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  1. #1
    Join Date
    Sep 2005
    Posts
    287

    Fast, Accurate, Hole Centre Marking

    Mach3
    Candcnc electronics
    Sheetcam
    Hypertherm PM1250

    In the beginning, to mark hole centres I did hole centre piercing (drill operation with plasma tool in Sheetcam), but yuk I didn't like that, a ragged hole with a hard nitrided surface, requiring cobalt drills to get through. So instead of piercing I tried either very short pierce delays or no pierce delay at all to give me a dimple on the surface of the steel. Problem then was I could never get a nice shallow round crater in the top of the steel, it was more like a shallow hole but I'd often get a bit of blowout at the side.

    Anyway to cut a long story short I ended up learning microcontroller programming and built a dedicated external circuit to go between the computer and the plasma cutter. I now have the fast accurate hole marking I've always wanted. I get nothing more than a tiny round crater in the top of the steel, perfect for accurately locating a drill point or even a centre punch if I want to enlarge them.

    HOLE CENTRE MARKING WITH CNC PLASMA - YouTube

    I'd love to know if anyone knows of a way to achieve this result (i.e. using the same control gear as above) without having to resort to an independent external circuit.

  2. #2
    Join Date
    Oct 2006
    Posts
    58
    I do the same thing with my Samson table however, Design Edge software has a 'time to mark point' setting, that can go as low as 0.01 sec.
    Works a treat, I use it all the time.
    Attached Thumbnails Attached Thumbnails Capture.JPG  

  3. #3
    Join Date
    Sep 2005
    Posts
    287
    Cheers Benderart,

    Jim Colt reckons his Plasmacam has something similar too I think.

    So why do you use marking instead of cutting holes with the plasma ? Is it for the same reasons as me; accuracy and a nice round hole that's the perfect size. I wonder if a profile cutting and hole marking service would be of any value to fabrication mobs, or would they just go to a laser cutters and get their holes laser cut.

    Keith.

  4. #4
    Join Date
    Oct 2006
    Posts
    58
    Keith,
    Mine is the same system as Jim's, except I run a larger table.
    It all depends on the application.
    Recently I was cutting some 9" diff brake calliper mounts, 10mm plate with 10mm holes.
    At 65amps, you'll generally end up with hole taper so, marking and letting the customer drill himself, made for a more accurate part.
    Also works out cheaper for the customer than going laser.

    Mick.






    Quote Originally Posted by Beefy View Post
    Cheers Benderart,

    Jim Colt reckons his Plasmacam has something similar too I think.

    So why do you use marking instead of cutting holes with the plasma ? Is it for the same reasons as me; accuracy and a nice round hole that's the perfect size. I wonder if a profile cutting and hole marking service would be of any value to fabrication mobs, or would they just go to a laser cutters and get their holes laser cut.

    Keith.

  5. #5
    Join Date
    Sep 2005
    Posts
    287
    I didn't realise Samson was Plasmacam. I do have to say the Plasmacam boys do seem to think what good features they can put in a table controller. Jim also reckons his Plasmacam has much better motion control than the other table he has. If I remember correctly he said he gets better hole roundness than the other machine (don't know what type it is).

    I hope we can generally beat laser prices because we certainly can't beat the edge quality.

    Keith.

  6. #6
    Join Date
    Apr 2005
    Posts
    1194
    I saw it but it looks like your strait line piercing doesnt look strait when your done.
    We have had good luck with our Fadals milling mostly soft steel and aluminum up to 5 axis. We are always looking for spare parts If you have a broken down Fadal give a shout.

  7. #7
    Join Date
    Sep 2005
    Posts
    287
    My "linear rails" and v-rollers are nothing more than rusty bits of mild steel angle iron and also had some gritty bits on them. I also noticed that row mis-alignment and gave the rails and rollers a good sand down and wax before I did the main slat cut. Seems to have improved things.

    12 slats, 24 hole marks per slat then the same again in my slat toppers. 6mm bolts going in 6mm holes, no free movement of the bolts in the holes and everything is lining up great, so all I can say is I'm quite elated with the accuracy for a "centre punch mark" made with a plasma torch.

    "Strait" (a passage of water) is spelled "straight" by the way, and "your" should be "you're" (meaning "you are"). Like yourself just pointing out anything negative in your post.

  8. #8
    Join Date
    Apr 2005
    Posts
    1194
    LOL...sorry to nitpick but it looks like your "straight" line didnt pierce "straight". Is it optical in the video? Have you put a straight edge on it? It looks like there is either some spatter on top or the line of little pierces runs left and right a little.
    We have had good luck with our Fadals milling mostly soft steel and aluminum up to 5 axis. We are always looking for spare parts If you have a broken down Fadal give a shout.

