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CNC? I don't get why!

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  • CNC? I don't get why!

    As I like to stir up things, I will throw one out that is likely to bring some responses.

    What I don't get is: what is the big interest among home shop folks for CNC? What I mean is, isn't the fun and challange of machining to do it yourself?

    I understand that some complicated curves can only be done accurately with a CNC machine, but how often are such curves actually made?

    It also seems to me that some relatively complex curves, like conic sections, can be made using relatively simple jigs. Making the jigs is also a fun project.

    So, why spend so much money on the CNC stuff?

  • #2
    Plain and simple:
    I built a cnc lathe (and now building a mill)
    to teach myself how and WHY it works.
    One of the main reasons I became a machinist was I love a challenge!
    Never stop learning. Embrace new technologies and cherish the old ones.
    please visit my webpage:


    • #3
      Accuracy, Repeatability, Complexity.
      Its cool to watch it work like a robot and robots are very cool.

      Its also kind of like watching someone else dig a trench on a hot day while being the supervisor in the shade.

      It keeps both hands free for drinking coffee and such.


      • #4
        Cause my home brewed cnc bridgeport will drill about 120 holes in about 20 minutes within about .0005 accurracy. Mine was stripped here, modified here, runs here. I got the software code, the schematics and the know how to play with it.

        I love my cnc. Only limited by my imagination and I dream a lot.



        • #5
          I like to know how things work and the best way is to build them! I took a clock apart when I was a kid, learned how to make the hands go around fast, have been taking things apart and building things ever since. I THINK I am beginning to understand how stepping motors work. No, I don't know what I will use the CNC lathe for but I'm having fun while I'm learning!
          I other words, a challenge to keep me young at 74!


          • #6
            John F. is correct, gotta keep the brain safe from atrophy, I am only 65, still learnin'


            • #7
              While it is true you can do things the hard way - only a fool reinvents the wheel because "he can". That is a piss poor excuse for ignoring a valuable tool at your disposal. If you can afford to use it do it, you can put your mind to bigger and better things that you may have not been able to do if you had to rely on superior machining skills with antiquated equipment. If you got the money and can afford it do it. If you have to do it on the cheap like many do, there is no shame in making do with what you have.

              Only caveat here is try not to rub it in other peoples noses and respect the fact that some of us have other priorities - like a family to feed. So please respect one anothers dignity and don't call their equipment junk or crap - even I have to make do with what I can afford these days.

              In other words...there is nothing wrong with CNC except it is too darn expensive for all of us to play with! Even though the most expensive part - I already know you have sitting in front of your face reading this message - is not the biggest hurdle. What to do? What to do? Where to start? Damn good Questions. Maybe some gorilla should babysit you hosers though a mockup . Hmm? Have to think on that one... What say the hosers?

              [This message has been edited by Thrud (edited 03-08-2004).]


              • #8
                Has Thrud been hitting the hard cider again? His commentary tonight seems a little,


                Pursue Excellence and the rest will follow.
                Pursue Excellence and the rest will follow.


                • #9
                  Because it's there.

                  And the thing about accuracy, and the thing about speed, and the thing about repeatability, and the thing about learning, and the thing about being able to do something you can't manually, and the thing about sitting back and watching it go while I sip coffee. I remember my first power feed, I thought it was great just watching the lathe make chips on it's own.

                  Paul A.
                  Paul A.

                  Make it fit.
                  You can't win and there is a penalty for trying!


                  • #10
                    Cause it is cheaper then a manual milling machine with DRO? With motors for sure? with the future in mind for really sure.

                    I see them all the time cheap like on ebay, now they seem to be going up in price thou. It is a buyers market. My machine is a 1976 model.

                    I now have >$6,000+<$6,250 in mine.. More then I wanted to for sure. Tooling is included in that price. where else can you get a machine accurrate to .0001 for less then 10k? Mine has a 10"x18"x5" work area. Since the software upgrade I am redoing, the wiring. What a toy. A santa claus machine.

                    I even got a program that records the joystick movements to a gcode program for replay.. I wrote it myself. Read that "teach mode"


                    [This message has been edited by ibewgypsie (edited 03-08-2004).]


                    • #11
                      For the home shop enthuastisat, it is kind of a branching out of the hobby, and adding areas of expertise, flexability, and interest. Kind of like computing, where a 286 will run many a program none the less, but a Pentium or AMD 2 gig+ chip is kind of interesting to many of us as well.

                      In the end for the HSM, it is what you like.

