CNC Plasma Table Using Cut50 Cheapo plasma cutter

[MeJasonT]

I started work on this project as I had one specific thing in mind.
I wanted to cut out a plate of a ploughman with horses and plough to put on my father’s grave.
He had farmed for 89 years on the home farm in Cumbria Uk, the significance of the horse and plough was that in 1957 he was the world horse ploughing champion, he won again in 1958, lost to Canada in 1959 (which he said was a fix, apparently the award was given before all the competitors had finished and before their time was up). However he did win it back in 1960. So the seed was planted for a plasma cutter.
Having built a 3D printer I decided that CNC was a piece of cake, I had a friend who works for a paint factory who provided me with some nice stepper motors and H bridge controllers and the rest just happened.
The guts of the machine is a GRBL based controller (many thanks to those guys for their excellent work and their willingness to share it).
The thing that makes my machine different is that I have used a cheap 50A HF start Plasma cutter and managed to overcome the High frequency noise affecting the electronics by controlling the plasma unit by means of fibre optic.
The HF start was converted to Pilot ark by grounding the electrode for 0.5 seconds to strike the ark, I used a very nice motorcycle starter motor to switch the contact which is capable of handling 600A for 10 seconds.
It is my intention to publish all of my drawings and work for this project in due course.
There is still some work to do, calibration, dispelling gremlins etc.

http://bengler.no/grbl
https://github.com/grbl/grbl
https://github.com/gerritv/Grbl-Panel/wiki

[auswelder]

Hi,

Nice project, can't wait to see more details & photos

Interested in any info regarding solving the noise issues with the plasma as I am planning to use a cut 40 but and am a bit worried about frying the cnc electronics. Also how are you find cut quality with it?

Thanks

[DIYer]

Thanks MeJasonT! We've added your CNC Plasma Table to our CNC category,
as well as to your builder page: MeJasonT's Homemade Tools. Your receipt:

CNC Plasma Table by MeJasonT

tags: CNC, plasma, controller

[AdrianH]

Great Minds on the plasma cutter.

Cut 40 and home made table, caps and Zen diodes at this end.

Adrian

[john johnson]

I have been looking for just the right idea and it got the brain in motion thanks for your help.

[MeJasonT]

I thought i had better add some more pictures to wet the appetite, i'm still formulating the the build instructions and getting all the drawings together. I have realised that i will have to put the printed circuit board layouts onto pdf as the software i use (Proteus)
does not seem to transfer files well to other vendors software, I will however be producing the Gerber files which should be transferable. The mechanical files will be in DWG format.

My Electronics have been built into a IP67 Enclosure


The power supply is producing a regulated 48vdc for the stepper drivers and motors, as these are industrial beasts and paired, i didn't see much point in changing anything. Having read numerous posts on stepper drives it looks like makers like us need to look more closely at the voltage and amperage of our motors and using the right sized stepper drives to suit our needs. Stepper motors are quite forgiving and will work on voltages higher and lower than those specified Its then up to the stepper drivers to handle the correct amount of current. The actual load/torque required for driving an X,Y,Z table isn't actually that high. The Nema 17 12v motors are just as capable of driving a table as those i have used. hell there is some grotesque 3D printer builds out there which manage to build some reasonable stuff. Always remember, trial and error is a well practice method of engineering. The bouncing bomb may have been mathematically and scientifically designed but the targeting came about by accident using a home made sextant and trilling the drop height until it was perfect, victory was built on such precise guess work. My ideology is don't waste money, try not to spend money, recycle every thing possible and leave the maths and science to the boffins-whilst they are talking about it i'm building it. I saved my last employer a fortune in his Petroleum R&D company.

The Plasma table start with the bedways/axis, you need to decide how big you want to make this thing. making a cutting area larger than an 8 ft x 4 ft sheet of steel is probably pointless for DIYers, then you have got cranes/hoists etc to get the plate onto the machine etc. I aimed for 3ft x 3ft and failed miserably OK one way but the Y axis i limited myself by recycling the lead screw.
I will use the table i have built for now until i grow out of it.

slides for axis.
I found a few pictures of various designs of slides on this very site. some required a plasma cutter to cut out various shapes - hello, i haven't built the thing yet. So following my non scientific farmer son approach i went for a simple design.





