[schoobie]

Just trying to justify and understand the $2,399 bucks to be spent on this accessory.

I want to start a shop and this accessory represents a third of the cost of the machine.

Is this accessory needed only to cut high precision parts? Or is needed even for simple and non-industrial cuts?

Is this nice-to-have only or a must?

Need some reference to do the purchase.

Thanks!

[Torchhead]

Do some research. You can get a Digital Torch Height (aka ATHC) for less than 1/3 of that price including the control software.

You need to provide some form of height control unless you have a spring loaded head and a drag tip. You have to cut at .063 above the material moving at 100 to 300 IPM. Thin material buckles enough to cause tip crashes. If the material is not perfectly level you have added problems.

For 2400 bucks you can get a complete electronics bundle including motors, drives and power control with a digital THC.

Tom Caudle
www.CandCNC.com
http://www.CandCNC.com/SolutionsMenu.htm

[schoobie]

The one I am looking at is the one Torchmate has on its catalog.

[Mike@Torchmate]

Depending on what you are cutting I would almost justify it as a must unless you intend to build some type of manual plate following height control for the torch.

If you are cutting light gauge material up to slightly thicker plate (.1875" or .25") the material will most likely warp causing the tip to crash and drag on the plate, which ruins consumables and will likely ruin your cut as well. The AVHC will retract a certain distance in between cuts, so that when the torch is rapid traveling across the plate at 300 i/pm tip-ups in the plate won't hit the torch causing even further damage. At the beginning of every cut it also re-senses the material to ensure it is starting at the right height.

When you add up the cost of burnt up consumables, ruined plates of material, and potential broken torch head, it does not take long to make up for it's price.

[LenMcC]

i'm planning to order a torchmate with athc in early january, and i expect the athc to be worth every penny.

[schoobie]

what sizes are you choosing for the table?

[LenMcC]

4x8 or 4x10. i'm 90% sure we're getting the 4x8. we receive material in 4x8 sheets, and soon we'll be moving to 4x10s, but we don't cut more than 4ft wide strips off the long dimension at a time, so we have no need for the extra 2ft, i don't think.

also, we cut expanded and perforated aluminum, which i'm pretty sure would wreak havvoc on the torch head without the height control.

[Mike@Torchmate]

also, we cut expanded and perforated aluminum, which i'm pretty sure would wreak havvoc on the torch head without the height control.

If you are cutting expanded or perforated material the height control will have to be set in manual mode and special precautions must be taken to ensure the torch tip does not move below the material. The pierce sensing must be set so that at the bottom of the AVHC travel the torch tip is sitting above the material. This would ensure that even if it senses over air the torch still backs up to the correct cutting height and does not drag the material.

[LenMcC]

yeah, i figured we would have to set a minimum plunge so the machine doesn't think the material dropped away. you don't see perforated sheet as a problem, though, right mike? i know i talked to someone (probably not at torchmate) that said perforated is no problem. i may have seen a video of a plasma table cutting perforated, too, but maybe not...

[Mike@Torchmate]

yeah, i figured we would have to set a minimum plunge so the machine doesn't think the material dropped away. you don't see perforated sheet as a problem, though, right mike? i know i talked to someone (probably not at torchmate) that said perforated is no problem. i may have seen a video of a plasma table cutting perforated, too, but maybe not...

We have cut perforated material a lot here in the shop. There are a few conditions though. It has to be done in manual mode, otherwise when the cutting arc moves from pilot to transfer arc the voltage reading will change dramatically causing the height control to respond. The second is that the plasma cutter has to be in the Perforated material cutting mode in order to maintain the pilot arc across the gap and as soon as it senses the material it activates the cutting arc again. The last is the cutting speed, if it's too fast the arc may not transfer in time to sever the material.

[LenMcC]

Perforated material cutting mode

i like the sound of that mode. fortunately, we will cut primarily one perforated pattern in one thickness, so that should make dialing in settings easier.

these could be ignorant questions, but:
1) does transfering between pilot and cutting arc so many times each cut shorten the life of consumables or the machine or anything else?
2) what's the difference between pilot and cutting arcs? why can't it maintain the cutting arc across small gaps?
3) do slower speeds mean more dross? or do slower speeds mean we'd just need to reduce the current (and/or other settings) to match the speed?
4) does manual mode mean the height control is disabled?

thanks!!

