Speeds available with the 12x36 Atlas Lathe

• Wikipedia: speeds and feeds

Some recommended cutting rates are:

Aluminum and Brass -- 400 sfm
Mild Steel -- 90 sfm

Alan uses:

Alloy Steel             -  60 sfm
CRS - cold rolled steel -  80 sfm
mild steel              - 120 sfm
Bronze                  - 150 sfm
Aluminum                - 300 sfm
Brass                   - 600 sfm

Mild steel can be hot or cold rolled (mild refers to a steel without alloying elements, and fairly low in carbon). Cold is stronger and has a lower recommended cutting speed.

Many other recommendations can be found. These recommendations are for an alloy steel cutter. Speeds for carbide should be higher.

Setting speed on the Atlas

The double pulley on the motor shaft should have the small pulley on the right (closest to the motor).

• Position A - belt on pulley to the right (on small motor pulley). Slow speed set
• Position B - belt on pulley to the left (on big motor pulley). Fast speed set

The other belt can be placed in 4 positions, which we call "4" on the left (the small spindle pulley) to "1" on the right (the large spindle pulley).

Page 45 on the Atlas lathe manual presents the following tables, for use with the standard 1725 RPM motor:

Here are the speeds with direct drive:

Motor Belt	Spindle Belt Position
Position	4	3	2	1
A	685	418	266	164
B	2072	1270	805	500

And, here are the speeds with the back gear engaged:

Motor Belt	Spindle Belt Position
Position	4	3	2	1
A	112	70	45	28
B	345	211	134	83

It is simple math to calculate the spindle speed to obtain a desired cutting speed. Given the diameter of the piece being turned (in inches) and the desired cutting speed (in SFM -- surface feet per minute), the spindle rpm is given by:

rpm = sfm * (12/pi) / d

Here is the ruby program I used to generate the following table:

• mkspeed.rb

Diameter of Work (inches)	Desired surface speed (feet per minute)
	30	40	50	60	70	80	90	100	120	150	200	300	400	500
0.062	1833	2445	3056	3667	4278	4889	---	---	---	---	---	---	---	---
0.125	917	1222	1528	1833	2139	2445	2750	3056	3667	4584	---	---	---	---
0.188	611	815	1019	1222	1426	1630	1833	2037	2445	3056	4074	---	---	---
0.250	458	611	764	917	1070	1222	1375	1528	1833	2292	3056	4584	---	---
0.375	306	407	509	611	713	815	917	1019	1222	1528	2037	3056	4074	---
0.500	229	306	382	458	535	611	688	764	917	1146	1528	2292	3056	3820
0.625	183	244	306	367	428	489	550	611	733	917	1222	1833	2445	3056
0.750	153	204	255	306	357	407	458	509	611	764	1019	1528	2037	2546
1.000	115	153	191	229	267	306	344	382	458	573	764	1146	1528	1910
1.250	92	122	153	183	214	244	275	306	367	458	611	917	1222	1528
1.500	76	102	127	153	178	204	229	255	306	382	509	764	1019	1273
1.750	65	87	109	131	153	175	196	218	262	327	437	655	873	1091
2.000	57	76	95	115	134	153	172	191	229	286	382	573	764	955
2.500	46	61	76	92	107	122	138	153	183	229	306	458	611	764
3.000	38	51	64	76	89	102	115	127	153	191	255	382	509	637
3.500	33	44	55	65	76	87	98	109	131	164	218	327	437	546
4.000	29	38	48	57	67	76	86	95	115	143	191	286	382	477
5.000	23	31	38	46	53	61	69	76	92	115	153	229	306	382
6.000	19	25	32	38	45	51	57	64	76	95	127	191	255	318
7.000	16	22	27	33	38	44	49	55	65	82	109	164	218	273
8.000	14	19	24	29	33	38	43	48	57	72	95	143	191	239
9.000	13	17	21	25	30	34	38	42	51	64	85	127	170	212
10.000	11	15	19	23	27	31	34	38	46	57	76	115	153	191

The following table appears on page 47 of the Atlas lathe manual. It is like the above, but shows exact speeds that can be achieved by moving the belts on the Atlas lathe. Speeds were selected in some way that would be "closest" to the exact speed shown above. The selection is usually, but not always, lower than the exact speed.

Diameter of Work	Surface Speed in Feet Per Minute
Inches	30	40	50	60	70	80	100	120	150	200	300	500
0.0625	2072	--------------	--------------	--------------	--------------	--------------	--------------	--------------	--------------	--------------	--------------	--------------
0.125	805	1270	1270	2072	2072	2072	--------------	--------------	--------------	--------------	--------------	--------------
0.1875	685	805	805	1270	1270	1270	2072	2072	--------------	--------------	--------------	--------------
0.25	418	685	805	805	805	1270	1270	2072	2072	--------------	--------------	--------------
0.375	266	418	500	685	685	805	805	1270	1270	2072	--------------	--------------
0.5	266	266	418	418	500	685	685	805	1270	1270	2072	--------------
0.625	164	266	266	418	418	500	685	685	805	1270	2072	--------------
0.75	164	164	266	266	418	418	500	685	805	1270	1270	2072
1	112	164	164	266	266	266	418	418	500	805	1270	2072
1.25	83	112	164	164	164	266	266	418	418	685	805	1270
1.5	70	112	112	164	164	164	266	266	418	500	805	1270
1.75	70	83	112	112	164	164	164	266	266	418	685	1270
2	45	70	83	112	112	164	164	266	266	418	500	805
2.5	45	70	70	83	112	112	164	164	266	266	418	805
3	45	45	70	70	83	112	112	164	164	266	418	685
3.5	28	45	45	70	70	83	112	112	164	164	266	500
4	28	45	45	45	70	70	83	112	164	164	266	500
5	28	28	45	45	45	70	70	83	112	164	266	418
6	28	28	28	45	45	45	70	70	83	112	164	266
7	28	28	28	28	45	45	45	70	83	112	164	266
8	28	28	28	28	28	45	45	45	70	83	164	266
9	28	28	28	28	28	28	45	45	70	83	112	164
10	28	28	28	28	28	28	45	45	45	70	112	164