How many have actually needed high speed THC

[beefy]

Just a curiosity question here.

You've got the traditional THC controls where the CNC controller (e.g. Mach3) receives THC UP / THC DOWN input signals from and external THC. The controller then sends out step/direction signals to the Z driver/motor. This is what I've been using since day one.

Then you've got generally faster THC controls where the Z motor is not controlled by the CNC controller, but by a separate dedicated THC controller. I've ordered and am waiting for a Neuron Lite THC which is such an example. I'll be using it with UCCNC from Cncdrive.

My question is, for those of you that have used the traditional THC UP / THC DOWN control, have you ever been limited in what you can cut, i.e. did you ever need the higher THC speed and couldn't do a job because your THC simply wasn't fast enough.

We see videos of corrugated iron being cut and the Z doing a pretty good job of raising and lowering the Z. Quite impressive but as for myself I haven't needed that yet, and I'm more curious about "normal" sheet cutting and where you must have the faster THC speed.

Keith.

[Metriccar]

The most I've stressed the THC was from cutting diamond plate steel with the diamond plate side up. I could always put the diamond side down but I didn't want to scratch it loading it on the table.

[steel 35]

I have been amazed with the ability to follow a moving target a few times

[beefy]

The most I've stressed the THC was from cutting diamond plate steel with the diamond plate side up. I could always put the diamond side down but I didn't want to scratch it loading it on the table.

Good example of when many people may need higher speed / better reaction time. But what type of system did you pull it off with. Was it a basic one that received THC UP/DOWN input signals from an external THC.

Keith.

[Metriccar]

It's a Plasmacam, so however it works.

[see&see]

I was in a hurry and cut a little 4" part from 1/4" MS today and had the cut direction going the wrong way leaving the part hanging in mid air and it fell down about a half inch to the grate just before the cut was finished.. The torch followed it right down and still cut the part perfect.. Amazing!

[beefy]

It's a Plasmacam, so however it works.

Ah, I'd say that's in the higher performance category. Pretty sure PC use servo motors all round and I think they are a pretty fast table.

In 3 weeks, I'll be working at a joint that has a Plasmacam, should be interesting although I wouldn't buy one for myself.

Keith.

[beefy]

I was in a hurry and cut a little 4" part from 1/4" MS today and had the cut direction going the wrong way leaving the part hanging in mid air and it fell down about a half inch to the grate just before the cut was finished.. The torch followed it right down and still cut the part perfect.. Amazing!

Ha ha, another good advert for Plasmacam. Sounds like their THC is definitely a fast one.

Anyone cut thin plate or checker plate with a standard THC UP/DOWN type system ? Thin plate can warp with the heat as you cut it so the THC control must keep the torch moving fast enough.

Keith.

[jimcolt]

The Plasmacam THC uses a stepper for the z axis, (servos on x and y) however it is adequately fast for every situation I have used it for.

Most THC systems have the ability to adjust z axis speed, some will even allow you to tune z axis acceleration. When your speed or acceleration is set too high on the z axis you will experience some oscillation (up/ down sewing machine effect) that will have an effect on cut edge quality as well as collisions with the material.

The mechanics of the z axis lifter (slide assembly and drive....which is often a screw) are critical as well....any slop or play and this will cause overshoot and oscillation as well.

Hypertherm's high end industrial THC systems have the ability to make adjustments at 1000 ipm, however the actual height correction (less than .001" inch at a time) is usually at much slower speeds in order to not create edge roughness associated with z axis moves. The 1000 ipm is used more for productivity reasons, reducing cut to cut cycle times, etc. Don't plan to use a Hypertherm THC on your entry level table....unless you plan to spend around $12k just for the THC! Jim Colt Hypertherm

[adbuch]

..

[beefy]

.

[adbuch]

Sorry Keith - it is not clear to me how to start a new thread on this board or I would have done so originally. I do not know how to delete the post, so I edited it to remove the content.
David Buchhauser

[jimcolt]

David, I responded to your post on the Plasmacam Owners community. Jim Colt

[beefy]

Sorry Keith - it is not clear to me how to start a new thread on this board or I would have done so originally. I do not know how to delete the post, so I edited it to remove the content.
David Buchhauser

Thanks David, much appreciated.

Keith.

[SeanP]

I can't say I have needed any faster thc than what I'm getting from my Cand CNC parallel ports system Keith, I keep thinking I will test it with some wild angle but never have done, had some wild enough rising aluminium strips at times which it's done fine with, even when you get a strip jump up from expansion it soon gets back the right height.
Surprised how well it did cutting 2'' holes in 4'' pipe not so long ago, tracked it well.

