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  1. #21
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    THC is torch height control. I.E. Z axis. Either that or it is the substance that makes is possible to enjoy Grateful Dead music.

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    Quote Originally Posted by Speedie View Post
    Servos require reduction and that gets expensive. A servo is either on or off and requires an encoder for movement. This also does not guarantee position which is one of the sale hypes you hear in the CNC world. Without a scale to check actual position and a feedback logic you are not guaranteed position with a servo. A solid developed torque curve where you running your table rapids is always a good bet.


    Look if you want a plasma that will last you a long time that is a different ballgame. If you want to cut for a year then move on you can buy just about anything on the market.
    Yes. In many lower power applications, the cost and setup of a servo system, that does not offer any better resolution than a properly setup stepper system, is not worth it. And Yes the encoder feedback is only a good as your registration method, no different than a stepper system; pulse count is only as good as your starting point.

    The G540 does not have an isolated power supply. The inputs will use a 48V power supply as their ground and as their safety ground. Once you get some stray frequency you start to degrade the inputs to the point they burn out. The system will move anything around but is not made for certian applicaitons. It may even last a *while
    I had to look at the G540 manual as I have never used one, but looking at it from a power/torque side. I see that the inputs are not isolated, which I agree is a no no, but they are sourcing 12v( I assume from the cpu) inputs to ground. I can't say whether pnp/npn makes any difference, but in industry, isolation is a must when it comes to PLCs, encoders, cpu comms, etc.

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    Here is a quick top ten list of the advantages and disadvantages of both steppers and servos pulled from ***ZONE. Not really about plasma tables in particular, and is more about the building your own, but will give you more insight about the motors that are moving x,y,z in whatever system you choose to buy.
    Top Ten Stepper Advantages:

    1) Stable. Can drive a wide range of frictional and inertial loads.
    2) Needs no feedback. The motor is also the position transducer.
    3) Inexpensive relative to other motion control systems.
    4) Standardized frame size and performance.
    5) Plug and play. Easy to setup and use.
    6) Safe. If anything breaks, the motor stops.
    7) Long life. Bearings are the only wear-out mechanism.
    8) Excellent low speed torque. Can drive many loads without gearing.
    9) Excellent repeatability. Returns to the same location accurately.
    10) Overload safe. Motor cannot be damaged by mechanical overload.

    Top Ten DC Servo Advantages:

    1) High output power relative to motor size and weight.
    2) Encoder determines accuracy and resolution.
    3) High efficiency. Can approach 90% at light loads.
    4) High torque to inertia ratio. Can rapidly accelerate loads.
    5) Has "reserve" power. 2-3 times continuous power for short periods.
    6) Has "reserve" torque. 5-10 times rated torque for short periods.
    7) Motor stays cool. Current draw proportional to load.
    8) Usable high speed torque. Maintains rated torque to 90% of NL RPM
    9) Audibly quiet at high speeds.
    10) Resonance and vibration free operation.

    Top Ten Stepper Disadvantages:

    1) Low efficiency. Motor draws substantial power regardless of load.
    2) Torque drops rapidly with speed (torque is the inverse of speed).
    3) Low accuracy. 1:200 at full load, 1:2000 at light loads.
    4) Prone to resonance. Requires micro-stepping to move smoothly.
    5) No feedback to indicate missed steps.
    6) Low torque to inertia ratio. Cannot accelerate loads very rapidly.
    7) Motor gets very hot in high performance configurations.
    8) Motor will not "pick up" after momentary overload.
    9) Motor is audibly very noisy at moderate to high speeds.
    10) Low output power for size and weight.

    Top Ten DC Servo (brush type) Disadvantages (besides higher relative cost):

    1) Requires "tuning" to stabilize feedback loop.
    2) Motor "runs away" when something breaks. Safety circuits required.
    3) Complex. Requires encoder.
    4) Brush wear limits life to 2,000 hrs. Service is then required.
    5) Peak torque is limited to a 1% duty cycle.
    6) Motor can be damaged by sustained overload.
    7) Bewildering choice of motors, encoders, servo drives.
    8) Power supply current 10 times average to use peak torque. See (5).
    9) Motor develops peak power at higher speeds. Gearing often required.
    10) Poor motor cooling. Ventilated motors are easily contaminated

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    I think you would be crazy not to get Z axis/ height control.

    Anytime you are cutting any piece of metal, the heat will cause it to move. Fact of life. Sometimes it will move more, sometimes less- for instance, its not uncommon, if you are cutting close to an edge, for a 1/4" wide piece to curl up as you cut past it, til its sticking up 3" or more.

    thin stuff will warp, depending on material, speed, and shape of cut.

    And any time the metal moves, that affects cutting quality.

    If your torch can automatically adjust height, you get fewer crashes, fewer wasted scrap parts, and better overall quality of cuts in a wide variety of materials.

