CNC Machining Guide

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Sigma Lab Guide on CNC Machining

What is CNC?

CNC or Computer Numerical Control, is the name for a section of machines that use computer interpreted code to move a tool in order to remove material from a blank and create a finished part. These tools range from the 3D printer and laser cutter in the lab, to routers, lathes, and mills. These machines can give far more accuracy when machining parts, but can be more difficult to use.

Why use it?

The CNC router in the shop, properly called the 'Michelangelo 3D Modeler,' is most useful for many of the jobs that can't be done on the laser cutter or the 3D printer. It's fast spinning tools make it ideal for cutting pockets into hardwood, or engraving text into metal. It also is very multidimensional, in that it has 3 or 4 dimensions that it can cut in, as well as being very versatile to begin with.

How do I stay safe?

The CNC router is most likely one of the most dangerous tools in the lab, as it can cause some very expensive damage to the tools, and the machine itself. Additionally, there is always the potential to break a tool and send pieces of it flying in every direction. -When operating the CNC router, it's recommended that you have a teacher assist you while using it. -Secure any loose strings, hairs, or clothes before operation. -Wear safety goggles when operating the router. -While the tool is spinning, never open the safety doors of the router. -Before removing the finished part, make sure to hit the emergency stop button. -And remember, if anything sketches you out, just don't do it.

How do I use it?

The use of the CNC router is split up into 3 sections. Creating your part in CAD, create the tool paths for your part in a CAM software and converting it to G-Code, and then using the G-Code to machine your final part. I'll go in depth on how to do the second two, as at this point you should be able to design parts in Solidworks.

This video by a talented home machinist should help out.

CNC Dummies for Routers

CAM Software

By using CAM software, you can turn 3D design files into tool paths, and then those tool paths into G-Code. The first order of business is to have CAM software. The easiest CAM software is HSM Express for Solidworks, made by Autodesk. This is the easiest software to use by far.

  1. First, open up your design in Solidworks.
  2. Navigate to the section of the upper toolbar labeled 'CAM.'
  3. Create a new job, and open the 2D milling drop down, and select the option most suitable for the area that you want to clear out. For example, for an inlay cut, I would use a 2D pocket to clear the material.
  4. Once you select that, you must specify the tool for the action. We have a set amount of tools in the lab, that should be around the CNC machine. Different tools have different uses, For example, a flat end mill does a really good job at clearing out lots of material, and leaving nice flat bottoms with more accurate corners. Depending on the size of the tool and the scale of your part, you should select different tools. It's most recommended to familiarize yourself with different types of tools before proceeding past this step. To select the tool that you have in HSMExpress, you need to search the internet for the tool that you have based off of the number at the end of the tool. From that, you can filter the tools on the tool page to find the tool that you need.
  5. After specifying the tool, you can designate the area that you must clear.
  6. HSMExpress will begin generating tool paths, and you can visualize those by right-clicking the tool path in the CAM manager on the left side. If the tool path says that it is invalid, you may want to check the size of your part and the size of your tool, sometimes your tool will be too large to accurately generate the tool path. Always make sure all of the tool paths are accurate.
  7. Once you have verified that the tool paths are accurate, you're ready to post-process.

Post-Processing

Because the machine that we have in the lab is quite weird, there are some different steps for post-processing.

  1. In HSMExpress, click the post process button.
  2. Under the post configuration section drop down, select 'FANUC / fanuc.'
  3. On the properties, disable 'Allow Helical Moves.'
  4. The program name must be a number to save it, so set it to a memorable number.
  5. Once you've selected the post-process button, there are some things that you need to edit in the G-Code.
  6. Find and remove G94 and G40 from the G-code at the top. It will probably be in line N10 with G90, G17, G49 and G80.
  7. Remove the two lines that say G28 G91 Z0. There will be one early in the code and another near the end.
  8. Remove the line that reads G43 Z0.6 H**, whatever number appears after the H, That line probably will be N60.
  9. Remove the line that reads G54
  10. Remove the line that says G90
  11. At this point, you should be done. Put your G-Code in the shared file, and make your way to the CNC router.

Using the CNC Router

The final and most nerve-wracking step of the process is actually turning that code into a finished part.

  1. Get up out of your seat and go to the machine shop.
  2. Please get a teacher or someone with more experience to help you set up, and machine your part. We'd rather not cause unnecessary damage.
  3. Select the blank that you are going to machine into your final part and secure it to another piece of wood (currently MDF is used to secure other blanks). This could be secured with screws, or if it's extremely thin you can just use the suction through the MDF.
  4. Use wrenches to change the tool at the end of the spindle and try to fit the tool tightly. Use the wrenches to tighten it in.
  5. Press the green button on the CNC and turn the vacuum suction on.
  6. Turn on the PC and open Velocity CNC. Velocity CNC should connect to the router. If not, check the cables.
  7. When in the machine, go to the top of the screen and find the option to 'Clear Machine.' This should be under 'Coordinates.'
  8. Under the jog tab, move the end of the spindle to the top left corner of the blank. Once it's in the top left, adjust the Z of the machine so that the spindle is a fair bit off of the table. Once it's in the correct place, under 'Coordinates' select 'Zero Machine.'
  9. In the top left corner, open up your G-Code. Most likely there will be errors with the placement of the part on the bed. Disregard these for now.
  10. Now you'll be selecting the place for your part to be cut. In the display, you should see light blue lines, and then the red lines of your code. The blue lines are the bounds of the machine. Move the spindle towards the bottom right and under 'Coordinates' press 'Zero Program.' You should see that the red lines moved in relation to the blue lines. Adjust the program zero without changing the machine zero until your code is within the blue boundaries and you aren't receiving any errors. Finally, move the spindle until it's just barely touching the blank, and for the last time press zero program. At this point, you could be done, but I'd recommend jogging the spindle to the top left and bottom right of where your part will be cut out, just so you can assure it's within the material that you have placed on the bed.
  11. It's finally time to cut. Go get some safety glasses, and press 'Start.' I stand just a little bit back from the machine because frankly, it freaks me out a bit. Watch your part closely as it's being machined, and if anything looks out of the ordinary or not coming out how you like it, hit the bright red button on the side of the machine to stop it. You can always take another shot at it.
  12. If it's come out how you like it, hit the red button and turn off the suction, and remove your finished part from the machine.
  13. Be a good person and make sure to clean out the CNC and leave it in a better state than you found it. Remove the tool from the spindle if you're done using it, and place it back with the others.
  14. Congratulations! You've now learned how to use the CNC router. Be safe, this is a lot of power for one person to have :^)

Quick videos that may help!

CNC Basics 2

NYC CNC HSMExpress CAM

These two guides are made by a very skilled home machinist and should give a bit of visual help on the whole process.