Our CNC routers have a functional bed size of 4 feet by 8 feet. Height limitations are more complicated and may vary depending upon project dimensions, tool choice, and toolpath design. The combined height of the material and cutting tool cannot exceed 8.75 inches [see diagram A]. If your material is too tall, the cutting tool will not be long enough to cut all the way through the material. Thicker materials must be cut on a different machine.
CNC coordinators are available for consultation and walk-up file preparation/execution during their posted shifts, check the calendar below for shifts. You may also email cncfablabcoordinators@umich.edu to schedule a consultation.
Procedure
1. Consider
The first step is to have a good grasp of what you would like to do. What material would you like to use? What size is your project? What end-product do you want? What machine would you like to use? All CNC Lab assistants are available for consultation and walk up file preparation/execution during their posted shifts (see calendar above).
2. Talk with a Coordinating TA
Think of the Coordinating TA as an advisor for your CNC project. The Coordinating TAs hold regular office-hours to meet with anyone seeking to use the CNC machines. To speak with the Coordinating TA, first look at their office-hours posted on the Scheduling TA Calendar (see above). You can reach the Coordinating TAs by emailing cncfablabcoordinators@umich.edu and request an appointment during an available time slot. The Coordinating TA will reply to confirm the appointment. If the calendar is full, you may also stop by the Lab during scheduled office-hours as stand-by.
Bring your file(s) to the appointment with the Coordinating TA. He or she will review your geometry, discuss material choices and answer all your questions. At the end of the appointment, the Coordinating TA will work with you to schedule a cut time with a Lab Assistant on the CNC Calendar. Note that both Calendars (CNC and Scheduling) are available above.
3. Prepare Materials
The FABLab sells limited supplies of MDF, LDF, Baltic Birch Plywood, and Polystyrene Foam. Please check with Lab Staff for current pricing and stock availability.
If you are laminating material for a CNC cut, apply glue evenly and thoroughly upon a clean surface before placing it in the vacuum-press table for no less than 6 hours. The total drying time should be a minimum of 24 hours before the scheduled cut time. Use Gorilla glue if you are laminating foam. Verify that material dimensions do not exceed the table size (4′ x 8′). Full instructions for the vacuum-press table can be provided by Lab Staff.
4. Cut with a Lab Assistant
Arrive to your scheduled shift with your prepared file(s) and material. Upon arrival, a Lab Assistant will prepare your Mastercam file and cut your project. If you have prepared your Mastercam file already, the Lab Assistant will review it before cutting. It is required for the student to be present for the duration of the cut.
5. Clean Up and Pay
It is the student’s responsibility to clean up after the cut is complete. All scrap material must be taken to the outside dumpster and all debris/dust must be swept and discarded. Once cleanup is complete, the Lab Assistant will give you a pay-ticket for the cut. Pay for all materials and CNC cutting at the Media Center. Students who have outstanding charges or do not clean their scrap will not be able to schedule future appointments. Make sure to keep a record of your transaction.
Important Information
Aesthetics
The final appearance of your project will be affected by both tool selection and toolpath design. The use of different cutting tool end geometries will change the tooling marks on your project [see diagram B]. The specified step-over will determine the smoothness of the machined surface [see diagram C].
Tool Selection
CNC router tools are optimized for particular applications on specific materials. The Fab Lab maintains a large inventory of tools for different tasks. Ensure that you have chosen the best tools for your project by reviewing the tool chart. In general, larger tools will cut more efficiently, but smaller tools may be necessary for more detailed geometry. Use large roughing tools to take away large volumes of material, large finishing tools to refine broad regions of material, and small finishing tools to refine detailed areas. Always try to use the largest tool possible for your specific application.
Tool Geometry
Typical end geometry on CNC router tools is either flat or rounded. End geometry will affect the appearance of your machined surface [see diagram]. The cutting edges of the tool, the flutes, come in two primary varieties: up-shear and down-shear. Another commonly used tool is called a compression bit, which is a kind of hybrid, combining up-shear and down-shear flute geometry. More specialized flute geometry can provide more sophisticated cutting action. Review the tool chart or speak with a Lab Assistant to learn more about specialized tools.
Toolpaths
There are many different way to generate a valid toolpath. Each with their own advantages and disadvantages. When dealing with a surface, there are two types of toolpaths: roughing and finishing. These are described below along with specific toolpaths types.
Roughing Toolpath
A Roughing Toolpath is a toolpath that removes a large amount of material quickly. It cuts at incremental depths (depth cuts) and stays offset from the finish surface.
Finish Toolpath
A finishing toolpath only routes the finish surface and does not do any depth cuts.
Contour
A contour toolpath not to be confused with “surface contour” is used with curves and lines. It is typically used to do profile cuts from sheets of material such as ply and mdf. It is one of the most frequently used toolpaths and easiest to set up.
A pocket toolpath uses closed curves and removes all of the material within the curves boundary. The user sets the depth.
Parallel
A parallel toolpath can be used for both roughing and finishing. It generates toolpaths that route in parallel. This toolpath while robust can take a substantially longer time than other toolpaths.
Scallop
A scallop toolpath is one of the most frequently used surface toolpaths. It can be used for both roughing and finishing. A scallop toolpath generates itself based off of the geometry of a surface. Essentially, it takes the border of the surface and offsets it in while remaining flush with the surface. It does this repeatedly until it reaches the center of the surface. This toolpath is quick and efficent.
Surface Contour
A surface contour creates contour lines based off of a predefined increment. This can be useful when creating a topo-model since it is creating elevation lines.
Radial
Radial is a novelty toolpath that generally doesn’t get much use. It creates radiating toolpaths based upon a defined point. The further away from the point the less refined the surface.
Materials
The most common materials used on the router are foam, mdf, and plywood. The Fab Lab has 2-foot sections of 2″ blue foam available for purchase in 1-foot increments. Less common materials, such as plastics and cast plaster, can also be successfully machined on the router. For these materials, it often is best to speak with a Lab Assistant about specific material concerns. Metals and glass cannot be cut on the router. These materials are better suited for the CNC waterjet or CNC mill.
There is limited storage in the router bay available for material that will be machined within 24 hours. All material should be clearly labeled with your name and the date. Material left in the Fabrication Lab for more than one week will become the property of the lab.
Good material preparation is critical. The most common problem we experience is the delaminating of material during cutting as a result of poor preparation. Ensure that all material is laminated with a continuous layer of material-appropriate glue and clamped with adequate pressure for at least 24 hours.
Contact
You can reach the Coordinating TAs by emailing taubmancollegeRouter@umich.edu and request an appointment during an available time slot. The Coordinating TA will reply to confirm the appointment.