  9. #9
    Join Date
    Jul 2005
    Posts
    2415
    Quote Originally Posted by Beefy View Post
    I'd love to know if anyone knows of a way to achieve this result (i.e. using the same control gear as above) without having to resort to an independent external circuit.
    Hey Beefy! Pick me Pick me!:wave:


    I did this:

    1. Made the POST recognize a Drill function as a short pierce
    2. Added a couple of variables to SheetCAM TNG via the POST (a feature that can be used for all kinds of stuff).
    a. Added a value called Peck Delay that sets the "One shot" time to fire the torch
    b. Used the Start Depth as the pierce height so you can change it from the normal plasma pierce height.
    3. Added a drill tool to the toolset to use for that operation (must have Rotary Cutting option turned on in your SheetCAM Options/Machine Options

    I used the Drill type tool/operation for two reasons:
    1. It will automatically find the center of a hole so you just draw the holes where they go and it pecks the center.
    2. The Drill function can be detected by the POST engine and different parameters applied.


    Attachment 227600

    Note: You have to have SheetCAM TNG 5.0.17 or Development 5.1.30 and my special POST to get the Peck Delay input to show up

    So you group the holes together (best to make them all a standard size that will match the drill size you have defined) on a layer
    Then you apply the drill tool to the operation(s) that are for center marking. It will move to the first hole center, touch off, raise to the height you have in the Start Depth , fire the torch for the amount of time int he Peck Delay. It hen raise to Rapid Height moves the next hole and does it again. You can mix it in a job with normal cuts. If you chose to actually cut the hole rather than just mark it you simple pick a plasma tool to do that operation rather than a DRILL.

    With MACH3 you have a lot of programming options. Combined with the right POST you have an even a wider set of options.

    Depending on which CandCNC THC you have, you can go way beyond just the typical pierce and cut moves. It is even possible with our TAP(tm) option for the Hypertherm using the optional RS485, to do a "Soft Pierce " (or surface mark) by turning down the cut current automatically at a given condition.

    If you would like to try it out contact me via e-mail and tell me what POST you use now and what hardware you have. The one I have it working with now is our advanced setup with our DTHC (either II or IV) and a Hypertherm 65 with the full TAP interface.
    This may sound somewhat complex but its a lot easier than learning to program a microprcessor and build external hardware

    We have a lot of users that use a plate marker (pneumatic) controlled out of our hardware and SheetCAM to precisely mark hole centers and engrave part numbers and bend lines. It is a pretty easy option to add since all of our current POSTS have the plate marker tool built in and you just need to set the offsets in the POST one time for the marker. You can run a mixed job just by selecting a different tool for a group (layer) of objects.

    Another way to do it would be to just write a macro (I would use m4) to fire a short burst using a direct call to the output , a timer loop and then turn it off. Then you use the m4 code instead of the m3 on just the peck spots. Have not tried it but the SheetCAM method is a lot more flexible since it becomes just another tool to pick in the cut process.



    TOMcaudle
    www.CandCNC.com

  10. #10
    Join Date
    Sep 2005
    Posts
    287
    Hello again Tom, thanks very much for that write up. Very interesting technique and a definite one for my archives.

    However, I don't believe it will work for what I am trying to achieve. I will explain:

    Your last paragraph mentioned making an M4 macro to deliver a short burst to the Mach output (Torch On signal). This is what I had done before I built my little board. It worked (almost) but with severe limitations.

    The macro code was:

    ActivateSignalOutput1
    Sleep (150)
    DeActivateSignalOutput1

    I modified the post processor to replace the M03 with my macro based on the tool number. It's so true what you say about the power hidden in the post processors. I wish I understood the code much better, in time maybe.

    I reduced the sleep duration until it got to a point where the torch didn't even fire, then added a bit more time. Even with the shortest sleep duration I still couldn't get the small crater mark I wanted. I had to disconnect the ground lead to achieve that. The other problem was this short "torch on" duration would only fire the torch while the post cut air flow was not on. After complete confusion as to why, Jim Colt told me the post cut airflow had to stop, the nozzle retract, and the torch re-fire. Of course the "torch on" signal had been and gone by the time the torch was ready to fire again.

    So the conclusion I drew from all of that was I needed more than just a very short duration signal to fire the torch. I needed to issue a "torch on" command, then the system would have to WAIT until the XFER signal arrived, and then immediately remove the "torch on" signal. So my board is effectively a closed loop system which monitors what the torch is doing and reacts accordingly. I use zero delay from the point the XFER signal is received. With this method I can leave my ground lead connected, and I don't have to wait the horrid 10 seconds (post cut air flow) between hole markings.

    I don't know yet if there is a way to implement the above paragraph in a dedicated macro. The VBA code would need to monitor the ARC OK input then immediately give the DeActivateSignal Output1 when the ARC OK was received. The reaction time would probably be a tad more than my dedicated board with it's very fast relays but it may still work OK.

    My ultimate method of hole marking will be a small centre drill in an electric die grinder. The smaller centre drills have an 1/8" shank which is exactly the same size as the collet. I guess I've always wanted to do something with a microcontroller as well as learn how to make my own circuit boards (UV process) and this opportunity put real purpose into the game, instead of just learning something pointless like how to flash some LEDs or something LOL. It's another great tool in my workshop being able to design a useful circuit and actually construct it, so the learning will come in handy for other things.

