10 Things a CNC Milling Beginner Needs to Be Successful


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  1. #1
    Gold Member BobWarfield's Avatar
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    Default 10 Things a CNC Milling Beginner Needs to Be Successful

    Check out my blog post:

    10 Things Beginning CNC Milling Machine Users Need to Succeed « « CNCCookbook CNC Blog CNCCookbook CNC Blog

    I'm interested in feedback on some of the other things that will help a beginner come up to speed more quickly. It should make a good thread if you make suggestions along those lines.

    Best,

    BW

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    1) Get a copy of Machinery's Handbook
    2) Read Machinery's Handbook
    3) Refer to Machinery's Handbook often
    4) Don't be cheap and then complain about it
    5) Learn manual milling before CNC
    6) DON'T keep doing the same things over and over and expect different results
    7) If any way possible, be in face to face contact with other machinist and learn from them

    That is all I got for now.



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    Purchase and read Smid's CNC books, including the Fanuc Macros book, even if you are using Mach. You'll think differently afterwards. If you have any computer programming background, this will provide the 'missing link', and stop the grumbling about what Mach 'can't do' . Yes it can, you just need to learn how.



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    The two most dangerous words in CNC machining....

    "Watch this."

    ....I do have a recommendation about the Z height gizmo...
    for years I've used a gage block, one I've dedicated to the machine.

    Bring the tool down to slightly BELOW the gage block, then using the handwheel, slowly, and by .0001" increments, bring the cutter UP till the gage
    block just barely clears your desired Z-zero. Add the gage block thickness (or subtract, depending on your control and method) to the offset value.

    MAJOR CAVEAT!!! Before you attempt to slide the gage block under the tool...TAKE YOUR HAND OFF OF THE HANDWHEEL!!!!!!!
    Using carbide tools, a tenth the wrong way can crack a tool, and you won't know it. Using HSS tools doesn't do anything any good either.

    Using gage blocks will also help in establishing a Z when none exists and you need a known reference, like the table, for instance.

    ...btw.... did I mention TAKE YOUR HAND OFF OF THE HANDWHEEL!!!!!!!



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    Registered fizzissist's Avatar
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    Default Worth Repeating!!

    1) Get a copy of Machinery's Handbook
    2) Read Machinery's Handbook
    3) Refer to Machinery's Handbook often
    4) Don't be cheap and then complain about it
    5) Learn manual milling before CNC
    6) DON'T keep doing the same things over and over and expect different results
    7) If any way possible, be in face to face contact with other machinist and learn from them



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    Gold Member BobWarfield's Avatar
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    Great replies, thanks! I'll definitely include most of this in the follow up post.

    While I will recommend Machinery's Handbook (and I do own not just that one but several others and more than one edition of Machinery's), I'm not so much a fan that I would list it as #1, 2, and 3. A lot of the information in it is either not very up to date or much easier to come by elsewhere. It has feeds and speeds for example but it suffers from both problems. I mostly use my Handbook for specs on things like threads or fasteners.

    What are some other books people like for beginners to have on hand? I mentioned Machine Shop Trade Secrets. Metalworking Sink or Swim is one I liked even better and will mention in the follow up post.

    Smid's books are great, but I ultimately concluded after reading all of Smid's work plus a whole ton of controller programmer guides from the manufacturers that there is a LOT Mach is missing, LOL. It all had to be written into my G-Wizard g-code simulator.

    OTOH, there are some things you can do in Mach but not in the commercial controllers that are quite nice too, largely in the area of UI work. A friend just spent thousands on a new probe package for his Fadal and has the pleasure of sifting through tons of macros on the machine and trying to remember what does what and which arguments to pass to make it do what he wants. The nice screens people have put together for probing are just not there unless there is some conversational option I haven't seen yet.

    One of the areas I struggle with is how to help beginners with CAD/CAM. The problem is that it's hard, and all the software is different. I haven't found too many rules of thumb that seem like they apply across most of the packages to help the beginners. Any ideas there would be much appreciated.

