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  1. #51
    Again, very usfull stuff in there.

    Am using motors as i can easly get the resloution i need and if i make a mistake i can change them reletivly cheeply,

    Nor you can wear Hiwin bearings if properly mounted. When you have them in your hands you will see why. They will be probably that last element in a machine to fail.
    You not considering the difference in wear when using stone, Its not just the heavy use on the machine parts, your basicaly air-rating grinding paste. allthough the powder feels fine and soft, on a particulate level, its rock hard and sharpe. vacuums and covers can pre-long bearing wear, but, you are going to wear rails and bearings when cutting or surfacing stone. Then think that large beds are hardly every fully utilised, everybody's got there own favourite sweet spot on there machine were most of the smaller jobs get done, so you get uneaven wear.

    If you then want to surface a large bit of stone, 1500mm by 800mm, you would see the wear patterns in the surfacing as the rails and screws go between the commonly used area and the less used area.

    There are other considerations as to why it might be a good idea to have the bearings as the failure points. Re=straightening a frame, or gantry, is quite a long and complex job, that involves building a jig, usualy into a thick concrete floor, and gooing through a heating,cooling and tighnening routines, then when its in shape, heat it and cool it to even the stresses.

    8/10 times, it would be cheaper to just remake the gantry, and salvage the unbent parts.

    whereas, if you specifically design your frame for the bearing to be the week point, servicing is easier, serviced periods are calculable and variable depending on machine use. and as long as your bearings will fail, beyond the maximum cutting forces your machine will exert, then you could consider it a safety feature.

  2. #52
    Quote Originally Posted by george uk View Post
    whereas, if you specifically design your frame for the bearing to be the week point, servicing is easier, serviced periods are calculable and variable depending on machine use. and as long as your bearings will fail, beyond the maximum cutting forces your machine will exert, then you could consider it a safety feature.
    Your correct about stone being grinding paste but don't agree that you will be designing in the rails to be a fail point.?. . . . They will naturaly be a fail point because they are moving components, has will the be ballscrews and nut.
    So instead of designing in what will happen anyway put all your design efforts into the best way to limit or avoid this.

    Best why I know off is to cover and conseal so get them either up high out the way or under neith and under cover.!! . . . . Now Remember you'll be using Mass's of water which tends to run down hill, also gravity brings droplets down eventually so personally I'd be looking to get the rails higher rather than lower and still under cover has much possible.

    Then you have the Ballscrew or R&P debate.? At 3mtr length then the Only way I'd use ballscrews is if they used rotating ballnuts. Which would actually help with reducing the number of rotating parts and be much easier to cover and conseal.
    To use rotating ballscrews at 3mtr length would require at least 25mm Dia screws which then takes you into large Stepper motors/ drives etc added to this the fact your gantry will be heavy anyway means even larger motors or going with servo motors and all that comes with them.!
    This is why ballscrews and long machines don't match perfectly well and if you find any long machine that use's Ballscrews you'll see they often have large diameter screws with a Large pitch thats geared with ratio to keep the rotation speed down and whip from happening. They also have servos on the ends because steppers can't handle the torque required to Accel and Slow from traveling a heavy gantry with large rotating mass.!

    R&P is there foreoften used when accurecy isn't the prime concern because it's less expensive and has less rotating Mass. Down side is it's less efficeint and more exposed and prone to interference from debris getting into the workings so again needs careful placement and consealment.!!

    Which I'd use would depend on machine design and my budget.? Probably Ballscrew because I prefer them but 100% it would be a rotating nut and up high out the way along with the rails. This is where all my design efforts would be concentrated and even if it cost extra money to put up high and under cover because of building in the extra strength required I would do it to save on the down time which would come from replacing worn components.

    Machine setup can take many hours or days and even weeks at DIY level if your after close tolerances so anything to reduce this or limit having to disturb the finely setup machine would be my prime concern along with strength and accuracy.