    I've only got your basic MP3000 DTHCIII plus your PN200. I get a seriously big pet lip when I look at your latest systems. Hopefully I'll eventually make money with my workshop and upgrade to one of your newer systems and the latest Powermax.

    Thanks very much again for your input Tom.

    Keith.

  11. #11
    Join Date
    Jul 2005
    Posts
    2415
    I went back and looked at the SheetCAM Post after some testing. The only thing that did not work was the first mark duration was way too long. We realized that that was because the purge air was not on and evidently the plasma extends the time to do the air start cycle. So,,,,,I went in and used a condition already in the POST to detect if it is the first cycle and I added code to first touch off, then raise the torch to 1", short fire the torch (to start purge air) and then drop it to the START DEPTH (drill tool parameter). The THC is not even triggered so there is no need to sense the ARC OKAY. I also added the option to set the Hypertherm current to any level for the marks. Of course, that feature takes our "TAP" option where we can directly control the Cut Current and Air pressure on the Hypertherm that have the RS485 Port option. We are still testing (actually one of my customers is testing). I will let you know the results.

    Save up your cash and get an upgrade of the Hypertherm to a 65 or larger with their RS485 port option, and add our HyT-Connect RS485 SIM interface and you will be amazed at some of the advanced things you can do with a CNC plasma cutter. Actually your DTHCII will do full TAP (or the DCC) functions just like it is. The DCC adds the option to embed all of the DTHC settings in our G-Code and to turn the DTHC on/off dynamically in a cut path and works with ANY plasma cutter. The TAP adds the ability to change the Hypertherm settings (normally done with the knob) as well.

    TOMcaudle
    www.CandCNC.com

  12. #12
    Join Date
    Sep 2005
    Posts
    287
    Tom I've wanted one of your latest systems (& latest Hypertherm) for ages, just don't have the cash yet. Saving up means I have to have some spare cash to save up LOL.

    I screwed up when I said "MP3000 DTHCIII". It should have been more like MP3000 UBOBIII-DTHC, quite basic compared to your latest systems, but still great, and still makes me smile when I see it operating.

    My reason for sensing the Arc OK was not because of the THC (my board operates completely independent of Mach. Mach only says to me board, "Hey, give me a short torch crack", then my board does its' own thing). It was so that my board would only remove the TORCH ON signal when the plasma cutter had "told it" that the arc was on, i.e. remove the TORCH ON signal immediately upon receiving the ARC OK. It is the only way (so far) that I have found to give a very short arc duration. Like I said earlier, even using "ActivateSignal Output1", etc could not give me this result, no matter how short I set the Sleep duration. The crater was still too big. Setting the Sleep duration under 100 (1/10th second) was risky and often caused no fire at all. I don't know why, is it a Mach thing. My board does not work on the principle of a short duration signal, it simply gives the TORCH ON command then WAITS until the XFER / Arc OK is received, then immediately terminates the TORCH ON signal. I like the idea of feedback where the Hypertherm "tells" my board when it has fired. That way, whether it's the very first fire with no air flowing, a fire in the middle of post cut air flow, etc is all irrelevant. The only thing that matters is the system knows exactly when the torch has fired and it immediately terminates it, thereby giving my much desired super short "crack". At least with my system / Mach I could not get Mach to give me the short torch crack I needed, so I went external to and hardware independent of Mach/PC to acheive it. My board is mainly about that. Even if I can learn all the post processor mods, etc, won't I still be at the hurdle of Mach not being able to give that short duration output.

    I hope I explained that OK.

    Keith.

  13. #13
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    Jul 2005
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    2415
    You of course can test any input for activity in MACH (arc ok being one) and make a decision based on it being in a condition. You cannot keep a macro in a loop because it has a finite life span (about 100 ms) I am not quite sure why the short duration ON/OFF did not work because I am doing it from GCODE and it seems to function okay. The only block we hit was on the first mark versus the others. They were pretty close together so the purge air was still on. We also turned the current way down so it would not instantly blow through.

  14. #14
    Join Date
    Sep 2005
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    287
    Thanks for that info about a macro time limit Tom. I wonder if a 1/10th second is enough time for a VB Script in a macro to turn the torch on, wait for Arc OK, then turn the torch off. That's about the limit of my knowledge with Mach programming so far. If there's another way in Mach to wait for a signal I don't know about it yet.

    It's interesting that you mention turning the current down to avoid blowthrough. That indicates to me a relatively long torch on duration, which was one of the hurdles I just could not get past. I've looked at my PM1250 timing charts and if I've read them correctly, the Arc OK signal may arrive at a current level below the set value (i.e. before it ramps up to set value). Maybe that is why I don't need to reduce my current. I still have to test my board with the full 80 amps (only used Finecut nozzles so far). To give you an indication of how small the crater is, it's about 1mm in diameter and less in depth. The only way I could get anywhere near that before was to remove the ground lead.

    Keith.

  15. #15
    Join Date
    Sep 2008
    Posts
    18

    Re: Fast, Accurate, Hole Centre Marking

    Keith,

    Thanks for posting your plate marking system. Since you have been using it, have you noticed any difference in consumable life?

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