CNC Plasma build

[MattH]

I’m currently in the process of converting one of our 8x4 routers into a plasma table.

The build will consist of:

• Tekcel CNC table retro fitted with 400w AC servos
• Hypertherm Powermax 45xp
• PriceCNC THC
• Mach3 with Ethernet smoothstepper

The table and existing controller and motors have been removed from the table (these will be spares for our other two Tekcel routers):



Old 250w brushed DC servos next to the new 400w brushless AC servos:

 

[MattH]

 

[pressbrake1]

Dc servos used to drive me nuts back in the nineties!

 

[MattH]

To be fair the Tekmov controller in the Tekcel routers works very well, but it’s a closed system so it’s easier for me to rip it all out and replace it with standard parts.
AC brushless servos have so much more torque and speed.

I have a set of DMM Dyn2 drivers and motors that I’m hoping to use, these were left over from a router project and they got replaced with Leadshine EL5 units.

The DMM drivers have no opto isolated IO and are fairly basic. I’m just waiting on some HCPL2631 optos to arrived to test the integration with my 24v Controller IO.

If they prove to be no good I will use a set of Leadshine EL5’s that I have on the shelf which has industry standard IO and are much easier to interface too.

Here’s what got removed to make way for the new electronics:

 

[MattH]

Crazy busy with pre-Christmas orders at the moment so haven't progressed this much.
The idea is to work on it over the Christmas holiday so we can be cutting in the new year.

My opto isolators arrived so I could test the DMM servos with the ESS and MB2 board. The cheapo opto-board I'd grabbed wouldn't cut it as the rise time was only 18us and the pulse train is 5us.
The HCPL2631's have a rise time of 50ns so plenty fast enough.
I mocked it up on a breadboard and confirmed they worked while and then designed a quick PCB for all of them.
Just waiting on he PCB's to show then I can build all the electronics into the enclosure on the machine.

Now I know which servos I am using the next step will be to re-make the motor mounts to take the bigger servos.

 

[bletchmonster]

This thread is hastening my journey to the terminally bewildered!
I've wanted to build a cnc plasma for a long time but reading the above information makes me think I would be better just buying a turn key machine.

 

[MattH]

Not to put you off but building any cnc from scratch even a basic little stepper machine, takes hundreds of hours of reading and research.

I've built a few different CNC's over the years based on a number of different controllers and hardware. Even with that background I've probably put 30-40 hours of reading in on this project so far.
That includes researching THC controllers, interfacing with the Plasma power source, floating Z or Ohmic sensing, differential interfacing to the servo drives, refreshing myself on tuning the servo drives, Plasma screensets for Mach3, postprocessors for Sheetcam etc etc.

The list goes on and on.

 

[MattH]

PCB’s arrived from China today.

Very pleased with them and the service. £10.95 for 5 boards made and delivered within 7 days.

 

[MattH]

Back on this project now after the Christmas rush.

After messing around with the intermediate opto board between the controller and driver I have moved in to a new plan.
I couldn’t stop getting rf noise induced into the circuit and causing problems.

The issue was the the controller I was using is 24v differential IO and the motor drivers only take 5v ttl.

So now I’ve bitten the bullet and opted for a different controller and BOB which suits the drivers.

For those interested I’ve gone from an ESS - MB2 - DMM driver to a UC400ETH - DMM BOB - DMM Driver.

Now the electronics are confirmed I am working on the machining.

I have now modified one of the X axis motor mounts to take the bigger AC servos (just waiting on some 24t T5 pulleys to complete).

Today I machined a new Z axis mounting plate for the floating Z.

 

[MattH]

I mounted my second vice in my first so I didn’t have to change the primary vice’s jaws.
This allowed me to size and square the plate:




The plate holds a small rail and probe switch, this allows the plasma torch to touch the material and then set an initial pierce height. I still need to build a torch holder to mount to the carriages.

 

[MattH]

Thankfully now the interface board has arrived from Canada the electronics are confirmed and I can move on.

As I purchased a UC400ETH controller which can work with Mach 3 or UCCNC I decided to buy a UCCNC license as it's much better than Mach 3.



There will be a second small breakout board connected to the number 2 LPT port on the UC400, this will give me the IO I need to communicate with the THC and trigger the plasma unit.

But for now I can move on to the motor mounts, I've modified one of the X axis mounts and the new pulleys should be here tomorrow.
So now I've got to make a broaching plug to enable me to cut the 5mm keyway in the pulleys.

 

[MattH]

This is one of the existing motor mounts modified to take the bigger motor.
It's just waiting on the correct sized pulley and belt.

I have had to gear the axis up as the original motors had 12t pulleys which are to small to fit the bigger shafts of the AC servos.
I will be fitting 24t pulleys thereby changing the intermediate gear ratio from 4:1 to 2:1.

It's not a big problem though as the original DC servos only had a max running torque of 0.35 NM at 250W (and they we're only being driven by a 180W H-Bridge).
The AC servos have a max running torque of 1.27 NM.

The original setup as a CNC router had a max configured speed of 15M per minute (I don't know the max mechanical speed), with the new servos this will be increased to max mechanical speed of 37.5M per minute and I'll probably configure the software to a max of 30M/Min.

Can't see me going over 15M/Min when cutting with the plasma though and that would be pretty thin stuff.
Fast rapids do have a big impact on overall cutting times though.

 

[daedalusminos]

I'm liking this build but pondering....

Plasma cutting is essentially non contact and relatively slow....do you really need those beefy motors?

 

[MattH]

Not really but I had a full set of 400w servos spare.

I couldn’t use the control and motor driver hardware that was in the CNC as it’s a closed system.
I could of left the DC servos in place but then I’d have to buy DC drivers to suit.

 

[MattH]

Still waiting on the correct size belts for this project.

Today I machines the pulleys.

Drilled and reamed to 14mm, 5mm keyway broached on the Arbor press and two M4 grub screw locations drilled and tapped:

 

[MattH]

Not a bad fit:

 

[ukracer]

I'm liking this build but pondering....

Plasma cutting is essentially non contact and relatively slow....do you really need those beefy motors?

if you knew Matt you would not be asking that question...lol

 

[MattH]

Still progressing this.

Working on getting the control cabinet finished:

 

[eSCHEn]

Still progressing this.

Working on getting the control cabinet finished:

View attachment 209808

That is a lovely neat install Matt, well done

 

[ukracer]

Still progressing this.

Working on getting the control cabinet finished:

View attachment 209808

Too damn neat...as always.