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.
The double pulley on the motor shaft should have the small pulley on the right (closest to the motor).
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:
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And, here are the speeds with the back gear engaged:
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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) / dWhat many books do is to let 12/pi be approximated by 4, which is entirely adequate, yielding slightly higher speeds, but not enough to matter. I generated the following table using the proper value for pi, namely 3.14159.
Here is the ruby program I used to generate the following table:
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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.
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0.0625 |
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0.125 |
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0.1875 |
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0.25 |
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0.375 |
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0.5 |
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0.625 |
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0.75 |
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1 |
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1.25 |
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1.5 |
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1.75 |
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2 |
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2.5 |
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3 |
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3.5 |
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4 |
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5 |
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6 |
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7 |
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8 |
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9 |
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10 |
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Tom's home page / tom@mmto.org