Is Initial Height Sensing Necessary?

[IndustrialRec]

Hey guys super newb question I'm sure, but we just built our CNC table with ball screws and linear guides. We went with a Hypertherm 85 w/ Machine Torch and went through BOSS for a magnetic breakaway torch holder. Also using Proma 150 THC with Mach3 and Sheetcam. We do not have any ohmic sensing collars or floating head switches to do initial height sensing...... So is it necessary? Am I missing something simple? Any help would be great! Thanks!

[acourtjester]

One of the more important things with CNC Plasma cutting is having the correct height for piercing when starting a cut operation. There are many post here about the problems around that point and what happens. You should have both on your table, at lease a floating head assemble. With both you have a way for your table to know where the surface of the metal is and a safety if one does not to protect your torch.

[beefy]

Hope you did your homework regarding using ball screws on a plasma table. Depending on your max speed and table length you could get whipping of the leadscrew.

Imagine you start off with your slats perfectly flat and parallel to the X and Y axis, then theoretically you wouldn't need initial height sensing or torch height control (assuming no warping of the metal sheet and it is also perfectly flat). However, you'll get slag on top of the slats at some point, or thinner sheet may warp while cutting and a perfectly set up table goes out the window as far as knowing for sure where the exact height of the top of the sheet is.

I wouldn't take a shortcut on initial height sensing, otherwise you may find yourself paying for it with damaged nozzles, etc.

Keith.

[IndustrialRec]

Thanks for the input guys!

[jimcolt]

One pierce too close on material thicker than about 1/8" will damage the nozzle orifice. Pierce height and pierce delay time are absolutely essential , but only if you want the best cut quality and consumable life! Jim Colt Hypertherm

[IndustrialRec]

One pierce too close on material thicker than about 1/8" will damage the nozzle orifice. Pierce height and pierce delay time are absolutely essential , but only if you want the best cut quality and consumable life! Jim Colt Hypertherm

Thanks for the heads up Jim. I believe I have the Hypertherm settings for pierce height, delay, cut speed etc. in my Sheetcam. As long as I zero out to the surface of the plate at the beginning of the cut, those settings as well at my THC should take over correct? Thanks again!

[Nacs Fab]

Your machine will need to sense the top of plate on prior to each pierce. Since I am pretty sure Proma THC does not have any type of ohmic sensing, you will need a floating head with limit switch and will need to set your switchoffset in the Sheetcam Post file (which ever one you are using). Changing your sheetcam post can be further explained once you get to that point. You will need to design and install a torch holder that has a linear slide or something precision, that will allow your Z to drop down and "zero" based off of it tripping the limit switch I mentioned - basically the .25" of travel the limit switch itself requires to trip fully. Then Mach can follow sheetcam parameters and raise the torch from that known point, to pierce height, drop down and begin cutting. It will be at that point your THC will take over.

Here is one of our Member's video showing it in action.

https://www.youtube.com/watch?v=irhDCCx9JCg