[SeanP]

Most THC systems have the ability to adjust z axis speed, some will even allow you to tune z axis acceleration. When your speed or acceleration is set too high on the z axis you will experience some oscillation (up/ down sewing machine effect) that will have an effect on cut edge quality as well as collisions with the material.

Thanks for that info Jim, I spotted this the other day and eased the acceleration off a bit on the Z, stopped that slight judder I was getting sometimes on 10mm and over.

[tcaudle]

Thanks for that info Jim, I spotted this the other day and eased the acceleration off a bit on the Z, stopped that slight judder I was getting sometimes on 10mm and over

Strange.. since the parallel port MACH has no acceleration curve while cutting under THC. The THC rate is a % of Z velocity. Acceleration is instant
The THCrate typically works around 20 to 30% on a Z set for 100 IPM. That gives you about 20 to 30 IPM versicle speed. You can figure what rise over run at 30IPM will handle at something like 225 IPM horz (about a 10% grade) If the grade is steeper than that the torch will hit the material.

[beefy]

I can't say I have needed any faster thc than what I'm getting from my Cand CNC parallel ports system Keith, I keep thinking I will test it with some wild angle but never have done, had some wild enough rising aluminium strips at times which it's done fine with, even when you get a strip jump up from expansion it soon gets back the right height.
Surprised how well it did cutting 2'' holes in 4'' pipe not so long ago, tracked it well.

Thanks Sean,

that's exactly the type of info I'm after. Like Tom mentioned Mach3 does not have acceleration/deceleration applied to THC moves, and this has the side effect of reducing the max THC velocity before the motor stalls (i.e. it is limited how fast it can go from zero to applied speed, or from one direction to the other instantly).

I haven't tested it yet but the UCCNC controller DOES have acceleration/deceleration applied to THC moves, and that is supposed to allow the THC to run at a much higher feedrate. If that is true, and yet you've had decent results with the Mach3 parallel port system, things could be promising for my own build with UCCNC, though I won't be as optimistic to expect it will handle corrugated LOL.

Keith.

[tcaudle]

You will get somewhat higher speeds but it will result in more overshoot and more instability at those speeds unless you have some way to do PID in the velocity curve. The more expensive Neuron that is basically a stand alone THC (does not use UP and DOWN back to the software) does have PID. The DTHCII you have is the last model we used the internal THC logic in MACH3. The later versions controlled Z directly and used a Inverse Non-linear PID loop to make it move at high speeds with stability. Like it or not the torch mechanics and the Arc gap voltage are a positional feedback loop (servo). i understand you are not looking for performance and cost is the primary driver but it all depends on what you are willing to accept in terms of cut quality and consumable life.

[beefy]

i understand you are not looking for performance and cost is the primary driver but it all depends on what you are willing to accept in terms of cut quality and consumable life.

That's not quite the way it is Tom, cost is not the primary driver, but customisation is. I started off with your MP3000 system and it's still hooked up to this day but the "black box" all in one side of things meant I couldn't modify or add to it. That's what got me started on my own design.

I've been working for some time on my own personal system, in which I'm aiming to include all sorts of features that I cannot find in any system (i.e. all together).

I realise about the PID in the Neuron and I've bought that one to get me by while I continue my journey with my own design. It's not a bad system and has quite a few good features but unfortunately seems to lack the capability of turning the torch on and off during motion, quite a serious omission for when I need to cut holes and turn the torch off before XY motion has stopped. Maybe that will get added in the future.

At this point in time PID programming is beyond my skill set and that's why I'm wondering how far the basic THC UP/DOWN signal type control will get me. So long as I don't go above the speed such a system can handle, my cut quality and consumable life will be fine. As a matter of fact it can be detrimental to have too fast a THC speed when cutting thicker metal that doesn't need it. You even said yourself some time ago that it can be advantageous to reduce the THC speed when cutting thicker metal. You were talking about the THC speed beating the Tip Saver reaction I beleive (I have the post recorded somewhere in my archives). Most of my cuts are 3mm and up so super fast and accurate THC response is not really needed.

Keith.

[BTA Plasma]

When you start to cut faster you need your THC and Z axis to react faster to not crash. But this alone is one of many requirements for a high performance THC. Even when your cutting slowly that variation in tip voltage caused by a slow THC will shorten the life of your consumables and basically everything at the end of the torch. Do you need it? No ...not if you plan on spending more money than you need to and as long as you have that machine. Should you get one? Yes if its in the budget.

[beefy]

Even when your cutting slowly that variation in tip voltage caused by a slow THC will shorten the life of your consumables and basically everything at the end of the torch. Do you need it? No ...not if you plan on spending more money than you need to and as long as you have that machine. Should you get one? Yes if its in the budget.

Agreed >> IF << it is a SLOW THC. But it would have to be slow indeed not to be able to adjust for a slowly varying torch height (voltage).