    And not all metal is flat from the supplier.

    Do you have a 4' wide, 12 roll flattening mill that will flatten a piece of 1/4" plate?
    I didnt think so.
    So if your 1/4" plate, from the yard, has a 3/8" bow in it, from end to end, thats enough to screw up a cut that was perfectly adjusted at one end, by the time you reach the other end. Unless you want to babysit every cut and manually adjust height.

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    Anchorman--If you'll bother to scroll down on this same forum page or do a search on plasma cutting on this site,
    there is quite a bit to be found that will help you and answer questions which you didn't even know to ask.

    It's obvious that you have done neither.

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    thanks, but no thanks, dave powelson... sometimes sifting through the glut of information and reading about a new and unfamiliar topic can be overwhelming when a question + simple answers is all that is needed. 85 companies making this equipment? that's a lot to sort through alone, let alone to figure out what options I would want. I got most of the information I needed from some people who responded with useful answers to my simple request for other people to share their experiences with me based on my needs. Now I have spoken to representatives of a few of those companies mentioned, and received quotes and information about their machines. If you have anything constructive to share with me and others in this thread, I'm all ears (and eyes). If not, please walk on by and ignore.

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    Quote Originally Posted by anchorman View Post
    thanks, but no thanks, dave powelson... sometimes sifting through the glut of information and reading about a new and unfamiliar topic can be overwhelming when a question + simple answers is all that is needed. 85 companies making this equipment? that's a lot to sort through alone, let alone to figure out what options I would want. I got most of the information I needed from some people who responded with useful answers to my simple request for other people to share their experiences with me based on my needs. Now I have spoken to representatives of a few of those companies mentioned, and received quotes and information about their machines. If you have anything constructive to share with me and others in this thread, I'm all ears (and eyes). If not, please walk on by and ignore.
    Hi Anchorman. Hopefully this paste below will help steer you toward a quality driver package in the price range we are talking about. Choose a quality plasma cutter, the gecko g540, and proper care to ground and shield your system, and I think you will be very happy with the results. Show me a machine under 15 grand that uses a better driver and I will be very interested in checking it out. Some people will tell you to get $2000 dollar rails (x3) and so on, and blah, blah, but let's face it, not everyone has $20k to throw in to one of these. And there is really no need to. Somewhere in the $5k range, if made properly, will serve you well for years to come. Here is a article I found on the internet about the G540. It is a good write up and there is nothing incorrect in it.


    Overview

    Hooking up a stepper drive system can get complex and expensive. First you pick out the stepper drives you need, then a breakout board, and you might have to add on other boards to get features like VFD output, charge pump circuit, etc. Then once you get all of those boards you have to spend a lot of time figuring out how to hook it all up properly. Gecko reduced both the complexity and cost of setting up smaller systems by designing all of these features into one compact unit.

    The G540 is composed of four individual G250 motor controls, which plug into an optically isolated break-out-board with a standard DB25 connector and everything comes in a hard anodized aluminum case which is easy to mount and easy to wire up. Other built in features include a charge pump circuit (it can be bypassed with a switch on the back panel), two high current outputs that can directly drive relays, four isolated inputs, an enable input, and an isolated VFD output.

    Connections to the motors are made with DB9 connectors (included), and programming the drive current is done with a resistor soldered into the DB9 (1K per 1A or motor current). Each of the four drives has an individual trim pot to optimize the low speed smoothness of each axis.

    The G540 has four general purpose isolated inputs. These inputs may be used as limit switches or for any other purpose. You can connect SPST switches or PNP type sensors to these inputs. (Sensors must be separately powered.)

    Two general purpose high current outputs are also built in. These outputs may be used to drive relay coils or for any other purpose. The outputs are rated at 1A and 50VDC maximum. Connect one end of the load to the output and connect the other end of the load to a positive DC voltage. This voltage may be the G540 power supply or it may be a separate power supply having a different voltage.

    An analog output is provided for controlling things like VFD (speed controls). This is a 0V to 10V opto-isolated analog output. The VFD OUT goes to 0VDC while the G540 is disabled. The voltage source for this output is provided by the drive or an external voltage source.

    If you compare the cost and complexity of configuring an equivalent stepper drive system out of separate components it is easy to see that the G540 is the way to go. It provides all the features that 99% of folks want at an unbeatable price.
    Features

    The Gecko G540 is packed with features that make it the choice for small to medium sized CNC machines. If you compare the cost and complexity of configuring an equivalent stepper drive system out of separate components it is easy to see that the G540 is the way to go. It provides all the features that 99% of folks need at an unbeatable price.

    The G540 contains four separate G250 stepper drives that all plug in an optically isolated motherboard (BOB). The motherboard isolates all the signals to/from the DB25 connector the VFD output is also isolated from the rest of the circuitry. This isolation not only protects your PC from the high voltage of the drives (in case something goes wrong) it also serves as a type of noise filter keeping noise from the drives from working back into your PC.

