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Thread: A New CNC Build

  1. #1
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    Default A New CNC Build

    Hi All
    Well, I’ve caught the CNC bug and am about to start on building my first machine. Theoretically, if I do a good enough job, it should be my only machine, but I know, once hooked, like most people on this forum, I’ll just keep on going.

    I’ve been lurking in the background for quite a while now, but during that time I’ve been fortunate to have visited Rodm a couple of times and received lots of advice from him and had quite a few email discussions about all sorts of things. Rodm is one of the most obliging people I’ve ever met, and I’m grateful for his help. It seems that just about everyone else on the forum is the same and very generous with their help and encouragement.

    I’ve pretty much settled on what I want to build and have already purchased some of the materials I need from our popular Chinese supplier. I’ve got my rails and bearings for the X and Y axis’ as well as ball screws, bearings and a linear actuator for the Z axis. I’m hoping to achieve a usable envelope of about 900 x 850mm. I'm using steel from my stockpile for the base and have just bought some aluminium for the gantry. So, I'm set to go.

    Anyway, I will log the build on the forum with lots of photos, and I’m hoping for lots of ideas and comments. I’ve changed my mind on a lot of things based on the discussions in this forum and I’m sure there will be a lot of changes as the build progresses. I’m gonna need lots of help.

    Cheers
    Geoff

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  3. #2
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    Default

    Hi Geoff,
    Look forward to seeing your build.
    Remember lots of photos.
    Cheers,
    Rod

  4. #3
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    Hi geoff, yep you struck the right person for help with rod, I dont think theres many people here in the west that rod hasnt helped in some way or another. That being said, most of us here are willing to help out, remember what goes around comes around, so if you get stuck and need some items welded or modified etc drop us a line.

    Steve

  5. #4
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    Rod....Not a lot to see yet, but here's a couple of pics of some of the gear I've got together for the build so far. At least I can see if my picture posting works.

    Steve....If I get myself stuck along the way, I'll be sure to give a shout. Thanks

    I'm hoping to get a good start on the base this coming weekend.

    Geoff

  6. #5
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    Default

    Hi Geoff,
    I can see a problem already - your shed is way to tidy to work in.

    Nice collection of parts there and should be strong with the steel sections you have lined up to use.

    Look forward to some progress.
    Cheers,
    Rod

  7. #6
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    Hi Rod

    It’s amazing how one can deceive with photos. You only saw the clean bit that I tidied for the photos. If I showed the rest of the shed, you’d very quickly change your mind.

  8. #7
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    Hi Geoff,

    Good start with all the bits there
    Cheers,
    Bob

    http://www.woodworkforums.ubeaut.com...og.php?u=14230 CNC Router Wood Suppliers

  9. #8
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    Default

    OK…. Now for the start of the questions

    I’m fairly happy, so far, with my plans for the base/table and the gantry for this machine, but I have no idea which way to go when it comes to the electronics. I’m capable of putting together some circuit boards and wiring as I’ve done a fair amount of hobby electronics over the years. But, in relation to CNC, I have no idea what I need.

    I’m thinking I will need to use something like Nema 23 425oz.in motors to power this thing and I don’t see any problems there.

    What I can’t make up my mind about is whether to go for xylotex or gecko drivers, especially since the geckos are on sale at the moment. I have gained the impression that the geckos are better, but I don’t really know why.

    Can anyone enlighten me about the advantages/disadvantages of one over the other?

    I’ve noted mention of “Smoothstepper” in other threads and gained the impression that it is needed if you want to use the gecko drivers. Is this right, or can the geckos be controlled directly with Mach 3. (I did say I have no idea).

    The more I think about what I need to get, the more confused I become.

    HELP!!!

  10. #9
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    Geckos are the better of the two options because they have mid band resonance compensation and other refinements that Xylotex don't have. Both do the same job but Geckos will do it smoother and take your motors past where the Xylotex will stall.
    There are probably better ways of explaining this so others chip in if you can.

    Xylotex are an excellent entry level board and I have been using them for three years without a problem so I am not knocking them at all. Given the Geckos are on sale the price is about equal so the choice is easier at the moment.

    Smothstepper is a USB rather than parallel port interface to your drivers. As new computers and laptops do not have a parallel port they have developed the smoothstepper which is a USB in and two parallel ports out. You get the advantage of faster and sharper signals plus a few things more. Both Xylotex and Gecko run on the parallel port signal out of the smoothstepper. It is not essentail to have a smoothstepper if your computer has a parallel port.

