CNC Plasma Table Project/upgrades

[Hood]

I have never used or even seen a shielded torch so I can't say how they fit together or work.
Regarding the cut height, my THC has a pot on it to adjust the arc voltage and thus I can lower or heighten on the fly, it is very handy when doing a new thickness or material type as I can intentionally choose a higher voltage than I think and then tweak as the cut progresses. I then write down what the voltage was and I am set for the next time

 

[Brad93]

1.5mm cut height on a hypertherm

 

[Munkul]

This is a steep learning curve. Using sheetCAM, using the sf2100 controller, and using the HYD THC, along with setting pierce height, times, cut voltages, feed speeds, slowdown for circles and arcs.. The list goes on!
Today I made some progress with the water table.


I also cut some plates for a rough and ready job, 6mm flange plates with 19mm and 13mm holes in... What a mess. It left jagged holes no matter what I did.
Anyway last thing tonight I worked out the problem. Something to do with the way sheetCAM switches the arc off at end of cut. The table is still decelerating and it cuts it off early assuming the table has finished it's travel. I think it's an SF2100 feature. Anyway, the problem is fixed by adding a few mm of overcut.

Bad cuts


Fixed cuts. Using a sheetCAM rule to give 60% cut speed on holes under 20mm. Seems really nice quality.


Another issue is that my nozzles are only lasting a few cuts before they blow the end out slightly and start cutting wonky and giving bad directional taper. I think it's pierce related, as my air is clean and dry (refrigerated dryer compressor and extra prefilter). I'm playing with the initial height sense and the pierce time and a few other settings, I think the THC is driving the nozzle too close to material before it starts moving and this is blowing the nozzles.
At least the Jasic nozzles are £3 each and not £12 like the Thermal Dynamics ones!

 

[Erie Fred]

The water table looks to be maybe 4" deep max ?
Are the slats going to be on top, or down inside ?

 

[Hood]

My table is only about 100mm deep, in fact only about 75mm water depth, works great and no wet sleeves picking out bits that fall through the slats

 

[Erie Fred]

My table is only about 100mm deep, in fact only about 75mm water depth, works great and no wet sleeves picking out bits that fall through the slats

View attachment 474563

Yes.

As I do thick oxy cutting, I made it a little bit deeper, 5" deep.
I see you have the water set about 1/2" below the points which I find about right as well.

Some think the water is a spark trap and have 2"-3" below the slats before the water surface.

 

[henry Kadzielski]

I think the THC is driving the nozzle too close to material before it starts moving and this is blowing the nozzles.

My two cents worth. I also use sheetcam. There is an option to set the pierce height (Hypertherm is about 4times the cut height). Since my plasma is connected to and controlled via the software I have 60% soft start on the pierce. Once the pierce delay had finished I have set 10mm of forward movement before we get torch height control. Post pierce delay the torch goes to the cut height, which is set from when the torch does a touch off. The Hypertherm uses shielded nozzles but when piercing, having the torch height right and out of the way helps life greatly.

 

[Munkul]

My two cents worth. I also use sheetcam. There is an option to set the pierce height (Hypertherm is about 4times the cut height). Since my plasma is connected to and controlled via the software I have 60% soft start on the pierce. Once the pierce delay had finished I have set 10mm of forward movement before we get torch height control. Post pierce delay the torch goes to the cut height, which is set from when the torch does a touch off. The Hypertherm uses shielded nozzles but when piercing, having the torch height right and out of the way helps life greatly.

My main problem is the control. The sf2100 control has practically no say over the THC, all it does is send a start signal to the THC and waits a certain amount of time for the THC to:
1. Drop the z axis to touch off
2. Raise to initial height
3. Fire and pierce

The pierce time is set in both the THC and sf2100. I've set it long in the sf2100 because if I forget to set it in both, then it starts moving before it's through. But I think the problem with that is that the THC voltage control kicks in too early so it starts driving down before it moves. Does that make sense?

Ultimately, they're both dumb systems, the Z axis is fundamentally a basic 24VDC motor and everything is driven from a timer.

I need to upgrade it all to a proper control and put a stepper motor on the z axis. But firstly I need a water table

I've made the table 80mm deep and plan to run it filled to 75mm max which is where the slats will be. Not sure why I didn't go deeper because there are no depth constraints... Digging around online some water tables are only 50mm deep so I thought it was deep enough...