I ran the slides on a 1" steel angle, up to 4ft this should be reasonable strong and take the weight of the Y axis carriage. if your intention was to build a larger machine then i would consider using 1 1/2" or 2" angle.





due to the expense of acme threaded worm screws and all the hardware required to hook them up, i opted for a chain drive which works perfectly. I had the added advantage of having a right angled 10:1 ratio gearbox, to be fair i used it to reduce the profile of the machine rather than needing the extra torque for the X carriage. The right angled gear box gave me the advantage of attaching the motor along the side of the frame instead of it sticking out at 90 degrees.

Well i hope this is enough of a taster to get you hooked
more to follow
Jason.

[MeJasonT]

Oh i forgot to mention the slats, I cut lengths of 1" box section and welded them onto the inside angle of 1" steel angle, the slats are 1" x 1/4 steel bar the width of the bed and were used as the spacers and for alignment when welding in the box section. The slats just drop into the frame on completion and can be replaced as thy get cut to shreds. The frame is set on top of a tanked table, in my case an old steel silage trailer side, this will be my water bath to extinguish the sparks and hep reduce some of the nasties produced when plasma cutting. I'm sure if you have decided to build a plasma table you will already know what one does and the results and byproducts you get from one, I wasn't a chicken farmer so no sucking of eggs will take place here.

[MeJasonT]

There has been a couple of guys who have already enquired about eliminating HF noise so i will quickly let those guys know how i reduced the noise to a sufficient level for the machine to operate.

DO NOT USE LAPTOPS
umm not totally true just try using and older lead brick one, windows 98 ilk.
unfortunately the software may dictate something that requires windows 7. If you choose win8 or Win10 then you are taking your life in your own hands. nobody uses such pants.

Many new laptops are susceptible to RFI noise, they are designed to handle it internally but when it comes to plugging USB peripherals in their stability goes to pot. For some reason laptops from around the Vista OS era and before seem to be more noise immune. If any one would like to add to this reasoning it would be much appreciated

Mains/power filtering
The laptop power supply is best fed through a mains EMI/RFI filter
http://www.ebay.co.uk/itm/2-stage-Ma...oAAOSw4q9XTyuh

There are various types ie. how they are installed and what power rating you require.
this type requires a little electrical know how and the ability to insulate the electrical connections. They are good at removing surges and transient noise.

Stepper Motor Electronics/Drivers
always try to get opto isolated inputs or if you are building your own electronics build it in to your design, that way you can create a barrier between your control electronics and your stepper motor/drivers.
This type of driver are ideal as they provide the level protection needed
http://www.ebay.co.uk/itm/CNC-Single...kAAOxyBvZTWWD7

If possible don't run the motors and the control electronics from the same power supply, again this will create a physical barrier.

Always keep in mind the motors are made up of huge coils of wire - the best aerial in the world.

Earthing.
Earth every thing, table, carriages, PC, bench. each metal surface should be individually wired back to an earth rod stuck int ground. the earth rod is only for plasma cutter DO NOT use any mains supply earth point, you will effectively take away the ground protection from you home/workshop supply - this will lead to injury and death. Do NOT do it.
I will try and post the guys forum post from hypertherm who gave excellent advice on the best practice of earthing.

Screening
Screen all signal and motor cable or use screened cables, i found i needed to externally screen using a braided sleeving.
add EMI filters to you signal, motor and USB cables. USB especially, i ended up having to use a USB opto isolator (at 40 bucks was probably the most expensive part of the machine).
The braided sleeving should also be wired back to your earth rod, don't forget to screen the electrode cable with the braid and earth it. Do not do the earth clamp cable, Idiot. that causes a whole heap of mental pain. It effectively makes an ionic earth path through the atmosphere. Its that old Kirchoff law of dividing current in circuits, it produces very poor plasma ark's anyways.

Fit 10uF capacitors across the End Stop/limit switch inputs on the pcb (Neg pin to Gnd, + on signal - my electronics are designed so that the micro switch grounds the signal line when triggered).

