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  1. #21
    Quote Originally Posted by JunkieHobbo View Post
    I have looked through the Forum and have seen a machine similar to JAZZCNC with lower sides, made by Jonathan. I have PM'd him to see if he can post more pics of it as it looks like it would do the Job.

    I'm sorry I forgot to reply to your PM earlier about pictures of my machine and things. Had a bit more work than usual to do at Uni. Looks like Jazz has saved me the trouble of answering lots of questions :)
    There's quite a few pictures in my build-log, especially towards the end:

    http://www.mycncuk.com/forums/showth...outer-building

    (starts off embarrassingly bad then gets better!)

    There are a few things I will change on the machine. Essentially just a stronger Y and Z-axis with profile rails, but like Jazz I have an 'unusual extra strength' design for that. Instead of having one piece across the gantry there will be two, with one Y-rail on each, and a box shaped the Z-axis operating between. Having said that it's still strong enough to cut aluminium at a decent speed 1.5mm DOC, or more with reduced finish which is not bad considering only round rails. I just want to see how much better I can make it...

    If you need any more of specific parts just let me know and I'll take them.

    I'd be inclined to add some triangles to that frame to stop it skewing.

  2. #22
    Hello,

    My name is Carlos and i'm form Portugal.

    I want to built a CNC router to make 3D wooden molds.

    I was thinking in the xx axis use racks instead of ball screws, (the racks in the place of the ball screws, put the xx motor in the middle of the yy axis and using a shaft with a pulley at each end).

    In terms of accuracy, racks is worse than a ball screw??

    I want the router to make molds, for it I need a lot of precision. (For this kind of work an error of 0.1 mm (0.0039 inches) is an huge error.)

    Would you, please, give me your opinion about the racks?

    Thanks.

    P.S.: Sorry for my English...

  3. #23
    @JAZZCNC: No worries, I am really appreciative of your Help and anything that can help me make a better machine I will gladly accept, keep on picking!

    OK, I have made some changes as you suggested, I have gone with 80mmx40mmx3mm, every penny helps! Regarding the Flat plates, I get what you mean but how would you do it, would you mount a plate on the upright and also on the base of the 80x40 that will hold the rail, picture is worth a 1000 words.....:whistling:

    I have noted down your points regarding the Z-Axis, once I get to the Z-Axis I will incorporate the suggestions.

    Belts, I am convinced it is the way to go now, only 1 Stepper, I am assuming a larger stepper than Y&Z? Do you have some pics of your setup using the Belts, I have looked around and was not really able to find any good pics for reference to build on.

    Here is an updated drawing, I added in some triangles as Jonathan suggested, I was just going to add some tabs to mount the panels to but Triangles will work and also add extra support.

    Click image for larger version. 

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    If the base is good I can then work on the X-Axis rails and Belt drive.

    That is some seriously nice work there, hopefully once I get my machine up and running I will be able to produce something half as good!

    @Jonathan: Thanks for the advise, I added some triangles they will have uses, one for support as you mentioned and secondly to hold my "Dirt Splash Panels" up, see the pic above. I might have some more questions as I progress but for now the pics will do great!

    @m.marino: I will be going with 2 Ballscews on both sides of the X-Axis, and will be driven by one stepper and a belt. Added a Center brace as suggested by yourself and JAZZCNC's example. I have about 1200mm x 1000mm x 1000m Space to work with, so I want to build the Biggest/best possible machine to fit into that area.

    @C.AlveSilva: I am by no means a Guru on this but from what I have researched and have learned from the guys on the Forum, Ballscrews are the way to go and Profile rails.

  4. #24
    Quote Originally Posted by C.AlveSilva View Post
    Hello,

    My name is Carlos and i'm form Portugal.

    Would you, please, give me your opinion about the racks?
    Sorry Carlos didn't see your post.

    If you want to do mainly 3D work and fine tolorences then I suggest you use ballscrews on all Axis.

    Rack is ok for general profiling and machining etc but to do really accurate work with lots of repeatabilty then requires Hi quality Rack & pinions and because often with R&P you have to gear then you'll also need Hi quality gearing units or Pulleys and belts.! . . . All these will cost more than cheap chinese ballscrews and possibly perform no better if not worse.!

    So IMO ballscrews every time. Thou this does depend on length of machine and even then I'd still consider using them just with a rotating ballnut.!!

  5. #25
    Hi JunkieHobbo,

    Couple of things regards the frame.! It's weight and the ease of build and adjustment.?
    I know on my Cad model it looks like the frame is all welded but it's not and actually bolts together quite a bit. Really my models are not fully accurate models regards detail and more for me to visulise so don't pay massive attention to the detail. Thou they are to scale and dimensionally accurate regards materials and compnents which is also why I use them so I can judge component fit etc.

    When you build this machine you need to incorparate as much adjustabilty as possible. Thats why the plates on the uprights for the top rail section to sit on.
    On the machines I'm building now the main frame(excluding adjustable bed) is actually made up of 5 pieces bolted together (7 if you include top rail sections)
    This gives adjustabilty in lots of ways and also helps with moving around.!!!!. . . . . It will be very very heavy so makes life much easier when in pieces.

