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  • Small machines & CNC

    CNC is kind of always thought of as a production process. I bought a large CNC bed mill at work, but I have homebuilt CNC minimill size machine in my garage. It occurs to me that with inexpensive CNC programs and inexpensive CAM to write programs that people with small machines really can get a huge benefit from CNC.

    For instance I needed to make couple of sheetmetal parts with a couple 5mm holes and a 12mm hole. It doesn't matter that I don't own a drill in either size, or that my machine couldn't handle a 12mm drill in stainless. A 1/8" endmill did the job nicely.

    I needed to face of some short 1-1/4" Od stainless rods. Standing up in a lathe chuck clamped to the table I programmed a spiral in from the outside to the center using a 1/4" endmill, the biggest the machine would handle in SS. Slow cutting on a small machine. Who cares, I worked on other stuff while it did the job.

    Tell me you guys with tiny machines get great joy from turning cranks for hours to remove a relatively tiny amount of material? I'll bet with every turn you are thinking power feed or sending it to someone with a bigger machine. The CAM program lets me generate programs for tiny tools taking hundreds of passes in just minutes.

    Everyone thinks you need ball screws and such to make it practical. Thats simply not true. If you can make a part cranking handles CNC can do the same job on the same machine. I'd like to have a tool changer, but when the goal is just to make the part and you don't care if it runs by itself for hours you start picking the largest tool that can do the snallest feature and let CAM create hundreds of passes for the big stuff if needed.

  • #2
    Originally posted by garyhlucas View Post
    ....

    Everyone thinks you need ball screws and such to make it practical. Thats simply not true. If you can make a part cranking handles CNC can do the same job on the same machine. I'd like to have a tool changer, but when the goal is just to make the part and you don't care if it runs by itself for hours you start picking the largest tool that can do the snallest feature and let CAM create hundreds of passes for the big stuff if needed.
    Is not the ballscrew advantage due to

    1) the "CNC" having NO IDEA how far it has moved the table? (with CNC the screw is turned "by the dials", only nobody measures the part, which can be done easily when working by hand. As people din in our ears, working "by the dials" leads to errors when the screw is not accurate. But the ballscrews are made to a known tolerance, and can be chosen to match the needed precision. The regular leadscrew has backlash, and an unknown precision, not to mention variable wear along it. Those things mean that the precision of the result depends on a host of factors which are likely to be a problem.

    2) the large reduction in backlash with ballscrews? With hand turning the dials, one can work "across backlash" by taking it up, AND by suitably applying drag, etc with table locks, or locking unused axes so that backlash is not an issue. If you do not lock unused axes, you often get chatter and a jumping table as the cut changes direction, at least. Possibly also during the cut, depending on material being cut, cutter, etc, etc.

    I would think that with typical used machinery (and some NEW chinese machinery), that CNC would produce a horrible chattered result, just as if you took some utter newbie and told him or her to "just turn the dials". The usual backlash would have the table juddering all over the map on a cut, because there is no means of automatically locking the table.

    With the ballscrews, it would seem that accuracy is just a matter of $$, and judder /chatter is nearly eliminated by the low backlash.
    Last edited by J Tiers; 07-21-2017, 02:20 PM.
    CNC machines only go through the motions

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    • #3
      it depends. If the machine is newish with unworn screws you can make accurate parts. If you are relying on a DRO to compensate for backlash and screw pitch error and convert that to CNC you are going to be in trouble when it comes to making accurate parts unless you completely map the screw or go to a dual loop servo setup. Also a lot of work on cnc is done with climb cutting since the screws have almost no backlash, try this with a machine with slop in the screws and you can end up with broken end mills or gouges in the work.

      You can get fusion360 that has cad and cam built in, so there is your cheap software. I dont miss manual mills in any way.

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      • #4
        Originally posted by garyhlucas View Post
        Tell me you guys with tiny machines get great joy from turning cranks for hours to remove a relatively tiny amount of material?
        -I wouldn't say it's a "joy", but for a one-off job shop, or custom work like mine, in many cases a CNC machine takes longer to do the job, since there's a lot of 'cut and try' in many cases.

