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Author Topic: THC Setting Issue?  (Read 10718 times)

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Offline stirling

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Re: THC Setting Issue?
« Reply #10 on: August 12, 2014, 11:36:59 AM »
A THC loop of 150ms is pitifully slow. I can't see you getting much in the way of performance. All feedback loop systems operate behind the curve but apart from anything else - at 3300mm/s feed you're going to be a massive 8.25mm behind. I know you don't have the right system to use my THC but just to add perspective - at 3300mm/s feed mine would be just 0.055mm behind the curve (1 ms loop).

Offline Davek0974

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Re: THC Setting Issue?
« Reply #11 on: August 12, 2014, 02:29:35 PM »
1ms is amazing!

They do another unit with a response of around 80ms I think which controls the z motor directly and not through Mach, the issue with using that is that you lose the antidive feature in mach3.

What was the reason I couldn't use your system??  (Can't remember)
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline stirling

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Re: THC Setting Issue?
« Reply #12 on: August 13, 2014, 03:38:19 AM »
There appears to be a belief with some THC manufacturers that Mach's internal THC functionality presents some sort of bottle-neck and hence they tout "standalone" as some sort of remedy to this. Some even blame Mach's "slowness" for causing "head bouncing". This is NOT the case. Mach's internal functionality simply responds to the up down signals sent by the THC hardware and it does this at KERNEL FREQUENCY so with even the lowest kernel of 25KHz it's responding within 40 MICRO seconds - orders of magnitude faster than any THC loop that I know of.

The problem is that SOME THCs are firstly slow and secondly not very smart or even smart at all in how they "condition" the signal. Mach will just do what it's told and if its not told very well it's hardly fair to blame Mach. It's "worrying" is it not, that some THC manufacturers out there clearly don't really understand how Mach's THC functionality works.

Note - this is not to totally dismiss "standalone" THCs - they have their uses - the main one being that they can more easily be made system independent - i.e. they'll work across say Mach3/4/LinuxCNC/whatever - but siting Mach's "slowness" is not one of them and is plain wrong. (I'm currently debating whether to do a standalone version of my system for this reason of system flexibility).

You can't use my system because your Hypertherm model doesn't support the Hypertherm robotics interface.

Offline Davek0974

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Re: THC Setting Issue?
« Reply #13 on: August 13, 2014, 03:56:10 AM »
Thanks, I would never infer that Mach is the bottleneck, and also If i were to produce a unit like a THC i make damn sure I knew how Mach would react when connected.

Anyway, if i were to say change to a Hypertherm PM45 Would that help? I believe that is a "proper" cnc plasma cutter????

Having seen how useful this machine is, I am now looking at upgrades.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline stirling

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Re: THC Setting Issue?
« Reply #14 on: August 13, 2014, 12:10:51 PM »
Yes - the P45 is the lowest power/price Hypertherm system that has the machine interface which my THC is designed to use. Just note that if you decide to go that route you'll also need the machine torch. See www.razordance.co.uk/THC.htm for more details.

That said, I note from an xml you posted here ages ago that unless things have changed your Z axis isn't the fastest on the block so that's going to limit you to some extent whatever system you use.

Offline Davek0974

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Re: THC Setting Issue?
« Reply #15 on: August 13, 2014, 02:00:50 PM »
Thanks Stirling.

I think the z axis is on a 2mm screw pitch, it was a pre-built z axis system, presumed it was "normal" ?

According to hypertherm guru Jim Colt, at the same power level, on the same material, the 30XP cutter will give the best results, so for the present at least I am sticking with that system.

I will have a further play around with the THC system.
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.

Offline BLM

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Re: THC Setting Issue?
« Reply #16 on: August 13, 2014, 08:40:09 PM »
Hi Sterling,
      I am getting a Hypertherm HD3070. Is your THC able to work with that? I am using an Ethernet Smooth Stepper and I use Ohmic height sensing with a floating head. any thoughts?
        Thanks, Brian

Offline stirling

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Re: THC Setting Issue?
« Reply #17 on: August 14, 2014, 03:57:49 AM »
Hi Brian

Never tried it on high def cutters but according to their manual (p246) the cnc interface on Hypertherm's high def cutters is completely different to their "standard" def cutters - so I'm pretty sure the answer is a no. TBH - if I were looking at high def - I'd be looking beyond ALL the "budget" THCs. Hypertherm's offering costs several grand for a reason.

Offline stirling

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Re: THC Setting Issue?
« Reply #18 on: August 14, 2014, 04:28:27 AM »
Thanks Stirling.

I think the z axis is on a 2mm screw pitch, it was a pre-built z axis system, presumed it was "normal" ?

So just do the maths. How fast does your motor have to spin to handle the slope in the metal you want to handle at the XY feedrate you want to cut at.

Offline Davek0974

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Re: THC Setting Issue?
« Reply #19 on: August 14, 2014, 05:05:33 AM »
Ouch, maths! ;)


What i think is the issue, is that the motor will spin at whatever rate i have in THC Rate (currently 5) for as long as the THC box sends the up signal.

But, with the bad loop-speed it has, it is telling the system UP for too long due to the loop response. This makes the system overshoot so it then tells it DOWN straight away and we are into see-saw country in no time at all.

To counter this I have set the THC Rate low BUT this now means the system only works for thick/slow cuts, going to thinner metal means more speed which means I need a faster THC response rate so I up the THC Rate setting a bit but then that only works on fast cuts.

I think it's just a crap THC box really, there is plenty more speed available in system, I just can not use it properly to my best advantage.

Does that make sense???
Bridgeport Mill, Mach3 V062, CSMIO-IP/A controller, AC Servo Drives.
Plasma table, Mach3 V062, Step motors, C&CNC THC.