Machsupport Forum
General CNC Chat => Show"N"Tell ( Your Machines) => Topic started by: MachinistSF on November 17, 2011, 06:25:04 PM
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Hi,
I just cut the first pieces with my new DIY CNC plasma today!!
It uses 3 steppers with chain drive for all axis. Z is a floating design with limit switch
for detecting zero at plate surface with G28.1 Z. Movement is 70cm x 70cm.
Torch is a PT-31 machine torch. Steppers are controlled with chinese 3-axis
TB6560 card - replaced 12V fan with 24V one and removed the "current
reduction when not moving" feature.
I initially had problems with RF interference from the Chinese CUT-40 HF-start
plasma, but I managed to solve the problem cheaply. I added a ground wire to
the copper electrode sticking out from the plasma torch - this way it creates always
a "pilot arc" (at full current) and initiates the cutting reliably without HF interference.
Without this it would not ignite reliably and would emit HF interference, causing
limit switches to trip, USB mouse at PC to stop working etc.. None of that now,
the immediate arc to groundwire will shunt the RFI, I'd say.. Based on some test
cuts, it works very nicely. I figured out that the electrode is touching ground through
the workpiece anyway, so it won't hurt connecting ground to the electrode always - and
this way it ignites reliably. It will also send a nice plasma flame to air if it is far away from plate!
I'll send some photos later. Now the main point is that this way one can use the
cheapest of the cheap Chinese CUT-XX plasmas for CNC, to save amateur costs!!
I haven't seen this anywhere else so I might have invented a new thing here!
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Here are some photos.
First one is an overall photo. The control electronics box is not shown. Plasmacutter is with the unit in a shelf. Ground is connected to clamp and the support "mesh" for part. It is so close to ground so it won't take much space when not used - I can put it under table.
Second is of the torch holder with z movement. There is also z touch sensor - the movement up and down is with chain (hanging from chain), and when z touches chain becomes loose and the lever to spring loaded microswitch opens. I think this is a novel design, I have not copied it from anywhere.
Third is the torch tip. There is a ground connection to tip with alligator clip. This modification produces a "pilot" arc from the torch. Without this it does not work ok with cnc use as ignition is unreliable.
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Here's a video!
http://www.youtube.com/watch?v=-VcNw8eoFVo
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It can be seen from video that it doesn't yet have THC.. I plan to install one based on a panel display with modbus communication. I'll connect a voltage divider to the display 0-10V input, and MACH3 modbus protocol support will directly read the voltage from the display (scaled based on voltage divider) via rs-485 bus from PC. Then the MACH3 plugin for THC will handle the Z control based on this voltage. But, it is not really very high on my list of things to do as it works quite nicely without THC on thick plates at least.
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The moving mechanics and motors are connected to safety ground, using a star ground scheme.
The plasma cutter ground is connected only to ground clamp (to be connected to plate to be cut), the support mesh for part to be cut, and the tip of the torch.
This arrangement is done so there is no plasma current flow to safety ground. These two grounds are mechanically separated by 6mm plastic plates, separating the base of the machine from the aluminium bodied moving mechanics. I think this is essential safety feature - otherwise there could be a ground loop burning the safety ground wiring with 40A plasma current. Just like with welding - you never connect safety ground to welder ground, so welding current can't flow through safety ground wiring (melting and burning it) if you forget to connect ground clamp of welder to a safety grounded item to be welded.
The wiring to control electronics is long enough that I can roll the plasma cutter mechanics outside.. That way there is not dust problem at all, as I can close the door when I plasma-cut. Of course, it limits me so I can't plasma-cut if it rains outside but I can live with that.
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This is cool! Thanks for showing.
Dan
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Great Ideas.
Thanks
Thorsten
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Hello, very nice project, will test into my CNC and CUT40 cutter. Question: connecting the tip to earth wouldn't destroy the tip if you trigger the torch away from the plate? I think that making the way you did, the plasma beam will cut the tip itself? Thank you for sharing your project!
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Hello, very nice project, will test into my CNC and CUT40 cutter. Question: connecting the tip to earth wouldn't destroy the tip if you trigger the torch away from the plate? I think that making the way you did, the plasma beam will cut the tip itself? Thank you for sharing your project!
The tip will propably be destroyed if you trigger the torch away from plate FOR A LONG TIME. Short times didn't matter, I did try that first to see if it would work at all. In the normal use, the arc transfers from the tip ground to the plate (to be cut) ground almost immediately. After this, only part of the current goes to the wire connected to the tip - and the resistance of the thin wire is much higher than the actual ground resistance to the plate (to be cut).
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Hello, very nice project, will test into my CNC and CUT40 cutter. Question: connecting the tip to earth wouldn't destroy the tip if you trigger the torch away from the plate? I think that making the way you did, the plasma beam will cut the tip itself? Thank you for sharing your project!