        Everyone thinks you need ball screws and such to make it practical.
        -No, you need to have a CNC machine to make it practical. You can still buy decent used manual machines, or even new import machines, for far less than even many used CNC machines, and I'd wager that for many of us, who don't have a solid background in computers, CAD and CAM, that money would be better spent getting a bigger machine. A Bridgeport sized mill would have had little or no trouble drilling that 12mm hole, especially if you step-drilled it a couple times first. Your rod facing likely would have been easier and faster done in the lathe- any machine that can take 5C collets would have accepted 1-1/4" rod easily.

        Doc.
        Doc's Machine. (Probably not what you expect.)

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        • #5
          First of all my machines were a titch over tiny.
          Did I get tired of turning dials , not for the most part . I did have power feed on the mill table.
          I knew how to make parts, a lot of one off work, a lot of of hey let's change this or that while in process to make things look better. A lot of faster to do it than to program it.

          But now I got to ask you..... if the cnc program **** itself, can you go over to a manual machine and still make a part ?
          Are you a button pusher or a machinist ?

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          • #6
            Wearing out a small machine tool doing a huge amount of toolpaths to accomplish a relatively easy task for a bigger machine does not sound like a good solution.

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            • #7
              Non-CNC people think it takes a long time to design a part and create the gcode. CNC people know better

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              • #8
                Tiny machine guy here, there's no joy at all in cranking those handles. Seriously, I hate it and it sucks. I would love to convert my little mini mill to CANC, don't get me wrong, but I'm not going to any time soon.

                First problem is cost. Factoring together stepper motors, control boards, the ball screw upgrade I'd need to actually get accurate parts, software and various mounting brackets I'd end up paying double or triple what I did to buy the mill. Much as I'd like to, I can't swing that

                Second big thing is speed, funnily enough. If I needed a batch of identical parts then cnc would be faster, but for a one-off that's just a few holes or steps, odds are I can have that knocked out faster manually when compared to the time itd take to draw up the part in CAD and get the machine set up.

                There's also the added complexity of drawing parts in CAD, exporting the gcode, making everything play right, getting tools set up, etc. Again, if I were knocking out batches of 10 or 20 identical parts on a daily basis CNC would make sense, but I'm a home shop hobby guy. A CNC mill would be awesome to have and I hope to get there one day, but it's really not economical for me in terms of time or money

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                • #9
                  Originally posted by elf View Post
                  Non-CNC people think it takes a long time to design a part and create the gcode. CNC people know better
                  They're both right. Some parts are going to be fully specified and cut faster than you can manually machine it, but other parts will be faster to machine by hand.

                  Where CNC gains a huge advantage is either in long runs (where the operator can walk away) or multiple parts. I just cut some new circuit boards last week using a g-code file I made last fall. All I had to do was spend 10 minutes to reacquaint myself with the cut process (drill, V-cut, endmill cut) and load up a blank PC board.

                  Would you guys consider it real machining if you turned a knob and a controller sent the magical smoke signals to the machine to do the actual turning? Mach3 has a Joystick plugin that would let you do basically that.

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                  • #10
                    Originally posted by elf View Post
                    Non-CNC people think it takes a long time to design a part and create the gcode. CNC people know better
                    -CNC people think it takes just a few minutes to learn.

                    Seriously, I've been told for years now how "easy" and "simple" it is, four keystrokes and two mouse clicks and you have a fully detailed 3D model and a full CAM toolpath that you're so confident in you can slap the "start" button and go binge-watch Game of Thrones for the next three hours.

                    As in everything, there are places where CNC is better, and there are places where the manual machines are better. And, as is true for all of us, there are those who have been fully immersed in CNC since the paper-tape days, and those who would still have a VCR blinking "12:00", if they still owned a VCR.

                    Doc.
                    Doc's Machine. (Probably not what you expect.)