[Mike@Torchmate]

1) does transfering between pilot and cutting arc so many times each cut shorten the life of consumables or the machine or anything else?

Yes, it can wear out the consumables faster, depending on a few factors like speed and the size of the gap the torch will have to cut across.

2) what's the difference between pilot and cutting arcs? why can't it maintain the cutting arc across small gaps?

The pilot arc is a small arc where it is basically searching for the ground through the material, once it has found that ground the machine transfers to a cutting arc which is where the amperage comes into play. It can maintain a cutting arc across small enough gaps where the torch can be severing one cut and then make contact with the next.

3) do slower speeds mean more dross? or do slower speeds mean we'd just need to reduce the current (and/or other settings) to match the speed?

In general you would use the appropriate speed and amperage settings as you would for the same thickness in flat plate, and then adjust from there. If you slow it down alot you may need to decrease the amperage on the plasma cutter to compensate, otherwise it could result in more dross build up.

4) does manual mode mean the height control is disabled?

The AVHC would not be completely disabled no, it will still sense pierce height and retract between cuts. It will just maintain the pierce height across the entire cut.



Hope that has answered your questions so far.

[LenMcC]

awesome. thank you so much.:cheers:

[agelkom]

Also you can use capacitive sensor to stop diving the torch head with your torchmate.
visit www.agelkom.com.tr

[Torchhead]

Also you can use capacitive sensor to stop diving the torch head with your torchmate.
visit www.agelkom.com.tr

Don't bet on it! The capacitance of a metal plate changes across a wide range as it gets cut. Too many conditions in the real world make capacitive sensing for plasma not effective. For THC the distance you have to maintain can be less than + - .020. (.5mm) Since the total gap is often .060 or less the excursion over that will cause head crashes or lost arc. Even with Arc volts sensing it's a challenge to hold the gap in the noisy world of plasma cutting.

A university (under a grant) set out to test and report (Whitepaper) on all of the ways to sense height on a plasma cutter. Thousands of dollars later and months of work they found Arc volts sensing (duh!) was the most accurate and reliable. They looked at laser, capacitive and arc volts. There is a distinct reason that all commercial Torch Height Controls (Hypertherm, Burney, etc) use arc volts sensing......it works.

Capacitive sensing might work for oxy-fuel where the plate is thick, does not tend to warp (as much) and the feedrates are slow.

If you use it for the initial height (touch off) setting then there are other ways a lot cheaper. A simple floating torch holder and microswitch will do the job more accurate and reliable and help with tip ups and head crashes. It works on dirty metal, rusty metal, and is the same foe aluminum, Stainless, mild steel and brass. Even ohmic sensing (using the tip and workpiece as a "switch" to sense the material) has it's limitations and problems.

One of the advantages of having the control software (Z under control of the toolpath software) is you can introduce parameters like a MIN and MAX excursion for the head to keep it from diving too low. Those are standard parameters in the THC section of MACH (THC Corrections setting). Since MACH knows the position of Z at all times, even under THC moves it can stop the head from diving below a preset absolute value. It also allows you to set things like anti dive that has to know the toolpath (actual cut velocity) numbers to preven head dives on tight curves and corners.

TOM CAUDLE
www.CandCNC.com

[agelkom]

