Turning and Boring / A specialized treatise for machinists, students in the industrial and engineering schools, and apprentices, on turning and boring methods, including modern practice with engine lathes, turret lathes, vertical and horizontal boring machines

by Franklin Day Jones

Grinding a Lathe Tool.—The way a turning tool is held while the top surface is being ground is shown to the left in [Fig. 14]. By inclining the tool with the wheel face, it will be seen that both the back and side slopes may be ground at the same time. When grinding the flank of the tool it should be held on the tool-rest of the emery wheel or grindstone, as shown by the view to the right. In order to form a curved cutting edge, the tool is turned about the face of the stone while it is being ground. This rotary movement can be effected by supporting the inner end of the tool with one hand while the shank is moved to and fro with the other.

Often a tool which has been ground properly in the first place is greatly misshapen after it has been sharpened a few times. This is usually the result of attempts on the part of the workman to re-sharpen it hurriedly; for example, it is easier to secure a sharp edge on the turning tool shown to the left in [Fig. 12], by grinding the flank as indicated by the dotted line, than by grinding the entire flank. The clearance is, however, reduced and the lip angle changed.

There is great danger when grinding a tool of burning it or drawing the temper from the fine cutting edge, and, aside from the actual shape of the cutting end, this is the most important point in connection with tool grinding. If a tool is pressed hard against an emery or other abrasive wheel, even though the latter has a copious supply of water, the temper will sometimes be drawn. When grinding a flat surface, to avoid burning, the tool should frequently be withdrawn from the stone so that the cooling water (a copious supply of which should be provided) can reach the surface being ground. A moderate pressure should also be applied, as it is better to spend an extra minute or two in grinding than to ruin the tool by burning, in an attempt to sharpen it quickly. Of course, what has been said about burning applies more particularly to carbon steel, but even self-hardening steels are not improved by being over-heated at the stone. In some shops, tools are ground to the theoretically correct shape in special machines instead of by hand. The sharpened tools are then kept in the tool-room and are given out as they are needed.

Cutting Speeds and Feeds.—The term cutting speed as applied to turning operations is the speed in feet per minute of the surface being turned, or, practically speaking, it is equivalent to the length of a chip, in feet, which would be turned in one minute. The term cutting speed should not be confused with revolutions per minute, because the cutting speed depends not only upon the speed of the work but also upon its diameter. The feed of a tool is the amount it moves across the surface being turned for each revolution; that is, when turning a cylindrical piece, the feed is the amount that the tool moves sidewise for each revolution of the work. Evidently the time required for turning is governed largely by the cutting speed, the feed, and the depth of the cut; therefore, these elements should be carefully considered.

Cutting Speeds and Feeds for Turning Tools[1]

Steel—Standard 7/8-inch Tool								Cast Iron—Standard 7/8-inch Tool
Depth of Cut in Inches	Feed in Inches	Speed in Feet per Minute for a Tool which is to last 11/2Hour before Re-grinding						Depth of Cut in Inches	Feed in Inches	Speed in Feet per Minute for a Tool which is to last 11/2Hour before Re-grinding
		Soft Steel		Medium Steel		Hard Steel				Soft Cast Iron		Medium Cast Iron		Hard Cast Iron
3/32	1/64	476		238		108		3/32	1/16	122		61	.2	35	.7
	1/32	325		162		73	.8		1/8	86	.4	43	.2	25	.2
	1/16	222		111		50	.4		3/16	70	.1	35	.1	20	.5
	3/32	177		88	.4	40	.2	1/8	1/32	156		77	.8	45	.4
1/8	1/64	420		210		95	.5		1/16	112		56	.2	32	.8
	1/32	286		143		65	.0		1/8	79	.3	39	.7	23	.2
	1/16	195		97	.6	44	.4		3/16	64	.3	32	.2	18	.8
	1/8	133		66	.4	30	.2	3/16	1/32	137		68	.6	40	.1
3/16	1/64	352		176		80	.0		1/16	99	.4	49	.7	29	.0
	1/32	240		120		54	.5		1/8	70	.1	35	.0	20	.5
	1/16	164		82		37	.3		3/16	56	.8	28	.4	16	.6
	1/8	112		56		25	.5	1/4	1/32	126		62	.9	36	.7
1/4	1/64	312		156		70	.9		1/16	90	.8	45	.4	26	.5
	1/32	213		107		48	.4		1/8	64	.1	32	.0	18	.7
	1/16	145		72	.6	33	.0		3/16	52		26	.0	15	.2
	3/32	116		58	.1	26	.4	3/8	1/32	111		55	.4	32	.3
3/8	1/64	264		132		60	.0		1/16	80		40	.0	23	.4
	1/32	180		90	.2	41	.0		1/8	56	.4	28	.2	16	.5
	1/16	122		61	.1	27	.8	1/2	1/32	104		52	.1	30	.4
1/2	1/64	237		118		53	.8		1/16	75	.2	37	.6	22	.0
	1/32	162		80	.8	36	.7		1/8	43	.1	21	.6	12	.6
Steel—Standard 5/8-inch Tool								Cast Iron—Standard 5/8-inch Tool
Depth of Cut	Feed	Soft Steel		Medium Steel		Hard Steel		Depth of Cut	Feed	Soft Cast Iron		Medium Cast Iron		Hard Cast Iron
1/16	1/64	548		274		125		3/32	1/32	160		80	.0	46	.6
	1/32	358		179		81	.6		1/16	110		55	.0	32	.2
	1/16	235		117		53	.3		1/8	75	.4	37	.7	22	.0
3/32	1/64	467		234		106		1/8	1/32	148		74	.0	43	.3
	1/32	306		153		69	.5		1/16	104		51	.8	32	.0
	1/16	200		100		45	.5		1/8	69	.6	34	.8	20	.3
	3/32	156		78		35	.5	3/16	1/64	183		91	.6	68	.0
1/8	1/64	417		209		94	.8		1/32	135		67	.5	39	.4
	1/32	273		136		62	.0		1/16	94		47	.0	27	.4
	1/16	179		89	.3	40	.6		1/8	64	.3	32	.2	18	.8
	3/32	140		69	.8	31	.7	1/4	1/64	171		85	.7	50	.1
3/16	1/64	362		181		82	.2		1/32	126		63	.2	36	.9
	1/32	236		118		53	.8		1/16	87	.8	43	.9	25	.6
	1/16	155		77	.4	35	.2		3/32	70	.4	35	.2	20	.6
1/4	1/64	328		164		74	.5	3/8	1/64	156		77	.8	45	.4
	1/32	215		107		48	.8		1/32	116		57	.8	33	.8
3/8	1/64	286		143		65	.0		1/16	79	.7	39	.9	23	.3

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