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MonoNeuron
07-13-2008, 08:50 PM
Hi Guys,
Could someone enlighten me on how to set up the Z axis for my plasma?
I have bought the MP1000C from CandCNC.com and Tom says I need to install a micro switch for the height adjustment and torch set off procedure. He spends quite a lot of time answering other peoples questions so I thought I would come here and leave him alone for a while and see what you guys can come up with.

I have no idea how to set this up.

Do I install the micro switch at the bottom of travel and zero from the top of the plate or do I set the switch at a known height from the table and input the thickness into Mach3 and work from there?
Where do I set the switch? 1" above the table. 3" maybe?
Do I make it adjustable so I can slide it along and set it anywhere for any height?
Will it get in the way of the torch when it cuts corrugated iron, for example, if it's set too low?

I am in a quandary so any help will be gratefully accepted.
Richard.

Torchhead
07-13-2008, 11:10 PM
You missed an important part. The switch is part of the Floating Torch Holder. It allows the torch to ride up and down a few inches independent of the Z movement

It's like the coil springs on a 58 Buick Roadmaster. When the torch moves down for a Reference (Z Home) the torch tip strikes the metal and starts to shove the floating part up. A switch is mounted so that upward movement of the torch on it's floating holder trips the swtich after "?" amount of movement. That stops the REF move. The overtravel between the time the tip just touches the metal and when it trips the swtich is called the "SwitchOffset". That will vary from machine to machine but will be a constant on any one machine.

The switch is mounted so that the action of the floating holder moving up trips it. It's far above any cutting or material.

By doing this it will automatically find the top of any thickness (or warped) piece of material and reset Z so when the code says "lift .125 and fire" for a pierce it's .125 above the material at the pierce point.

SheetCAM has variables in the POST to enter in your SwitchOffset value and a RefDistance value (in MM) that determines the Pierce Interval (how often the torch touches off). It then does auto-touchoff at preset intervals to compensate for warped or unlevel material and get a perfect pierce each time.

So the switch does not hang down or touch anything but the floating torch holder
slide. There are several photos on the CandCNCSupport Yahoo Forum in the photos section and there is a file with pictures in the Files section.

You gonna cut corrugated iron? You will need to make sure the Z is fast enough to keep up with X & Y. Remember that the Z under THC control runs at a percentage (THC Rate) of full Z velocity to prevent lost steps. Too many rapid short moves in opposite directions to use any Accel or Decel numbers during cutting. The lower velocity compensates for infinite Accel. If you make the Z too fast it will decrease the resolution and that causes overshoot (head oscillation) problems.

TOM CAUDLE
www.CandCNC.com

MonoNeuron
07-14-2008, 09:21 PM
Thanks a bunch yet again Tom

Ahhh, The old 58 Buick Roadmaster trick. I should have thought of that earlier. :)
I have seen a lot of photos but could never see what or why the extra slide was there but the pics you directed me to are just great and now I am armed with a lot more information and everything is getting a lot more clearer.
I couldn't find any posts on the forum here on the Zone outlining this.
I am still having problems with the controller and it may be a dud parallel port card. I tried to get one in town over the past few days but either they had thrown them out because no one wanted one for the past 4 years or they just don't stock them anymore. I ordered 2 from the Philippines for $24 which should arrive in a few days.
Until then I will get into building the floating Z axis and rip out the parallel port card from my laser and try that.
As it stands now with no plasma cutter connected I have a continuous light on on the arc good on the front panel and no matter what I do I can't get it to turn off. It also pulses on and off at about 1 sec intervals when I jog the Z axis up and down then stays on when I stop jogging.
None of this is still making any sense to me so I will get back to you when I install the new parallel card.
I think building the laser table was way more easier than the plasma cutter, even with all the problems I had with that
Thanks for your continued help, Tom
Richard.

Robin Hewitt
07-17-2008, 06:27 AM
I drop the torch under it's own weight (approx 2 lbs) until it rests on the metal then back off.

Of course if the weight of the torch flexes the sheet then it follows the torch up when I think I'm lifting clear.

If this is a work around I would love to understand it. Unfortunately I'm not au fait with the 58 Buick Roadmaster :)

Big John T
07-17-2008, 09:54 AM
I drop the torch under it's own weight (approx 2 lbs) until it rests on the metal then back off.

