584,812 active members*
5,484 visitors online*
Register for free
Login
Page 6 of 6 456
Results 101 to 108 of 108
  1. #101
    Join Date
    Aug 2009
    Posts
    291

    Re: Need help - Fixed gantry design

    You laugh at string levels, but watch what the guy in the video below does to level a welding table.

    https://www.youtube.com/watch?v=kjaSy_SmYsQ

    If all the pads (upright and rail) are at the same level, it seems to me it simplifies the machining. For good enough, you would work off a flat surface with machinist level to grind your way to perfection. Blanchard grinder ("Our largest 100 HP 60 inch chuck Blanchard grinding machine will cut the stock quickly and it allows us to grind parts up to 72” diagonally.") or even surface grinding ("We offer tight-tolerance surface grinders with sizes up to 32″ x 96″ and 16″ x 168″) as options at large outfits. They can also do stress relief if you think it needs it and/or don't want to setup a bake oven.

    But, yeah. This is one area that I haven't seen discussed a lot other than people using large mills where they work to complete the flatwork. I have a crude surface grinder fixture idea bouncing around in my head.

  2. #102
    Join Date
    Aug 2009
    Posts
    291

    Re: Need help - Fixed gantry design

    Quote Originally Posted by RCaffin View Post
    Yeah, hollow tubing is a LOT lighter, isn't it?
    Is there much difference in rigidity between solid bar and 1/4" tube? Some, but not a lot. The hollow tube will however ring a lot more I think.

    Cheers
    Roger
    Right, it's actually pretty interesting.

    2x2x24" solid, 500lbs applied force
    Deflection: 0.0576000"

    2x2x24" .24 wall
    Deflection: 0.0842606"

    2.25x2.25x24" .24 wall
    Deflection: 0.0567138"

    3x3x24 .125 wall
    Deflection: 0.0387087"

    Increase the 2x2 1/4" wall tube by 1/4" and you have less defection than the solid.
    By 1" and you can halve the wall thickness and still be less than the solid.

    Of course, that's not the only characteristic we'd be chasing, but interesting none the less.

  3. #103
    Join Date
    Jun 2004
    Posts
    6618

    Re: Need help - Fixed gantry design

    Pretty sure it has to do with surface area.
    I had some 7/8" stainless hex bar that I was sure was fairly rigid at short lengths. I was amazed at just how much I could deflect that supported on the ends on a bench. 30" length. I won't say wet noodle, but it was not far off.
    It deflected more than 1" x 1/8" square 6061 aluminum tube the same length.
    Lee

  4. #104
    Join Date
    Sep 2006
    Posts
    6463

    Re: Need help - Fixed gantry design

    Hi.....the concept of solid steel bar for a build is mainly to offset the factors that go for an assembly of the various frame parts.

    It takes many hours of machine work (if you have one) to interface bolted items but with an all welded solid steel bar build it's just put together, align by whatever, and hit the welder.

    Very true there is a weight factor to consider, but given the choice of a relatively light construction
    ;cos the tubing wall cannot be bought any thicker and the fact that having a tubing wall will allow distortion from the rapid heat build up as opposed to a solid bar not moving ........I proposed the solid bar as an option to consider.

    It comes down to proportions for the actual frame size.

    I don't think I'd consider going to a bigger than a 6040 build without first estimating the overall weight of the frame.......but it would not approach a Bridgeport weight.....ever.

    In the aforementioned design I would go to two bars for the X axis cross beam.....this would be more in proportion than a single solid lump of ferrous.

    I doubt anyone would be brave enough to build in solid bar stock........but the concept of an immovable frame is one that is the holy grail for mill or router design and the fact that the machining input is of the minutest makes it a quick build by any standards.

    I would even go so far as to state that no machining for the linear rail seats on such a build is a possibility if you know your fitting by the judicious application of an angle grinder and a straight edge......BTDT.
    Ian.

  5. #105
    Join Date
    Aug 2009
    Posts
    291

    Re: Need help - Fixed gantry design

    Quote Originally Posted by LeeWay View Post
    Pretty sure it has to do with surface area.
    I had some 7/8" stainless hex bar that I was sure was fairly rigid at short lengths. I was amazed at just how much I could deflect that supported on the ends on a bench. 30" length. I won't say wet noodle, but it was not far off.
    It deflected more than 1" x 1/8" square 6061 aluminum tube the same length.
    It has been a long time since physics, the biggest thing I remember was make a beam taller if you can.
    https://www.engineeringtoolbox.com/b...on-d_1312.html

    So it is based on surface area, but the height of the object plays a bigger role. For a rectangular solid, the Area Moment of Inertia Ix = b h^3 / 12 (where h is the height and b is the width in cross section). Height being cubed plays a big part next. When calculating the deflection, the beam length and load are divided {in part} by the moment of inertia thus a larger AMOI means a smaller deflection.

    You can also think about an iBeam. One side in tension, the other compression. As you approach the center, these forces drop to zero. Extra stuff between the flanges not helping soo much.