Even a fast THC first requires a variation in tip voltage in the first place to cause it to adjust.

I think things are being dramatised a little for the sake of sales here. Sorry but that's what I'm seeing.

I can't see how consumables are going to have any shorter life so long as you are cutting at a feedrate that your THC is capable of adjusting for. If the THC can move at a rate faster than what the voltage is changing then it's keeping up just the same. It's only when the THC is not fast enough that the system cannot maintain correct cut height, and consumable life and cut quality may go down.

I've been cutting plenty of 3mm and thicker steel and watched the Z corrections under THC control. And my Z is pretty slow with only a 15% THC Rate in Mach3 (Candcnc MP3000). I regularly watch the voltage deviation too and it tracks very close, which basically means the correct cut height is being maintained.

And as I previously said, Tom himself even said you don't always need fast THC control and it can be counter productive. An example is when you go over a void in thicker metal and the high speed THC quickly dives to correct the voltage and slams into the surface (i.e. the super fast THC reaction beats the Tip Saver / Void Lock). Since Tom mentioned that, I've since seen it recommended to slow THC reaction speed to suit the metal being cut. No need for a Ferrari engine in a haulage truck.

As for the

"Do you need it? No ...not if you plan on spending more money than you need to and as long as you have that machine. Should you get one? Yes if its in the budget"

You make it out that a user will automatically be spending more money on consumables. As said above I don't think that's true, and it will only be the case if the THC cannot keep up with the rate of change of voltage (cut height). I'd say spend the extra if you think you'll ever need to cut thinner metals at the associated higher speeds, or you may want to do checker plate with the bumps side facing up, or you plan on doing corrugated, etc. That's when a fast THC will maintain cut height, and the slower one won't.

[BTA Plasma]

You make it out that a user will automatically be spending more money on consumables.

Try to imagine the torch cutting and reacting in Z axis to tip volts. Now imagine a moment while its cutting where it is closer or further away than the actual recommended cut height and it tries to follow but doesn't react until it is several volts away or over shoots its target voltage. That is what a slow or course THC will do. This will cause you to loose a percentage of the usable consumable life of your consumables even at slower speed cutting. By allowing moments between adjustments or moments between actual cut height to occur. This is why a high performance THC is vital an virtually any cut speed.

[tcaudle]

A Moped will get you to the store just as easy as a Mustang GT500. Maybe not as fast, maybe not as comfortably and perhaps a bit wetter in the rain but if your goal is to just to GET there then why spend the extra bucks?

Just a few observations though.
. You shouldn't be crossing over other kerfs/voids to begin with . That is Pilot Error . Only time you should cross a kerf is at the ending of a closed object as it approaches the beginning. That occurrence can be stopped using a Velocity Anti-Dive because the trajectory is going to slow down as it decelerates at the end,
.
I don't know a single Engineer or Programmer that does not think they can do a better job on a design or software than any other person. I think its part of the personality of those trades.

[beefy]

You make it out that a user will automatically be spending more money on consumables.

Try to imagine the torch cutting and reacting in Z axis to tip volts. Now imagine a moment while its cutting where it is closer or further away than the actual recommended cut height and it tries to follow but doesn't react until it is several volts away or over shoots its target voltage. That is what a slow or course THC will do.

Like I said before I think you are comparing a VERY SLOW system with a very high performance one. To get several volts away from the Set Point because the THC is so slow, simply means that THC is way out of its league and cannot keep up as required. However, if the voltage change is only moderate and THC speed/reaction is accordingly moderate (or slightly better), it is going to keep up and you won't get several volts away from the set point. Likewise your consumables are not going to deteriorate faster.

I think THAT needs to be imagined.

Getting back to what I mentioned earlier about UCCNC applying acceleration to it's THC moves. Many of these high performance PID controlled THCs actually use steppers, and the reaction time of the system is limited by the stepper acceleration/deceleration. No matter how good the electronics/software, you can't make a stepper motor accelerate or decelerate faster than it's capable of.

This is why a high performance THC is vital an virtually any cut speed.

Sorry BTA but I find that completely untrue. I mean cmon, vital at any cut speed ?

This is starting to sound like marketing scare tactics. Look, personally I always want the best and am willing to pay for it (I just paid A$1050 for the Neuron delivered), and I would recommend users buy the best fastest THC if they think it they will require it capabilities at some point. But I'd never say they'd need it for slow cut speeds and slowly varying cut volts, otherwise they'll be paying through the nose in consumables. I think a clear detailed technical explanation would be in order to back up that claim.

Like how is the voltage going to end up way off course when due to a slow cut speed the voltage would only change very slowly and even a pretty basic THC can easily make and adjustment it time to keep the voltage within the set point.