A Sine Vise can be used with either manual or CNC machinery to securely position a workpiece surface at a precise angle to the cutting tool.  Using a Sine Vise can make a lot of difficult work holding jobs easy, and is often the only way to drill holes at a precision angle.

Once you know how, Sine Vises are a snap to set up.  All you need is a set of gauge blocks and a calculator.

This video from Tormach shows how to do it properly.

After a good machinist’s vise, a Strap Clamp Kit (also known as a T-Slot Camp Kit) is the probably the most important tool available to a machinist for secure work holding.

These kits will work with any machinery that has T-slots on the table – milling machines and drill presses come to mind.  You can buy the kits in a few different sizes; make sure you know what size your T-slots are.  Most small machines use a 5/8″ T-slot.

This video from Tormach shows basic Strap Clamp techniques, and also a few clever tricks as well.

If you’ve got a CNC Mill, like the Tormach PCNC 1100 handy, Thread Milling is a great alternative to Power CNC tapping.  Instead of using a tap, you use a form cutter and program it to cut a helical tool path based on the diameter and pitch of the thread you want to make.  You can cut both outside and inside threads with a thread milling technique.  You can also use this technique to cut tapered threads like pipe threads, left handed threads – even custom thread pitches you can’t readily find in stores.*  Why will STEM students be interested in Thread Milling?  Well custom bike parts, for one – pedals, cranks,  headsets, etc., all have features that can be made with CNC Thread Milling.

They make thread mills, like these from Vardex, but they can be a bit spendy for occasional use in the STEM classroom.  A simple V-cutter (also known as a double-angle cutter) can be used to accomplish the same result on a budget.

*Click here for a great description of basic thread concepts from Park Tools

Here’s a quick demonstration of the video demonstration of the technique from Tormach.

These tool paths were made with the Mach3 programming wizard for thread milling (included with Tormach PCNC Mills).  Its a parametrized programming tool  that’s pretty straightforward to use.

As for holding a shaft or cylinder vertically, there are a lot of options, including:

V Jaws in a Vise.  Easy to use can accommodate a wide range of sizes.

3 JAw Chuck mounted to the Mill Table.  Will accommodate large diameter cylinders.

5C Collet Closer Mounted to the Mill Table.  Easy to use and very robust, but limited to diameters < 1″ or so.  You’ll also need a set of 5C collets.

Give it a shot.  Once you you get started with thread milling, all that you’ll be left wondering is why it took so long.

Here, Tormach machinist Mike Corliss demonstrates the proper procedure for squaring a block on with a milling machine.  Doing this right will ensure that you have 6 perpendicular faces to work off on your workpiece.  This is an easy skill to learn, but getting good results takes some attention to detail and procedure.

Tools you’ll need:

•  - A Good quality Vise.  If you don’t start with a vise that’s square, you’ll have no chance of ending up with a square part.  Also, make sure to square the vise to the milling machine – here’s our tutorial on how to do that.
•  - Parallels, or something similar – a set like these will do the trick.  The important thing is that what ever you use is precision ground.
•  - Large diameter cutter.  We’re using a fly cutter here, but you could also use a face mill. (For a simulated flycutter,  try using the face mill with only one insert installed.)
•  - Smaller diameter endmill.  We use a 3/8″ cutter in a TTS Set Screw Tool holder, but anything similar will do the trick.
•  - Granite Surface Plate and 123 Block.    You’ll need to use these as reference surfaces to check your work
•  - File and/or Deburring tool for cleaning up the edges

Introduction

This lesson progresses through the basic steps required for digitizing a part on the Tormach PCNC 770. CNC Digitizing is a process using a tool probe and a CNC mill to reverse engineer physical parts into 3D CAD software models.  There are two discrete steps to the process:

1. Point Cloud Generation. Here, the touch probe is used to record a data set of discrete XYZ points. The number of points collect (density of the point cloud) ultimately determines the fidelity of the model. Mach3, the CNC control software for the PCNC 770, has a digitizing wizard to easily gather coordinate data from the desired part and makes this step relatively straightforward.
2. Surface Creation. Using CAD software tools, the collected points in the data set are turned into a solid surface. This is sometimes called “skinning”.  This can be done with a number of CAD tools available in the market today.  In this demo, we use a popular open-source software suite called Blender.