    Cheers,

    BW

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    http://www.cnccookbook.com/CCGWizard.html


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    I like to use a precision 6mm roller as a gauge block - using the same "moving away until it fits" system. You can flick it against the tool tip and it gives a good sense of progession as you get closer and closer until it flies underneath. It can also tell you how even are the teeth on your cutter if it sticks under only one.

    Since I'm into smaller machining rather than larger, my constant guide is Tubal Cain's "Model Engineer's Handbook".

    Manual milling is very useful. You learn to listen to the cut, to see the character of the swarf change as you vary the feed. If you're sure of the grade of material you're cutting you can use and trust a feeds and speeds calculator. But most of my stuff is rather uncertain so you just get a sort of instinct for it.

    Decent tools - I'm for that!

    Decent vice and/or clamping - definitely.

    I'm not so sure I'd start with Aluminium. It can get sticky. Brass is fine as long as your tools are gripped in well (I've had a few dig-ins in the past, before I learned that you also need good chucks). I like steel, I love cast iron.

    Somone to watch, to learn from. You know you're getting somewhere if they start to listen to what you have to say.



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    My main emphasis on Machinery's Handbook is not just speeds and feeds. It has a whole wealth of information including math skills, tool making, technical data on gears, and on and on. Even some of the reasoning behind various cutting techniques is discussed.



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    #1 Buy the simplest CAM software you can afford to get away with. Buying top-line software because "someday you might need to do that" sentences you to years of fighting with the complicated software, when you instead need to "just get it done".
    #2 Get G-Wizard, and back the setting down to turtle to start with. PAY ATTENTION to tool deflection on small bits!
    3. Cut in foam first



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    People have missed the obvious need, access to a CNC machine. Reading books is very valuable but sometimes having hardware right in front of you makes learning easier and quicker.



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    Member christinandavid's Avatar
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    Quote Originally Posted by txcncman View Post
    6) DON'T keep doing the same things over and over and expect different results.
    Don't do things differently everytime and expect the same results...

    DP



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    I love Machinery's Handbook, it' heavy enough to be a reliable doorstop
    Seriously it is a bible of sorts and I do own a copy. In the workshop 'Machinist's Ready Reference' comes in handy and you don't feel as guilty about the greasy fingerprints.
    Of course if Bob's software is used only the keyboard gets dirty

    An important thing for any cnc user is understand your machine control . For example: the concept of offsets, the coordinate systems (world and local), how the offsets relate to each other, where the offsets are stored. G&M code varies between controls as well. Your list is aimed at Mach users but understanding the workings of Mach can't be over emphasized,

    #4 MDI
    Yes. IMBO using cnc without G code knowledge is like working with the lights out
    (in my biased opinion)


    #6 height gauge/edgefinder
    Nice stuff to have. Like a previous poster I get by without.

    Anyone who says "It only goes together one way" has no imagination.


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    and you forgot #1,
    separate bank accounts *

    *(actual results may vary)

    Anyone who says "It only goes together one way" has no imagination.


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    I thought of one to add to my list.

    1) Get a copy of Machinery's Handbook
    2) Read Machinery's Handbook
    3) Refer to Machinery's Handbook often
    4) Don't be cheap and then complain about it
    5) Learn manual milling before CNC
    6) Learn manual (hand written - brain thought out) CNC programming before attempting CAM.
    7) DON'T keep doing the same things over and over and expect different results
    8) If any way possible, be in face to face contact with other machinist and learn from them



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    Learning M&G code is very important. This comes from a guy that doesnt know it, but programs every machine in my shop.
    It really chaps my ass when my operator talks to me in G code and its like he speaking spanish.
    I know I need to sit down and learn it, but I got lazy. When I have a bunch of awesome operators that got my (uneducated) back, its easy to rely on them.
    They can read the screen like a book, it amazes me.
    I will not hire an operator that doesnt know it. I have in the past, and it bothered the hell out of me.
    Ive got guys on my floor that can program some very complicated stuff by hand.

    So a big yes to M&G code.



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    I totally agree with manal machining experience prior to CNC. It forces the use of common sense, logic & process planning. It also ties together the feel, visual/sound effects, & resultant impact on the workpiece & cutter.