 

[Munkul]

I also did some digging for the future.
Once again I'm impressed at the mechanical design of this table. There is zero backlash in anything. The geared turndown on the motors is good, and the mechanism for adjusting the pinion to the helical rack is decent. It's physically impossible to upset the gantry by pushing on it from one side, it's so stiff.

The downside is the motors, they seem very cheap... Y axis is driven by 2x nema 34 8nm motors which should be ok, except the gantry is massive and made from steel... It's heckin chonky, very heavy! I believe that if I push the motors too hard acceleration wise, they'll lose steps. I'm thinking of upgrading at least the Y axis motors to hybrid steppers, 12nm with an 80v power supply, something like this:

STEPPERONLINE 12Nm Nema34 Closed Loop Stepper Servo Motor Driver CL86T V41 Kit | eBay UK

2-Phase Hybrid Stepper Servo Driver CL86T. Holding Torque 12Nm. 1 xClosed Loop Stepper Driver 0-8.2A 24-80VDC for Nema 34 Stepper MotorCL86T V4.1. Closed Loop Stepper Motor + Driver Kit included 1 x Nema 34 Closed Loop Stepper Motor 12.0Nm(1699.68oz.in) Encoder 1000CPR.

www.ebay.co.uk

Is this a sensible idea? Or are they not much of an upgrade?

 

[m_c]

Motors that size really need high voltage (aka mains powered) drivers, at which point you'd be as well swapping to servos.
Usually you're also likely to get better performance from a smaller motor spinning faster, however if the gantry is heavier than it needs to be, then that is going to be the bigger restriction on performance.

Personally, if that gantry is steel construction, I'd be looking at remaking it from aluminium, as you'll get more performance improvements from lightening the gantry, than throwing more powerful motors at it.

 

[Munkul]

Motors that size really need high voltage (aka mains powered) drivers, at which point you'd be as well swapping to servos.
Usually you're also likely to get better performance from a smaller motor spinning faster, however if the gantry is heavier than it needs to be, then that is going to be the bigger restriction on performance.

Personally, if that gantry is steel construction, I'd be looking at remaking it from aluminium, as you'll get more performance improvements from lightening the gantry, than throwing more powerful motors at it.

I get your point, but I don't want to do that. It'll be a few 100 quid for ally material, that's ok. But it'll be about 20 to 30 hours of my time, which is not ok, as I'm time poor enough, and my head is already filled with stuff from my main job and my side hustle... I only have so much grey matter
The other fact is that the gantry is extremely well built, all mating surfaces are machined to one another, and it's just a well built bit of kit, albeit probably twice as heavy as it should be.

I could spend up to £1000 on motors and drivers fairly happily as long as I knew it was going to work. Hybrid steppers seemed to be a good way to go...

In fairness, I haven't even checked the voltage they're getting driven with... if its only say 48v then upping the power supply and drivers would be the first thing.

 

[m_c]

The problem with any kind of stepper, is torque drops off with speed, and generally the larger the motor, the quicker it drops off.

On something like a router (which going by the general construction of your machine, I'm guessing they've simply modified a router to a plasma cutter), that generally isn't that much of a problem as you won't normally be cutting at higher speeds, the steppers just need to be able to handle accelerating the weight/inertia, and lowering acceleration to achieve that on a router isn't usually a problem.
However on a plasma cutter, where you're likely to need to maintain relatively high speed around corners, steppers are likely to struggle.

In your case, unless you spend extra money on NEMA34 size servos (proper AC/DC servos are available in NEMA sizes, but they're not that common, and more expensive), you'll have to modify the motor mounting brackets.
Swapping to bigger closed loop NEMA steppers should allow you to eek out a bit more performance, and run closer to the limit of the motors, but similar sized servos (750W is probably around the size you'd need) will likely be cheaper, and not need an additional power supply.

 

[Erie Fred]

what's all this need for speed ?
Machine looked to be cooking along faster than I would have run it, and the holes came out nice & round.
It's not a laser.

FWIW that THC & torch lifter, IIRC you can get a stepper motor set-up, check the manual for the THC under options.

 

[Misterg]

I believe that if I push the motors too hard acceleration wise, they'll lose steps.