Mouse and keyboards
well that's a bowl of contention right there, they suck up noise like no tomorrow. most users are simply moving the PC away from the vicinity of the table. just don't rule it out as a likely source of noise if your program/PC keeps crashing.

The Plasma Cutter,
run the power cable away from the table as best you can, try not to use extension cords as these with only 1 wrap on the real are fantastic noise makers/inductors.

run your plasma cutter and PC from separate wall outlets.

the ark gap inside the plasma cutter/machine can be a huge source of noise. This is not for the faint hearted however some builders have reported on the web that setting the correct air gap can reduce some of the noise. I am not going to advocate it here, you will need to do your own research and decide if its something your are going to attempt and are capable of.
in any case never remove the cover unless you are aware you are voiding your warranty and you have the plug held in both hands, if its in your hand its impossible for it to be in the wall at the same time.

Last but not least i had to switch off hardware limits option in my Grbl firmware and use software limits instead.
the only disadvantage is that i cant home the bed automatically i have to point it at the position i want it to start at and zero the axis there. the mechanical stops are still wired and will stop the machine if it tries to make a run for it out of the door.


more will become clearer as i get my backside into gear and produce the documentation for my table.

EMI Filter

6 Pcs Clip On EMI RFI Noise Ferrite Core Filter for 5mm Cable WK | eBay

Braided Sleeving

Tinned Copper Sleeving Braid MBS 95-10.0mm - 10 metres (RAY-101-10.0 equivalent) | eBay

[MeJasonT]

Still related to HF noise as you have to overcome triggering the machine on whilst maintaining directional control without the noise created by the Plasma/machine generated noise affecting your control.

Triggering the Plasma cutter was a real pain in the butt, every time i triggered the torch the controller would hang up (GRBL/Arduino UNO Pcb). The HF noise just saturated any circuitry i tried using to switch the pilot ark and trigger on.
Whilst sitting in the one room in the house where im alone and can have deep thoughts without interruption - the toilet.
Hey guys you should try it, it only fails if you have a partner who comes in and talks to you - Its bliss the only place in the world i'm free to think.

So the idea, optical fibre. light is unaffected by noise,et voila.
There is plastic fibre out there which is cheap and can by driven using simple electronics

Attachment 12542

and the fibre
High performance plastic Fiber optic cord SH4001 | eBay

complicated isn't it

I used two single ended fibre links ie they are simply switching circuits not 2 way communication links.
one for the trigger and the other for the Pilot Ark.

The cheap Chinese plasma cutters are scratch start like an ark welder, this is obviously difficult to do with a CNC table, it would require the tip to be moved using a Z axis command to strike an ark then move back up to clear the work for the cut.
timing would be critical, when would you move off to make the cut. This is now getting into the realm of a torch height controllers, a topic for another day.

This guys post on machsupport.com explains how converting a HF plasma cutter into a Pilot Ark machine
https://www.machsupport.com/forum/in...?topic=20076.0

I use a motor cycle starter relay to make the contact, there are Gcode commands i use to switch on the Pilot Ark long enough to strike an Ark the it is disabled saving consumables. There is no harm in leaving it on but your tips will only last an hour for a few cuts. The trigger on the gun has been removed and my second relay operated by another Gcode command controls the triggering of the plasma cutter

motor cycle relay like this one
12V Starter Solenoid Solonoid Relay Quad ATV Motorcycle BRAND NEW | eBay

I'm using the Spindle enable and suds pump commands for my triggering and pilot ark control.

Here is some of my inspiration

IRNAS :: Good-enough useful-open-hardware CNC/Plasma cutter - Plasma cutter selection

IRNAS :: ToslinkCNC - Optical communication for CNC control - design overview

[MeJasonT]

Still working on electronics.
I have had the table cutting but wasn't 100% happy with the frigs i had to use to get the table going, in short i had to disable the end stops when running as the plasma cutter emitted so much HF noise the end stop micro switches were false triggering. I also had a small issue with cutting arcs and had to change the Gcode to linear movements only.
I have built another control box with opto isolation to handle the plasma triggering and the end stops, isolating all of the table side wiring from the electronics. Still need to test it all.