    As far as solids go a 6' 2x4 in 1/4" cost me ~$42 and 52lbs not the easiest thing to handle, but not too bad. I've never seen thick, solid bar stock in any useful lengths. I'm sure you'd have to purchase new and have cut to length as 6' would be 163lbs. If available as drops ($0.80 clean metal) that would cost $130.

  6. #106
    Join Date
    Sep 2006
    Posts
    6463

    Re: Need help - Fixed gantry design

    Hi, in the design we are looking at, there are no unsupported columns like you have on a mill which is all about a toffee apple on a stick syndrome..... the higher the top the more wobble you get etc.

    I proposed solid black hot rolled bar for a CNC router frame build........that puts it in a box like structure where all the frame components are supported by one another once welded together into a composite structure.

    It is quite easy to list and get a precut supply of solid bar from the supplier ready for the welder, and this makes it very transportable.

    The main advantage would be the miniscule amount of actual milling work you'd have to indulge in to produce the main X and Y axes for the linear rail seats........the frame requires practically no other milling to make it a frame.

    I'm thinking in terms of a moving table 3040 work envelope to mill ANY material.

    That gives you 300mm X 400mm and approx 200mm under the gantry crossbeam.

    Apart from the height, 300 X 400 full table coverage is quite a job size.......all column mills do not (cannot) cover their entire table length......a 400mm X axis coverage on a column mill is a very big table length, and this router proposal is designed to cut all metals not just wood and maybe aluminium.

    I think the design that has so far appeared is an ideal layout for assembly and forms a rigid base for the Y axis on top of the 2 bars that go between the column uprights........even if it was made in steel tube.
    Ian.

  7. #107
    Join Date
    Apr 2007
    Posts
    1955

    Re: Need help - Fixed gantry design

    I read though the thread - lot of interesting approaches, so I will throw my opinion in as well just for fun.

    1) I don't find welding tubes together precisely all that easy, not do I find grinding a tube flat all that fun. I am sure that an experienced person can do it, I can't.

    2) One way to make a flat surface on a piece of tube steel is to make a sort of moat and pour self leveling epoxy in. Self leveling epoxy isn't just thin, it has flow agents to make it really wet out very flat, usually with a bit of lip at the very edges. Once you have pieces like this, you can use them as reference surfaces.

    3) Two tubes with flat surfaces like this can be bolted together - flat face to flat face - at a 90 degree angle to make a very easy to make, naturally squared up interface. As an example - the uprights and the gantry cross beam.

    4) Bolting these beams together can be easily done by drilling a hole large enough for a socket wrench to go inside of the tube, and then a smaller hole where the two faces will bolt together. All this requires is a drill press - nothing fancy at all. It helps with final alignment if you add a screw to help with the fine adjustments though.

    5) If you continue this concept down to the lower frame, the tube that attaches will now be a flat reference from the upright to at least part of the table.

    6) A string with a weight on it can provide a convenient and natural way to make sure that the uprights are really vertical, and then a pour of epoxy will make the top of the tubes that form the lower frame naturally flat and perpendicular to the upper frame items.

    7) Your system is small - take advantage of this by using just one, slightly larger rail for the motion of each axis rather than trying to align two of them on each axis. Aligning two each precision rails to each other is a lot of work and not at all needed for a system this size.

    These concepts may or may not work for you, but I have tried building routers "from the outside in" and in the end found it much easier to start "from the inner most part (spindle) and work my way to the outside".

    Not claiming to be an expert, just failed several times along the way.

  8. #108
    Join Date
    Sep 2006
    Posts
    6463

    Re: Need help - Fixed gantry design

    Hi, practice makes perfect as long as you are well schooled in the practice.......or whatever it takes to get you to the finish line or the skill level in the practice element is low.

    I wouldn't subscribe to the practice of the self leveling epoxy as it's to alien to my way of working......but it could work if you want to get there.

    The very real problem is not having a true reference surface to work from........even a slab of granite work top is better than nothing.

    It gets worse when the build is on the large side.
    Ian.

Page 6 of 6 456

Similar Threads

  1. Fixed Gantry Design
    By CatalystGilles in forum DIY CNC Router Table Machines
    Replies: 16
    Last Post: 06-05-2018, 06:18 PM
  2. Hybrid Design - Fixed Gantry Router for High Speed Aluminum Milling - Metal Nibbler 5
    By Bob La Londe in forum Uncategorised MetalWorking Machines
    Replies: 7
    Last Post: 04-10-2014, 05:16 PM
  3. Fixed Gantry Design Question
    By ynnek in forum DIY CNC Router Table Machines
    Replies: 25
    Last Post: 04-22-2012, 10:26 PM
  4. Small Fixed Gantry Design
    By praneetn7 in forum DIY CNC Router Table Machines
    Replies: 24
    Last Post: 03-26-2012, 05:08 AM
  5. 8020 Fixed Gantry Design
    By jupdyke in forum DIY CNC Router Table Machines
    Replies: 7
    Last Post: 12-30-2010, 11:48 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •