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7x10, 7x12, 7x14 Mini-Lathe Information

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A calculator is being worked on right now and when completed will be located in the CALCULATORS section of the site.

There are few things to remember when turning and milling and drilling. The material, its size along with the cutting tool and its size determine in combination with data provided from machining experience dictate the speeds and feeds along with the depth of cut recommended. As with many things, it all "depends" on a variety of factors. Here's a basic recommendation from various sources including some common machining "manuals":

Let's start by saying that the empirical data provided for SFM (surface feet per minute) is a recommendation based on historical experience. This is not an end-all chart. After determining the SFM, you'll need to take into account the stock being used. We're providing here examples for turning. One thing you'll note is that turning aluminum versus steel yields vastly different speeds. In general, turning steel requires SLOWER speeds than aluminum on the order of 2x.

RPM = spindle revolutions per minute
SFM = surface cutting speed in feet per minute
D = diameter of the rotating workpiece

Recommended Surface Feet Per Minute (SFM):

Material Lathe Mill Drill
Aluminum 150-400 400-1000 300
Brass 150-700 300-700 200
Bronze 80-150 70-90 100
Cast Iron 40-90 60 80-100
Machine Steel 100-200 80-100 80
Malleable Iron 70-120 60-80 90

When in doubt, you can average out the range to yield a number in between.

We often turn 1.5" diameter CRS (cold roll steel) and 6061-T6 aluminum rod in the lathe. This is how the recommended spindle speeds woul compare:

Steel (using SFM = 150 = [(200-100)/2]+100) yields the following:

RPM(steel) = 150*4/1.5 = 400RPM

Aluminum (using SFM = 275 = [(400-150)/2]+150) yields the following:

RPM(aluminum) = 275*4/1.5 = 733.33RPM

Let's run some more numbers to see if this relationship is linear between aluminum and steel cutting speeds for varying diameter stock:


As you can determine from this graph, the spindle relationship between the two metals follows each other and that the difference is roughly 2X. That is to say, if you're turning a 1" dia. workpiece in aluminum at 1200RPM, when you switch to free-machining steel, you'll need to adjust the speeds to roughly half, or 600RPM. Also important to note that for diameters starting around 1" and over, the speeds remain fairly constant. The big drop-off occurs (rather exponential speed increases) occur for diameters smaller than 1" or so.

For milling information (for now), you can reference a useful page from another website:

You will need to do your own calculations, but what's useful is that they factor in the number of flutes and other relevant considerations to determine the ideal speed and feed.

We will also post one for lathe work in the future.


Looking for mini-mill help and how-tos? How about lathe help and how-tos?

We're prototyping a benchtop CNC vertical mill using the DigiSpeed-XL interface card for Mach, Dart Controls and KB Electronics KBIC/KBMM 90VDC motor controllers, 1.5HP treadmill motor from Surplus Center and a R8-spindle head from the X2 mini-mill - not to mention Gecko servo drives and an entirely closed-loop system. Come take a look!

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