    Even if you have the luxury dfearnow has, G&M code knowledge is extremely important for trouble shooting purposes AT VERY LEAST!! No CNC operator should EVER have to ask what G0/1,G2/3,G41/42,G81,M3/4/5,M8/9,R??,I/J/K, etc.........means!!!!!! If they do, they shouldn't be on the machine (even though we have some that do. But hey, I'm not the suporvisor). You have to know this to understand if the machine is doing what it's being told to do, if the post is doing what it's told to do, or if the cam system is providing good data (& these are only some of the variables). Not to say you need to know every code of every control by heart, but you should definitely know where to find them & know the major/basic ones.

    One more point to stress. IMHO. NOBODY should EVER change a feed/speed without having first calculated chip load. This formula is very simple & SHOULD be known by heart by any person with the ability to make such a change. Again, I wish I could say that was the case with 100% of our folks. (Which is why I stress this in response to your question).

    Hope this feedback has some value.
    Dave K.



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    Gold Member BobWarfield's Avatar
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    Folks, I just published the second installment:

    10 More Things Beginning CNC Mill Users Need to Succeed

    Thanks so much for the great ideas for what to include in the second 10 things a beginner ought to learn or do.

    Best Regards,

    Bob Warfield

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    http://www.cnccookbook.com/CCGWizard.html


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    Member dertsap's Avatar
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    simple basics
    dial ,feeler gauge , hammer , single block and or dry run


    .

    A poet knows no boundary yet he is bound to the boundaries of ones own mind !! ........


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    Bob, Good job. I want to point out, for the benefit of others, that even in Machinery's Handbook itself it states more than one time that the speeds and feeds listed as only recommended starting points. Also that tool suppliers, while they are quite insistent their tools can perform certain speeds and feeds, are still recommended starting points. I have had a tool sales person standing next to me with egg on their face more than once when their speed and feed did not work and their new super tool went away in a flash of glory. My favorite story to relate was when Iscar came out with what they were calling a "shredder" mill. The tool salesman, who I have known for years and consider a friend, was making the claim, "This mill can take full diameter depth of cut, full width at XX.X feed at XXXX RPM in mild steel." So, we tried it in some A36 plate I was cutting from square to round. The tool made the first pass around as advertised. But only made about 1/4 of the next pass before it snapped. We looked at each other and he said, "Well, I guess it won't do that after all." Then we put in another new tool and modified the depth of cut to 1/2D and feed rate to about 1/2 also (closer to what was recommended in Machinery's Handbook as a starting point) and the tool finished the rest of the job just fine (about a 25% improvement over the previous tool and feed and DOC). The moral of the story is that while the new tool was an improvement, it was not "all that" as advertised by the tool supplier.

    Finally, I want to add that machinists need to learn a machining technique that I call "Reality Check". If something sounds too good to be true, it probably is. "Reality Check" sometimes can correct "Freshman's Dream" errors. "Reality Check" is reading the G-code and moving your finger around in the air to "trace" a tool path and realizing you wrote code to rapid the boring bar out of the part on the X axis through the side of the part before withdrawing it on Z first.

    Last edited by txcncman; 04-26-2012 at 02:00 AM.


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    Never heard it called that but I do that "reality check" myself. It saves
    embarrassment.

    As a former "machinist" (he was a good one too) & programmer here used to say, "you'll only hit it once". LOL. The boring bar thing is an easy & common mistake to make (at least on our system). Our posts were originally set up to send the machine to tool change in the X first (without doing any Z checking or move on ID tools. The cam system does not retract the tool at the end of a boring sequence. After getting all the paramters set to generate the tool path they wanted, the programmers looking at the computer screen would sometimes (myself included) miss this as they were now focused on the next tool path. The result = "boom" if the programmer doesn't "reality check " it & the operator dosen't catch it in dry run. Very seldom do we find an issue inside the toolpath itself, but simple tool changes can be dangerous if you don't give them proper attention. We've also incorporated some conditional position checking in the posts to reduce the chances of such an error.



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