“One factor that is often overlooked when trying to improve a finish application is the toolholder. If the toolholder is old, and the pocket that holds the insert is worn, the insert may move. Any movement of the insert will create chatter and result in poor surface finish,” said Mitchell.

Ear pits (preauricular pits) are often a rather subtle finding on physical exam. They are located at the superior attachment of the pinna to the face and may be unilateral or bilateral. Up to 10% of Asian infants will have pits -- they are less common among caucasians and African Americans. There is a rare association between ear pits and Brachio-Oto-Renal Syndrome so audiologic testing of these infants is recommended, but otherwise this is considered a benign finding. With an isolated pit, renal ultrasounds are not generally recommended. Screening for associated renal anomalies becomes more important when other anomalies are present, when there is a positive family history of deafness, renal pathology or auricular malformations, or when the mother has a history of gestational diabetes.

“When roughing, it is best to use a tool capable of a high feed to remove material quickly. When finishing, it is generally best to have a light depth of cut and conservative feed rate,” explained John Mitchell, general manager, Tungaloy Canada. “However, if the depth is too light, it may cause the tool to rub and not cut. A 0.020-in. depth of cut is good for finishing in manyapplications.”

“When milling a slot, the cutter should be changed rather than the chip breaker for better chip evacuation. If the setup is unstable, then the grade of insert should be changed to a tougher grade,” said Hagan.

Best insert radius for finishingcar

“When roughing, a coarse-pitch cutter can be used for better chip evacuation, and a fine pitch for finishing if the surface finish is important,” said Hagan. “A light depth of cut for finishing is good, but it must be the same or more than the radius. If not, the insert will push the material, rather than cut, resulting in poor surface quality, burred edges , and shortened insert life.”

Noseradiusand surface finish

Here is another infant with auricle malformation. The ear is hypoplastic and low set. Again, because genetic syndromes are frequently associated with abnormal ear shapes, a careful physical examination should be performed. Even in the absence of other findings, referral to a pediatric ENT specialist may be indicated, as an abnormal pinna may be an indicator of internal ear abnormalities.

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It is important to examine the stability of the setup, type of milling application, and coolant usage. These are all key factors when choosing a chip breaker.

A larger nose radius also enables a heavier cut to be made, which is necessary when you’re cutting hard-to-cut materials.

This pinna deformity, where the superior edge of the helix is folded down, is known as lop ear. Again, it is typically an isolated finding. This is another deformity that may be improved with splinting.

Best insert radius for finishingsteel

“Every material is different and choosing a chip breaker for a material is not as easy as opening a catalog,” said Tom Hagan, milling product manager for Iscar Tools Canada.

“An insert is capable of feeding only at one-half of the nose radius. Once this is exceeded, the surface produced is similar to a thread,” said Mitchell. “Therefore, use the largest radius possible to produce the best finish and not create chatter.”

The decision whether or not to use coolant is one that is often hotly debated. It usually comes down to the type of operation being performed (such as deep cavity milling), material type, and type of insert.

There is a direct relationship between the size of the insert’s nose radius and the surface finish produced. While it’s true that a smaller nose radius decreases the pressure on a tool, it also limits the feed rate that can be used.

Insertnoseradiuschart

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“An insert with a large nose radius can take more punishment,” said Hagan. “This means that tool life can be extended, particularly if you are working with difficult-to-chip materials.”

Here, the low set position of the ear (also hypoplastic) can be appreciated. If an imaginary line is drawn from the outer canthus of the eye straight back to the occiput (here the occiput is just where the edge of the blanket meets the head), a low set ear will fall completely below the line. An ear with normal set will cross or touch the same line. This infant had trisomy 18 as an underlying etiology.

Bestcarbideinsert for finishing

Technique also plays a role in achieving fine surface finishes, and creating a chip that is thick-to-thin should be the goal.

Another factor that needs to be taken into consideration is the insert material. In a light finishing pass, a cermet insert often can produce a better finish.

Chip breakers can reduce cutting pressures and produce chips that can be evacuated more easily. In materials that produce long, stringy chips, a chip breaker can help produce smaller chips that exit the cutting zone quickly and easily.

While some experts say that the same inserts can be used for both roughing and finishing, with the roughing being performed by a slightly used insert and finishing with a new one, Mitchell suggests using one tool for roughing and another for finishing.