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                    • #11
                      CNC is great. The world turns on it if you will. I use it professionally a great deal. I design stuff in CAD. I program G-code by hand or using CAM. I'm also a 'youngish' guy. Some people think immediately that I'm all about computers.

                      But I do get joy out of turning handles. And turning handles sometimes is very efficient - CNC isn't always better. At work I've watched people spend a couple of hours drawing up a bushing in CAD, programming it in CAM, and taking it over to the CNC lathe to cut. When I pointed to the manual machine in the shop and said you could have made that up in 20 minutes the people look at me with strange looks and I school them on the picking the right tool for the job.

                      If you are using your CNC mill to make electronic enclosures - 3D printing is even faster.

                      Of course the quickest way to get the job done isn't the only part of the story. Craftsmanship is something that I deeply respect. Let's not downplay the human element in all this. I'm thinking about George Britnell right now. I think if a large number of our population shut off the television and cut out the mindless fecal material and focused on learning a craft the world would be a much better place.

                      Just my 2 cents.
                      www.thecogwheel.net

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                      • #12
                        Hear, hear.

                        Over on PM, there was a thread about the new Clickspring series on rebuilding the Antikythera Mechanism. One particularly coarse poster suggested it was both stupid to waste the time doing so (since others have built copies before) and if you were going to waste the time to do it, it would be better to produce the thing using CNC, as it'd be faster to complete and more precise.

                        Which, of course, missed the entire point behind Clickspring's series, which, if you haven't seen it, is to produce a copy of the mechanism, using period-correct tooling. Which he also has to make.

                        It was like telling van Gogh he should have just taken a photo of that starry night.

                        CNC very much has it's uses and place, but the day of the manual machine is still long from over.

                        Doc.
                        Doc's Machine. (Probably not what you expect.)

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                        • #13
                          The whole World turns on Colchesters...... I believe that came first.

                          I don't think I would have a whole lot to talk about to a CNC operator.

                          I had my lathe for a time in my buddies shop. Beside it were 2 other lathes, 2 turret mills, all manual. Hogging the corner was a good size matching center, sitting idle. He did not know how to program it, but it used to run making parts for him.....but the products changed, so he works on other stuff . He replaced it with a 2 post car Hoist.
                          Most of the work making custom motorcycle parts for customer bikes is more of the one off variety
                          Far more interesting maybe less financially rewarding...but he is better off ..No production schedule.
                          When the chopper craze was it its height he had several CNC shops making stuff for him, I ran a few pieces on the turret lathe for him.
                          There is definitely a place for CNC machines, but not in every shop.
                          Last edited by 754; 07-21-2017, 08:21 PM.

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                          • #14
                            Originally posted by epicfail48 View Post
                            Tiny machine guy here, there's no joy at all in cranking those handles. Seriously, I hate it and it sucks. I would love to convert my little mini mill to CANC, don't get me wrong, but I'm not going to any time soon.

                            First problem is cost. Factoring together stepper motors, control boards, the ball screw upgrade I'd need to actually get accurate parts, software and various mounting brackets I'd end up paying double or triple what I did to buy the mill. Much as I'd like to, I can't swing that

                            Second big thing is speed, funnily enough. If I needed a batch of identical parts then cnc would be faster, but for a one-off that's just a few holes or steps, odds are I can have that knocked out faster manually when compared to the time itd take to draw up the part in CAD and get the machine set up.

                            There's also the added complexity of drawing parts in CAD, exporting the gcode, making everything play right, getting tools set up, etc. Again, if I were knocking out batches of 10 or 20 identical parts on a daily basis CNC would make sense, but I'm a home shop hobby guy. A CNC mill would be awesome to have and I hope to get there one day, but it's really not economical for me in terms of time or money
                            I am replying to your post because you illustrate the misunderstanding the most. While I have AutoCad, Rhino, and SolidWorks most of the CNC machining I do is not done using those tools. I use a program called CamBam running on the same PC that runs Mach 3. It is also available in Linux running next to Linux CNC. It has a rudimentary Cad function built in so no need to draw and import from another program, although I most certainly can.

