So Adam, you’re building a robotic cutting machine… How do you plan on getting the cutting tool to draw the pretty pictures on your workpiece? Hopefully this post will answer that question at least from the hardware perspective.
30,000 ft View of Components
The machine has a gantry that moves across the x axis of the workspace. The cutting tool is mounted to a carriage that traverses the gantry in the y direction. I’m using x and y fairly arbitrarily as I’ve seen different machines oriented differently. This carriage also raises and lowers the tool in the z axis.
This motion is actuated by stepper motors through rack and pinion gears. More on steppers later, but for now just know that they’re a type of electric motor able to rotate a specified number of degrees and stop. Some folks use servo motors here, but they’re beyond my requirements and budget, so I’m not going to get into that discussion at this point.
Stepper motors are connected to controllers that tell the motors when and how far to turn. Each controller is connected to the power supply and the break out board. The break out board interfaces with a PC via parallel port. The break out board may also have inputs for limit switches, emergency stops and torch height control. Torch height control measures the voltage of a plasma cutter’s arc to determine its distance from the workpiece. (Similar concept to why I kept blowing the breaker when I was stick welding and let the electrode get too far from the weld…) This is handy when you’re cutting material that isn’t perfectly flat.
There are several options when it comes to acquiring and assembling the electronics portion of a CNC table. One can purchase components separately, as part of a package deal that include various combinations of parts, or as a turn key kit including motors, controllers, power supply, torch height control, enclosure and wiring.
|Ad Hoc||Partial Kit||Turn Key Kit|
|Controllers / BOB||$260||incl.||incl.|
|Torch Height Control||$268||$268||incl.|
|Misc. Cables, Switches, Cooling||$250?||$200?||incl.|
|Time||30 hrs?||20 hrs?||incl.|
|Support||None||None||Included + 2 yr Warranty|
|Total||$1294 + time||$1256 + time||$1575|
I put together the above table to try to compare the options for putting together the electronics for my table. The “Ad Hoc” column is basically sourcing different components off ebay. The “Partial Kit” column is using the supplier recommended in the Bill of Materials that came with my gantry kit. This kit uses slightly less powerful motors than those quoted in the other two columns. The “Turn Key Kit” column is the Dragon Cut 620-4 kit from candcnc. The THC quoted in the first two columns is a really basic unit. I’ve seen it demoed on youtube, and it seems to work all right. The candcnc THC seems more robust though. It also has custom integration with Mach 3 software and is made and supported in the USA.
I think the table pretty much speaks for itself. There’s no way the time and (most likely) frustration of putting together one of the DIY options is worth the $300 difference. This is especially true if you take into account the warranty and support going forward.
On that note, I wrote Tom at candcnc an email asking for clarification on which of his systems would be best suited for my project. His site advises using the 620 oz. in. motor kit for gantry weights over 50 lbs. I figure that’s almost exactly what my gantry will weigh. I wasn’t sure if that advice was assuming one or two motors to drive the gantry. He responded within an hour with a very informative email. He informed me that they assumed two motors driving the gantry, so the 620’s are the way to go.