Of course if the weight of the torch flexes the sheet then it follows the torch up when I think I'm lifting clear.

If this is a work around I would love to understand it. Unfortunately I'm not au fait with the 58 Buick Roadmaster :)

If you have problems with the sheet flexing you can counter balance your torch or use a micro switch that is extended with a small air cylinder to feel for the top of the material then retracted out of the way before cutting.

John

Torchhead
07-17-2008, 10:46 AM
A simple bolt and spring at the top of the Floating holder to provide up bias against the weight works fine. I mounted a small block with a through (clearance hole) on the Z plate and tapped the top of my floating torch holder. With a long bolt and a spring between the head of the bolt and the small block it wants to lift the bolt Up. When screwed into the topof the floating holder it pulls the holder up. The tightness of the bolt determines the uplift force. I can dial in whatever amount I need. For really thin material the table slat setup needs to be closer spaced to provide more support under the material.

Big John T
07-17-2008, 10:56 AM
Torchhead,

Elegant and simple solution. Very nice. I tend to over design things sometimes :)

John

Robin Hewitt
07-18-2008, 02:36 AM
Had an idea but I don't quite understand how a plasma cutter works...

There are two connections to the torch, the loose wire goes to the cutter nose. If I could fire a a low voltage spark down that I could tell if it was touching metal same way a spark eroder knows when it's touching metal.

That wire can't be a solid ground, so what does it connect to inside the plasma box? Can I switch it with a fat relay?

Torchhead
07-19-2008, 11:52 PM
It's called ohmic sensing. It not a spark but a low current where the torch tip shield is isolated from the body and has a connection back to a sensing circuit. When the tip touches the metal (other side of the circuit you get current flow) It sounds simple and elegant....only problem is it sometimes fails to work if the tip gets dirty or the surface you are cutting is oily or rusty, so they normally back it up with a torque sensor on the Motor to keep from driving the torch too far and busting the tip.

A good engineer knows when to stop designing. The simplest circuit that does the job and is the most reliable wins out over elegance.

BTW low voltage won't spark across a gap. The insulation factor of dry air at sea level pressure is 10,000 volts per inch. To pass current you have to exceed the breakdown insulation of the media. That means .01 inch needs over 100 volts. To get a good spark you need many times that.

You might be able to measure a current between the electrode lead (which in some machines is in contact with the tip) and the work clamp when the tip comes in contact with the metal but it would need to be integrated in with the plasma electronics. I know that a TD machine will not fire if the tip is setting on metal (at least on some models) so they have to be able to sense the short. An external circuit would have to measure millamps of current at low voltage then be able to survive hundreds of amps at hundreds of volts. It could also suffer from the same problems as ohmic sensing so a backup method to stop the probe move would be needed. If you abandoned the floating head the tip would have to stop pretty quick or you would end up with a box of busted ($$$) barrel rings and tips.

TOM CAUDLE
www.CandCNC.com

Robin Hewitt
07-20-2008, 06:57 AM
A good engineer knows when to stop designing. The simplest circuit that does the job and is the most reliable wins out over elegance.

Engineers do not necessarily make good designers, too tied up with worrying about the ins and outs of HOW to make it. A good designer simply puts in everything he wants, the engineer then has to try and get him to compromise for what can reasonably be made :D

If I took over the connection to the torch tip, applied some capacitance and charged it 50-100 volts before starting the descent to look for metal, a sudden drop in volts would indicate that I had found it. The dialectric would be either rust or guck on the sheet to be cut. I just need a few volts to cut through that guck.

The problem is where does the wire go inside the cutter? Presumably the cutting current goes to the inside electrode. The other cable must be for the initiator spark. I think the initiator sparks to the central electrode to ionise the air coming out the tip. Everything I read is a bit vague on initiator sparks, probably because thee are different ways of doing it :confused:

I need to know what goes down that wire that connects to the outer electrode.