Essential Components:

Before you begin, you’ll need the following software and hardware tools:

A Primer on Digitizing Probes

Digitizing Probes can be thought of as a simple switch interfaced to the CNC control system as an input.  The deflection of the probe tip either makes (or breaks) an electrical circuit.  The change in the circuit’s state (usually input voltage) is used to signal to the control when the probe has come into contact with the surface.  Most CNC controllers use the G31 command for probing:

G31  X~ Y~ Z~ F~

When executed, this command will move the probe in a straight line towards location XYZ and feed rate F.  If the probe trips prior to reaching XYZ, the probe will stop, and the trip location is stored in the control.  A digitizing program is essentially a series of G31 commands at different XY grid locations that records each XYZ trip location into a data file, known as a point cloud.

Mach3 has a programming wizard that will automatically generate a digitzing program and write a point cloud file.   You can read more about the details of programming using the G31 command here.

Point Cloud Generation

1. First select a part you wish to digitize/reverse engineer.  As mentioned before, parts without sharp corners work best.  Secure the part to the milling bed via clamps or a vise.  The digitizing wizard requires the size of the envelope to digitize, therefore roughly measure the length, width and height of the part.  Measurement can either be done using measurement equipment (metal rule works fine for rough measurement) or the jog feature on the mill.  When all measurements are recorded move the probe to the desired starting position.
2. Proceed to the “Digitization Wizard” within Mach3.  Select “Wizards” on the top menu bar, then click “Pick Wizard.”  The window appears showing all the available wizards.  Scroll and select the wizard named “Digitise Wizard” by Art Fenerty.
3. Proceed to enter data in each input box with the data for the previously measured part envelope.  Note:  All dimensions measure from the current location of the probe.  Low feed rates obtain more accurate samples, but also increase the digitization time.  A sample screen is shown below.
   
4. Once dimensions are entered click the “Create and Load G-Code” button.  This generates the probe toolpath.  This may take a few minutes to compute for a fine resolution digitization.  Once the G-code is created the machine the main screen appears.
5. Once the setup is complete, click “Start” on the Mach3 interface.  The code will prompt the user to save the output points in a file.  Select a location and a specific name for the digitized points.  The file extension is arbitrary.  Depending on the resolution, digitization will usually take several hours to complete.

Software Installation

1. Converting the point cloud data to surface data will require additional software usually not included in basic CAD software packages.  For this tutorial Blender Foundation 3D software will be used.  Blender is free/open source and works on multiple platforms.  Blender can be downloaded from Blender.org.
2. Once Blender is installed, an add-on needs to be downloaded to add the ability to skin (make surfaces) from a point cloud.  The add-on is written in Python programming language and can be downloaded from the Blender Artists Forum.  Download the file “98 t25_PointCloudSkinner1_Umbrella.py.”
3. Once the point cloud skinner add-on is downloaded, the file needs to be placed in the correct directory.  Copy and paste the “98 t25_PointCloudSkinner1_Umbrella.py” file into the add-on directory for Blender, C:\Program Files\Blender Foundation\Blender\2.61\scripts\addons. (Note: the path may slightly vary depending on the version of Blender and the operating system.)
   
4. The add-on is now in the correct directory and now needs to be enabled.  Launch the Blender Software (Start>All Programs>Blender Foundation>Blender).  Once the application launches proceed to “File>User Preferences.”  On the left hand side of the user preferences window select “Mesh.”  Click the checkbox to the right of the add-on labeled “Mesh: Point Cloud Skinner,” to enable the add-on.  Lastly, Click “Save as Default” to enable this add-on every time Blender is started.  Once completed, close the User Preferences window.

Importing Digitized Data Points:

1. Open a new file in Blender (File>New).  The initial cube should be deleted.  Right-click the cube and press “X” on the keyboard.  Then select “Delete.”  Next, the workspace view should be changed.  Change the view on the top drop-down menu from “Default” to “Scripting.”
   
