Building CNC Plasma Table

[rehoward]

Hi all, new guy here,
I am in the process of gathering parts and info for a CNC cutting table I would like to build. I am using a Lotos LTP5000D for power supply and now am shopping for a machine style torch for it. Here are some questions that I have. BTY, I am on a tight budget so I am looking at Chinese stuff as it is so cheap to buy.

I see there are quite a few Chinese knockoffs at rediculously low prices. Which one is best? I know that is probably a silly question because most of them look very similar.

I have a Lotos LTP5000D power supply capable of providing 50 amps. I will use it maxed out only occassionally. It also features a pilot arc which I assume is a small high frequency high voltage initial arc which the main arc follws.

The Chinese machine torches seem to be mostly of the P80 variety. The consumables are cheap. Is this a good size tip or would something else be better?

Should I buy a torch with a metal body or will a plastic body work?

Some have an extra pigtail with a 2pin or 3 pin connector. I assume I will not need this on the machine type gun. I think the 3 pin receptacle on the plasma machine will be used instead and be routed to some sort of controller provided by the 3 axis driver and I/O. Is this correct or does I/O require a seperate board? Are there control cards specifically designed for axis control on a plasma table? Maybe I can tie into the 3 axis controller I/O to turn the torch off and on?

The power lead on these Chinese machine torches all seem to have a brass female fitting on the end of the hose. With my unit the female fitting is mounted on the plasma machine. Is this a common problem? Is there a gender change adapter available to correct the mis-match?

Is there any standard for fittings used on a plasma cutter?

Whew. More questions than I thought. Many thanks for any and all input.

Randy

[acourtjester]

I can only tell you my experiences when I first started into CNC plasma cutting (with no outside influences). Here is a video of the first table I built, this shows a P80 torch I bought from eBay, and it used HF start using a Everlast multi welder (with Plasma). Many of the things you are concerned with are valid. First one of the p80 torches did not work as the air passages were no complete (no air flow.) and there is no way to tell if the fitting will match you hose. Another thing is the nozzles are large and no real size selections, they are just made to blow through metal when cutting, no real detail. There also is another machine torch called a P81 I used on a longevity I 80 plasma similar to the other torch with the same complaints. And be very careful ordering from China due to the Corvid -19 shipping is almost not working at all.

[rehoward]

What would be a better choice in nozzle size to get good detail? Most of my cutting will be 1/4" and under. What is the microswitch for on your torch holder? Thanks

Randy

[rehoward]

I see that some machine type plasma guns have "blowback start". What is this and is it a requirement for a machine torch? My power unit has a pilot arc. I was thinking that would be adequate for a DIY plasma table.

Randy

[acourtjester]

Here is the switch I use, I like the roller type and use them for all home/limits on the tables I build.
https://www.ebay.com/itm/New-AC-380V-15 ... 1438.l2649
The "blow back" type torch is an internal operation of the torch itself and a torch cannot be changed from one to the other. This is the concept but may differ from torch to torch, the electrode and nozzle are in contact when not cutting and the air inrush causes them to separate. This causes an arc which is the start of the Plasma development for the cutting operation. I'm sure others will give a much more detailed description but that is the basics of it. The pilot arc or HV start is actually used to create the arc for starting the plasma and is an electrical action similar to a spark plug
spark, or tig arc start this is why there is a lot of noise with that type. If cutting 1/4" and thinner a smaller nozzle would give better detail, there are other things that also affect cutting like a swirl ring. A swirl ring helps to control the flow of air for the cutting operation for cleaner cutting.

[acourtjester]

here is a description of the plasma cutting operation
https://www.lincolnelectric.com/en-us/e ... works.aspx