MonoNeuron
07-23-2008, 10:20 AM
I finished the floating head a few days ago and my new parallel port cards arrived today so I will be busy out back finishing the plasma cutter off over the next few days...in the cold...Brrrrrr. damned Antarctic wind!
I have 1 question though and that is where do I connect the switch for the height sensing?
Does it go on the Z axis limit or the Z axis home or is it a different switch I know nothing about. Can't seem to find any info on this :-)
here are some shots of the floating head for all and sundry.
It has about 8mm of travel which I think, if I understand the concept, will be enough travel for it. After all, it only has to trip the switch and then move a known height which I think I can find out by jogging the Z axis in Mach.
I just hope I can get it all together soon.
Rich.

Torchhead
07-23-2008, 12:43 PM
Limits on a machine just stop the motion signals....You use the Z home signal since the touch-off sequence looks for a specific signal and stops then backs off slightly. The code to do all of that and reset the Z to the proper 0 height AND then raise to the correct pierce height come sout of the POST in SheetCAM.

MonoNeuron
07-23-2008, 09:01 PM
Thanks Tom. Great help.
Keep your fingers crossed it will all work for me today. :-)

MonoNeuron
07-24-2008, 09:25 AM
Ah, Geez,
Just when you think things will go your way Murphey and his whole family come along with a lawyer.
I fitted the new parallel card today then spent the next 4 hours trying to install the damn drivers for it. I must have tried 30 - 40 different ones as they supplied a disk with a whole host of generic drivers for it but no install tool.
Anybody who has tried this will know what sort of shambles you can get into really quickly. How sick I am of restarting Windows.
I then tore out the parallel port card from the laser and installed that (after finding the disk hidden in some dark place) only to find that my original problem is still there.
When I jog the Z axis the torch turns on and off at 1 sec intervals almost like it was trying to find a stable arc then cuts off. I have the Plasma cutter disconnected from the sensor card and just watch the led an listen for the relay click
When I short out the torch trigger pins on the sensor card the Y axis drives toward the front of the machine and the Z axis lowers and I have to stop it with the reset button.
The torch or arc good light stays on all the time and the controls on the Mach display do nothing to turn the torch on or off and now I don't seem to be able to upload values from Mach to the torch height control.
I checked the cables again to see if I had some crossed wires but no, I haven't
Tomorrow I will take screen grabs of all the Mach screens then make a video to send to Tom so he can actually see what is going on. I will post it on YouTube because it will probably be a big one.
It took 8 months to sort out my laser so I should be used to this but I grow weary of it.

Why Me!

Rich.

MonoNeuron
07-25-2008, 05:24 AM
I have taken a video of what is happening so I hope the quality is good enough to be able to see properly. It's shrunk down from 280Meg to 20 meg and when you do that, quality suffers a fair bit but here's hoping.
I do hope Tom can make some sense out of this and from what I can tell the problem is all in software. It's almost as if some of the wires are crossed over especially when the X and Y axis move when shorting the trigger pins. I have checked all the cables and they are all ok and no wires are crossed over and all have the same impedance.
Weird, just weird.:withstupi
Here is the link in YouTube

http://www.youtube.com/watch?v=2IurtWpAkU8

The quality is pretty crappy but if you have an understanding of Mach3 then you should be able to make out what is going on.
I just found out that YouTube videos maximum time is 10 minutes or 1024 Meg in size, that's why I couldn't upload the last 3 times as my original video was 16 minutes in length. I cut out most of the crap and left the most important stuff so I hope someone can make sense out of it.

Rich.

MonoNeuron
07-25-2008, 11:15 AM
I have checked for a ground loop and didn't find one. I tested with the power cable plugged in and I got a signal from the multimeter saying I had continuity between the case of the PC and the Plasma Table. I then unplugged the power supply to the monitor and the PC and tested again and there was no signal so it looks good for having no grounding problems. All the grounds go back to 1 point through the power distribution box/sub board and into an earth stake just outside the shed. The Z carriage is isolated from the rest of the table assembly by the nylon rollers and rubber toothed belt. The X axis gantry can be earthed or grounded through the roller chain and drive sprockets on the Y axis and through the bearings.
I hope this helps.
Rich.