2. A new layout should appear.  Click the “+” on the scripting window to create a new text block.  Give it a name such as “ImportPoints.py”  Be sure to add the “.py” extension, to make the file a Python script.
   
3. The digitized data from the file needs to be converted to a format compatible with the 3D software.  A script has been made to convert the output file from Mach3 in Blender.  Go to http://groklab.org/tormach/2012/04/04/importing-points-to-blender/ to obtain the script code.
4. Copy and paste the code into the scripting window.  Make sure the indentation of the file does not change when pasting.
   
5.  At the top of the pasted code one line reads: path=’C:\\test.txt’.  This needs to be changed to the location of the digitized point file on each specific computer.  For example: path=C:\\Users\Me\Documents\DigitizingData\Mydata.dat’
   
6. Once completed, Click “Run Script” to import the data.  This should import the point cloud to Blender.

Result:

Skinning the Points

1. First points need to be selected for skinning.  Most times the user will want to skin all the points at once, but refinement of the skinning can be done by only selecting a few points at a time.  First click the object labeled “My Digitized Data” from the Outliner (model tree).
   
2. Enter the Edit Mode by pressing the “Tab” key.  Here multiple points can be selected.

• Press “A” to toggle select all/deselect all points
• Right-Clicking points will select individual points, hold “Shift” while right-clicking for multiple points
• Press “B” to select points by drawing a box around the desired points

Once the desired points are selected, press “Tab” again to exit Edit Mode.

1. Next, it is time to set up the skinning parameters.  Click the “Scene” tab in the properties window.
   
2. Scroll to the bottom of the Scene properties tab.  At the very bottom there is a panel labeled “Point Cloud Skinner.”  Change the target object from “Plane” to “My Digitized Data.” Distance to skin should be set to a size slightly larger than the distance between individual points (e.g. 0.050).  For most cases ratio for axis and ratio for grid do not need to be changed.
   
3. Once parameters are set, click the “Skin” button.  Skinning can take up to 10 minutes for high resolution data.

Saving the File

1. Once the skinning is finished, click “File>Export,” a list of possible output file types appears.  Select a file type that works well for the desired CAD/CAM software.  In addition to exporting the mesh, saving the Blender file is beneficial.  The Blender file can be reopened and reused when new digitization files need skinning.

Troubleshooting and Skinning Tips

Often times the skinning will not be correct on the first try.  Slight modifications to the skinning parameters may produce better results.  For digitization points that have large changes in point spacing (i.e. sharp changes in z-direction depth) the distance for skin parameter will need to be changed depending on the section of points.

Selecting Faces, Points, Etc.

All manipulation must be done in Edit Mode.  To enter Edit Mode press “Tab” with the object selected.  Common selection methods are:

• Right-Click – Select single point
• Shift + Right-Click – Select multiple points
• A – Select/Deselect All
• B – Bounding Box Selection
• X – Delete Selection

For advanced selection methods:  http://wiki.blender.org/index.php/Doc:2.6/Manual/Modeling/Meshes/Selecting

Manually Making Faces

Within Edit Mode select three or four vertices.  Press “F” to make a face between these points.  For advanced mesh making tools:

http://wiki.blender.org/index.php/Doc:2.4/Tutorials/Modeling/Meshes/Fill_Faces

 Special thanks to Brian Johns of University of Iowa for development of this lesson concept.

Essential G-Code:  A Simple Introduction  to CNC Mill Programming

Overview

G-Code is the programming language for the majority of CNC Machine tools, including CNC Mills and CNC Routers, as well as many other tools used in automated manufacturing, including CNC Lathes, Pen Plotters, Press Brakes, Grinders, 3D printers, and much more.

Even the simplest CNC milling machine understand several dozen G-codes; however, a complete knowledge of all available codes isn’t necessary to program simple CNC operations.  This lesson focuses on simple program construction and syntax, basic motion commands (G0, G1, G2/G3), and Absolute/Incremental (G90/G91) motion definition.  The lesson includes several example student activities, as well as a pen plotting exercise that can be easily adapted to any CNC Mill.

