CNC Torch Table/Research Development

Overview

CNC Torch Table

• Torch Table Blog Post
• Torch Table Concept
• Plasma Cutter Design
• G-code
• Torch Table Motors
• LinuxCNC

Torch Table Trouble Shooting

For those extra hard to reach bugs

• Check stepper motors
  • They should turn when powered off, so the whole table should move freely. If it doesn't fix it.
  • When the motor controller is powered on, with the PC disconnected, the stepper motors should be locked in place or provide significant resistance.
  • If everything checks out, the motor driving circuitry and the stepper motors are at least working correctly.
• Check the PC parallel port.
  • You can do this with a multimeter and LinuxCNC. If you test one of the pins under control and its jumping around like crazy then the computer is at the least sending something with the parallel port
  • There are options to change the parallel port address from the default. In the case of the IBM laptop, the parallel port was 3BCH, which is a hex value.
• Check the pinout of the cable.
  • In our case we used a shielded straight pass through cable, which means each pin on either side corresponds to its matched up pin on the male/female connector.
  • If it's different than what you think it should be, according to whatever motor controller you're using, you can adjust the pin out in EMC2. Look up how to do this.
• Check installed version of Linux.
  • In the version we used, there was an issue where the kernel drivers for 8.4 weren't compatible with 8.10 and above. This means that it installed fine but there wasn't an option for using the special real time EMC2 kernel. The fix is to reinstall using either the live CD which will leave you with a clean Ubuntu install with the software already installed (very convenient if it works), or installing from scratch Ubuntu 8.4 and installing the package seperately from [[1]]

Work piece table

I designed a modular table that could be used by itself or strapped together to make a larger table. I also designed a method to use bricks as the under surface to protect the metal the table is made from getting cut by the plasma cutter.

To accomplish this feat I chose a space frame structure made up of eight 2.5' by 2.5' by 1' cubes. They used 11 gauge 1.5" diameter square tubes and used 26 inches of tube. Some material is lost due to cutting and the exact dimensions aren't as important because the height will be adjustable with bolts on the feet.

The bricks are held in place by placing 2.5 foot long angle beams across the top of the square such that a brick can be placed so the sides of the brick rest on the walls of the angle beam, not on the apex. The weight of the brick keep the angle beams in place and the angle beams rest against the inside of the space frame to keep the bricks from pushing the angle beams apart and slipping through.

Another neat aspect of this idea is that there are several ways to adjust the height of the table. One method is to raise and lower the bolts, but this will only net you an inch or more of precise motion. The other option is to rearrange the brick pattern such that they stand taller lenghwise, this uses more bricks but also makes the table taller by several inches without doing something you might be doing anyways like switching the bricks over to a less burnt section. It is still unknown how good a work surface bricks actually are. It is hoped that they will be sufficient as they are a bountiful resource at FeF.

Review

Please submit comments here. Please review our design rationale first.

Particular points:

• Suitability of 3x1/8" cold rolled rail as a guide
• Suitability of thin gauge 1" square tubing for most of the gantry
• Structural or stability issues?
• Acceleration issues?
• Feasibility of using a laptop and compromises therefrom?
  • run [realtime latency test] before getting too attached - laptops are notorious for hardware timing glitches.
    • Lawrence: Performed, just not documented. We were getting in the 30-50 micro seconds range which is acceptable for right now. We have several other computers but the laptop was the only one that didn't have an immediate hardware issue.
  • dust generated by plasma will get in keyboard and fan, wear out quickly. hard to replace laptop parts.
    • Lawrence: Good catch. this is especially relevant since the recommended parallel cable length is 3 feet to 6 feet and the motor controller box itself has rather shortish cables. The ideal solution is to use something that is more robust and able to be isolated like an embedded processor in an enclosure. Best for version two. for now however,the best option will probably be a dust cover for an external keyboard and a foam fan filter for the motor controller and final pc configuration.
• Suitability of plasma cutter?
• Potential improvements?

See Also

• Lawrence_Kincheloe_Contract2
• XYZ Table

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