T H E B A J A G U I D E T O M A C H I N I N G : M A S T E R C A M

Written By:

David Adams

Queen’s University

October 2010

TABLE OF CONTENTS

Introduction ............................................................................................................................................................................... 3

Basic Milling ............................................................................................................................................................................... 3

Step 1: Save your file as a .DWG .................................................................................................................................... 4

Step 2: Open and centre part in Mastercam ............................................................................................................ 6

Step 3: tell mastercam what machine you are using ............................................................................................ 7

Step 4: Tell mastercam what your stock looks like .............................................................................................. 7

Step 5: Make your toolpaths........................................................................................................................................... 8

Step 5.1: Center drill the holes ................................................................................................................................. 8

Step 5.2: Drill the 0.25” holes .................................................................................................................................. 10

Step 5.3: Drill the big holes ...................................................................................................................................... 12

Step 5.4: Rough out the high precision Bore .................................................................................................... 12

Step 5.5: Finish the hole to precision ................................................................................................................... 16

Step 5.6: Cut the square hole ................................................................................................................................... 17

Step 5.7: Cut it out ........................................................................................................................................................ 17

Step 6: Verify it ....................................................................................................................................................................... 18

Step 7: Post the program .................................................................................................................................................... 19

INTRODUCTION

This guide was made to teach new team members the basics of machining. As an example, I have will take you through the Mastercam setup for a simple 2D part with some of the features that will appear on a Baja part.

BASIC MILLING

In this lesson, you will make this part:

For the sake of this tutorial, we will say that this part will be made out of 6061 Aluminium. Most Baja parts are made from this material. In addition, we will say that the 1” bore in the middle of the part is going to be a bearing fit, and should be made to high tolerance (say + 0.001”).

Right away, you should immediately be thinking about how we can make this, and ideally if we can do it in one setup. The good news is that yes, this can be made with only one setup on the mill (you won’t have to flip it over, or unclamp it in any way until it’s done. There is, however, one feature that is impossible to make. I won’t give it away just yet but try to guess what it is. Making this part involves several kinds of toolpaths including drilling, pocketing, precision boring, and milling contours. We will work through every step to make it.

STEP 1: SAVE YOUR FILE AS A .DWG

For this tutorial, you should first make the part shown above in SolidWorks. Once you have a solid model, select File-Make Drawing from File. This will open a dialog with several parameters. Make sure that “display sheet format” is unchecked, then click OK.

FIGURE 1: MAKE SURE THAT DISPLAY SHEET FORMAT IS TURNED OFF

In the drawing view window, drag a view into the screen that shows the part from the top down. It is vital that it shows the top and not the bottom, because you want to have all of the features visible. Once you have the part in the screen, make sure it’s scaled 1:1 by clicking on it, and selecting 1:1 from the scale options.

FIGURE 2: SCALE THE PART

Finally, make sure that the part is in inches. Importing the part in millimeters will wind up with a part that’s 25.4 times the size it should be. Change the units by selecting tools-options then under the document properties tab select units and click on IPS.

FIGURE 3: UNIT SELECTION

Finally, save your file as a .DWG. This is what you will open with Mastercam.

STEP 2: OPEN AND CENTRE PART IN MASTERCAM

In Mastercam, open the .DWG file you just saved. If it looks like nothing happened, don’t worry, chances are it just came in outside of your view. Press F9 to display the coordinate axes, and zoom out (scroll out on the mousewheel) until you can see both the part and the origin. In a second we will be moving the part to the origin, but first we have to think about what we want the origin to be. Whenever possible, the origin should be some point that is easy to reference. If there are existing edges on the stock, they’re great to use to find the center. Since this part will be cut from ribbon stock, with excess material on all sides, it doesn’t matter too much so long as when we set up the mill there is enough stock on all sides, but you should always think about how you will find the center once the part is on the mill.