Lesson Concepts

• Basic Program Construction
• Absolute vs. Incremental Programming
• Learn Fundamental G Code Programming Commands
• CNC Pen Plotting

You can learn more about specific G -Codes here: Tormach Machine Code Reference.

For a complete treatment of G-code programming concepts, I recommend reading CNC Programming Handbook, by Peter Smid.

Helpful Prerequisites Concepts

• Cartesian (XYZ) Coordinates

Defining Location: Cartesian Coordinates

To move a CNC mill, a list of sequential points are given to the machine to program a tool path.  This works much like a “Connect-the-Dots” puzzle.  The locations of the points are given in Cartesian (XYZ coordinates) and can be represented on a sheet of graph paper. Each line (sometimes called “block”) of G-Code can be thought of as a instructions to connect the next “Dot” in the tool path sequence.*

Two Methods of Movement: Absolute vs. Incremental

The two methods of movement when using a CNC mill are absolute and incremental movement.  Absolute movement uses the origin (X0Y0Z0) as a reference.    A familiar analogy to absolute programming is GPS coordinates.  If given instructions to move to 41° 51’0 N, 87° 39’ 0 W, everyone reading this material would meet at a single point.

Incremental programming uses the current location as a reference.  Sticking with the same analogy, consider two people at different GPS locations.  If both are told to move incrementally 1 mile to the east,  the end location would not be the same, because the end point is dependent on the current position.

Both absolute movement and incremental movement have advantages and disadvantages in machining.  Incremental programming is good in cases of patterns or repetitive movements, such as making twenty holes spaced 1-inch apart.  One disadvantage of using incremental programming arises if a mistake is made in a program.  If one movement is incorrect the rest of the movements in the sequence are also dimensionally incorrect.  The majority of CNC programming  is done with absolute programming; however, incremental has its place as well.

At the start of each G-Code Program, it needs to be decided whether the program will be in absolute (G90) or incremental (G91) mode.

G-Code 101

The most commonly used CNC programming language is G-code.  The program consists of lines with G and M commands.  G commands are known as movement commands or functions.  M commands control other essential CNC machine functions, like spindle on/off.  Each command starts with either the letter “G” or “M”, followed by a number, i.e. “G01″,”M08″, etc.

The table below lists a few of the most essential G code commands:

Let’s take a look at the three basic movement commands: Rapid Motion (G00), Linear Motion (G01), and Arc Motion (G02/G03)

G00: Rapid Motion

The machine will move rapidly using a G00 command.  These rapid moves are intended for movement when the tool is not cutting the material.  A sample line of rapid movement can be written as:

How fast is “Rapid”?  It’s determined by the CNC machine designer.  In the case of a Tormach PCNC 1100 Series 3, the rapid motion limit is set to 110 IPM.  Any G00 command will move the mill at a straight line velocity of 110 IPM to the XYZ coordinate location specified.

G01: Linear Motion

Linear moves are specified as a G01 command.  The program will perform a straight line from the current position to the desired end position.  A linear move to the Cartesian position X=1.0 Y=1.0 should be written as:

N05 G01 X1.0 Y1.0

When executing the first G01 command in the program a feedrate (F) must be included.   A linear move to the Cartesian position X=1.0 Y=1.0 at a speed of 20 inches/min can be written as:

N05 G01 X1.0 Y1.0 F20.0

Example 1:  Star

Try writing a program that draws a star using both absolute (G90) and incremental (G91) programming modes

Example Star Program (Absolute Programming - Linear Moves Only)
%
N05 G90 G20	(Absolute & Inches)
N10 S6000 M03	(Spindle On, 6000 RPM) 
N15 G00 Z0.25	(Rapid Move)
N20 X0.0 Y0.85	(Rapid Move)
N25 G01 Z-.125 F20.	(Linear Move, Feedrate)
N30 X0.51 Y-0.68	(Linear Move)
N35 X-0.81 Y0.26	(Linear Move)
N40 X0.81 Y0.26	(Linear Move)
N45 X-0.51 Y-0.68	(Linear Move)
N50 X0.0 Y0.85	(Linear Move)
N55 G00 Z0.25	(Rapid Move)
N60 M05	(Spindle Off)
N65 M30	(End Program)
%