    All of the features of the G540 is wrapped up in a heavy duty anodized aluminum case. This provides a stepper drive system that is not only easy to hook up but it is also easy to mount.

    Feature List

    All LPT interface pins optically isolated
    Four isolated inputs
    Isolated VFD output
    Two high current outputs, can drive relays
    Can be interfaced with 3.3V or 5V signals
    Users selectable Charge Pump circuit
    Over current protection
    15VDC~50VDC Operation
    Four individual 3.5A G250 Stepper Drives
    Motors connected by heavy duty DB9 connectors
    Motor current programmed by resistor in DB9 connector
    Anodized aluminum case

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    At first glance it appeared that the inputs were not isolated. Good to know they are. Thanks for sharing.

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    I have 3 G540s on my desk with burned out OUTPUTS from high frequency. I can tell you they dont work for very long if you have RF noise. The latest one is from batch # R10. You just dont have enough isolation in these little drives for that type of application. You can however get away with it for a while. I will trade any one of these for one that is working 100%.

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    We've got a Torch-mate 4x4 table running for 6 month now. In my opinion its a reasonable Plasma for the price, but we needed to make quite a few modification, e.g key-ways on all gears, to make it usable and somewhat accurate. I checked the steppers and they are insanely precise, and as Torch-mate claims it's actually accurate enough to draw something on a penny (when its calibrated). Overall it does a decent job right now, but we put quite some work into it making it that usable. I think the biggest we were able to cut was half inch steel and it did a good job, the smallest was 20G Aluminum and it delivered quite a nice cut.

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    We have a Shop Sabre from Minn. They are great. The machine is very well put together. The software is pretty easy to use, yet of industrial quality. Service is super. We had a small problem and they were able to talk a senior in high school through the trouble shooting and repair. The machine is built to last. Believe me I know, I have high school students who can be hard on machines. The price was fair especially for what you get. I would have no problem buying from them again if I needed to. Just so you know I am not paid to say good things about the machine, I do it because it's a great machine.

  13. #32
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    I've built my own table with a cutting area of 1500 x 2400 mm. Gecko drives are excellent quality and run stepper motors cool. Had a Leadshine drive which cost more than one of my Gecko drives and it was absolutely crap, my motors would stall all the time.

    Highly recommend a water table or downdraft suction. The amount of black dust made is unbelievable and travels everywhere before settling. It will kill any electronic PCBs is may get to settle on.

    Torch height control - don't need one ?????????????!!!!!!!!!!!!!!! Let's think about what happens during a cut. My Hypertherm torch cuts at 1.5mm above the metal. For a quality cut this gap needs to be maintained. Worse if the material raises at any point your torch tip can end up dragging on the material. Warpage during cutting can cause the material to rise. Even if all your table slats are perfectly level/flat and parallel with the table X & Y axis, you quickly get slag forming on top of them which stuffs this accuracy up.

    Steppers or servos. Quality steppers and drives (my thumbs up for Geckos, G203V in my case) run lots and lots of tables. Once a table gantry gets to a certain weight you may need servos with reduction drives. The key with plasma cutting is acceleration and this takes torque. Steppers lose torque as their rpm increases whereas servos I believe actually get a bit of torque increase at higher rpm. For the size of table you want I'd say steppers are fine.

    Many manufacturers talk about accuracy. They will often use repeatability which I find very misleading. If a rail was curved then the curve in the cut will always repeat quite accurately. They may talk in thousands of an inch as far as their rail accuracy is concerned. Perhaps get them to put a large peice of board on the table and fine tip pen on the z-axis and draw a square. Measure the 2 diagonals and see if they are exactly the same. The biggest affect on accuracy will probably be the plasma jet itself, it is "floppy" and the bottom trails as it moves along. This lag in the jet can transfer to a new line after you go around a sharp corner, etc. Your air supply needs filtering and drying to give max quality cuts and make your consumeables last a lot longer. It's not just the table accuracy.

    The software (cam) needs features like looping on corners to get around this slope issue. Can the z-axis touch off before every pierce to find the top of material, then raise to pierce height to blow a hole. This reduces your consumeables cost a lot when piercing at the correct height. You can get 3rd party software from the likes of We-cim which has much more features and I think you can make custom lead-ins for example. The features in the cam software can be an important consideration in addition to the table.

    Getting on cnc & plasma forums will give you a lot of focussed info, good luck.

    Keith.

