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  1. #61
    Quote Originally Posted by Ross77 View Post
    Looks good. I would probably extend the gantry uprights down to the floor so the more area would be available for welding and increase rigidity. the vertical rails could then drop down and increase the bearing spacing a bit more.

    I think golden ratio is 2:1 so if the y axis is 800 mm wide then you need 400 mm bearing spacing. as you pointed out one change can affect another and you will need to look at flex in the mounting plates and possible bracing,


    Do you think the gantry uprights need bracing as well? looks quite tall

    It may have already been mentioned but how to plan to keep all the surfaces perfectly aligned whilst welding and given the surface tolerance on steel c section?

    Extending the gantry uprights down seems good idea -this node should be rethink with the bracing and reinforcement plates in profiles.

    My aim is to design parts that can be done by both DIY and machining method.
    machine bad is Ok -it has surfaces to be leveled on top -preferably positioned on the same level-that is way stand the gantry leg here at the moment

    Y beam is the same -can be done on both way

    Z beams will be separated and bolted so it is similar to Y -I do not want to weld a U form and do something with frame -it makes my life hard
    rather to make strong flange nodes and the careful assembly and adjustment will give the accuracy (especially the two parallel surfaces)
    Nodes will be oriented and fixed with parallel pins.
    That is only may plan for now -God knows nothing about it.
    Last edited by vargai; 19-12-2014 at 09:38 AM.

  2. #62
    That design will be a night mare to build and setup which isn't required and will have no gain over other simpler designs. C channel is bad choice due to it being bendy/twisty in relation to boxsection.
    I don't think you have really thought about the complexitys and realitys of building this design.?

    The C section inner surfaces won't be flat so will need milling for the rails. Then you have the problem of making sure the uprights are perfectly parallel in 2 planes and perfectly perpendicular in the other.!! . . 99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.
    Any surfaces that where milled flat and true won't be flat and true after welding so this will be a waste of time and you have no way mill when welded up.
    There is a no provision for adjustment and the design is such that there is no room for any error to be taken out.

    Boxsection will work far better and be much easier to setup or deal with alignment errors after welding.
    The slight difference from ideal bearing loading which Ross suggested won't make any differance to the machine in real world performance or longevity but it will to your mental health and sanity when setting up.

    Also the Uprights need far more bracing as any deflection here will show at the cutter and finish quality. Personally for best strength and bearing loading I would have double uprights each side of gantry with 1 rail on each upright and the uprights would be braced in 2 directions.

    I feel If you go with this design you'll regret it come setting up time.!

  3. #63
    Quote Originally Posted by JAZZCNC View Post
    99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.
    Quote Originally Posted by vargai View Post
    I do not want to weld a U form and do something with frame -it makes my life hard
    First of all thank you for giving me a 0,0000001 chance.
    This is a design evolution process with analysis, checking, listening to the pointers . I am not able to put a ready for production plan on the desk right now and I am patient and have time. Bad design leads to a better one. (in a good case)
    This is still a study where I try to find the place for all the function.

    Some detail explained in written form and never meant to weld this construction otherwise I would need medical treatment right now.
    Yes, box section is better than C no question-even when equipped with bracing
    For some reason I supposed that box section is more inclinable to resonate than a thicker opened one
    The stronger the better so I am opened to the closed section
    Just a sketch about how I understood double upright braced in two direction

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by vargai; 19-12-2014 at 08:23 PM.

  4. #64
    Now you have got me with that constant changing of the design. Why don't you like one design, stick to it and further develop it to suit your needs. If you liked the before suggested design from the video in post #41, then just see what is good and what could be bettered. i would suggest even contacting the guy and asking him if he were to make it again what he would change and what he liked. That will save you a lot of unnecessary trouble and give you invaluable real life feedback. Thats why people stick with certain designs, cause they are good and there is feedback.

    I understand that the overhang of his design is bothering you, and it should be. Cause it bothering me. Not only the spindle, but the hole gantry overhangs. That kind of kills the good points of that particular design.

    One thing from a design point of view people should understand is that the fixed gantry design we discuss here has one really strong point. I am sure most people don't understand this point properly. Its not that the gantry is fixed. Its that the rectangle it forms is very big so its moment of inertia is incredibly big. So when changing that fixed gantry design/where it forms a portal with 2 legs/ in any way that compromises it main strength is not a good idea.

    Another basic point to understand is that all rests on a couple of bearing blocks in all 3 different coordinate planes. So no matter how strong you make the machine frame, the bearing spacing, placement and forces there will form the real weak spots.

    the purpose of the strong frame is to hold enough for the forces. next purpose is to minimize bend and twist which leads to minimizing vibration.

    What people fail to understand, i see it here and in the other forums, is that the machine frame should be sturdy to a certain point and then the aim should be to be integral. No need to make 1 ton machine when same could be achieved with integral 200kg one.

    Sturdy machine that is extremely rigid will ring like crazy if not integral. So thats when all make them heavy instead of making the design integral.

    By integral i mean designed so that all forces spread equally, neutralize themselves and no weak spots and overbuilds in any direction possible.


    Thats why there are some principle designs that all use, cause they are integral. Not that always people take full use of the possibilities with that design.

    I assure you that a properly designed L gantry will beat any day the fixed gantry design if its not properly designed.