(Example Star Program Incremental Programming - Linear Moves Only)
%
N05 G91 G20		(Incremental & Inches)
N10 S6000 M03		(Spindle On, 6000 RPM)
N15 G00 Z0.25		(Rapid Move)
N20 X0.0 Y0.85		(Rapid Move)
N25 G01 Z-0.125 F20.	(Linear Move, Feedrate)
N30 X0.51 Y-1.53		(Linear Move)
N35 X-1.02 Y0.94		(Linear Move)
N40 X1.62 Y0.0		(Linear Move)
N45 X-1.32 Y-0.94	(Linear Move)
N50 X0.68 Y1.53		(Linear Move)
N55 G00 Z0.25		(Rapid Move)
N60 M05		(Spindle Off)
N65 M30		(End Program)
%

G02/G03: Arc Motion

Programming an arc or circular move is slightly more complex than a linear move.  First, the path taken by the arc must be specified as clockwise (G02) or counterclockwise (G03).  Following the G command, there needs to be an ending point to the arc and a way to define the radius of the arc.   To define the radius of the arc, the miscellaneous commands I and J must be introduced.  The I-value is defined as the incremental move from the starting point of the arc to the arc center in the x-direction.  Similarly, the J-value is defined as the incremental move from the starting point of the arc to the arc center in the y-direction.  Starting at the origin, to draw a clockwise quarter- circle ending at X0.5 Y0.5:

N05 G02 X0.5 Y0.5 I0.5 J0.0

Example 2: Program with Arcs

(Example Program with Arcs)
%
O12345	(Program Name)
N05 G90 G20	(Absolute & Inches)
N10 S6000 M03	(Spindle On, 6000 RPM)
N15 G00 Z0.25	(Rapid Move)
N20 X-0.5 Y1.0	(Rapid Move)
N25 G01 Z-0.375 F20.0	(Tool Down, Linear Move, Feedrate)
N30 G02 X0.5 Y1.0 I0.5 J0.0	(CW Arc Move)
N35 G03 X1.0 Y0.5 I0.5 J0.0	(CCW Arc Move)
N40 G02 X1.0 Y-0.5 I0.0 J-0.5	(CW Arc Move)
N45 G03 X0.5 Y-1.0 I0.0 J-0.5	(CCW Arc Move)
N50 G02 X-0.5 Y-1.0 I-0.5 J0.0	(CW Arc Move)
N55 G03 X-1.0 Y-0.5 I-0.5 J0.0	(CCW Arc Move)
N60 G02 X-1.0 Y0.5 I0.0 J0.5	(CW Arc Move)
N65 G03 X-0.5 Y1.0 I0.0 J0.5	(CCW Arc Move)
N70 G00 Z0.25	(Tool Up, Rapid Move)
N75 M05	(Spindle Off)
N80 M30	(End Program)
%

Note:  Once a G command is given the machine will stay in that mode, therefore the G command does not need to be repeated on every line.  One G command is canceled by another G command.  The feedrate will also remain the same until another feedrate (F) command is given.  Programming languages that behave this way are called Modal languages.

Example 3: Fill in the Blanks

The following exercise is a use both Linear and Arc commands.

(Fill in the Blanks Program)
%
N05 G90 G___		(Absolute & Inches)
N10 S_____ M03		(Spindle On, 3000 RPM)
N15 G00 Z0.25		(Rapid Move)
N20 X0.4 Y1.0		(Rapid Move)
N25 G01 Z-0.125 F30.0		(Tool Down, Linear Move, Feedrate)
N30 G___ X_____ Y_____		(Point 1 to Point 2)
N35 _____  _______  ______		(Point 2 to Point 3)
N40 G___ X____Y____ I0.0 J-0.3		(Point 3 to Point 4, CW)
N45 G01 X0.4 Y1.0		(Point 4 to Point 5)
N50 _____  _______  ______		(Point 5 to Point 6)
N55 _____  _______  ______		(Point 6 to Point 7)
N60 ____  ______  ______  ______  ______	(Point 7 to Point 8, CCW)
N65 G__ Z0.25		(Tool Up, Rapid Move)
N75 M____		(Spindle Off)
N80 M____		(End Program)
%

STEM Activity: Program Your Initials

Given a 2”x 3”x 1” block, program your own initials onto the surface of the block.  To keep coordinates simple assume the coordinate system origin is in the bottom –left corner of the block.  Use the graph paper below to draw your design, and then create a program with G-code commands.