                      For the shop owner doing jobs for profit, it is time savings, bids won, and costs cut. Can be the difference between profit and loss, and even profit margins.
                      CCBW, MAH


                      • #12
                        I guess Paul's answer may sum it up the best: because it's there. It's another technology to investigate, it's interesting, it increases the range of things one can do.

                        Personally, it's not my thing. I've got enough projects lined up for several lifetimes anyway, and I enjoy doing manual machining. I got my fill of programming when I did it for a living. Programming a milling machine holds no particular thrill for me.

                        But I can see why other folks may find it fascinating. Whatever floats yer boat. The main thing is to enjoy what you do, no matter what it is.
                        Try to make a living, not a killing. -- Utah Phillips
                        Don't believe everything you know. -- Bumper sticker
                        Everybody is ignorant, only on different subjects. -- Will Rogers
                        There are lots of people who mistake their imagination for their memory. - Josh Billings
                        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                        Don't own anything you have to feed or paint. - Hood River Blackie


                        • #13
                          Some observations on DIY CNC......

                          On the DIY CNC lists posters are always looking for the cheapest way. Ballscrews for instance, like the cheap rolled ones with major backlash. This will usually result in less than satisfactory machine performance. Spend a little more and get good ones, in the long run you won't regret it. If the goal is accuracy, repeatabilty, etc cheap components just won't do it.

                          Several posters mentioned building their own machines so they'll understand CNC'ing. Not necessary, what's learned in building doesn't translate to using a CNC.

                          A home built machine with an inexpensive/free PC based control will not come anywhere near to matching the performance and features of commercial machines. The commercial CNC machine controls are quantum levels above the PC based versions typically used by home builders.

                          The CAD/CAM needs of home CNC'ers are usually beyond those of the typical small commercial CNC shop. The reason being the home guy won't be satisfied doing the typical simple operations we do in commercial shops. The home guy many times wants to do 3D surfacing operations which are only done in a small percentage of commercial shops.

                          The resale value of a manual machine converted to CNC will likely be less than the machine would have if it had not been converted. The reason is obvious, most conversions are so poorly done.

                          A DIY CNC conversion will have near zero resale value to a commercial shop because it won't be compatible with their existing commercially made machines.

                          For DIY you're better off adding a new control to an older CNC or NC with a dead control than trying to fit ball screws and servos/steppers to a machine not made for them.

                          It's generally a waste of money retrofitting something small like a Sherline since the cutting performance will limit the machine to soft materials. Cutting in steel will not be practical at any rate that will not leave you frustrated.


                          • #14
                            I do agree with most of what you have written about conversions but your are looking at this from a resale point of view, wheras the people often doing this conversion will stay with what they make for a long while.
                            I fully agree about converting a larger machine when purpose built ones with dead or outdated controls are so readliy available.

                            What I don't agree with is your last statement about the micro type machines.
                            OK if you are milling wings spars for a Boeing aircraft you could just be limited a bit on travels but they do have a very good use.
                            CNC encompasses a large number if disiplines and crafts, not all metal related or even if metal related size does come into it.

                            Two examples.
                            Microproto the UK sales arm of the CNC Taig mill regulary sell 30 machines at a time to the Covent Garden jewelery trade in London.
                            They just set them going and walk away.

                            The local colleges here in the UK like the US are been decimated as regards metalworking craft classes but the CNC side has been untouched, in fact if anything it's improving. You no longer need the series 1's that were prevalant in earlier years. In fact because of H&S they don't want them. The Taigs, Boxfords and Denfords are ideal for training. G Code for one of these is EXACTLY the same as for a 30 ton monster but with less H&S and space issues.

                            These machines DO have a place, OK they may not work to fast feeds and hold 0.0001" all day but when you are milling a logo, ring pattern or trying your name out in G Code does it matter?
                            No, all that matters is you get to learn and perhaps later you will get a chance to move onto a better machine, experiance wise you will be better for it.

                            John S.

                            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                            • #15
                              I built a big (14"x18") flat bed plotter from scratch about 15 years ago. I used honkin big 3 phase steppers and wrote the code to drive it all in assembler language. It is repeatable to about .001. Fun as hell to watch it print stuff, I wrote routines to do the alphanumeric characters, best line between points etc. It will plot at a rate of around 3000 steps per second, had to do some serious work on the accell/decell routines. I still have it and am seriously debating whether to tear it apart for the motors or convert it to a CNC engraver...
                              Free software for calculating bolt circles and similar: Click Here