“A lead angle will ease the insert into the material,” said Mitchell. “The lead angle starts to cut at the strongest point on the insert, unlike leading in with the nose radius. It will also help to lead out of the part. However, tool pressure is a consideration. If the part you are milling is thin-walled, flimsy, or poorly fixtured, a lead angle may have detrimental effects on the surfacefinish.”

“Roughing the part could be done with an insert with a large nose radius, large rake angle, and using a rapid feed rate. Then the finishing tool with the desired lead angle and radius could utilize a wiper flat, which flattens the part, giving a better surface finish,” said Mitchell.

Many variations in size and shape exist within the label of "normal ear", but in general, the normal ear is one is which all the structures (helix, antiehelix, tragus, antitragus, scaphoid/triangular fossa, and external auditory canal) are all present and well formed.

“If you have an insert with a 0.032-in. nose radius, you can’t perform a finishing pass where only 0.010 in. of material is left on the part,” said Hagan.

For example, when you’re using a 45-degree lead face mill, the cutting force will act downward at 45 degrees, perhaps causing the part to flex after the cutter has passed over the part. This in turn causes the back half of the cutter to recut the machined part, resulting in a negative impact on surface finish. A 90-degree cutter, however, creates cutting forces parallel to the part and willnot flex it, thereby producing a better finish.

Safety also is improved when this so-called birdnesting is eliminated because you no longer need to clear chips from around the tool and toolholder by hand.

In contrast to the previous photos, this pinna is not well-formed and is smaller than a normal ear. This is microtia, class II. Hearing evaluation is mandatory in these infants and referral to a pediatric ENT specialist is recommended. Fortunately, this infant was found to have normal hearing. Elective cosmetic repair was planned for a later date.

“Coolant in milling applications or interrupted cuts in turning applications should be avoided,” advised Mitchell. “It causes thermal cracking, shortens tool life, and will negatively affect surface finish. However, in a sticky material such as aluminum, nickel-based alloys, and low-carbon steel, coolant will prevent the material from sticking to the tool.”

Once again, the chance of a catastrophic tool failure occurring has been reduced, and long chips are no longer able to scratch the surface of the part.

Tool noseradiuschart

Choose a cutter that is smaller than the radius so you can program the cutter for a smooth transition from line to line.  This will eliminate sharp moves and a sudden dwell in the tool path.

Increasing surface feet per minute (SFM) reduces built-up edge (BUE). This will prolong tool life and reduce the chance that catastrophic tool failure will damage a finished part.

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Chatter caused by improper toolholding and fixturing, or by a machine tool that is not rigid, will create nothing but problems.

Also known as Satyr ear, Spock ear, or Vulcan ear, this deformity of the pinna is characterized by a flat helix at the superior pole, a third crus extending into the helix, and a flattened scaphoid fossa. When this deformity is severe enough to be of cosmetic concern, molding or splinting can be initiated by a plastic surgeon (within the first week of life for the best cosmetic results). As an isolated finding, cosmesis is the only concern, but the appearance will not improve with time. Exact etiology is unknown.

“Use an insert with a wiper is always my first piece of advice when surface finish requirements are important to a manufacturer,” said Hagan. “By using an insert with a wiper, you can create a smoother surface in the milling pass.”

Best insert radius for finishingmetal

“Arc-in and arc-out milling reduces impact on the insert edge because it creates an easy transition as the cutter engages the workpiece,” said Hagan. “The same applies when going into a corner.”

Best insert radius for finishingaluminum

Steel (ISO P) is a complex material and it’s only getting more complex. In a competitive market it is essential to keep progressing and find ways that can make your steel turning operations more efficient and productive.

This is the same ear as in the previous photo, viewed from the front. From this angle, the prominence of the auricle can be better seen. As an isolated finding, this ear shape does not require any further evaluation.

Also, ensure that the correct tool diameter is being used. The cutter should be engaged between two-thirds and three-fourths of its diameter.

Scrapping parts during the finishing stage is an outcome that no shop desires. A combination of proper tools and technique can keep jobs on time and on spec. But, what variables need to be considered before entering the finishing stage? To find out, CIM—Canadian Industrial Machinery asked experts John Mitchell of Tungaloy Canada and Tom Hagan of Iscar Tools Canada.

Rigid, stable workholding is also key. And, the higher the metal removal rate, the more important stable workholding becomes.