Download the Worksheet here.

You can turn any CNC mill into a pen plotter – all you need is a Sharpie marker and a tool holder or collet to hold it in the spindle.  On a Tormach PCNC Mill, a 1/2″ TTS Set Screw Holder is just the right size for a Sharpie marker.  Just remember to TURN THE SPINDLE OFF before running the program, or ink will be everywhere.

The Sharpie technique is a fantastic way to prove out simple engraving tool paths as well.

You can encourage advanced students to take things a step further by actually using an end mill to engrave into the surface of the part.  With a flat pieces of stock, you’ll only need to program a cut depth of 0.005″ or so.

Special Thanks to Brian Johns from University of Iowa from whose work this lesson plan was derived from.

Squaring a Vise to the table of your CNC Mill or Manual Mill is essential for accurate machine work.  Squaring the vise ensures that the vise jaws are parallel to axis motion (generally the X-Axis).

To properly square your CNC Vise, you’ll need two things:

-Dial Test (sometimes called a Last-word or InterRapid) Indicator like this one.  These work by registering the tip deflection of the dial.

-Tool Holder.  An ER-16 with a 3/8″ Collet works great for the dial mentioned above.  Buy them here.

Here’s a video tutorial on how to do it on a Tormach PCNC 770 Milling Machine

(BTW, some vises have keys available, which can also be used to align the vise.  Keys are handy and generally suitable for aligning the vise for most work, but be aware that they may need to be modified on a grinder to match the precision that can be achieved with the method above.)

How to use an Edge Finder

Here’s a video from Tormach explaining the most fundamental tool in precision machining, the Edge Finder.  Learning this skill is a cornerstone of machine shop success.

Don’t have an edge finder? Purchase edge finders here.

Simple, Worry Free Tapping with Spring-Loaded Tap Guide

Tapping is one shop skill that makes even the most experienced of machinists break out in occasional fits.  I think has to do with the fact that its often the final step in producing a finished part, combined with the fact that it’s also one of the most temperamental of machining processes.   You won’t have to ask too many machinists before hearing a tapping horror story followed by grumblings about how to fix the mistake:  helicoils, tap extractors, and left-handed drills.

To the uninitiated, there are two ways to tap, and both have their potential pitfalls:

Hand tapping:  Approachable, but can easily ruin holes because the tap can be positioned cockeyed.  They  make tapping stands that help, somewhat.

Power CNC Tapping:  Requires either a dedicated tapping head (think $) or a spindle with rpm feedback (think $$$).  Programming needs to be carefully considered – it’s not impossible, but it’s also not as easy as programming a simple drill cycle either.  This is because power tapping requires feed/speed coordination.  You’ll never meet a CNC machinist who hasn’t broken a few taps learning the technique, and the occasional breaks thereafter come with the territory – as I said, tapping can be temperamental.  Click here to read more about Power CNC tapping with a tapping head, if interested.

So what’s a STEM teacher to do?  After all, it’s probably the last night before the competition and you really just want to tap a few final holes in your team’s latest Battlebot without any late night headaches.  Is there another way?  Well..

If you are only occasionally tapping, consider a third approach: A spindle mounted spring-loaded tap guide combined with a tap wrench.  You’ll be able to use your CNC machine to accurately position over pre-drilled holes, and the tension applied by the tap guide keeps the threads straight and true.  You’ll also be able to gauge tap resistance by hand, which will keep you from inadvertently breaking off a tap in the hole.   Its both better and cheaper than a tapping stand.

This video from Tormach demonstrates the technique on a PCNC 1100 CNC machine.  You’ll be able to adapt the same principles to a manual milling machine as well.