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G-Wizard Machinist's Calculator: Quick Reference

The Quick Reference page includes a variety of helpful reference materials:

- Drill Index Chart

- Cap Screw Reference

- Weights and Volumes Calculator

- G and M-Code References for CNC

- Hardness Conversion Chart

- Rigidity Calculator

Drill Chart

The Drill Chart is a complete Drill Index-style listing of twist drills that includes their diameter in Imperial and Metric units, their name (designation), and uses for that drill.

Cap Screws

The Cap Screw page includes dimensions for common sizes of Socket and Flat Head Head Cap Screws, the holes they fit into, as well as what size hex key should be used with each size:

Weights and Volumes

The Weights and Volumes page is intended to assist with calculations of the weights and volumes for various materials in standard sizes that stock is normally available in. For example, Fabricated Sections are available in Pipe, Channel, Angle Iron, or I-Beam shapes.

The Plate/Bar, Tubing, and other Shapes choices require you to enter dimensions rather than selecting from the menu of common sizes.

To use the Weights and Volumes calculator, proceed as follows:

1. Select the material.

2. The material's density will be displayed immediately to the right.

3. Select the quantity of workpieces you want to calculate for.

4. Select the type of shape. You can use the Size menu and Fabrication type, or choose one of the other shapes (no Size menu for them).

5. Enter the Dimensions as needed. You can override the dimensions on the standard sizes.

6. Enter a Cost Per Lb if you want to calculate costing information.

The "Results" column will give you the results of the calculations.

Thermal Expansion Calculator

G-Wizard's Thermal Expansion Calculator...

It's pretty simple to use:

Select a material, and it will enter the Coefficient of Thermal Expansion for that material. Keep in mind the note at the bottom--it uses the average across many alloys. For more precision, look up the exact coefficient for your material and enter it. I'd wait to see what the average reveals and if its within a factor of 2x or so of worrying you, look up your exact material's coefficient.

Next, pick a temperature unit system, Fahrenheit or Celsius. Enter your Reference and Target temperatures. The standard temperature for measurements is 20 degrees C, and if you push the "Std Ref Temp" button that is what you'll get.

Lastly, enter a length and/or a radius.

Press Calculate and G-Wizard will tell you how much the temperature differential between the Reference and Target will move the material in length or radius.

Let's consider a simple problem you might use the calculator for. Too much bearing preload drives up temperatures, and in the worst case, it leads to thermal runaway which will destroy the bearings in a hurry. They get hot, they expand, that increases the preload, which raises the friction, which makes them hotter, so they expand more, yada, yada.

We can use G-Wizard to see how much expansion we're talking about. The screen shot shows the scenario. Imagine we want to run our spindle bearings up to the point where they're at 140 degrees. I've come across a number of references calling for this as a good goal or maximum for bearing temperature. Less and you don't have as much preload as you could. More, and you may have the thermal runaway situation or break down your bearing grease.

We can see that for a spindle 12" long and 2" in diameter, if we assume we're starting from the reference temp and running up to 140 degrees, we will see that spindle grow 0.006" longer and 0.001" larger in diameter. That's pretty significant when bearing tolerances are measured in tenths!

Or, consider a CNC machine's leadscrew. Let's say it is 30" long. It is precisely calibrated at the reference temperature, but we're running the machine on a hot day and we're spinning the heck out of that lead screw. So it creeps up to 98 degrees or so. How much longer did it get?

Turns out it grew about 0.0063". Heck, even if you're only machining a part that requires you to use 6" of travel, that's a difference of 0.0013" in length that goes against the accuracy of your handwheels or of your calibrated CNC servos or steppers. That's a lot of error!

Hence manual machines benefit from DRO's that tell how far the axis really moved and CNC machines benefit from scales that are essentially DRO's telling the controller the same thing. In some cases the CNC may rely on a temperature sensor to estimate, but the scale is a better solution because it tells how far the axis really moved.

G and M-Codes

The G and M-Code reference is a handy way to look up the codes. To use it:

- Select whether you want G- or M-Codes on the top line.

- If you select G-Codes, an additional set of selection buttons pops up like the ones shown in the screen shot. You can use these to narrow the list, for example to show just "Motion" related G-Codes like G0, G01, and G02/03. The capitalized letter tells you the keyboard shortcut on the buttons.

- As you select codes, there are notes associated with them that tell you a bit more. The screen shot shows how the "H" parameter is used with G44 for Tool Length Compensation, for example.

G and M codes are covered on the left, while on the right is a brief list of the other kinds of codes you can put in a CNC program.

Hardness

The Hardness tab provides a quick reference for converting between the different units of hardness.

Rigidity Calculator

A 1/8" endmill versus a 1/2" endmill...

The calculator breaks down how much each component, cutter diameter, cutter length, and cutter material, affects the overall rigidity. The length is measured from where the tool holder or collet ends to the deepest point where cutting occurs. So in this example, we're saying 1.25" down from the tool holder on the 1/2" endmil and 1/2" down on the 1/8" endmill. The result is that the 1/8" endmill is about 1/16 as rigid as the 1/2".

Consider some other scenarios we can analyze with the calculator:

• A 1/2" endmill at 1" depth is 1/2 as rigid as the one cutting 11/4" deep. Be careful with deep cuts and choke up on the tool as much as you can in the holder.
• A 1/4" endmill at 1" depth is almost 1/16 as rigid as the 1/2" endmill at 1" deep. Use the largest diameter endmill that fits your internal radii.
• A 5/8" endmill at 1" depth is 2.4 times more rigid than a 1/2" at 1" depth. I have a little 5/8" Iscar Helimill indexable cutter. Even though it adds a mere 1/8" in diameter, it is more than twice as rigid. That's why I like to rough with it.

For turners, you can get a sense of the rigidity of different boring bars from the Calculator as well. It's no wonder that using the biggest carbide bar that fits the hole makes such a difference!

If you're having a problem with deflection, try this calculator. I'd look at increasing rigidity 2-4x and seeing if the deflection problem doesn't go away or isn't greatly reduced. If it is still an issue, bump up another 2-4x in rigidity until you get rid of it.

Have you gone through Setup of your G-Wizard Calculator yet?

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