Ebay torch height control? Anyone use?
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  1. #1
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    Default Ebay torch height control? Anyone use?

    Proffessional Compact CNC Plasma THC Controller ( Torch Height Control ) | eBay

    Anyone tried one of these yet? Thinking about the home built CNC plasma table and would much prefer a THC.

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    I do not know about the merits of this one but yes we use a Height Control on our CNC plasma. You can do without but if you are into production it's a real asset. You have to make sure you have good grounds in order to get accurate voltage feedback to the controller. You will find you consumable life greatly increased. Also less headaches since you do not have to keep an eye on the gap all the time.

    I would be a little more comfortable in purchasing this one if there were more data on the external wiring. Sensing voltage in one thing but controlling the torch height motor is another entirely.

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    The REAL deal is that it only works well on strait cuts. When your cornering you need to balance tip volts and THC. A good THC will stop moving your torch down when it slows down for corners or radii. You will bury that torch in the corners with that cheap torch height control. Your motors will start to deccellerate but your torch is still cutting at whatever amperage you set it at so it will melt away material and start to dive because the material is further away. Maybe decent enough for a hobbyist that doesnt mind spending more on consumable but you wont get accurate geometry out of that.

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    WHat are the other choices, that wont break the bank?

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    Quote Originally Posted by Mebfab View Post
    WHat are the other choices, that wont break the bank?
    I am wondering if the program tells the THC to stop any torch height adjustments at corners only? Not being a programer I would not know for sure but it seems logical. How else would the THC know the difference between a corner and normal X/Y movement such as angles and radius?

    Just wondering....
    Walter

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    Quote Originally Posted by Walter A View Post
    I am wondering if the program tells the THC to stop any torch height adjustments at corners only? Not being a programer I would not know for sure but it seems logical. How else would the THC know the difference between a corner and normal X/Y movement such as angles and radius?

    Just wondering....
    Walter
    The logic senses the motor ramp down and slow down of actual tool path speed then stop the Z from moving. CandCNC.com has what I would consider the worlds 2nd best torch height control. The top dog is Hypertherm but only because they are using a dual gas torch setup. The downside of the Hypertherm unit is that to use it for lots of different types of material you will run into walls where you will end up having to lie to the control. Alot of the specifications for material and conditions are set by them in their labs through rigorous testing. They are #1 in the world no doubt about it. BUT the caveat here is that the settings for different options are often locked and are not tweakable whereas with a Candcnc DTHC you have the ability to control all facets and just recently you can control the amperage of the plasma cutter (Hypertherm 65,86,105 units only) when paired with sheetcam and the latest Mach 3 version. The Hypertherm control is easy to sue like most proprietary controls.

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    IMHO its the height control + cornering controls that's still the biggest stumbling block for the home brew cnc plasma cutters. It's the bit that really makes a big difference between plasma systems and there cut quality. Nearly everything can cut straights well these days, corners is IMHO the key issue, torch height, power levels all need to adjust to the deceleration & acceleration limits imposed by the motion set-up.

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    There is a glut of new plasma tables on ebay that are little more then home built. No torch height or at best the one above from poland and mach control.

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    Torch height control is the single most important aspect of any cnc plasma cutting system...if you are concerned with cut quality and consumable parts life. A properly designed plasma height control system must work in conjunction with the cnc control as well as the part program in order to achieve the correct pierce height, pierce delay time, cut height, and must have the means to ignore voltage anomalies caused by kerf crosssing as well as machine slowdowns due to cornering and fine feature cutting.

    All industrial quality (read more robust, more expensive) cnc plasma machines have full featured , well designed height control systems.....you cannot buy one of thes machines without height control. Unfortunately...many of the low cost, entry level cnc plasma machines that are designed for hobbyist or small shop applications offer height control as an option....which allows these machine builders to offer their products at lower prices. It is not a good idea to buy a cnc plasma cutter without height control....it will not cut as well and it will eat up consumables....resulting in higher cutting costs as well as poor cut quality.

    A basic height control will automatically locate the surface of the material to be cut, will retract to a user set pierce height (always higher than the best cut height), will then fire the torch at the pierce height and remain in place for a pierce delay time (to allow full plate penetration before the cut starts), then will index down to the torch manufacturers recommended cut height. Once the x and y axis get to the programmed best cut speed....an arc voltage feedback control takes over the real time control of torch to work distance by monitoring arc voltage (as measured from the torch electrode to the plate), and adjusting very accurately in order to maintain the correct torch to work distance. The cnc has to be able to "freeze" the arc voltage control during normal corner slowdown and kerf crossings, as well as at the end of the cut when the arc extinguishes...this height freeze is to prevent torch diving. More sophisticated height controls also have the ability to auto - calibrate torch to work distance to compensate for normal consumable parts wear....thus ensuring that cut quality will remain constant throughout the life of a set of torch consumables.

    A typical plasma height control system consists of a z axis motorized slide with mounting configuration for the plasma torch, a voltage divider /isolator circuit (to reduce the DC arc voltage signal and filter it to a usable level), an electronic control box that monitors the input, output (from CNC and plasma, and voltage divider), as well as associated cables and user interface panel. Some height control systems are "standalone" (will work with any plasma/cnc machine configuration) and some are integrated (designed to operate as an additional axis of the cnc machine.....and is operable through the motion control system software.

    They are typically a fairly high price addition to an entry level cnc machine.....but make the system cut like a cnc machine should.....in a hands off automated manner.

    The unit listed on the initial post appears to be just the arc voltage control circuitry.....you would still have to design an initial surface sensing process, the ability to retract to pierce height, a pierce delay timer...a motorized z axiss assembly to raise/lower the torch, etc. Sounds like some engineering and design and testing would certainly be involved to make this system work.

    Jim Colt Hypertherm

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    Digging up a dead thread to give a shoutout to an eBay controller that I recently bought and works well "THC3T-02: Stand Alone Plasma Torch Height Controller". It's got good instructions (typical translated English but it's understandable and has plenty of pictures), menu interface is good but the buttons could use debouncing (it'll move multiple steps through the menu rather than a single item per press - once it's set up you'll never touch it again so it's not that much of a problem). We didn't hook it up quite right on initial installation and it didn't blow up so that's a major plus. Installing the voltage divider is a little hairy, you need to be absolutely certain it's positioned a long way from any metal surface in the torch power supply and with the HF arc it can jump a long way - we haven't had any trouble with it but took a lot of precautions to make sure it was well insulated.

    I'm not a spokesperson for the company, but I read this thread when I was deciding what to buy and wanted to help someone else out with the same decision.


    Chris

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    Has anyone tried using the SH-HC30 or SH-HC31 torch height controller from ebay?

    SH-HC31 Plasma(Arc Voltage)/Flame CNC Cutting Torch Height Controller THC 22V | eBay


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