Pre build ponderings

[Ubatoid]

Well I've been lurking around this forum for a couple of months now reading about all the builds and projects and I have been inspired to build my own plasma table for our workshop. Before I go all out on my planned 2.5m x 1.25m build , I would just like anyone to point out any glaring errors I am about to make or to make any comments. We need to be able to cut 1mm mild steel upto 12mm and plan on using a Lincoln Tomahawk 1538 Plasma
I am going for a steel lower table with aluminium water quench tank, aluminium gantry powered by 2x Nema 34 steppers geared 2:1reduction , V rail one side with Cold drawn flat bar with roller bearing the other side, rack and pinnion drive on the X and Y and with a ball screw Z axis powered by a direct drive Nema 23.

Obligatory Mach3 and Sheetcam controls. A couple of questions though, I am not sure how to wire the limit and home switches, ie, where to make the connections.Do these go back to the LPT port on the PC wired into the serial lead and ground when made or should they be normaly closed ? I plan to use the CandCNC THC system, does this feed back to the MACH controller and control the hight via the Z axis or does it use a seperate actuator ?

Thanks for any comments in advance.

[Torchhead]

Home and limits connect to the Table I/O card (part of any of our plug-n-run systems). You can have 4 homes and unlimited limits (wired in series). One home (Z), is used for the "touch-off" sensor (IHS) in conjunction with a Floating Torch Holder. The DTHC does not control the Z directly. It sends signals to MACH that control Z. MACH has THC logic as part of it's core engine. Besides being integrated as part of the toolpath for THC moves, having a fully functional Z affords you a lot of flexibility on your machine. It's easy to switch over to other types of cutting (just load a different MACH Profile at startup), and you can even do mixed mode type operations (like plasma and scriber in the same job) SheetCAM has all of the auto-touch off moves, leadins/outs, kerf offset, pierce height, initial cut height, end of cut pause, etc.

The DTHC has been enhanced recently with a "Smart-Kut" feature that allows it to set it's own target height (Preset Torch Volts) by sampling the first few inches of a cut. It's an option on the screen controls. Coupled with the DCP-01 Digital Current Probe option you have precise control over plasma cutting.

If you need any further technical information then feel free to join my Yahoo Support Forum. Also it's not a bad idea to download the system user manuals from the Website. All of the information about switch connections and setting up MACH are in the manuals associated with each type controller. The front end electronics (PC interface) are the same on all of our systems including the DTHC. The DTHC Setup manual has a lot of information about the DTHC, DCP and how to connect to a plasma unit, and lots of general plasma cutting information and theory. While there is not a specific section on the Lincoln unit we can help you make the two internal connections you need for automated control.

TOM caudle
www.CandCNC.com

[Ubatoid]

Thanks Tom for the tip. I did indeed download the manuals and I am a lot wiser as well as being a little overwhelmed by all the new information. So it looks like I need to add a UBOB board to my shopping list aswell as a DTHC board. Floating torches is something I wasnt aware of. Am I correct in thinking this system isolates the torch from the Z axis by a spring loaded carriage, the torch being brought down at the start of a new cut until the torch slide activates a switch which gives Mach a known measurement to the top of the material therfore giving accurate pierce hight control ?

Thanks again for your input.