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Thread: Large Format 5-Axis Gantry Router

  1. #61
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    Default Re: Large Format 5-Axis Gantry Router

    On steel surfaces I routinely sanded long beams to about 0.02 mm flatness/straightness to mount linear guides in 25 / 35 mm sizes.

    A 50 mm wide steel flat, sanded with a *wide* (Festool 105) powerful belt sander and 40 grit paper will easily remove material in a controlled manner, to about 0.01 mm control in depth.
    The edges of the 50 mm flat get rounded, but the center part is flattish to better than linear guide specs of about 0.03 mm.

    No scraping needed, nor shimming.

    Using a ground machine-tool builders sharp straightedge, and a backlight, it is easy to see low/high spots on the surface.
    Then mark the steel with a sharpie, one line for small removal, more parallel lines for more removal.
    Then sand until the marks are faint, check, adjust.

    It is fast, and very accurate, you get excellent control.
    It is also noisy, dusty, unpleasant, hard work.
    The wide belt keeps the sander from digging in.

    If gross material removal is needed, a Hilti/similar small angle grinder and 45 grit flap wheel will remove metal fast, in a controlled manner.
    Then belt sand to finish.
    The grinder and flap wheel can cause tilts, so use judgement.



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    Default Re: Large Format 5-Axis Gantry Router

    good job



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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by peteeng View Post
    Hi Jono - I suggest you do a torsion proof test and measure its torsional deflection. I doubt if the bending stiffness will be the weak link as you say. Then back calculate the bulk shear modulus for the beam and see how you do compared to other structures eg riveted aluminium or steel (like aircraft construction) You'll only have one good opportunity to do this before you build it into the machine then you will know if you have made a good structure. The structure you describe has a small shear modulus and being square is not geometrical ideal. Then you'll have good info for when you build your next machine. I've been involved with composite structures for about 30 years and understand why you would build this way. Composite are great but they need to be executed correctly to get high mechanical properties. These days it's quite easy to get aerospace grade laminates in your garage using infusion methods.

    The discussion about mass as a damper is an interesting one. Adding mass is the easiest method to damp a structure, its harder to excite a heavy thing then a light thing. But if you want it to move fast this is a poor method as then you need more power to accelerate it. You won;t get a job in an F1 team or a Boeing design team if you say "let's add some mass here" So using the add mass approach we would make suspension elements on cars heavier or at least make the car heavier which is what the old american cars did. But if you want a performance structure then you have to lightweight the hell out of it and solve the resonance problem (if there is one) another way. There are many ways to dampen a thin structure, from adding creases, to adding soft stuff to it, to adding tuned dampers, to active dampers etc etc. If you want to up the game you have to up the technology. Cheers Peter S
    Hi Peter. The beam is built and the proof will be in the pudding. Regarding mass and moving fast (accelerating), this is one of the primary design considerations of course. I fully understand the relationship between mass and acceleration. That is why I built a composite gantry beam. Conversely, a component that does not move (the main frames) are made of steel filled with concrete and weigh a great deal. And the floor slab is 200mm of concrete. In any case all the design values are calculated long ago for the purpose of specifying equipment. Aluminium was not considered for the gantry beyond initial stages due to it's thermal expansion coef. The presence of mass in the form of a small quantity of core material is hardly having a major affect on overall mass, especially considering it relative to a steel design with similar stiffness (and probable residual stresses, have to heat relieve a 5.0m component somewhere). Steel and concrete have similar thermal expansion coefs. The steel laminated into the structure to receive the fasteners adds far more mass than the core material. And in any case, as I have said earlier in the thread, this beam is some what experimental. Hopefully I will be installing the gantry in the next short period. Your comments are all very good and I do hope that you won't take this the wrong way, but I do know all that stuff already, and with composites there is always many many ways to skin the cat. At the moment I am fighting with the mundane and time consuming issue of preparing flat and straight machine beds, so the higher level stuff is not at the front of my mind. J

    Last edited by jono5axe; 03-16-2019 at 09:04 PM.
    Jonathon Clarke
    www.solpont.com


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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by hanermo View Post
    On steel surfaces I routinely sanded long beams to about 0.02 mm flatness/straightness to mount linear guides in 25 / 35 mm sizes.

    A 50 mm wide steel flat, sanded with a *wide* (Festool 105) powerful belt sander and 40 grit paper will easily remove material in a controlled manner, to about 0.01 mm control in depth.
    The edges of the 50 mm flat get rounded, but the center part is flattish to better than linear guide specs of about 0.03 mm.

    No scraping needed, nor shimming.

    Using a ground machine-tool builders sharp straightedge, and a backlight, it is easy to see low/high spots on the surface.
    Then mark the steel with a sharpie, one line for small removal, more parallel lines for more removal.
    Then sand until the marks are faint, check, adjust.

    It is fast, and very accurate, you get excellent control.
    It is also noisy, dusty, unpleasant, hard work.
    The wide belt keeps the sander from digging in.

    If gross material removal is needed, a Hilti/similar small angle grinder and 45 grit flap wheel will remove metal fast, in a controlled manner.
    Then belt sand to finish.
    The grinder and flap wheel can cause tilts, so use judgement.
    Awesome feedback, thanks very much. I had already considered this, and back myself to be able to get precision results with an angle grinder, sander, scraper, etc, but goddam it, it is a lot of work...

