Plasma table build, first question....

[Web Goblin]

When you say torch height control are you talking about Initial Height Control for setting the start height or Arc Voltage Height control for keeping a stable height while cutting?

[Davek0974]

It was arc-voltage control I was mentioning. Not a mechanical height setting etc.

i can at least add it as an upgrade now :)

[Web Goblin]

Seeing as your cutting area is small you might get away without AVC if you get your table levelled to your torch.

[Davek0974]

Excellent, that's a plus point then :)

should be be some stuff coming today.

[Robin Hewitt]

Touch start really means angling in which is tricky. THC is for Americans who weld up massive plasma cutters with flood tables and then discover that they are so far off square there is no way they can possibly work without one. Then they read about pierce height and cutting height and they are so full of stepper motors that they can't see any other way to do it, usually ending up with the same motor they are using to move a 200lb gantry just to lift the torch.
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Do you really need mega speed? It is nice if you have to go to the opposite corner on an 8'x4' table to start the next cut, but are you really going to be pressed for time? That long repositioning may just factor in nicely as the duty cycle on the cutter.
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I think you do need 0.1 G acceleration minimum to cut corners. More is better. Working in G makes the sums nice and easy if you are running low friction linear bearings. If the gantry weighs X pounds then a force of X * 0.1 lbf will accelerate it at 0.1G

[Davek0974]

Brilliant, so doing away with THC, what do i need on the z axis?

does it just need a manual setting or is it best to have a stepper motor connected to mach3 so it can set piercing height then cutting height plus lift it clear to rapid.

my torch will strike at 0.5 to 1mm and cuts at 0 to 1.5mm or so, up to about 6mm thick, after that it must be dragged.

Speed is of little importance to me.

[Robin Hewitt]

I am sure it is possible without HF arc starting but I have never stopped to figure it out.

If you are only 1mm above and fixed vertical, where do the sparks go during the pierce?

Is there some software that will add a sideways component?

[Web Goblin]

Torch height control isnt just for large machines or under water cutting. It is there to keep the correct torch height so that the correct part of the plasma arc is cutting the material and giving the straightest possible cut.
Speed is important to plasma cutting. Travelling too fast will give apoor quality cut and you can easily lose the arc transfer or end up goughing the plate rather than cutting it. Travelling too slow will also give poor quality cut and also a wider kerf.

[Davek0974]

Thanks,
i am looking to add a z-axis after watching some videos on YouTube and playing with sheetcam and mach3.

It it will at least give me the option of adding THC later on with little hassle.

my torch does have HF start but not pilot arc.

[Boyan Silyavski]

You will need this Complete Compact THC MD system ( CNC Plasma Z axis controller ) | eBay, or at least half of it, it works with both type plasmas. Look at the videos in You tube or their web.

As to 0.02 precision, with a build like the one inspired you, you will be happy to stain in the 0.5mm ballpark. But having many alu profiles as you say, you could do far more precise build. Something like the cncrouterparts kits. Or round shaft inserted at the slots, could make cheap and precise rail

You can clock the belts on the long axis via shaft at one of the ends. In fact you should. My current machine is build like this.