Copied from a popular thread in the grabercars forum, CAD plans to build your own cnc router table are being made available to the general public.
If you want to see some photos of what Jim has built so far, please visit Image Gallery Here . Hopefully I will be able to update with more photos as Jim gets them to me.
Jim from Australia writes:
I use a CNC 5-axis router for making Foam Plugs. The machine is scratch built and the cutting area is 3m * 3m * 2m. I use the machine for building aircraft and boat molds. All up it cost me about $3000 AUD ($1500 US) to build. The router is a classic Gantry style unit. The slides are made using 2 pieces of equal angle to form an X with bearings between them. The XYZ axis is driven via a threaded rod suspended on each end with a pillow block bearing. I machined the threaded rod to attach a sprocket and ran a chain drive to a stepper motor. The router motor is a 17turn RC car motor running on 12V with a PWM speed control.
The motors and steppers are driven from the parallel port of an old PC using interface boards I assembled myself (kits) you can get them at http://www.oatleyelectronics.com/kits/k142.html (prices are Australian Dollars) (Steve’s note: does anyone know where to buy these items stateside?). Software on the PC is Mach2, which is found at http://www.artofcnc.ca/ you can download a free copy. To generate the CNC Gcode I use Featurecam.
I designed the parts in SolidWorks. Obviously my router is not big enough to do an entire plug in one go so I split it into sections using the split feature Solidworks. To each split section I then add locating dowels. This aids in assembling the plug from sections. The foam I use is standard 2-part Polyurethane expanding foam. I use fairly large cell foam as it much cheaper. Once the section is machined I spray it with a hibuild undercoat (spray on body filler) and machine it a second time. This leaves very little work to prepare the plug section for creating a mold. Once this is all done the sections are assembled to form the plug. The joins are filled and sanded to complete the plug.
Jim has decided to give his CNC router plans away for free. The Solidworks files are available for download here If you want the files in IGES format, you can download those here. (Note: files are packaged in compressed zip files. You must extract the files and keep the directory structure intact). Right now I am looking for someone to take the existing SW 3D files and convert them into working drawings. If you have Solidworks experience and want to help out, feel free to contact me about this.
You can get the 3D Solidworks viewer from the link to the left. This will allow you to view all the components and take the machine through all it movements as well as get the dimensions. The viewer is free.
My advice is to build a 3-axis machine first then upgrade that to 4,5 or 6 axis later. With 3 axes you can’t effectively cut anything along the edge without gouging. IE; it depends on the length of the cutter and how deep you can go before the collet hits the job. A 4 or 5 axis can get around this a fair bit but it still has limitations. You also have to have some very good software to generate Gcode for more than 3 axes. Its also a lot harder to get the Gcode right for more that 3 axis, IE; a lot more learning to do.
Here are some tips:
If you approach CNC as 2.5D (3 axis) all you need to do is make sure that
1. You have a flat surface on the underside
2. The cuts don’t allow the spindle to hit the job by cutting too deep. You can cut deeper if the cut slopes away at an angle
3. No undercuts if what you are cutting fails in any of these conditions you simply have to split the job up into smaller pieces to get around it.
You can use anything you like to machine your parts from however, the harder the material the longer it takes. I use foam because its cheap and quick to machine, although I have to do an extra finishing pass after applying hibuild primer, but again that’s cheap. There are lots of materials to use such as MDF, Clay, Wax among others. All have advantages and disadvantages. With foam I have no storage issues as I make it up when needed, its light, which is great for big molds, its quick to machine and cheap to make. Foam is not as good as say wax for the finish but after filler is applied there is no real difference. Best of all foam is cheap.
To prepare the foam I have to make up the blocks. I use a box to make the blocks. The base is an MDF sheet to which I screw on the sides. The sides are removed once the foam sets leaving the Foam Bonded to the MDF and ready for machining. I change the size of the walls depending on how big a foam block I need. The foam is split from the MDF at the end with a hot wire cutter that runs along the X-axis.
If you download the documentation (pdf) from the Oatley Electronic site, it will explain everything about interfacing the stepper motors. The sofware will drive up to 6 axis, Torch Contoler for Plasma, Digitiser, Servo or Steppers, Encoder feedback, and lots more. As for my setup I use Lpt1 for the XYZ axis and limit switches and LPT2 for the AC axis. LPT 2 is also used for the THC (Torch height control) on the plasma but that does not use the AC axis. If you use the controlers from oatley you need one constant current psu per axis plus one controler per axis. IE I have 5 controlers, 5 cunstant current units, 2 switchmode PSU (12V & 36Volt), PWM motor Control, THC, breakoutbaord with 4 relay outputs mounted in a 19in rack case. As for Art’s software you can use 2 lpt ports (5 inputs per port and 12 Outputs per port) USB (Up to 32 inputs and 32 outputs) Keyboard Emulation (any KBD switch) Joystick (USB or Game Port) for Jog functions Their is lots more options than that but thats the basics. As I said download the Software and Manual its all explained there.