The Craftmans Shop > New from Old
Titivating A CNC Plasma Table
RodW:
--- Quote from: awemawson on March 23, 2017, 10:16:29 AM --- I am undecided on exactly how I will locate both the HSR-15 sliders and the ball nut location,
--- End quote ---
I don't know if this will help you, but this is how I made my floating head Z axis using HGR15 rails.
This is the floating head
I've added an adjustment screw on the other side so I can keep the switch movement before triggering the sensor to an absolute minimum. Its just a countersunk screw with a lock nut to keep the plates apart. One day, I'll replace it with a nice knurled knob...
I know how you feel working out the design. What I finally built was probably about version 87!
I've got everything built except the table but its all cut up and ready to weld.
awemawson:
Thanks Rod.
At long last I've found a bit of time to go from a rendered model of the front plate to making a physical prototype. This will allow me to develop the Floating Z bit, and finally decide on which alternative mounting positions to use for the rail slides and the ball nut mount.
Fairly obviously the final version needs to be a tad wider to accommodate the counter bores for the M4 cap screws fixing the rail sliders, but with this mounted I can develop my ideas a bit further
PekkaNF:
--- Quote from: awemawson on March 30, 2017, 05:47:16 AM ---Thanks Rod.
At long last I've found a bit of time to go from a rendered model of the front plate to making a physical prototype. This will allow me to develop the Floating Z bit, and finally decide on which alternative mounting positions to use for the rail slides and the ball nut mount.
Fairly obviously the final version needs to be a tad wider to accommodate the counter bores for the M4 cap screws fixing the rail sliders, but with this mounted I can develop my ideas a bit further
--- End quote ---
Nah, just open then couterbore out with a slot drill, mechanically it will fine and look the part.
Out of curiosity....the "floating" feature is arranged with stepper motor control? Like Z-is sent from program and then there is a whizbox that superimposes torch control over that setpoint and drives the stepper?
Pekka
RodW:
--- Quote from: PekkaNF on March 30, 2017, 06:01:07 AM ---
Out of curiosity....the "floating" feature is arranged with stepper motor control? Like Z-is sent from program and then there is a whizbox that superimposes torch control over that setpoint and drives the stepper?
Pekka
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Plasma is a bit of a funny animal when it comes to CNC. The floating head is to find the surface of the material when initially piercing. The torch basically hangs on a section that can slide up when the torch head hits the material. This triggers a float switch (proximity sensor in my example above). So the torch then moves up to adjust for switch hysteresis and the material height is recorded. The torch then retracts to pierce height (say around 3-5mm) and turns on. The plasma machine sends a signal back to say the Arc has been established (ArcOK) and then the controller counts down for a pierce delay. After that, the Torch moves down to cutting height (say around 1.5mm) and then off it goes on its merry path to cut your part.
The problem then is that material is not dead flat and thin material can warp from the heat so most modern CNC Plasma controls measure the torch arc voltage as there is a linear relationship between cut height and arc voltage (voltage increases with Torch height). The controller then controls the Z axis height to keep the voltage at the desired level.
There are several other methods to sense the material. Ohmic sensing simply uses the material and the torch tip as an electrical switch (without the 300 volt arc frying your electronics). Others monitor Z axis torque (or current) so that when it starts to stall as its driven into the material, the material height is recorded.
So in summary, the plasma table is simply an XY machine where the Z is let to do its own thing to keep a stable arc voltage.
PekkaNF:
Thank you, I was wondering the rollercoaster drive on steel plate. Long time ago I was watching often even then old "optical" tracker of semiautomatic oxyburner to cut plates. They were not that simple to use and adjust. Sometimes the "seeker went wild" and run ofcourse torch blasting thick steel plate to art forms :doh:
Pekka
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