MonoNeuron
08-03-2008, 03:04 AM
Tom has been a great help so far but we still can't find the problem. Out of the 600 or so THCs they have sold at CandCNC he says they have never had this problem. I just love being an individual!
Tomorrow I will replace the PC with a lower class P4 300MHz instead of the core2 Duo 2.4GHz I am using now. There seems to be a cross over in the signals somewhere and when I jog the Z axis up and down the "TORCH ON" LED lights up on the MP1000-C when it shouldn't. Apparently it is physically disconnected from any connections inside the box so it should have no bearing on jogging, but it does. I don't know if the Duel Core PC chip would have anything to do with it but I will replace it anyway just because I have run out of things to test and adjust and Art Fenerty says in some of his instructions that Mach3 doesn't like multi core processors. (Good place to start me thinks).

So that's where we are at at the moment and I will keep everyone posted on how it goes and I do hope no one else has these problems. Everything should be Plug and Play and Tom and his mate have set everything up very well with good instructions which are easy to follow but sometimes the Gremlins creep in and give you a major headache.
It's just very frustrating testing for endless hours out in the cold.

Be well.
Rich. :withstupi

ajclay
02-24-2009, 10:09 PM
Well, what's the latest on the floating head on the Z axis? You think you could take a few photos and show what the out come was? I'm tracing your footsteps and need some help. Thanks, Aj ajclay@cox.net

MonoNeuron
02-25-2009, 05:00 AM
Damn!
I come to the Zone every few days and I had completely forgotten about this thread. Sorry if I had you waiting for answers as I know we all get very excited when close to fire up time.
I sent the torch height controller back and Tom's tech support found a blown chip inside, fixed it then sent it back.
I have it up and running but there are still issues with the controller but I think it is because I have the torch and motor wires in the same cable chain.
I went through all my tips the first 2 days cutting 6 jobs so I have to get it sorted out. The torch wouldn't lift when it was supposed to and bogged into the cut causing the plasma arc to burn out the tip. It happens very quickly too!
I haven't really done anything with it yet because I am lasering gifts for our wedding in a month or so but I will get back to this thread and finish it off at the first convenience.
I will try and find a few pics of the head and how it turned out.
Rich.

MonoNeuron
02-25-2009, 05:07 AM
One more thing.
I will be going away from the THK slide and will make a V guide slide for the Z axis. It will be a lot less trouble to maintain and all I will need to do is put a bit of grease on it occasionally unlike the THK guide that has recirculating balls that dust loves to get into and ruin.
Rich.

ajclay
02-25-2009, 07:10 AM
[QUOTE=MonoNeuron;573144]One more thing.
I will be going away from the THK slide and will make a V guide slide for the Z axis.

I too have used the vee wheels and rails. see the attached photos. I've made good progress over the past year or so on my project. The X - Y are moving and accept commands. I'm down to working on the Z axis and THC. I'm using Rutex controler parts and I'm trying to make to get things straight in my head on how the THC work mechanicly and with the compute boards. It seems to be a little bit of a task to say the least.

I need a votage divider as you were talking about a while back. Hypertherm told me yesterday that the J15 & J16 pins will never see full arc voltage. They will average between 70v - 180v DC. The Rutex needs 1 - 5 volts. Where did you purchase one?

Are you running a "floating head" type Z axis?

Thanks, Aj

PlasmaGuy
03-01-2009, 11:29 AM
Excellent photos AJ!

Who did you buy your vee bearings, etc from?

Tom

Torchhead
03-01-2009, 12:00 PM
I need a votage divider as you were talking about a while back. Hypertherm told me yesterday that the J15 & J16 pins will never see full arc voltage. They will average between 70v - 180v DC. The Rutex needs 1 - 5 volts. Where did you purchase one?

He has our MP1000-THC that comes with the THC Sensor Card and has the proper voltage divider (made to match what we use for divided voltage) and filtering along with the input for Arc OK and the Torch Relay.

J15 and J16 are FULL tip volts on the 1000 in the range you listed. Fine cut is done at about 80VDC and most other cutting at about 138 to 146 volts.

I notices you are using servo's. Are you using Rutex servo motor drives? Seems I remember they will take differential encoder inputs. Hopefully the USDigital encoders you have are either differential output to the Rutex or have a differential to single ended receiver if they go to Gecko's. With palsma even shielded cable may no be enough to prevent noise from getting into the encoder feedback lines. That will cause you positional errors. It hard to diagnose and harder to fix without replacing all the encoder system.

