today have been used for years. Operators, setup personnel and designers are familiar with them and feel comfortable using them. In addition, many people in the screw machine industry have a "bad taste in their mouth" when it comes to indexable, throw-away carbide inserts. When these inserts first began to become popular in other aspects of machining in the mid-1960s, people in the screw machine industry unsuccessfully tried them. At that time, the carbide grades and pressing technology did not exist to meet their requirements. A careful examination of the potential benefits will show significant improvements.

Thanks to www.productionmachining.com for the tip 2001

Turning and Boring Troubleshooting

Difficulty	Common Cause
Melted Surface	1. Tool dull or heel rubbing 2. Insufficient side clearance 3. Feed rate too slow 4. Spindle speed too fast
Rough Finish	1. Feed too heavy 2. Incorrect clearance angles 3. Sharp point on tool (slight nose radius required) 4. Tool not mounted on center
Burrs at Edge of Cut	1. No chamfer provided at sharp corners 2. Dull tool 3. Insufficient side clearance 4. Lead angle not provided on tool (tool should ease out of cut gradually, not suddenly)
Cracking or Chipping of Corners	1. Too much positive rake on tool 2. Tool not eased into cut (tool suddenly hits work) 3. Dull tool 4. Tool mounted below center 5. Sharp point on tool (slight nose radius required)
Chatter	1. Too much nose radius on tool 2. Tool not mounted solidly 3. Material not supported properly 4. Width of cut too wide (use 2 cuts)

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.

Machine Set up for Hard Turning

The key is to maximize rigidity. You should attempt to achieve the smallest possible tool overhang, and spindle rotation should put cutting forces into the machine bed. Stop cutting if chatter occurs. Coolant (spray mist or flood) is appropriate for continuous cutting--you can achieve up to a 20% increase in tool life with high-pressure coolants. Spray mist is often used in Europe, due to the high cost of disposal (since less coolant is used in all applications), and dry machining is being investigated aggressively in Europe. For intermittent cutting, do not use coolant. Dry cutting may benefit from the application of compressed refrigerated air.

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.

Advantages of Diamond Coated Inserts

Accuracy: The diamond coating is very thin, but very hard, and tools don’t change significantly in size during their life. For instance, the radius on an endmill will change by about 10 microns (0.0004") from when new to the point that it is worn out.

Speed: Diamond tools can typically be run at two to three times the surface speed of carbide tools.

Dry cutting: Diamond tools can often convert an operation from wet to dry machining, providing a significant saving in overall machining costs.

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