Machinistblog.com

Nice collection of information for machinists. Includes tap and thread size charts, standard drill sizes, counterbored hole sizes for cap screws, surface finish chart, basic numbering system for steels, machinability comparison of various metals, hardness conversions and tensile strength charts, metric prefixes, unit conversion chart and trigonometry calculations.

The Little Machine Shop has several nice online calculators that determine the best RPM to use when turning, milling, drilling or reaming various materials. Just look up the cutting speed (SFPM) for your material on the charts, and then enter it in the calculator, along with the diameter of your workpiece, to get the spindle speed (in RPM) that you should use.

Huge database of technical information and calculators for mechanical engineering, manufacturing and design.

A nice chart to print out and hang in your shop.

There are only a few calculators here that might be useful for machinists, but we've included this because there are dozens of other useful and free calculators here.

Need a really good owner's manual for your 7x12 mini-lathe? Then download Grizzly's manual for their lathe. It's excellent.

Indexable inserts use an identification system that describes their shape, size, and other physical characteristics. This is a short, concise and easy to understand explanation of it.

This book contains some of the most useful information found in the venerable and much larger Machinery's Handbook that is published by Industrial Press. Almost the entire book can be read online, although you can not print or save it. It can be purchased for about $20 (USD) if you would like to own a hardcopy.

A searchable database of material properties that includes metals, plastics, ceramics, semiconductors, fibers and other engineering materials. For metals you can find out about properties such as machinability, weldability, hardness, strength, density, elasticity, electrical and thermal properties, and composition.

Just choose your material and its diameter on this easy to use chart to find the RPM needed. Then look at the drawings to see where to set the mini-lathe's speed control knob to get that speed. (Editor's note: This appears to be for HSS bits. If you're using carbide bits then you can usually at least double the speed.)

Nice set of charts that can be printed in different font sizes. One lists decimal inch, fractional inch and millimeter equivalents. There is also a drill bit size chart listing all drill bit sizes from 1/64 to 1 inch, with letter bits A to Z, and all number bits from 1 to 60. Very useful to print out and hang in your workshop.

Yet another nice tap drill size chart for standard American and Metric size threads

Tapping drill sizes (in millimeters, decimal inches, fractional inches, letter and number drill sizes), for BA (British Association), BSF (British Standard Fine), BSC (British Standard Cycle Thread), CEI (Cycle Engineers Institute), ISO (International Standards Organisation) Metric Coarse, Fine, and Special Pitch, UNF (Unified Fine Thread), UNC (Unified Coarse Thread), and Whitworth Threads. This information was compiled by Brian Morgan and is clearly and neatly listed in a simple text file.