What is the exact voltage the Rutex needs? It needs to be a ratio of the actual volts and provide for worst case values. If the input goes to a processor chip (analog input) and it is not protected, any voltage over 5V even for a few milliseconds will burn out the analog input. There may be an internal calibration pot that lets you "scale" the input so that any divider network that gets you close will work...then again it may have to be pretty close.

I can do a quick calculation of values for you (and size/wattage needed) but I need what relates to what. At what output voltage (of the plasma) do you need the 5 volts? Can it go over 5 volts at any time?

TOM CAUDLE
www.CandCNC.com

jimcolt
03-01-2009, 02:36 PM
J15 and J16 in a Hypertherm unit are full arc voltage (not tip voltage...as there is no "tip" in a Hypertherm unit)..this is the same voltage that you could measure from the electrode in the torch to the plate. The Hypertherm rep probably meant to say that you would never read "open circuit" voltage from J15 to J16 as this unit uses a blowback style torch...meaning that the DC voltage is shorted (no voltage) until the arc fires.

Jim Colt Hypertherm

MonoNeuron
03-01-2009, 05:21 PM
Excellent photos AJ!

Who did you buy your vee bearings, etc from?

Tom

Hi Tom,
You could try these places.

http://www.tea.net.au/welcome.aspx?page=43 (Australia)

http://www.vxb.com/page/bearings/PROD/V-Groove-Bearings/Kit8353

http://www.cadcamcadcam.com/cncmachinecomponents.aspx

VXB have cheap bearings as does Cadcamcadcam (c/c)
I would go to c/c for mine as the price is comparable to the others and he is a small company that spends time here on the zone and you can get any length of V guide you want as he will cut it for you.
He only has 1 size though so if you need the bigger sizes for, say angle iron, then go to VXB as they have most sizes.
VXB also sell on eBay but the price is slightly higher to recover the auction costs.
Rich.

ajclay
03-01-2009, 05:25 PM
Tom, The parts came from Biship Wisecarver, but the don't sell direct. I had to purchse them from a bearing house called Motion Industries. They have a nice web site and make many different size wheels and rails. http://www.bwc.com Thanks, Aj

ajclay
03-01-2009, 05:48 PM
QUOTE
I notices you are using servo's. Are you using Rutex servo motor drives? Seems I remember they will take differential encoder inputs. Hopefully the USDigital encoders you have are either differential output to the Rutex or have a differential to single ended receiver if they go to Gecko's.

TOM CAUDLE
www.CandCNC.com[/QUOTE]


Tom, I'm running the rutex servo boards and using the US digital encoders: PN E5-1000-250-N-D-E-G-B. They are opiical diferential endders. I purchased the plugs from US digital and wired them up with CAT 6 wire to the CAT plug connection that fits the rutex. The wire is twisted pair and sheilded with a drain wire. Motors are 90v Keling except for the Z axis and that's a 24v pittman to work with the rutex THC. The motro power wire is twisted and sheilded also.

I have a drawing that I received from rutex on a 50:1 voltage divider and I'm in the process of checking it out and making a good drawing so it's easier to read. I want to get Jim Colt to take a look at it too, but I don't want to over burden him at the moment.

The THC is a little more involved than I thought. Getting the x y & z to move was easy comaired to this stuff.... One needs to have a full understanding of what it takes to make each componet of the system work before he can start on a THC.....

Aj

MonoNeuron
03-01-2009, 05:54 PM
Hey Ajclay.
Nice build on the plasma. I would get your wife or missus (or do it for yourself) to stitch up/Velcro a tube of canvas and slide it over your ball screw and glue/screw to each end to keep the grit out. Grease it up before hand.
It's amazing how much crap flies around when your cutting and also while it's sitting around collecting dust as well.

ajclay
03-01-2009, 06:38 PM
Hey Ajclay.
It's amazing how much **** flies around when your cutting and also while it's sitting around collecting dust as well.

I can tell this is going to one of those projects that just doesn't ever get 100% finished. I'm in the sheet metal business and when the machine is up and going I'm going to make shields for the cam followers, Vee wheels and the ball screw.. At least I hope to....