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    Quote Originally Posted by mancavedweller View Post

    Snipped

    Torch height control - don't need one ?????????????!!!!!!!!!!!!!!! Let's think about what happens during a cut. My Hypertherm torch cuts at 1.5mm above the metal. For a quality cut this gap needs to be maintained. Worse if the material raises at any point your torch tip can end up dragging on the material. Warpage during cutting can cause the material to rise. Even if all your table slats are perfectly level/flat and parallel with the table X & Y axis, you quickly get slag forming on top of them which stuffs this accuracy up.

    Snipped

    Keith.
    Keith,are you being sarcastic when you say you don`t need THC or do you mean it?
    If you mean it,how to you keep the cutting height constant?

    Mark.

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    Hi Mark,

    I wasn't actually sarcasm, it was more of a statement/question (question marks & exclamation marks afterwards). I consider torch height control vital.

    My table uses arc voltage sensing for on the fly adjustment of cutting height. This is acheived via the hardware and software that controls the machine. In addition to the main z-axis (leadscrew and linear rails) there is also a mini floating z-axis attached. This floating z-axis carries the torch and can move up and down just a few mm. There's no leadscrew, instead it simply falls to the bottom under it's own weight, although I put a counteract spring on mine so the torch "weighs less" and can push up with little force. This floating z-axis is used for what's called initial height sensing where at the start of a cut the torch rapids down to a programmed height, then slowly lowers further until the torch touches the metal. At this point, as the z-axis moved down further the floating z-axis can't go down any further so it "moves up" relative to the main z-axis, and trips a micro switch. Now there's an offset programmed into the software which is exactly how far you must now raise the z-axis until the floating z-axis bottoms out and starts lifting the torch again. That point of lift is material zero. The counteract spring helps stop thin plate deflecting and giving a false material zero position. Some tables I believe even have more than one method of initial height sensing, they also have proximity sensors for thin plate.

    The voltage height control value is preset in the software and a starting value comes from the Hypertherem (in my case) cut charts, which have travel speed, amps, voltage, etc for a given nozzle and thickness of steel. For best quality cuts, many do test runs on a flat sheet with the voltage control turned off. The cut height is programmed and a straight test run done and the voltage noted. Various speed, height, and possibly current can be slightly adjusted until the best cut quality is found then these parameters used for the "real" cut with the torch height control.

    Keith.

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    I would not buy a Torchmate again. Since Lincoln took over they S^%k . When my old computer crashed they said no problem send use 2400.00 we will send you new control hardware and software and you will be all set . So I have to get new computer and rebuild my machine ? yeah basically. Needless to say I did not do that and if I have to rebuild it won't be with Torchmate

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    Keith,thanks for that explanation.I`ve not quite got my head around it yet but will give it some thought.
    I have a plate rider on mine and keep thinking of upgrading but never get to the decision making stage.
    I get very high quality cuts but don`t get good consumable life.Never cut thinner than 4mm and rarely go above 15mm,all steel.

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    I've been running a Dynatorch setup for almost 4 years. They've been awesome with customer service and the table has cut tons and tons of metal-- all 1/2" or less.

    Torch height control is worth it. Don't buy a table without it. The simple fact is that anytime you're running a long cut, the metal is going to warp. If you don't have Z axis control, you'll probably end up crashing.

    One thing to keep in mind is that cutting with plasma is not comparable to adapting for a router. The router is going to add lots of resistance whereas the plasma has none. If you're thinking of retrofitting a plasma table in the future to run a router, you need to make sure your motors can handle the torque.

    Good luck.

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    Quote Originally Posted by Mark McGrath View Post
    I get very high quality cuts but don`t get good consumable life.
    The latest Hypertherms with the Duramax torch give very good quality cuts (Powermax 45/65/85). I've got an older 1250 but retrofitted it with the Duramax machine torch.

    Moist / dirty / oily air is the enemy of consumeable life, as is piercing too low. I made a refrigerated air drier out of a car airconditioner condenser and evaporator. Connected them in parallel to reduce air pressure drop. I used a window aircon unit and made a closed loop air circuit out of wood board so the cold air circulated through the fins of the cars condenser & evaporators. But then again if cash isn't a problem you could always just buy one, ha, ha.

    After that the air goes to a water trap then to a home made dessicant filter. Now don't laugh, I stuffed a 6 inch steel tube full of the absorbant material out of diapers. Then finally a real filter to make sure non of the diaper fibres get through.

    My air tank is pretty big and is buried vertically in the ground. I have a hose coming up from the bottom with a valve on the end so I can drain the condensed water. It's amazing how much comes out. The tank is straight after the compressor and acts as a good initial condensing unit for moisture in the compressed air. Being buried in the ground it stays cool even on hot days.

    I think a basic dessicant drier would become saturated very quickly if it had no other "pre-drying" methods.

    Keith.

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    candcnc has the lcthc torch height control for 249.00. works great.

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    Quote Originally Posted by najnielkp View Post
    candcnc has the lcthc torch height control for 249.00. works great.
    How many controls can it work with?


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