For this part, we will choose (arbitrarily) the centre of the leftmost hole (inside the square). This can easily be picked up by centering the tool on the stock. To move the part, select (from the top menu) xform - xform translate. Mastercam will prompt you to select the entities to translate. Since we are moving everything, you can either drag a box around the part, or select All-all entities. Press the green circle button to continue.

FIGURE 4: TRANSLATE DIALOG. MAKE SURE TO TELL IT TO MOVE AND NOT COPY, THEN PRESS THE +1 BUTTON

Make sure to select move, then press the +1 button, and Mastercam will ask you to select an entity to translate to and from. In this case, select the centre of the hole, then the origin. The part will now be centered on the origin. Save your work before you forget to.

STEP 3: TELL MASTERCAM WHAT MACHINE YOU ARE USING

Before you proceed with any toolpaths, you need to tell Mastercam what kind of CNC mill you are using, because they all have different postprocessors. For this tutorial, we’ll assume you’re using one of the HAAS mills. Select “Machine Type” -> Mill -> mpmaster. For reference, the TRAK mills are AG3peckdrl.

Once you have selected a machine, a machine group will appear in the tree on the left. This is where the toolpaths will be placed, in order of operation.

STEP 4: TELL MASTERCAM WHAT YOUR STOCK LOOKS LIKE

By telling Mastercam what kind of stock you are using, it become a lot easier to make sure that tools won’t crash into clamps or the bed. In particular the stock shape is useful in the verify option, where Mastercam will show you a 3D solid preview of the part as made by the toolpaths.

To add stock, expand the tree item labeled Properties under Machine Group-1. Click on the Stock setup button to open the stock window. For now we’ll say that the part will be made from a prismatic stock, 2.5x7x0.75 inches. In general whatever numbers you have here should reflect the true size of the stock. Add these values in to the stock window as shown. Make sure to select the Display button, then you can fine-tune the in view coordinates options until the stock looks nice and centered on the part.

FIGURE 5: STOCK SETUP WINDOW

STEP 5: MAKE YOUR TOOLPATHS

There are several operations that have to be done to make this part. We have to drill the holes, bore the precision hole, cut the square hole, and cut around the part. Obviously the contour around the outside has to be done last, because once it’s done there will be nothing holding the stock in place. The rest of the toolpaths, however, can be done in any order. As a general rule, however, I like to start by center-drilling the holes, because it gives me a good idea if the machine is doing something wrong before it starts seriously cutting things.

STEP 5.1: CENTER DRILL THE HOLES

Center drilling puts a small indent in the stock for a real drill to center itself on. When making holes, you should ALWAYS start with a center drill or else the drill will wander on the stock. To center drill the holes, select Toolpaths -> Drill toolpath.

A dialog may pop up asking you to enter a new NC name. Just click ok on this, and it will take you to the point selection window. Select the centers of ALL holes, including the square and bore, because they will all have to be drilled. Click ok to move onto the toolpath properties window.

This window is the part of Mastercam that you will see the most. This is where you seriously start machining. The first step is to tell Mastercam what kind of tool we’re using. To do this, press Select Library Tool, then select ¼” center drill. Clicking OK will return you to the properties window, with all kinds of really random values in the options. Set all of the values as seen below.

IMPORTANT! Make sure that ALL offset values in the top right reflect the tool number. If you do not the mill will move to the wrong Z-value, which might be below your part!!!

You can also tell it to turn the coolant on, by clicking Coolant and turning Flood on. For this tool, I usually use a feed rate of 5 inches/min and a speed of 1200 rpm.

FIGURE 6: TOOL PROPERTIES FOR A CENTER DRILL

To continue with properties, select the Simple drill-no peck tab. These options tell the mill how far to plunge in and retract. Always remember that depth values should be negative, or else the bit will try to cut to some point above the part. For center drilling, I usually use -0.22 as a depth. You can leave the rest of the stuff here at its default.