Also, I've got everything documented and plans drawn in CAD for the machine and power supply. All part numbers and costs. Also been taking notes thourgh out the build on how and what was done. I hope to offer a complete set of docs for someone wanting to build a uinit from scratch.

The information dosn't come easily out there. So many guys think you're going to take away from their business or be a threat of some kind. I'll give the info to anyone that wants it... FREE! and that means NO MONEY... The only catch is they will have to use basicly the same parts as mine...

Thanks, Aj

MonoNeuron
03-01-2009, 09:20 PM
Too right.
I am giving 5 people at the moment info on how to build a laser table and what NOT to buy due to my hard earned miss spent money when building mine. I won't show someone how to do it if they live in my area as I have seen it way too often how people want to break into your market for a share of what turns out to be about $2000 per year.
Those 5 people live in the UK, Africa and Canada/North America.
They will have very nice machines when finished.
I have had about 40 people contact me on how to do it but they find out very quickly that the cheapest you can build one for is about $4,500 with software and they aren't happy to spend the money.
So many people want stuff for $2 now-a-days. (I blame the Chinese) :-)

Right after you "finish" the machine you will find out what you could have done better because you learn so much during the build your knowledge bank increases dramatically and you will always come up with more ideas like an overhanging X axis to cut pipe on a rotary table etc.
It's a big monster you unleash when you start this stuff.
Rich.

ajclay
03-01-2009, 10:51 PM
.
They will have very nice machines when finished.
I have had about 40 people contact me on how to do it but they find out very quickly that the cheapest you can build one for is about $4,500 with software and they aren't happy to spend the money.
So many people want stuff for $2 now-a-days. (I blame the Chinese) :-)
Rich.


Wow, I don't see how you can build anything for 4500.oo. I must be approching $12,000 or so on mine. Plus I've got unlimited access to milling machines and lathes that I can use. If I had to pay someone to make the parts too.... WOW it would realy be out of sight. I wish you'd send me a photo of your machine when you have time.

I had all my photos of my machine from the fist piece cut till almost were I am now on here and it didn't generate any interest. Just a few comments on where to buy a few parts from and that was about it. ajclay@cox.net

AJ

MonoNeuron
03-02-2009, 04:08 AM
One thing about the "zone" is that if you are doing things right then you won't get any replies but if you look at your view counter you may have had 200 views of your thread.

I have also noticed that in the Plasma forums there are so many people building these things that your thread gets swallowed up very quickly by others and many may miss it unless they go to previous pages. It's always good to have a bit of info up your sleeve to post occasionally so your thread flips back to the top. {8-)
I rarely go "over the page" as I just don't have time to answer all the mail that answers generate.
I have learned a lot here and I try to give back as much "usable" information as I can and sometimes it's not very accurate but I give it a go.
You can look up my semi build thread on the laser if you search "Backyard Laser"
I will post some pictures of the plasma table soon. I drove my Axis' by roller chain as it was MUCH cheaper than the $1000 for rack that they wanted here. I think it cost me about $200 all up for the chain and sprockets and they are all industrial and cheap.
I found out you can't go much under about 20 teeth on the sprockets due to the cogging effect but it runs very smoothly with the 5 phase drives and motors I have.
I love those things and they are near servo performance with no maintenance.
I have a toothed belt on the X axis and I may at some stage change it to chain and sprocket to standardize everything.
Rich

agelkom
03-04-2009, 05:27 PM
Hi Guys,
Could someone enlighten me on how to set up the Z axis for my plasma?
I have bought the MP1000C from CandCNC.com and Tom says I need to install a micro switch for the height adjustment and torch set off procedure. He spends quite a lot of time answering other peoples questions so I thought I would come here and leave him alone for a while and see what you guys can come up with.

I have no idea how to set this up.

Do I install the micro switch at the bottom of travel and zero from the top of the plate or do I set the switch at a known height from the table and input the thickness into Mach3 and work from there?
Where do I set the switch? 1" above the table. 3" maybe?
Do I make it adjustable so I can slide it along and set it anywhere for any height?
Will it get in the way of the torch when it cuts corrugated iron, for example, if it's set too low?

I am in a quandary so any help will be gratefully accepted.
Richard.