[QUOTE=Torchhead;505354]
Mr. TOM CAUDLE says
Don't bet on it! The capacitance of a metal plate changes across a wide range as it gets cut. Too many conditions in the real world make capacitive sensing for plasma not effective. For THC the distance you have to maintain can be less than + - .020. (.5mm) Since the total gap is often .060 or less the excursion over that will cause head crashes or lost arc. Even with Arc volts sensing it's a challenge to hold the gap in the noisy world of plasma cutting.
Voltage controlled THC’s are definitely needed for all plasma config’s. However, they are not practical for intial height control..
A university (under a grant) set out to test and report (Whitepaper) on all of the ways to sense height on a plasma cutter. Thousands of dollars later and months of work they found Arc volts sensing (duh!) was the most accurate and reliable. They looked at laser, capacitive and arc volts. There is a distinct reason that all commercial Torch Height Controls (Hypertherm, Burney, etc) use arc volts sensing......it works.
It is true that all professional plasma manufacturers use Voltage controlled THC, but except for the lowest priced ones, they all have capacitive sensors as well.
Capacitive sensing might work for oxy-fuel where the plate is thick, does not tend to warp (as much) and the feedrates are slow.
It should be used
With a warped and irregular shape, the only method is to use a capacitive sensors.
If you use it for the initial height (touch off) setting then there are other ways a lot cheaper. A simple floating torch holder and microswitch will do the job more accurate and reliable and help with tip ups and head crashes. It works on dirty metal, rusty metal, and is the same foe aluminum, Stainless, mild steel and brass. Even ohmic sensing (using the tip and workpiece as a "switch" to sense the material) has it's limitations and problems.
You are right when considering hobby type and maybe some of the lowest priced CNC machines.
As you mentioned, using a switch is clearly very simple and cheapest way, but none of the higher quality products use a microswitch. Resistive sensors are not dependable due to possible presence of rust.
One of the advantages of having the control software (Z under control of the toolpath software) is you can introduce parameters like a MIN and MAX excursion for the head to keep it from diving too low. Those are standard parameters in the THC section of MACH (THC Corrections setting). Since MACH knows the position of Z at all times, even under THC moves it can stop the head from diving below a preset absolute value. It also allows you to set things like anti dive that has to know the toolpath (actual cut velocity) numbers to preven head dives on tight curves and corners.

Again, as you say, software control is always necessary, but it is not possible to know exact height variations generated during cutting process. Greatest and most common problems with TORCHMATE or same type height controllers have been torch head diving. Torch head under TORCHMATE control, touch the cut material and it actually might push it down until the Z motor stopped. When the head travels upwards, material may also change height upwards just before cutting begins. We actually observed many head crashes with expensive replacements following afterwards, with much time spent as well. Capacitive sensors relieve this problem due to contactless and fast sensing. Capacitive sensors do not cost too much anymore as some believe and they are the correct option for THC and even with a few cutting heads saved they are worth every dollar spent, especially when one considers also the time and materials saved.

Argun Gucdemir
Agelkom Ltd

[jimcolt]

Industrial use THC systems for plasma cutting all use Arc voltage feedback as the torch to work distance control for real time cutting. These systems have improved over the years through microprocessor control and with servo drives to control torch to work distance to within .005" of the proper height.

For applications requiring maximum consumable life and maximum productivity...it is imperative to have an IHS (initial height sensing) system as part of the THC. For initial height sensing...most of the latest technology THC systems use current sensing in the z axis to sense where the surface of the plate is...then retract to the proper pierce height before firing the torch. This technology drives the torch toward the plate...then on collision with the plate the addition force is sensed through the feedback circuit...the amount of force is adjustable so that it can overcome friction...yet not damage the torch consumables. As a backup (or primary) IHS...most THC's currently use "ohmic contact"...which senses an electrical connection between the nozzle shield and the plate. This function does not work in submerged cutting applications...or when the plate is primed or extremely dirty or rusty. The ohmic contact function is also used on some industrial height controls as a collision devise.....if during steady state cutting the torch contacts the plate (or a pile of slag)...the THC will rise a preset distance at high speed to avoid a collision, often saving the part being cut.

There are a ton of other features that are incorporated into the high end industrial torch height controls.....and are often reflected in the purchase price of these systems....which can be in the $12,000 range!

Jim Colt

[agelkom]

Dear Jim,
Would you please visit our site www.agelkom.com.tr for initial torch height sensing. Please comment and if you have any recommend please let me know.
Best regards,
Argun Gucdemir

[Mongkol]

Hi Argun,
Initial torch height sensing is THC or not. I don't understand.Pls advise.
How to differ with THC 300 or MP-1000 of candcnc product?

Mongkol

[jimcolt]

Initial Height Sense (IHS) is when the torch indexes toward the plate (before firing the plasma arc) and finds the surface of the plate....then retracts to the proper pierce height (which allows for maximum consumable parts life) before firing the plasma arc. It is imperative that a torch height control (THC) has this capability. Firing the torch at the correct pierce height is the single most important factor in making the consumable parts last the longest time.


Some THC's do not have IHS.....with these you must manually move the torch to the proper pierce height...the the THC takes over after the arc is fired to maintain the proper torch to plate distance during the cut.



Jim