FIGURE 7: CENTER DRILLING VALUES

STEP 5.2: DRILL THE 0.25” HOLES

Now that we have the holes center drilled, we can drill them. Let’s start with the ¼” holes on the right side of the part. Create a drill toolpath as before, and again select all hole centers. Even though only the three on the right are ¼” diameter, all should be drilled because the ¼” hole will act as a pilot hole for the left two. Add another tool from the tool library, this time a ¼” drill. Fill in the top right values as tool # 2, length offset 2 and head 2.

FIGURE 8: DRILL, TOOL 2

With the tool set up, click on the next tab. This time, select a Peck Drill cycle. Peck drilling means that the tool retracts out of the hole periodically to clear the chips. The peck depth is set by default

to 0.1”. Set a depth for this hole of 0.75”, because we’re going all the way through the part. Also make sure to turn Tip Comp on, to compensate for the tapered end of the drill. Press the tip comp button to bring up the tip comp options box.

FIGURE 9: DRILL CYCLE PARAMETERS

FIGURE 10: TIP COMPENSATION

Tell Mastercam to break through the part by 0.05”, so that it doesn’t leave any lip on the bottom of the hole.

STEP 5.3: DRILL THE BIG HOLES

The next thing to do is drill the ½” holes. If you have a pocket with a hole in the bottom, you should always drill the hole first, so that chips and coolant have somewhere to go, and the tool has somewhere to plunge through.

Create a drill toolpath by again selecting toolpaths -> drill, then select the left two points and click ok. In the properties menu, click to add yet another tool, this time a ½” drill.

FIGURE 11: PROPERTIES FOR DRILLING THE LARGE HOLES

Set the peck drill properties identical to the last operation, depth -0.75”, tip comp on and peck drill cycle.

STEP 5.4: ROUGH OUT THE HIGH PRECISION BORE

Next we will cut the high-precision bore. This is a two-step process, where we will first rough out the shape, then finish it with a high-precision path. To cut this out, select Toolpaths -> Pocket Toolpath. Mastercam will prompt you to select a chain. Select the circle, and an arrow will appear marking the direction the cutter will make around the hole. You should make sure that the arrow lines up with a climbing cut around the perimeter of the circle. If it doesn’t, click on the reverser button, also circled below.

FIGURE 12: CHAIN SELECTION SCREEN. CIRCLED ARE THE DIRECTION INDICATOR, AND THE REVERSER BUTTON

Click ok to proceed to the parameters screen. Add a tool with the “select library tool” button, in this case a ½” flat endmill.

Notes on tool selection: In general, you should always try to use the largest diameter and shortest length cutter that will fit in whatever you are doing. Short, wide cutters are much stiffer, and allow for a better finish and faster material removal rate. For cutting aluminium, try to use a 3-flute solid carbide bit. For cutting keyways and slots, use a two-flute to help clear chips better. For cutting on the sides of parts, you can use a 4-flute or more endmill, because they give a better finish.

Click ok to return to the parameters screen, and enter the parameters shown below. The values for speed and feed vary wildly depending on material and cutter type, but those shown are ok for general cutting of aluminium with a 3-flute carbide bit. If ever in doubt, ask one of the shop guys.

FIGURE 13: PARAMETERS FOR A POCKETING CUT

Next, move to the pocketing parameters tab. Add in the depth value for the pocket (the bore is ½” deep, so set depth to -0.5”). Since we won’t be able to take this all out in one shot, turn depth cuts on, and set the max rough step to 0.2”, as shown below. Also set a 5 thou stock to leave, so that once the toolpath is done you can measure the hole, and adjust the diameter so that it’s exactly what it should be.

FIGURE 14: POCKETING PARAMETERS

FIGURE 15: DEPTH CUTS OPTIONS

Next, go into the Roughing/Finishing parameters, and select True Spiral. Also make sure that Finish is checked off, so that the tool will run a finishing pass around the outside of the circle.

STEP 5.5: FINISH THE HOLE TO PRECISION

Now that the hole has been roughed out, its time for a second operation to finish this bore off. To do this we are going to be doing a circmill pass, where the tool moves in a circular motion around the inside of the hole, skimming off the last little bits.