You can use our Capacitive Sensor as a limit switch
Pleasw visit www.agelkom.com.tr

ajclay
03-05-2009, 08:40 PM
Jim Colt,

Things are getting deep to say the least on the THC. There is a lot of confusion on my end on how to hook up a voltage divider to the hypertherm 1650 to work with my Rutex THC board. I know you guys are saying to hook up the divider to pins 15, and 16. And the way we understand it, that is differential voltage. +300v and -300volts. So with that being said, then we'll have to use a ground of some sorts to be able to get those voltages. [ -300 and +300 ]

Can you explain it a little deeper on what each of these terminals [ 15 & 16 ] are putting out in voltages.

We can't go to the next step on voltage dividers for rutex till this is put to bed. It appears we will have to build two dividers for the use with rutex THC.

Thanks for al the help!

Aj ajclay@cox.net

PSS,,, is anybody in the zone using a Rutex THC boad? If so drop a note, I'm sure there will be other things to figure out. We need all the help we can get at this point.

jimcolt
03-05-2009, 10:04 PM
OK...I'll try again!

J15 and 16 (sorry, I do not have the schematic in front of me....one is negative and one is positive) are at the same potential as the electrode (negative) which is inside the torch, and the plate (positive). If you are plasma cutting a plate at a fixed speed....say 75 inches per minute, and the plate is exactly level.....the voltage reading from J15 to J16 will remain constant, it is a DC voltage, betwen 70 volts and as much as 200 volts. If you are reading 100 volts....and you mechanically raise the torch .020"......you will see the voltage rise approximately 5 volts.....consequently, if you lower the torch .020", you will see the voltage drop approximately 5 volts. If you keep the cut height at a fixed height, but lower the cut speed....you will see the voltage rise......this happens because the plasma system is still cutting at the same power level (Amps)....but produces a wider kerf, and the arc is longer as it must reach the plate....which reads a higher voltage.

A torch height control should not care about ground potential....it needs to read the length of the arc, which is measured as DC voltage. A longer arc (more torch to plate distance) equals higher voltage. The arc voltage is measured from electrode to plate, which is J15 to J16 in a Hypertherm Powermax 1650.

The voltage of a plasma arc is of relatively high potential for modern electronics, generally between 70 and 200 volts DC, and there is a lot of electrical "noise" present...due to the operating frequency of the plasma power supply and the constantly moving arc attachment point.

A voltage divider/isolater is usually designed to divide this arc voltage to a useable voltage level (usually less than 10Volts DC), and to filter the electrical noise out of the DC signal. So, what exists as actual arc voltage.....which may range from 70 to 200 volts DC, is divided (by a 50:1 voltage divider) by 50....and now the voltage range is from 1.4 to 4 volts DC...which is a reasonable voltage to use for feedback of the actual arc voltage at the torch.


This divided and filtered analog arc voltage signal tracks proportionally to the actual plasma arc voltage....and is fed into a comparator circuit that can control the up and down motion of a z axis positioner in order to accurately control the torch to plate distance while plasma cutting...dramatically improving cut quality.

In essence...the voltage divider adjusts the actual arc voltage as measured from terminals J15 to J16.....to whatever analog voltage the THC (Rutex, or other design) is compatible with. If the Rutex can handle 1.4 to 4 volts.....then a 50:1 divider is good. If the Rutex needs 2.8 to 8 volts, then a 25:1 divider will work.


Hopefully this explanation helps...


Jim Colt

ajclay
03-06-2009, 07:51 PM
Jim,
The confussion on our end stems from the rutex information saying that the THC board is looking for differential voltage of -5vdc to +5vdc. That is what making us think that pins 15 & 16 of the hypertherm is doing something else. If only I could get someone to confirm that one pin of the Hypertherm is 0vdc and the other one goes up to 300vdc depending on arc height we might be able to move past this. The manual only has -vdc and +vdc with no voltages.

The simplest things are the hardest because of no documentation....

thanks for your help, It's not taken for granted! Aj

ajclay
03-12-2009, 09:51 PM
I've been trying to make since of how the torch knows how and when to stop before it touches metal on a Rutex THC controle. It seems a few plasma machines use this method. It was clear to everyone except me. This is it in a nut shell.

torch goes up to the "home" position and hits a limit switch. The height isn't an issue... Goes up and stops...

