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Author Topic: China HF-start plasma CNC design!  (Read 14852 times)
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TSOffroad
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« Reply #20 on: April 01, 2013, 09:58:22 PM »


To be honest, I wanted to get more cutting depth and recently bought a new plasma with 25mm cutting capability. For this, I found Everlast powerplasma 60, which is a pilot-arc plasma and has 3-phase input so I don't need large fuses. Plasma cutter works fine, Everlast is a funny company though. Had lots of trouble finding who really sells the plasma cutter (official importer just said they'll have more in future, maybe next month, maybe later), and after buying the plasma cutter (from another company that apparently had bought it from official importer as it had their sticker) they didn't give me access to their official forum but banned me from the forum - just for registering. Really strange. However, the plasma works fine, and was really reasonable price. I'm using a modified WSD-60P torch.

As long as I used the "tuned" chinese HF start plasma, the consumable lifetime was about the same as using it with manual torch. Not that good but the consumables are cheap.

I have been happy with performance without height control so I have not implemented it.



What do you mean, how to wire the cutter? Power in, plasma on/off with relay (to torch "start switch" wires).



Ok....sorry to keep asking questions.  But plasma gets hooked up this weekend want to get it cutting ASAP.
Soooooo...my controller needs two wires for "plasma on"...these are the switch wires, correct ?

I also need wires for "arc ok" and arc voltage.  The voltage I assume will have to come from the torch leads in the form of "raw voltage", then divided.  What about the "arc ok" signal wires ?  Any thoughts ?

Thanks again in advance....
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MachinistSF
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« Reply #21 on: April 02, 2013, 04:04:58 PM »

Soooooo...my controller needs two wires for "plasma on"...these are the switch wires, correct ?

The wires going to the torch switch need to be connected to a PC controlled relay
that connects the wires together for starting arc. Just like pressing the switch on
the torch.

I also need wires for "arc ok" and arc voltage.  The voltage I assume will have to come from the torch leads in the form of "raw voltage", then divided.  What about the "arc ok" signal wires ?  Any thoughts ?

Arc ok needs some current transducer to measure the DC current to arc and a limit to set the signal
after reaching high enough current. I have not implemented it. I just wait a second after switching
on the arc.

Also I have not implemented arc voltage measurement.
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TSOffroad
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« Reply #22 on: April 02, 2013, 05:17:54 PM »

The wires going to the torch switch need to be connected to a PC controlled relay
that connects the wires together for starting arc. Just like pressing the switch on
the torch.

Arc ok needs some current transducer to measure the DC current to arc and a limit to set the signal
after reaching high enough current. I have not implemented it. I just wait a second after switching
on the arc.


Also I have not implemented arc voltage measurement.



Sooo...for the plasma on, I believe this is the relay board inside my controller.  So, hooking up the plasma torch wires to it should do the trick !?!?

http://probotix.com/relay_boards/rbx-1_isolated_3_channel_relay_board/


As for the arc voltage, It's looking like I'm going to have to get a current transformer and divide the voltage from that to get the 20:1 required input for thc.


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MachinistSF
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« Reply #23 on: April 03, 2013, 11:15:31 AM »


Sooo...for the plasma on, I believe this is the relay board inside my controller.  So, hooking up the plasma torch wires to it should do the trick !?!?
http://probotix.com/relay_boards/rbx-1_isolated_3_channel_relay_board/

Yes.

As for the arc voltage, It's looking like I'm going to have to get a current transformer and divide the voltage from that to get the 20:1 required input for thc.

No. Current transformer is for measuring current. It won't work with plasmacutter because the current is practically DC. You
would need a current transducer for DC (hall-sensor based, for example), and this signal could be used for producing an "arc ok"
signal.

