🌏 Blogs / Articles / News / Classifieds / Press Releases / PSA / Podcast / Poetry / Storytelling


Poetry (2)

Cutting Vibration

How To Control Vibration During Cutting During CNC Machining?Cutting vibration usually occurs in turning of slender shafts, turning of thin-walled parts, etc. Once the vibration intensifies, there will be intense vibration with an amplitude exceeding several tens of μm, usually accompanied by a large amount of noise. In the cutting process, the vibration may exceed 100μm. Although it can be processed, there will be obvious vibration scratches on the machined surface, which is not allowed on the finished surface.

Hazards Of Cutting Vibration

Vibration in metal cutting is a very harmful phenomenon.

  • 1. Affecting the surface quality of parts If vibration occurs during processing, there will be relative displacement between the tool and the workpiece, which will cause vibration marks on the machined surface, seriously affecting the surface quality and performance of the parts;
  • 2. When cutting vibration of the machine tool and tool life is reduced, the process system will continue to bear the action of dynamic alternating loads, the tool is easily worn (even chipped), the connection characteristics of the machine tool are damaged, and even the cutting process cannot be continued in severe cases;
  • 3. Noise is harmful to the health of the operator The noise generated in the vibration will also endanger the health of the operator. In order to reduce the vibration, sometimes the cutting amount has to be reduced, which reduces the production efficiency of machine tool processing.

Therefore, in order to ensure the normal operation of such machining equipment, the control of cutting chatter becomes more and more important.

The Causes Of Cutting Vibration

For the tool to vibrate when cutting the workpiece, the following three conditions must exist at the same time:

  • The first is that the rigidity of the process system including the tool is insufficient, resulting in its low natural frequency.
  • The second is that the cutting generates a sufficiently large external force,
  • The third is that the frequency of the external excitation force is the same as the natural frequency of the process system and then resonance occurs.

How To Eliminate Cutting Vibration

(1) Solutions

  • The first is to reduce the cutting force to a minimum,
  • The second is to maximize the static rigidity of the tool system or fixture and the workpiece;
  • The third is to create another vibration inside the tool holder to disrupt the vibration frequency of the externally excited cutting force, thereby eliminating tool vibration.

(2) Countermeasures

1. The first is to reduce the cutting force to a minimum

  • (1) Use a sharp blade to reduce cutting force
  • (2) When the depth of cut is constant, use a small tool nose arc radius
  • (3) For boring tools with slender shanks and turning slender shaft parts, 90-degree leading angle tools should be used
  • (4) For milling cutters with slender rods, circular blade milling cutters are the most beneficial for vibration reduction.
  • (5) The plunging method is often used when aluminum cnc milling deep cavities with slender rod end mills
  • (6) The face milling cutter adopts sparse tooth unequal distance milling cutter to reduce milling vibration
  • (7) The smaller the blade edge angle, the better

2. Improve the static rigidity of the tool holder (Static Toughness)

Use solid carbide or heavy metal toolholders to improve the static rigidity of the toolholder 3. Improve the dynamic rigidity of the tool—passive damping and vibration-isolating toolholders

3. Improve the dynamic rigidity of the tool—passive damping and vibration-isolating tool bar

Read more…

The poems discussed below—by Milton, Rossetti, and Hopkins—are just three of many classic poems that should be read and cherished by Christians today. The three selections are examples of what I call “devotional poetry.” They are taken from my new volume, The Soul in Paraphrase: A Treasury of Classic Devotional Poems (Crossway)—a collection of more than 90 poems that, when read devotionally, provide a unique way for Christians to deepen their spiritual insight and experience.

Along with the text of the poems below, I have included my commentary on them, which I hope will enhance your experience of the poems and highlight their specifically devotional aspects.

1. “When I Consider How My Light Is Spent,” John Milton (1608–1674)

When I consider how my light is spent,
Ere half my days in this dark world and wide,
And that one talent which is death to hide
Lodged with me useless, though my soul more bent
To serve therewith my Maker, and present
My true account, lest he returning chide;
“Doth God exact day-labor, light denied?”
I fondly ask. But Patience, to prevent
That murmur, soon replies, “God doth not need
Either man’s work or his own gifts; who best
Bear his mild yoke, they serve him best. His state
Is kingly. Thousands at his bidding speed
And post o’er land and ocean without rest:
They also serve who only stand and wait.”

The occasion of this sonnet is Milton’s becoming totally blind at the age of 44. An early editor coined what became the familiar title for the poem—“On His Blindness.” The poem develops two lines of thought, both encapsulated in the last line (“They also serve who only stand and wait.”). On the one hand, the poem is a statement of resignation, as the poet expresses an implied submission to the situation of standing and waiting. But the poem is also a statement of justification, as the poet finds a way to assert that “they also serve” who only stand and wait. The poet’s meditation is based on an underlying quest motif in which he searches for and finds a way to serve God acceptably. The poem is built around the implied question, What does it take to please God? The entire poem assumes that God requires service, and the key verb serve appears three times.