    Now I'm going to honest and blunt here George.!! . . . . I think you are going to waste an awful lot of time and money plus dissapointed with results because what your wanting to have is Large machine that is all things to all materials but haven't got a clue to just how hard that is to achive or make happen.
    When you go large even with machine designed just for one main purpose the design and build process takes you to new levels, expensive levels well above the average DIY build. SO to try and build a machine to be ALL THINGS to ALL MATERAILS with advanced features like 4th & 5th axis etc is a BIG BIG BIG under taking that would make even the most experienced DIY builder like Jonathan or Me sit down and think very very very carefully.? . . . . . To take a project like this on with NO experience is a recipey for wasting money and time .!
    My advice is don't do it and build smaller or focus at one machine designed for that main task, which at this size will still be a very very big challenge for some new.!!
    Last edited by JAZZCNC; 08-01-2014 at 09:53 AM.

  3. #53
    Hi

    I have reduced the length of the macheen to give me just under 2000mm cutting in X. I have really took a lot in that has been discussed on here,

    SO to try and build a machine to be ALL THINGS to ALL MATERAILS with advanced features like 4th & 5th axis etc is a BIG BIG BIG under taking that would make even the most experienced DIY builder like Jonathan or Me sit down and think very very very carefully.? . . . . . To take a project like this on with NO experience is a recipey for wasting money and time .!
    .

    Its not beyond my current skill set, althoug i have not built a CNC router before, i have had experience in pulling some quite complex tasks together, and i live in an area, full of engineering works, anything beyond of my level of accuracy, can be done by them. I do understand that it will cost a lot, perhaps around the 5k mark, without software. and i have a few month to do it, with the funds currently sat in the bank,

    I will try hard to put it in sketchup tonight

    Now I'm going to honest and blunt here George.!!
    , your not blunt, your straight to the point, and sharing your considerable experience.

    I think you are going to waste an awful lot of time and money plus dissapointed with results because what your wanting to have is Large machine that is all things to all materials but haven't got a clue to just how hard that is to achive or make happen.
    I do understand the difficulty involved, and the design complexitys, am not expecting to get thinks perfect first time, and i have budgeted some funds for mistakes.

    it would be a rotating nut and up high out the way along with the rails. This is where all my design efforts would be concentrated and even if it cost extra money to put up high and under cover
    agreed, my x-rails and screw, are the top of the frame/x Box, The Y/Z is underneath that. I would cover X with accordian or brushes for dust.

  4. #54
    Hi

    Can anyone see any problems or design issues with this described below.

    Standard re-enforced rectangle box frame made out of 80mm 80mm by 4 mill ( or 100omm ) 2200mm

    On top of that, down the X, Two bits of 160mm by 80mm, fixed, bolted to frame. I beleive i can get these true and level, ( with machineing and epox ). I then want to bolt rails ( round or square ) to the top and underneath of the overhang, both sides. Apart from the difficulty of getting the rails level to each other and true

    What other problems can anyone envisage. ?

    It would seem a very obvious design to give you close to equal forces in most directions but i can not see any machines designed the same way. The problems i have envisiaged

    Trueing and leveling for the Rails. ------- think i have that covered
    Deflection forces on overhang ------ Theses exceed the possible forces applied by the Z, so not a problem
    Nobody else usese this design -------- This is my biggest problem , there are a lot of clever people on here, noboby seems to do it this way -- why.

    Fire way with opinions , Am especially interested in anyone that has previously considered and discounted this.

  5. #55
    Quote Originally Posted by george uk View Post
    Hi

    Nobody else uses this design -------- This is my biggest problem , there are a lot of clever people on here, noboby seems to do it this way -- why.
    There is a reason skydivers pack 2 parachutes

    Just joking, couldnt help . Lets see the design when you draw it

  6. #56
    Hello George well intrested as You are building a machine for similar reasons,,
    I Spent a couple of years building sound rooms for recording studios (in my spare time)You tend to find out what dampens vibration, Which is Dry sand filled tubes and walling .if the sand gets wet then it doesn't help at all.
    Guts on masonry always under the table with a Drip check and should be dry when you look under when the machine is in full spray.

    the overhead type even when the Gantry is 600 higher than the workpiece still gets covered in Abrasive dust and the rails wear quite quickly.
    Ive seen at least 3 machines fail because of rails being on top or the side.
    Humphries Masonry in Hungerford their machine right before xmas rails scored by a pieces of stone about the size of grass seed and all the carriages and rails needed replaced. Blooming expensive 3 metre Kolb machine

    I had a look at a machine which uses 120x60x3mm 2400 on x and 1200mm on Y
    this machine also had Hexagonal rails and v rollers on the X with 45degree 45mm v rollers on the Y and Z. I cant find Hex rails on the net it all seems to be profile which Jazz suggest.