Say the torch is 2in above the table, metal .....just for an example.

The prox probes are even higher... say 4 inches....

the air cylinder pushes the prox probes down 2 inches till they it hit a ledge.... bolt.... or anything solid and stops the ram and downward movement of the prox probes.

When it stops moving down, the prox probes are even with the end of the torch tip..... at the same height or a known differential....

Now the torch, prox probes and air cylinder move down as a unit till the probes since the metal and stops the downward Z movement.

Now the thc knows where the torch tip is in relation to the metal regardless of the thickness....

The air is shut off on the cylinder and the prox probes retract.

Ready for arc start.

Aj

jimcolt
03-12-2009, 10:15 PM
AJ...that is probably how they work. It works exactly like the older Hypertherm torch height controls. Today....most height controls use ohmic contact (sensing electrical connection between the torch shield and the plate, and as a backup (in case you are cutting underwater, or on primed or masked plate) then the torch contacts the plate and the stall force is sensed in the z axis drive motor. These methods are more accurate as compared to the proximity sensor type IHS.

Jim

ajclay
03-12-2009, 10:37 PM
AJ...that is probably how they work. It works exactly like the older Hypertherm torch height controls. Today....most height controls use ohmic contact (sensing electrical connection between the torch shield and the plate, and as a backup (in case you are cutting underwater, or on primed or masked plate) then the torch contacts the plate and the stall force is sensed in the z axis drive motor. These methods are more accurate as compared to the proximity sensor type IHS.

Jim

When a guy has more money than time he can buy a Hypertherm THC unit. I have more time than money so I'm using Rutex and going this direction. (the less accurtate way, and consederably less money way) Thanks for the update on the new stuff. AJ

jimcolt
03-12-2009, 10:42 PM
I understand completely. Our lowest price THC is around $2500...it is an industrial robust design that meets CSA and European CE safety specs....and it survived Hypertherm's reliability lab (all of our products must pass this test process during their development stage...or they do not become a product).

Best regards and good luck, Jim

Torchhead
03-13-2009, 11:43 AM
This is like watching a soap opera (just kidding). If, at the end of all the gyrations, you are looking for a switch closure it seems to me that using the method we use (torch mounted on floating holder and microswtich to sense the upward movement) is SO much easier than the Rube contraption of air cylinders, solinoids, etc. Ohmic sensing is sexy but unreliable on rusty, dirty or painted material and torque feedback adds $$$ to the price and needs adjustment on thinner material. Sometimes simple is better. There are some photos of floating head designs on the CandCNCSupport Yahoo Group. We won't abuse you because you didn't buy our solution (:-)

TOM Caudle
www.CandCNC.com

Big John T
03-16-2009, 10:27 AM
AJ, I use the floating torch with a micro switch method and it has some drawbacks on thinner material when used near the edge. You may have guessed it moved the material giving a lower than actual top of material reading. Also it can be a problem with dirt on your rails or what ever you use to float the torch. I considered the prox method but opted for the simple micro switch as I didn't have room to mount one. The drawback on the prox is you will get different readings when your over the edge of the plate than when fully over the prox...

John

Torchhead
03-16-2009, 11:11 AM
For thin material where distortion from the touch off is possible put in an "up bias" adjuster. Just make a adjustable screw "lifter" that counter balances the weight of the torch/floating holder. I can cut 24 ga metal with little touch off distortion. With a compression spring and long bolt I have adjustment from firm to no down pressure at the tip. You do need to keep the slide clean and oiled. The plasma dust needs to be washed from the mechanism and it re-lubed. Test it with your hand and if you feel roughness or resistance do the cleaning. I found the spray type Brake Cleaner works to melt the residue from plasma smoke but it takes out all of the grease and oil too so that needs to be replaced. Something better than WD-40 is needed.

I mounted a small aluminum bracket on the plate that the floating slide is mounted to and drilled a through hole. I threaded a hole in the part of the holder that moves up and down and aligned everything so a long 2" bolt with a light compression spring slides up and down with the floating part. It acts as a up bias and also as the lower stop.



TOM Caudle
www.CandCNC.com