This poem is constructed on the classic two-part structure of the Italian sonnet. The argument in the first seven-and-a-half lines is that God requires active service in the world. This line of thought becomes an increasingly intense anxiety vision for the blind poet, who cannot perform active service. The sestet then offers an alternative type of service, placed into the mouth of a personified Patience. The alternate service consists of standing and waiting, and this has multiple meanings. It is an image of monarchy, first of all, and is offered as a picture of serving God in heaven as the angels do, in praise and worship. The last line also evokes a picture of a life of private retirement, out of the public eye, and it is helpful at this point to know that before Milton became blind he was a famous international figure in his role as international secretary to Oliver Cromwell.

The poem is a mosaic of biblical allusions. Particularly prominent are the parable of the workers in the vineyard (Matt. 20:1–16) and the parable of the talents (Matt. 25:14–30). Both parables portray God as the master who calls workers to their tasks and as the judge who rewards stewards for active service and punishes them for sloth. Also important is Jesus’s famous saying about doing the works of his Father “while it is day; night is coming, when no one can work.” The last three lines are based on angelology (the study of angels), and the contrast between active angels who fly about the world and contemplative angels who remain in God’s heavenly court.

2. “Good Friday,” Christina Rossetti (1830–1894)

Am I a stone and not a sheep
That I can stand, O Christ, beneath thy cross,
To number drop by drop Thy blood’s slow loss,
And yet not weep?

Not so those women loved
Who with exceeding grief lamented thee;
Not so fallen Peter weeping bitterly;
Not so the thief was moved;

Not so the sun and moon
Which hid their faces in a starless sky,
A horror of great darkness at broad noon—
I, only I.

Yet give not o’er,
But seek thy sheep, true Shepherd of the flock;
Greater than Moses, turn and look once more
And smite a rock.

This is a subtle poem in which the first three stanzas gradually build a tension that reaches a breaking point in the packed last stanza. The point of unity in the first three stanzas is the speaker’s self portrait of being unmoved by the spectacle of Jesus’s crucifixion. The speaker emerges as the archetypal outsider, ignominiously out of step with the sorrow that other people and even nature showed when Jesus was crucified. Even though the speaker does not respond with appropriate grief, the very pictures that the poem paints lead the reader to sorrow for the dying Christ. The imagery of the opening line—stone and sheep—are a subtle setup for the memorable last stanza.

The first three stanzas are the speaker’s self-address, but in the last stanza the poet turns in prayer to Christ. Having implicitly declared herself to be a failure in the Christian walk, the speaker asks for a rescue operation. The prayer draws upon three separate biblical reference points. The first is Jesus as the Good Shepherd who seeks and saves his lost sheep. The second is Moses, a supreme hero of the Old Testament and yet someone regarding whom Christ is declared superior in two famous New Testament passages (John 1:17 and Heb. 3:1–6). The climactic prayer—to be smitten by Christ and subdued by him—draws upon the Peter’s denial of Jesus. On that occasion, Jesus is said to have “turned and looked at Peter” (Luke 22:61), leaving Peter convicted. Further, the name Peter means rock, so (as the last line has it) Jesus can be said to have smitten Peter with his look, and additionally Moses smote the rock in the wilderness.

The devotional potential of the poem is at least two-pronged. One is to move us to the grief that we should feel when confronted with the details of Jesus’s suffering for our sins. The second lesson is that to follow Jesus requires that we repent of what is lacking in us and submit to him. As we live with this poem, it gradually emerges as a confession and plea for forgiveness.

3. “God’s Grandeur,” Gerard Manley Hopkins (1844–1889)

The world is charged with the grandeur of God.
It will flame out, like shining from shook foil;
It gathers to a greatness, like the ooze of oil
Crushed. Why do men then now not reck his rod?
Generations have trod, have trod, have trod;
And all is seared with trade; bleared, smeared with toil,
And wears man’s smudge and shares man’s smell; the soil
Is bare now, nor can foot feel, being shod.
And for all this, nature is never spent;
There lives the dearest freshness deep down things;
And though the last lights off the black West went,
Oh, morning, at the brown brink eastward, springs—
Because the Holy Ghost over the bent
World broods with warm breast and with ah! bright wings.

The subject of this sonnet is the permanent freshness that nature possesses: no matter what the human race does to exhaust nature, it remains perpetually resilient and living. The interpretive slant that Hopkins gives to this phenomenon of nature is the assertion that it declares God’s grandeur or greatness. The poem is thus a nature poem that becomes a psalm of praise, even ending with a specifically theological statement about the Holy Spirit in his role as Creator.

The poem is organized on a three-part, envelope principle. The first four lines celebrate what might be called God’s nature. The question that concludes this unit is actually a transition to the middle section, which describes the ways in which the human race does not reck or heed God’s rule. Lines 5 to 8 describe humankind’s “nature,” that is, their exploitation of nature and failing to nurture it. The last six lines then return to God’s nature, declaring that the creative power of the Holy Spirit makes nature indestructible.

As with other Hopkins’s poems, this one requires that we take the time to unpack the meanings of the individual images. Verbal effects like internal rhyme within a line and alliteration (repetition of initial sounds in words located close to each other) enliven the effect.

Read more…
Email me when there are new items in this category –

🔥Christian Music News