For measuring the voltage (which is also practically DC) you only use a resistive voltage divider with some additional components to
shield your electronics from high voltage (of HF start) and noise.. If you are not familiar with electronics, I wouldn't try to build
it but get a ready made THC which has the divider etc. in it..
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TSOffroad
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« Reply #24 on: April 03, 2013, 12:58:11 PM »


Yes.

Perfect.  Confirmed this with plasma table mfgr as well.


Quote
No. Current transformer is for measuring current. It won't work with plasmacutter because the current is practically DC. You
would need a current transducer for DC (hall-sensor based, for example), and this signal could be used for producing an "arc ok"
signal.

For measuring the voltage (which is also practically DC) you only use a resistive voltage divider with some additional components to
shield your electronics from high voltage (of HF start) and noise.. If you are not familiar with electronics, I wouldn't try to build
it but get a ready made THC which has the divider etc. in it..

I think CandCNC makes a "retro fit" kit for older cutters and those without divided voltage or arc ok signals.  At 132 bucks, this should get me the signals I need for the controller.

Cheers !

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TSOffroad
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« Reply #25 on: April 03, 2013, 03:27:34 PM »

Worked with table mfgr, think we've got it figured out !

I'll post in the forum (don't wanna hijack your thread) with results.  Thanks again for your help sir..
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pimpbike
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« Reply #26 on: April 12, 2013, 06:42:47 PM »

Hi MachinistSF I ran across this when searching Google. I saw your YouTube vid also. Instead of running a big long wire from tip to ground. Couldn't you just run a jumper wire at the front to the case from the ground clamp to the torch?
Also how has your plasma machine held up?

Dan
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MachinistSF
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« Reply #27 on: April 14, 2013, 02:46:48 AM »

Hi MachinistSF I ran across this when searching Google. I saw your YouTube vid also. Instead of running a big long wire from tip to ground. Couldn't you just run a jumper wire at the front to the case from the ground clamp to the torch?

You can run the wire any way you wish from the tip of the plasma torch (which normally anyway connects to "ground" via the work piece touching it when drag-cutting, before arc transfer to work piece from the torch front piece) to "ground". This additional wire just makes the "ground" connection to tip reliable always, even if the work piece has a coating or such..

By "ground" I refer to the ground clamp connection of the plasma cutter. This is actually plasma current + terminal, as you propably know.

Also how has your plasma machine held up?

It worked without problems for the while I used it, before upgrading to a bigger plasma cutter. I still have the chinese plasma for portable manual cutting, but use the Power plasma 60 at CNC.
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plasma-cnc-mach3
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« Reply #28 on: March 31, 2014, 10:23:08 AM »

Hello MachinistSF, great project!!! Congratulations!!!

I have been building a CNC plasma cutting machine ( 2.4m x 1.3 m active area) driven with chains too, I have a cut40 plasma cutter. The height control that I will to use is the g31 method with a macro for M03 code (floating head). I would like to know the values of parameters in the plasma cutter that you has set ( current and air pressure) and the speed for cutting ( of course depending of plate thickness).

My current setting is: 65psi air pressure, 25Amp for 3 mm plate.
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joeaverage
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« Reply #29 on: May 18, 2014, 02:50:22 AM »

Hi there,
great looking project.
I service and repair welding equipment including these wee plasmas. I think you might encounter some excess wear problems
by earthing the nozzle of your torch.
More sophisticated plasmas earth the nozzle so the HF can start, usually at reduced current, something like 20A to
prevent excess wear/overheating of the nozzle, this phase is called pilot arc.
When the arc is offered up to the workpiece the arc 'transfers' to the metal to be cut, the plasma uses a current sensor in the
earth lead and detects 'transfer' and then releases the earth off the nozzle and ramps current up to full current setting.
If the earth is not released off the nozzle a substantial fraction of the cutting current flows thru the nozzle causing wear and
overheating aside from depriving the main arc from its full cutting potential.
A hall effect current sensor and relay or IGBT would solve the prob.
Of course it may work well enuf as is without excess nozzle wear....
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