First step might be to see how far you can push the existing setup.

When I made my little CNC, I had a program that threw the machine around it's work area as fast as it could, 20-odd times, and then returned to the start point. I mounted a couple of indicators at the start point to check for any lost steps. (Set to zero before running the program, so should still read zero at the end of the program.)

Using this setup, I could tweak the speed and acceleration settings and it was obvious when I was approaching the limits. The actual running settings I used were 80% of these maxima.

 

[Munkul]

First step might be to see how far you can push the existing setup.

When I made my little CNC, I had a program that threw the machine around it's work area as fast as it could, 20-odd times, and then returned to the start point. I mounted a couple of indicators at the start point to check for any lost steps. (Set to zero before running the program, so should still read zero at the end of the program.)

Using this setup, I could tweak the speed and acceleration settings and it was obvious when I was approaching the limits. The actual running settings I used were 80% of these maxima.

I did this right at the start, but for some reason stopped trusting the settings and backed off the acceleration setting... Now I can't remember what it was so it's just running conservatively I didn't use a DTI, just a mark on a bit of plate. I like that idea a lot though, I think I'll do exactly that. I maybe can get a enough performance out of it to be happy.

 

[Munkul]

what's all this need for speed ?
Machine looked to be cooking along faster than I would have run it, and the holes came out nice & round.
It's not a laser.

FWIW that THC & torch lifter, IIRC you can get a stepper motor set-up, check the manual for the THC under options.

The speed is ok, it rapids at 15m/min, it's just the acceleration that sucks. Small holes in thin sheet at a decent speed are NOT round. The THC doesn't switch off properly on small holes either, so it starts diving if you go too slow. It's the SF2100 again. It's just not a good control. It has a setting for THC-off that just doesn't seem to work.
The HYD THC doesn't take a stepper, it's 24vdc only. It's completely based on time and not height/distance.
The z axis would easily modify to take a stepper physically, it's just that the controls won't drive it.

 

[DAPPH]

I did this right at the start, but for some reason stopped trusting the settings and backed off the acceleration setting... Now I can't remember what it was so it's just running conservatively I didn't use a DTI, just a mark on a bit of plate. I like that idea a lot though, I think I'll do exactly that. I maybe can get a enough performance out of it to be happy.

Even Einstein made notes in a note book for everything he did .

It helps , when a few minutes days or years later you need to recall what you've done , as you neck top commuter is very very fallible /

 

[m_c]

I did this right at the start, but for some reason stopped trusting the settings and backed off the acceleration setting... Now I can't remember what it was so it's just running conservatively I didn't use a DTI, just a mark on a bit of plate. I like that idea a lot though, I think I'll do exactly that. I maybe can get a enough performance out of it to be happy.

An issue with acceleration settings for stepper equipped machines, is acceleration can be higher at lower speeds due to the higher torque available at lower speeds. With older drives, there is also the issue of resonance, but any modern drive will likely have anti-resonance anyway.

A trick for CNC routers, is to have two different profiles.
One optimised for high acceleration with limited rapid speed, for small intricate work where you don't need large movements, and another with lower acceleration and higher rapid speeds for work where rapid speed is often reached. However switching profiles on a dedicated controller isn't usually possible.

 

[Munkul]

This is due an update.
I chopped out all of the internal deflectors. Very cheap and nasty, it wasn't really configured as a true downdraft table, more just some deflectors to drop all the crap down into one place.


I then dropped all of the crossbars by 35mm-ish. I left the two ends, but the rest were easy to cut and reweld as they were only welded down the sides.


Finished the water tray and test fitted. I made some riser bars for the bedbars, they sit loose in the water tray and transfer the weight over the top of the crossbars underneath.
The drain valve is a 1" ball valve I had lying around.







Today I pulled it all back out and gave the tray a good coat of epoxy paint.


Now I'm just waiting for some borax to be delivered, and then I can fill 'er up and apply sealant around the edges to the flashing.
I'm not confident I've made the tray deep enough to be honest. I'll have to try it and find out.

 

[Erie Fred]

Looks nice.
One leetle point on the 1" ball valve, I would put a elbow ahead of the valve, so the swarf does not sit on the
stainless ball, and etch it, also taking out the seals when operating it.