In down (climb) milling, what is true of the chip?

Chip is thickest at the start of the cut and zero at the end

Chip is zero at the start and maximum at the end

Cutter rotates opposite to the feed

Why is up milling preferred for scaly cast surfaces?

The cutter starts with zero chip thickness and does not strike the hard scale suddenly; backlash is not a problem

It presses the work on the table

It gives the best surface finish

What distinguishes a shaper from a planer?

In a shaper the tool reciprocates and work is small; in a planer the work moves and is large

In a shaper the work moves and is large

A shaper has several heads and a planer one tool

What is the drilling time for a 40 mm plate and 20 mm drill?

0.51 min, using L = 40 + 0.3 x 20 = 46 mm

0.44 min, ignoring the drill point

Practice · 4+2 marks

Milling, shaper and drilling machine operations

Short answer

Up milling: cutter opposes feed, chip starts thin, rougher finish; down milling: cutter moves with feed, chip starts thick, better finish, needs backlash eliminator. Shaper: reciprocating ram with quick-return; planer: work reciprocates. Drilling time for 20 mm hole: L = 40 + 0.3×20 = 46 mm, T = 46/(0.15×600) = 0.51 min.

(a) Differentiate between up milling and down milling. Write the working principle of a shaper and compare it with a planer. (b) Calculate the machining time to drill a through hole of 20 mm diameter in a 40 mm thick plate with a feed of 0.15 mm/rev at 600 rpm, taking the drill point allowance as 0.3 D.

(a) Milling, shaper

Milling removes metal with a rotating multi-tooth cutter while the work is fed against it.

Point	Up (conventional) milling	Down (climb) milling
Cutter rotation vs feed	Opposite to feed direction	Same as feed direction
Chip thickness	Zero at start, maximum at end	Maximum at start, zero at end
Cutting force	Tends to lift the work	Presses the work on the table
Surface finish	Poorer; rubbing at start	Better
Backlash	Not a problem	Needs backlash eliminator
Use	Rough surfaces, castings with scale	Finish cuts, thin parts

Shaper: a single-point tool is fixed on a reciprocating ram. The tool cuts on the forward stroke; on the return stroke it lifts (clapper box) and the table feeds the work sideways by a small amount. A quick-return mechanism (crank and slotted link) makes the return stroke faster. It is used for flat surfaces, slots and keyways.

Point	Shaper	Planer
Moving part	Tool (ram)	Work (table)
Work size	Small	Large and heavy
Tool	One	Several heads
Feed	Work moved after each stroke	Tool moved
Rigidity, cost	Lower	Higher

(b) Drilling time

Length to be travelled:

L = t + 0.3D = 40 + 0.3\times20 = 46\ \text{mm}

T = \frac{L}{fN} = \frac{46}{0.15\times600} = 0.511\ \text{min} \approx 30.7\ \text{s}

Answer: drilling time $= 0.51$ min.

✓ Answer checked by Claude Opus 5.5 (high effort)

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