  7. #57
    Hi Ramsbury

    Guts on masonry always under the table with a Drip check and should be dry when you look under when the machine is in full spray.
    I noticed that on the ones i looked at, am trying to avoid it, becuse of the rebuild time required if they do fail, Knowing that the rails and baering will fail, i want them accssesable without heavy lifting.

    I think the V barings and design styles on stone machines are to do with the machine weight, and i think , with the right design, you can reduce the required weight substantialy, making everything else easyer to make.

    With top mounted V Baerings, you need a considerable weight gantry, just to hold it on the rack. and there starts you chicken and egg game with motor sizes and rails.

    Wereas, i am considering, bolting on a lenght of 160*50 by 3mm , down the X, and mounting rails both on the top and underneith, using the shearing/form strengh of the baerings and rails to act like a counter weight when the Z is pushing down. Allowing the gantry to be considerably lighter, and easy to design.

    Am going a lillte under 2200mm on the X, becuase i think i need to maintain a relationship between the size of X, and the gap between to baerings on the Y width per side, to small a gap will allow to much resonence down the rails, With the Y Lenght at 1200mm, i think i need the Y width someware between 300mm and 400mm, That meens if i want a X cutting area of 2000mm i need an overhang of 200mm on each end of the X ( making the X approx 2500mm in lenght. Am working on the principal that the Y width needs to be at least 1/8th of the X lenght to counter resonance down the X Rails,

    I think ( scratching my head ) that the math works out, to give the Gantry enough force to not deflect under the chip loading of the cutter, pushing through stone.

    Do you get what i mean ?

    I was also thinking of fixing accordion cover to the X and Y if possible, to help counter dust

  8. #58
    All the machines I have for cutting stone have hex bar and rollers. which are on top rails and of course have easy access But the table is also on large V rails to load the stone one of them is worn so I don't get the Accuracy I need to Make stone profiles But its still great for straight cuts and 90 degrees . it only takes 15 mins to change the rails except on the Bottom as the rolling table weighs a ton.
    all the Hex rail machines with rails underneath do have difficulty changing and the gantry must be Supported when they are lifted off. But my attitude is if it needs changed Its done its work about 4 hours per rail to change only because they are bolted with Sunken heads. even mild steel rails last a lot of cuts and justifys the rail change

  9. #59
    Hi again ramsbury.

    This is stone machine specific,

    am thinking of adding rollers just beyond the start and end of the bed ( X ) and supports, to keep the machine size down. and allow me to do very big pieces.

    A column for example, or the upright part of a norman church door, or a church window upright

    If i have rollers at the end, and a support trolly, i can machine 2000mm per time, then just move the piece up the table and machine the remainder. If i can design this part correctly, i may even reduce the lenght of the bed. You can use a probe routine to make sure the piece is positioned carfully

    Also, am trying to decide between building rollers into the bed, that are jackable, or, an air table, to allow me to position heavy pieces of stone and move it around.
    Last edited by george uk; 11-01-2014 at 03:50 PM.

  10. #60
    I prefer an Overhead jib or gantry crane they are very easy to make
    and move.
    the Machine I wish to make has only its Gantry above its working table making things easier to put on and More important Taking off without damaging using either clamps or Vacuum lift regarding heavy objects , straight onto a waiting vehicle or storage area.
    I don't do granite worktops and all the gravestones I do are Hand cut and hand finished.
    Raised side rails prohibit the full use of the table, as most lifting equipment needs its own space usually 100mm margin area.

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