    And IMHO after playing a lot and rethinking all designs and reinventing the wheel, my conclusion is that if all things taken into account we must not forget that we usually use only 2.2 -3kw spindle, using only 6-12mm bits, so we should not forget the strongest point of each design and choose it when needed, cause at the end they will all work if made properly.
    Last edited by Boyan Silyavski; 20-12-2014 at 12:37 AM.
    project 1 , 2, Dust Shoe ...

  5. The Following User Says Thank You to Boyan Silyavski For This Useful Post:


  6. #65
    Im very new to this, but that was a great post silyavski.

  7. #66
    Quote Originally Posted by silyavski View Post
    And IMHO after playing a lot and rethinking all designs and reinventing the wheel, my conclusion is that if all things taken into account we must not forget that we usually use only 2.2 -3kw spindle, using only 6-12mm bits, so we should not forget the strongest point of each design and choose it when needed, cause at the end they will all work if made properly.
    Now your getting what I've been trying to tell you for nearly last 2yrs. . . . . . . It gets even more stupid than just the spindle because half the time these massively over engineeered machines only ever cut wood or foam.!!! CRAZY

    This design and the over hang are no problem what so ever.! . . Milling machines and Many large commercial horizontal designs use much much larger overhangs but rest of the machine is built to match.
    Like Boyan rightly points out your design is weak where it matters most and not very well thoughtout in other areas. This why I would support and brace the uprights on 2 planes and support the gantry on 2 sides with rails.
    The over hanging spindle wouldn't bother me in the slightest with correctly sized and spaced bearings. But if you want the best layout which is slightly more complex and costly then have the Axis which the spindle travels on supported both sides so effectively having a Box in Box arrangement.

    Personally like Boyan says don't re-invent the wheel just make it fit your purpose.!!
    Last edited by JAZZCNC; 20-12-2014 at 11:44 AM.

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  9. #67
    Well to be fair the first post did say 1000N cutting force so guessing big cutters will be used and with 0.05mm accuracy that's not much error budget within the whole machine.

    Without getting in to complex design calcs the quickest and most economical solution is to over engineer the frame. The extra weight can be benificial and also a problem with regard to acel-decel and dynamic loading but this design stops all the loading being transferred to the x axis like a moving gantry. So wont be as much of a problem.

    The natural progression of a diy machine is to upgrade so having a strong sturdy frame means you get bigger steppers or higher powered spindle at a later date.

    I know that the machine will be limited by its spindle power and cutter diameter and in fact tool deflection will be the ultimate limiting factor to cutting and feed speeds but this isn't a commercial machine.

    I always believe that the machine should be designed from the cutting tool back through the spindle and the rest of the machine. Maybe It would be better to start again with the design spec to confirm what spindle and cutters will be used and go from there. :0)

  10. The Following User Says Thank You to Ross77 For This Useful Post:


  11. #68
    Quote Originally Posted by JAZZCNC View Post
    Now your getting what I've been trying to tell you for nearly last 2yrs. . . . . . . It gets even more stupid than just the spindle because half the time these massively over engineeered machines only ever cut wood or foam.!!! CRAZY

    This design and the over hang are no problem what so ever.! . . Milling machines and Many large commercial horizontal designs use much much larger overhangs but rest of the machine is built to match.
    Like Boyan rightly points out your design is weak where it matters most and not very well thoughtout in other areas. This why I would support and brace the uprights on 2 planes and support the gantry on 2 sides with rails.
    The over hanging spindle wouldn't bother me in the slightest with correctly sized and spaced bearings. But if you want the best layout which is slightly more complex and costly then have the Axis which the spindle travels on supported both sides so effectively having a Box in Box arrangement.

    Personally like Boyan says don't re-invent the wheel just make it fit your purpose.!!
    Yeah Dean, i hear you now. Just needed to spend my first 1000kg of steel so i could understand you better . You know, new toys, new experience...
    project 1 , 2, Dust Shoe ...

  12. #69
    Quote Originally Posted by Ross77 View Post
    Maybe It would be better to start again with the design spec to confirm what spindle and cutters will be used and go from there. :0)
    I have changed the design and want to include the spindle being important( and heavy) part so the parameters:
    3 kW motor + belt driven spindle with a later ATC option
    Cutters "anything" that the motor can drive ( in plastic I can use 50 mm face mill :)
    100-10000 rpm( so conventional machining range)
    one option is AC motor +VFD -only the motor is 25 kg I know
    other:s cheaper type servo motor or similar- designed for this purpose
    I need some help in this subject to choose.
    I made some searching but still have not find too much here.
    Something I found on Blakburn's post but its reading is not aloud for small children.
    So pls point it to if any is here
    Thanks
    Last edited by vargai; 28-12-2014 at 10:44 PM.

  13. Quote Originally Posted by JAZZCNC View Post

    The C section inner surfaces won't be flat so will need milling for the rails. Then you have the problem of making sure the uprights are perfectly parallel in 2 planes and perfectly perpendicular in the other.!! . . 99.9999999% Nailed on that you won't be able to weld this up and keep parallel/perpendicular in all planes.

    I feel If you go with this design you'll regret it come setting up time.!
    This is so important when developing your design. I don't know how much experience you have welding? But things will distort and if you are just starting out you want to be able to weld in a flat position as much as possible. Building in adjustment is key - especially if building using limited equipment and skill. You can draw to crazy levels of accuracy but when it comes to drilling a hole or cutting to 0.1mm using the kit you have in your garage!???

    With my cheap drill press, cut off saw and stick welder I have needed some tolerance building my frame and I have seriously taken my time!!!

    You are doing the right thing sharing on here though you will get some v helpful advise.

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