The tip will propably be destroyed if you trigger the torch away from plate FOR A LONG TIME. Short times didn't matter, I did try that first to see if it would work at all. In the normal use, the arc transfers from the tip ground to the plate (to be cut) ground almost immediately. After this, only part of the current goes to the wire connected to the tip - and the resistance of the thin wire is much higher than the actual ground resistance to the plate (to be cut).
Just adding.. Also in normal drag cut you are grounding the tip to the piece to be cut..
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Thanks for the reply. I think that what you made is exactky the same thing that Longevity plasma did. They claim to have a pilot arc plasma, and indeed they have, just like your machine they use a wire to ground the Tip ( not shown, but think its it). The price is very like a chinese price. They claim to work with CNC as well, but there is a video in their forum showing how to install their machines in a Torchmate CNC table. Seems to be a lot of problem with the HF, as they show how to properly ground the system because of the HF interference issues. Will try this on my CNC and CUT40 just like you did. Lets see if I get interference like they had or if your tip ground eliminates the HF just like in your machine. Again, thank you for sharing your ideas.
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I tried this on my cut50D and still have HF interference, must have some wires touching inside of case but using it free hand the plasma works great. any suggestions ?
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The arc itself still radiates plenty of RF interference, like any arc. Also there is high current flowing in the cables at dozens of amperes of arc current, run by some inverter. The control electronics must be properly shielded and grounded with any plasma cutting.
However, this interference seems to be a lot less than the interference from the sparks from HF start when the cutting arc (from torch to piece to be cut) doesn't start immediately. The interference from the "pilot arc" (of grounded tip HF start torch) is somewhere between those two - less than HF start, but more than just the plasma arc. Also the arc transfer happens much faster with the "pilot arc" as the pilot plasma stream hits the piece to be cut and heats it and destroys any coatings, so there is less time for interference problems before real plasma cutting starts. It works nicely for manual plasma cutting too - much easier to start cut with painted plate!
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Just purchased a burntables unit, should be here in a few weeks. I've also purchased a machine torch for my simadre cheap chinese "Cut50" unit. I'm going to try and use it to get buy until I can get my hands on a larger hypertherm unit. With that said....you talked about grounding the torch head. I can see where you have the alligator clip...but where does it go to to get grounded ? Do you have it specifically to the grounding rods or just to the ground on the plasma cutter. Any help is appreciated.
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Just purchased a burntables unit, should be here in a few weeks. I've also purchased a machine torch for my simadre cheap chinese "Cut50" unit. I'm going to try and use it to get buy until I can get my hands on a larger hypertherm unit. With that said....you talked about grounding the torch head. I can see where you have the alligator clip...but where does it go to to get grounded ? Do you have it specifically to the grounding rods or just to the ground on the plasma cutter. Any help is appreciated.
The wire is connected to the plasma ground (where ground clamp (connected to piece to be cut) is also connected already).
I connected the wire to the connector that attaches the ground clamp thick black wire to the plasma cutter plasma ground connector. When you pull the black rubber away there is an allen key connection inside. Just slide extra wire there.
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My next questions would be....
How's it holding up ?
Are you using AVHC ?
How long do your tips last ? (piercings ?)
Thanks again for the reply's....helps alot !
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I would also ask,
Do you have any info on how you wired up the cutter ? I've been working for days to get some info with no success...
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How's it holding up ?
Are you using AVHC ?
How long do your tips last ? (piercings ?)
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.
Do you have any info on how you wired up the cutter ? I've been working for days to get some info with no success...
What do you mean, how to wire the cutter? Power in, plasma on/off with relay (to torch "start switch" wires).
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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 by the Tuned Chinese HF start? is it in their plasma cutter or an external device? Can you explain it?
Thank You
dwdw
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What do you mean by the Tuned Chinese HF start? is it in their plasma cutter or an external device? Can you explain it?
Thank You
dwdw
Please, read the start of this thread to see how I "tuned" the chinese HF plasma (not everlast) to get it to work like pilot-arc plasma, by adding ground wire to tip of the plasma torch..
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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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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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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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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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Yes.
Perfect. Confirmed this with plasma table mfgr as well.
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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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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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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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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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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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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First of all, thanks for the great contribution MachinistSF.
I built a cnc plasma cutter and i am having the same problem with HF interference (I suppose that is the problem), when I activate the relay that turns the plasma on, the usb communication with the computer is lost and the screen blinks. My question is, if it is caused by HF interference, does the ground wire (that would generate the pilot arc) have to be connected to the plasma ground or does it have to be connected to the ground rod in earth?. Sorry if the question is quite obvious but i am not a specialist. Another question i have is , do i need an additional circuit to support the pilot arc wire in order to cut contact when it begins to cut the metal?. I am working with a chinese plasma, named NEO P8014
Thanks!