KSA FAB LAB > CNC Routers

PRODUCING A MILLING CUT FILE

Milling cut files can be produced in several different ways - the easiest is to use the MillWizard software that can be found in any of the Fab Lab computers. Another option would be to generate the toolpaths in the 3D modeler of your choice, and convert it via a DXF using the ShopBot 3 software. For the purpose of this software, however, we will use MillWizard to generate the tool paths.

Prerequisites

Before opening MillWizard, you should generate the surface or object you wish to produce in the 3D modeler of your choice (this tutorial uses FormZ). This tutorial uses the object pictured at right. It is a simple terrain model, measuring 7' in X, 3' in Y, and 4" in Z. The object has already been placed at the origin, with the long dimension extending in the X axis.

This file will be exported in STL format, although MillWizard is also capable of reading DXF and 3DS formats.

The MillWizard Interface

The MillWizard interface is shown at right; there are three main areas.

The first is the view window at lower left, where you will see the object you are working with.

The second is the details panel on the right side. This is where you will be prompted to provide information about your file - by filling in each field and pressing the "Next" button, the software will guide you step-by-step through the process of producing your part file.

The last area holds the icons along the top of the window - these are used to look at your object from different angles (top, front, or right side views, or axonometric projection).

Here the STLÂ file has already been opened, and we are ready to proceed.

The second step is to determine which face should be milled. In this example, we want to produce the top surface of our model, so we select "Top". At the bottom of the details area you can see that the model is oriented with its longest side in the X axis - which corresponds correctly to the ShopBot work area. If this was not the case, we could rotate the model 90 degrees by checking the "Rotate Model by 90 degrees" box.

The next step gives us the option of resizing our source model. In this example, we have already scaled the data in our modeler - so we can leave the scale set to 100%. If you are working with full-scale data, however, you can use this step to scale your model appropriately.

The Cut Plane step allows us to specify the maximum depth we want to cut. In this example, we have set the cut plane to the 0 position, meaning we want to cut the entire volume of our object. Had we set this to 2", only the top half of our model would have been milled.

The next step, Setup Material, allows us to specify the depth of the material we will be milling, and place our data at a location within that material.

In this example, we have indicated that we are milling a 6" thick slab of material. We have also indicated that the highest point of our model should be 1/4" in below the top surface of the material, leaving a material base about 1 3/4" thick.

It can be helpful to position your model just below surface of your material to remove any material logos, incidental damage, etc that may mar the top surface of your material.

The Roughing Tool screen is optional, and invoked by checking the "Generate Roughing Pass" box at the top of the details panel. In our model, the maximum depth we are milling is over 3", and we do not have a router bit this long. This requires us to produce roughing passes to remove most of the scrap material. The details of those roughing passes are determined here.

Type: This can be either End Mill or Ball Nose, and refers to the end condition of your router bit. End Mill bits have a square profile, while Ball Nose bits are rounded.

Diameter is the cutting diameter of your bit. For roughing passes, it is better to use larger bits to quickly remove more material. For finishing passes, smaller bits are usually better because they can produce finer details.

Cutting Length refers to how deep of a cut your bit can produce. It is better to make this length somewhat less than the bit is actually capable of (in this example our bit actually has a cutting length of 1.25")

Stepover is the distance between each pass over the material. Theoretically this could be the same as the Diameter setting, although in practice this often results in fins of material being left behind. For roughing passes, 90% stepover seems to be a good figure, while a smaller stepover (around 50%) can be better for finishing passes. Generally, more stepover means a faster cut, while less stepover produces greater resolution.

Spindle Speed is the rate at which the router spins. The current ShopBot controller cannot itself vary the rotation speed of our router, but it is good to specify this number anyway. Our router can spin at speeds from 10,000 to 21,000 RPM; the 16,000 RPM we specify here is a decent setting for milling foam.

Feed Rate and Plunge Rate are the speeds at which the router will move through your material. Feed Rate is the horizontal (X&Y) speed, while Plunge Rate is the vertical (Z) speed. These settings will be included in your SBP file, so it is important to specify them accurately. Feed rates can be set higher than plunge rates, but the two should not be vastly different. The speeds specified here (240" and 120" per minute) are decent settings for milling foam, and work out to 4" and 2" per second (which is how they would be specified if you were to enter them in the ShopBot software).

The Finishing Tool screen is essentially the same as the Roughing Tool screen.

In this example, we are using a 1/8" diameter bit to finish our model, so some of the settings have been adjusted accordingly - such as Diameter, Cutting Length, and Stepover.

Other settings, such as the Spindle Speed, Feed Rate, and Plunge Rate, are more a function of the material being milled - so they are the same as for the roughing pass.

The Strategy panel allows us to specify several basic parameters of the milling job.

Machining Direction allows us to set up milling passes along the X axis, Y axis, or both. Performing passes in both directions will result in a smoother model, but will take twice as long.

Machine Z Zero position asks where the Z axis has been zeroed - if you follow the tutorials found elsewhere on this site, specify "Top of Block" here.

Allowance asks how much extra material should be left behind by the roughing and finishing passes. The allowance should generally be greater for roughing passes to ensure that the finished object's surfaces are only processed by the finishing bit.

Safe Z Height determines the height at which Jog operations are conducted. This should be high enough to clear any material restraints you will be using, such as metal clamps.

Add Border asks you how much of a border to mill around the sides of your object. While it is possible to specify 0 for a border, doing so will result in your object being milled at the absolute lowest point possible in your material.

This option can also be tricky because, as in this example, if your model has steep sides (in this case, 4" high in some places) the ShopBot will try to mill that entire face with a bit that is only 1/2" long - potentially ruining your part! If you are worried about this happening with your part, contact Matt for more assistance.

The Calculate panel takes all the settings you have previously specified and calculates the toolpaths that will be used to produce your object. You can calculate roughing and finishing passes separately or together.

After the toolpaths have been calculated, you can view a simulation of your part being produced, and get an idea of what the finished object will look like.

In the example at right, the simulation has already finished playing - which is why the object has apparently changed from blue to gray.

The Save Paths panel is where you can save the roughing and finishing files that will actually be fed to the ShopBot.

In this example, the roughing and finishing passes can only be saved separately, and the "Save Combined" button is grayed out. This is because we have specified different bits for our roughing and finishing passes - were we using the same bit for all of our cuts, they could be saved in the same file.

We have also specified the ShopBot in the "Select Machine" dialog box, ensuring that the file we produce will be entirely compatible with the Shopbot software.

At this point, you have successfully created the ShopBot Part (.SBP) files necessary to mill your object. At right, the roughing file generated in this tutorial has been opened with a text editor such as Notepad. In extreme cases, it may be necessary to edit this file by hand - if you feel this is necessary in your case, ask Matt Bernhardt for guidance.

You are now ready to take these SBP files to the ShopBot. The next step is to secure your material, orient the tool, and execute these files.

Executing A Part File

ShopBot Overview