                            So lets take a simple example, like taking an 1/8" off the top of a 2" square block. How much programming is required? In CamBam I draw one straight line about 2-1/2" long. I select it and apply a profile operation. I set a cut width of 2-1/4", a feed speed, cutter diameter, amount to remove, amount per pass, and that is about it. I press generate G-code and and open Mach 3 and load the file. I move the cutter to near one corner without touching the part and Zero the X and Y values. I move over the part and lower the tool till it just touches a 3/8" round pin rolled under the tip and then enter .375" in the Z. Adjust the manual spindle speed and press start. That's it. Want a second part, change material, press start. Squaring up blocks, a very common task is just as simple. Want a finish pass, just type in how much.

                            People tend to talk accuracy of machines without understanding accuracy. Ball screws may improve the accuracy a bit, but the real reason for using them is speed. The ground acme screw servo drive on round ball ways CNC I had 20 years ago was extremely accurate. It cut at 20 ipm and rapid at 40 ipm. My homebuilt stepper driven THK high precision ball screw and ball slide CNC rapids at 300 ipm, and I often cut aluminum and plastics at more than 100 ipm! However a 300 lb machine will never be the equal of 3000 lb machine in accuracy. Lots of you make very accurate parts on old machines that you know aren't very accurate, because you know how to compensate all the inaccuracies. Putting motors on the machine you have will improve the accuracy and the finish of the parts you make absolutely no question. Machine stiffness, part holding, spindle run out, tool run out, tool deflection, part deflection, all those things make ball screw accuracy a moot point. Even the most rudimentary CNC programs now do backlash compensation that does a very respectable job of dealing with backlash. Constant exact feed speeds, and uniform step overs produce the nicest finish with every tool. I cut a part and check it, make a quick adjustment and get a very accurate part. The next one needs no compensation, it's just run the program again. Just like manual milling I sneak up on dimensions and compensate as needed. What counts in CNC is repeatabilty not accuracy. CNCs are very repeatable which is a huge advantage.

                            The costs have come down dramatically. The Chinese steppers and drivers, surplus power supplies, an old PC and Monitor make this all possible if you forget spending money and lots of time on those ball screws. How do you pay for it as a hobby? You save money. Instead of buying that rotary table the CNC lets you do without. Instead of a big box of tools like boring heads and all different size drill bits, especially large ones, you just mill out the holes with small cutters and save that money. I bought a vise then used the CNC to make complete sets of hold down clamps. I don't own a lathe but use the CNC spindle to turn small parts and even really large diameter short length parts that would never fit in a lathe I might own. I can do engraving on any surface, even complex curved ones. The stuff you can't even make on a manual machine without lots of expensive accessories is huge!

                            So here is how you get there. Download the latest version of CamBam from their website. It is free for 40 sessions so you don't need to buy it right away. I made so many parts before I used up 40 sessions I felt guilty and bought it sooner! By the way I actually worked as manual programmer for a couple of years, I don't bother any more since getting CamBam. Try it, draw stuff, apply Machining Operations, create tool paths, generate G-code and edit the files to see what a CNC machine eats. Once you have convinced yourself you can do this, get a demo copy of Mach 3 and see how it creates a real CNC control on your PC. Collect as much of the parts you need surplus before you buy any new stuff. My control cabinets, power supplies, linear rails, structural materials, and lots of mechanical parts were bought cheap. Make the stuff like motor mounts and such before you buy any new parts. That way when you buy the new stuff the time to completion will be very short, and you will already know how to use the software needed. Lots of us are happy to help you pull it off too.
                            Last edited by garyhlucas; 07-21-2017, 07:45 PM. Reason: missing words

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                            • #15
                              There's buggies and buggy whips, and there's cars.

                              Take your choice.

                              I have no issue making one part cranking handles. Even complex parts.

                              When you ask for 10 more, or 5 more identical parts, I want CNC.
                              CNC machines only go through the motions

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