Notes on precision boring:

While a circmill pass is usually all you need to make a bore good enough to fit a bearing to, there is a higher precision and more accurate way of doing things, called a boring head. A boring head holds the tool eccentrically, and you can adjust how far from center the tool is, meaning you can mechanically set the diameter, and simply plunge the tool down to cut the bore. A boring head is the best way to make a super accurate hole, but it is often harder to use and includes more going back and forth.

FIGURE 16: A BORING HEAD

To make a circmill pass, select Toolpaths -> Circle Paths -> Circmill and a drill point selection window will pop up. Instead of selecting the point at the middle of the hole, select Entities, then click the outside circle around the bore. Make sure that tool 4 is selected, feed 5 plunge 5 and spindle 1500 rpm. In the Cut Parameter tab, make sure that compensation type is set to Wear. Setting this to wear means that when you are on the mill you can fine tune the bore diameter by telling the mill the cutter is a different size. Next, in the Multi Passes tab, turn multi passes on, with 0 roughing passes and 2 finish passes at a spacing of 0. This creates a spring pass, which will create a better finish by getting rid of tool deflection effects. In the linking parameters tab, set the depth to -0.5, and finally turn the coolant on.

FIGURE 17: MULTI PASSES

STEP 5.6: CUT THE SQUARE HOLE

I mentioned earlier that there was one feature on this part that cannot be made as it appears in the drawing. You may have figured out by now that there is no possible way to machine the square edges in this feature, because no matter what you do there will be a radius left from the cutter. For this tutorial we will assume that it is acceptable to have radii in the corners, but you should always remember when designing a part that features like this are not possible.

To cut this square hole, we will use a pocket path. Select Toolpaths -> Pocket Toolpath, then select the boundary of the square. Make sure that the arrow is pointing in the direction of climbing cut. Because I’m lazy let’s assume that the radius on the edges won’t matter, we can use a ½” flat endmill. Using a federate of 15, plunge 8 and spindle speed 1500 rpm. Next, add a finish pass, spacing of 0.01, make sure the select “machine finish passes only at final depth.” Next, turn on depth cuts, with a max rough step of 0.1, and a finish cut with a step of 0.05. Next, in the linking parameters set the depth to -0.5.

STEP 5.7: CUT IT OUT

Now that the features on the part are done, you can cut it out. To hold the part in place, we are going to add tabs. By adding tabs, the mill leaves a little bit of material at the bottom of the part to hold it in place while it finishes things. You can later break the tab off and sand it smooth. To cut the part out we’ll use a Contour pass. Select Toolpaths -> Contour toolpath and select the outside of the

part, again being sure to make the arrow point in the direction of a climbing cut. We’ll use the same ½” flat endmill, and the same feeds and speeds as before. Set depth cuts to 0.1, with keep tool down turned on. Turn on Break Through to 0.05 to make sure the tool goes all the way through the stock. Use 1 roughing pass spaced at 0.1, and one finish pass spaced at 0.05. Make sure to machine finish passes at final depth and keep tool down. Finally, turn Tabs on. You can play around with the settings here until the tabs are in the place you want them to be, but set the width to 1”, and thickness to 0.02.

STEP 6: VERIFY IT

Mastercam has a nice built-in feature called verify that lets you see what the part is going to look

like before you put it on the mill. To run verify, select all toolpaths using the select all button ,

then press the Verify button . The screen will show the stock, and pressing play on the verify window will show what the tool will do.

FIGURE 18: VERIFY WINDOW

STEP 7: POST THE PROGRAM

Now that the program has been written, you can run the post-processor to turn it into G-code for

the mill. To post the program, first select all toolpaths with then run the postprocessor by

pressing . Also, if you want to know more information about the program or see a tool motion

more in depth, press the backplot button: . This will tell you things such as how long the toolpath will take to run, and is useful to making sure a tool won’t crash into anything. Finally save your .NC file to a floppy disk, and you are ready to put it onto a mill.