    The Xylotex is a stand alone board and you can plug your parallel cable in to the Xylotex. The Geckos you need a break out board (Bob) to complete the parallel port interface to the drivers.. Lots of options there from about $20 upwards.
    Try
    www.CNC4PC.com
    http://www.homanndesigns.com/
    and there are heaps of other options.
    Cheers,
    Rod

  11. #10
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    Default

    Geoff, to clarify just a little bit further, I could be wrong so if anyone else knows better correct me accordingly.

    Serial port "printer port" etc, all different names for the old communication highway in and out of your computer, have some advantages over the newer usb ports. The old serial port supplys a steady and constant voltage, which allows the xylotex / gecko driver board to run correctly, the newer usb ports dont supply a solid steady power they pulse the power on the line, which is good for connecting and disconnecdting usb devices but not good for cnc driver boards.

    Also laptop serial ports unfortunatley supply something like 3.3 volts instead of 5volts which unfortuanltley wont drive your board either
    Last edited by simso; 12th November 2008 at 09:24 AM. Reason: As per Bobs post below, I had referenced com ports as serial ports my mistake, yes they are not the same

  12. #11
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    This is getting more confused...

    Rod was right when he said that newer computer's don't have a parallel port so he uses a smoothstepper to even out the voltages and to serve the functions of 2 x parallel ports.

    The old system uses a computer with a parallel port and if you need it a Break-out-board that can have 5 volts applied to it which then negates the parallel port that only has 3.3 volts and even works on the notebooks.

    Mine is a Dell 2.4Ghz pentium with a parallel port so I don't need a smoothstepper.

    Parallel ports are different to Com ports
    Cheers,
    Bob

    http://www.woodworkforums.ubeaut.com...og.php?u=14230 CNC Router Wood Suppliers

  13. #12
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    Default

    Hi Rod, Simso, Crocky

    Thanks for that. I have a 3Gghz Pentium 4 computer which I will be using for the CNC machine. It has an enhanced parallel port, so I think I'll go with the gecko drivers and a BOB to connect them up with.

    If, further down the track, I need to upgrade the PC, I can look at a Smartstepper then if the needs be.

    Next thing to think about is the power supply. Any recommendations? I'm quite capable of building my own, but I'm not sure what kind of voltage and current ratings it needs to have. Bearing in mind that I'll be using the geckos and 425 oz.in Nema 23s, again, any suggestions?

    Are the 425 oz.in steppers the right choice? The gantry will be just over a metre wide, all aluminium, but with an 800w spindle attached, it's still going to be fairly heavy.

    Cheers

  14. #13
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    Default

    Hi Geoff,
    Here is a link to work out the specs of a power supply to run your motors.
    http://campbelldesigns.net/files/pow...ply-part-1.pdf

    On the Gecko site this document helps you work out the motor size and suitable Gecko driver.
    http://www.geckodrive.com/support.aspx?n=558539

    Cost may come in to play and you might have to accept a less than perfect match for your machine and upgrade later if needs be.
    You can go up to 497oz in Nema23. 3 Amp/phase and 3.6 volts
    Cheers,
    Rod

  15. #14
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    Default Push

    Hello Geoff,

    I'm not sure if this is correct and have been looking for ways to work it out without any luck, but.

    If you are using 425 inch ounce motors then it would seem that with a direct drive you would have 12kgs of push on your machine IF, the torque was turned into push, if the pulley had a radius of one inch, ( 425 divided by 16 divided by 2.2 - oz's to lbs to Kgs ) given that most ball screws we use have 5 turns to the inch, that figure could be multiplied by 5 to give 60 Kg of shove.

    I know that it is almost impossible to stop a machine and to do so requires some effort.

    Of course all this may be a bit rubbery and if anyone can shed some light on if this is right or wrong please do.

    Don't forget that the weight will have some inertia but it will be supported on linear bearings that will make it move easily, you may have to " fiddle " with your ramp up and down times.

    Good luck with your buiild.

    Ed

  16. #15
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    Quote Originally Posted by Geoff Sims View Post
    Hi Rod, Simso, Crocky

    Thanks for that. I have a 3Gghz Pentium 4 computer which I will be using for the CNC machine. It has an enhanced parallel port, so I think I'll go with the gecko drivers and a BOB to connect them up with.
    If you plan on using the Gecko 251 drivers your maximum voltage should be 50 volts and I would recommend a keling 48 volt power supply at 7.3 amps and keling KL23H276-28-4B motors which are a perfect match. I know because that is what I have after much research. I also have a 800 w spindle

    If you have your heart set on larger motors then don't use the G251's they wont use enough voltage and you wont like them.
    Cheers,
    Bob

    http://www.woodworkforums.ubeaut.com...og.php?u=14230 CNC Router Wood Suppliers

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