    Regards the plates there's several ways but this is how I do it.!. . . Basicly I machine flat plates with both holes and M12 nuts welded to them which are then weld onto the uprights, taking care to get them square as possible to the boxsection.
    !!!!!!! (This next bit will be hard to explain so bear with me.!!!)
    The plates are longer than the upright section for the middle uprights so can be bolted either side of uprights into the top rail section which has nuts welded into it. The end upright plates are only longer on one side so bolted on inside from below into top rail then another bolt accessed thru the open ends into plates which have M12 nuts welded to them.
    These plates could be drilled and tapped but that would require thick plate so thats why I use welded M12 nuts. The same M12 nuts are welded into the top rail as the 3mm box section doesn't allow enough thread.
    It may sound faffy and complicated but in reality it's not and doesn't take long if you have a decent drill press and can weld half decent.

    The frame pics below will give a better idea. I'm still building the frames but when get a chance then I'll post a few pics of the actuall steel work, when I'm further along I'll probably start a thread showing it(them) coming along.

    Regards the belt drive then there's better ways than I've done it. Mine was rushed and thou it works very well it's not pritty so wouldn't do it that way again or recommend you follow it.
    I've done a quick alteration of my frame and mock up to give a rough idea of one way, needs belt tensioner etc but should give you an idea.!! There's other ways if you look around and easily done with motor at same end in line with belt acting as the tensioner incorporation with an idler.

    Hope this helps.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  6. #26
    @JAZZCNC: Thanks again for the reply and your time.

    Quote Originally Posted by JAZZCNC View Post

    When you build this machine you need to incorporate as much adjustabilty as possible.

    I really like your way of thinking, that the machine should incorporate adjustability. I like the modular approach aswell, I do feel this would be a far easier build for me by doing it this way with minimal welding.

    BUT

    Just a quick question, I know another question! :whistling: Will the bolted sections hold up and keep structural stability as good as the welding would? I am asking because it is a CNC machine that works on precision and bolts are " not a fixed" part of the structure, so there is a chance for them to loosen, how would you solve this problem? Then again, I could be obviously missing something here as usual.

    Regarding the Plates, the pics answered my Question 1000%, Thanks again!

  7. #27
    Quote Originally Posted by JunkieHobbo View Post

    BUT

    Just a quick question, I know another question! :whistling: Will the bolted sections hold up and keep structural stability as good as the welding would? I am asking because it is a CNC machine that works on precision and bolts are " not a fixed" part of the structure, so there is a chance for them to loosen, how would you solve this problem? Then again, I could be obviously missing something here as usual.
    Well think about it Just about every CNC machine even those costing 10's thousands of pounds are bolted together in some form or another. . . . They are not welded in one piece.!!
    The bolted sections will hold up fine so long as you use correct size and good quality bolts and tighten them correctly. If you want to ensure they don't move then use locking/locateing pins.!!. . but they don't move if good quality bolts with locking washers with a bit of thread lock for good measure.!

  8. #28
    Jazz is right on this very much so. My table is totally welded and it turned out fine? well not true, even with all the care in the world the bed still needed a lot taken off the surface to get a straight bed. In most cases that is fine but if i had used bolts i could have adjusted a lot of that out before surfacing. Just to add a bit more to the design try and include adjustable feet, can make a world of different to noise as well as helping adjust to unleveled floors. It aso makes it much easier if you ever needed to move it as well.
    If the nagging gets really bad......Get a bigger shed:naughty:

  9. #29
    @JAZZCNC: OK, back to the drawing board as they say! I will look into using bolts as I mentioned in my previous post, it will make life ALOT easier for me if there is not alot of welding to do.

    @2e0poz: I am going to see what I can draw up using Bolts and some welding, I have a feeling I am going to end up with something similar to JAZZCNC's design. Regarding the Feet, that was always in the Plan, just never showed it in the drawings, I learnt my lesson on that one already.

  10. #30
    Quote Originally Posted by JunkieHobbo View Post
    it will make life ALOT easier for me if there is not alot of welding to do.
    Actually doing it the way I have means in the terms of building it makes it harder and longer bolting to together, there's actually no less welding required.?
    Welding takes minutes per joint.! . Cutting the plates, Drilling the plates, Drilling the matting sections and welding/grinding in the plates/nuts etc takes meny hours.

    You have to take much care when cutting the steel that the ends are square so when you weld the plates they are square. If the plates are not perfectly sqaure then when you bolt the sides to the base pieces they wont be square and much shimming will be needed. The goal is to reduce shimming as much as possible.
    The way I do it is to tack the plates top & bottom then bolt them together to check fit, If far off then grind either the top or bottom tacks off and adjust with No1 special re-alignment knocking stick.:naughty:.
    Then when happy weld full joint. This gets me very close thou the plates can and do move with the heat from welding so need rechecking/adjustment, for the final adjustment and close fit I can just skim a little of the plates with grinder. After this I'm pritty much spot on square and if not then just minor shimming will be required.

    So as you can see it's not easier by any means.!! . . . BUT . . it should also show you how important I feel and know having this adjustment abilty matters to a accurate machine because NO WAY would I go to all this trouble if I could just weld the bugger up.:nope:

    That said my way of building makes it harder because I didn't want lots of bolts and external plates showing so used the mix of welding and bolting.
    If you wanted could build using just plates/bolts and very little to non welding if you wanted, it's just lots of plates,drilling and bolts because the plates would have to be both sides of each joint. . . . It would still be very strong and have lots of adjustment just not so good looking.!!

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