    I also need flatness across the bed, at the edges as well.

    When you quote those figures "to about 0.01 mm control in depth" , over what distance?

    When you quote "part is flattish to better than linear guide specs of about 0.03 mm", what is this linear guide spec? over what distance? is that the stated rail straightness, or do you have something that specifies a bed flatness requirement?

    Jono

    Jonathon Clarke
    www.solpont.com


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    Default Re: Large Format 5-Axis Gantry Router

    One of advantages of epoxy is that you do get a coplanar surface for your rails quickly and easily.But it may introduce unacceptable flexion with what would seem to be heavy gantry and z.



  6. #66
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    Default Re: Large Format 5-Axis Gantry Router

    I rarely wade into this sort of thing because of the flak I get in forums but I find comments like I can hand grind something with 40 grit to 10 micron flatness to be unacceptably optimistic. I regularly have to specify turned and milled product to tight tolerances and even using a $500k dollar machine it's tough getting to 0.010mm flatness over a reasonable distance. To achieve this sort of thing you have to grind or use a multi million dollar mill that's good for 0.001mm. The way to achieve this sort of thing by hand is laborious but doable. Its the 3 surface trick. You get three long flat objects (say a suitable aluminium extrusion). . You then use a contrast like engineers blue on the required surface. You then wipe the surface with board 1 until you remove the blue. You reblue and use board 2 then you use board 3. You work down the grits until you get to where you want. Along side of this you blue board 2 and wipe with board 1. You then do same with board 2 & 3 and rotate the boards. In this way the boards get flatter and the surface gets flatter. Once your happy with the surface your done. You can probably get away with 2 boards. This is how this sort of surface has been done for centuries by stonemasons and then engineers before machinery existed to do this sort of thing. Plus you use a scraper for the high spots so you don't dip the low spots. . Do the best you can with the dollars you have. Keep making. Peter

    Last edited by peteeng; 03-17-2019 at 06:39 AM.


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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by jono5axe View Post
    I think that I can officially declare that self leveling epoxy sucks.

    Maybe for small areas it is ok, but for longer beds it is just not possible to get it to flow out flat enough. Even when being very exact with putting the right amount in specific zones to ensure that the required flow is minimal and just local leveling is sought, I am still getting poor results. If I am not careful I can get high/low spots of +/-1.0 mm or more (which is I presume the form of a frozen flow wave) but even a good pour is high/low of +/- 0.1 mm or more over 300mm spans. Epoxy is a special low viscosity resin and gel time is two hours so that is all fine. Lots of hand work required (precision hand sanding, staight edge, precision level checking) to get it in any kind of shape. Across the bed is OK (level and flat) but longitudinally is rubbish.

    [Note: I am putting a gauged plate on top of the epoxy when flat. This plate follows the faults in the epoxy to a degree, for example +/- 0.05mm over 300mm]

    Question:

    Regarding flatness of beds for linear rail mounting (medium precision/preload) can anyone please tell me tolerances for flatness. Generally the linear rail manuals do not state tolerances on the bed flatness requirements, just stating "flat and straight mounting surfaces". I have found various info that would suggest max allowable values of 0.02mm out of flat over 500mm (for medium precision/preload rails up to 45mm) but this maybe seems a bit extreme to my thinking. Please if anyone has any knowledge here I would be grateful to hear it.

    At the moment it looks like I have a lot of hand scraping ahead of me.
    That's a big number .02 for that type of linear Bearing just figure how much clearance is in the Bearing and that is the max tolerance you can have on the flatness of the mounting surface, A preloaded Linear Bearing you don't have anything to play with for rail flatness tolerance, using epoxy it is not an ideal mounting surface as it will deform when you torque down at each Rail mounting point, any mounting tolerance you had will be lost just with the deforming of the surface

    Mactec54


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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by mactec54 View Post
    That's a big number .02 for that type of linear Bearing just figure how much clearance is in the Bearing and that is the max tolerance you can have on the flatness of the mounting surface, A preloaded Linear Bearing you don't have anything to play with for rail flatness tolerance, using epoxy it is not an ideal mounting surface as it will deform when you torque down at each Rail mounting point, any mounting tolerance you had will be lost just with the deforming of the surface
    The epoxy was just the 'flat & level' foundation for the (metal) machine bed plates to sit on.

    Jonathon Clarke
    www.solpont.com


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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by jono5axe View Post
    The epoxy was just the 'flat & level' foundation for the (metal) machine bed plates to sit on.
    No Problem then

    Mactec54


  10. #70
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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by peteeng View Post
    I rarely wade into this sort of thing because of the flak I get in forums but I find comments like I can hand grind something with 40 grit to 10 micron flatness to be unacceptably optimistic. I regularly have to specify turned and milled product to tight tolerances and even using a $500k dollar machine it's tough getting to 0.010mm flatness over a reasonable distance. To achieve this sort of thing you have to grind or use a multi million dollar mill that's good for 0.001mm. The way to achieve this sort of thing by hand is laborious but doable. Its the 3 surface trick. You get three long flat objects (say a suitable aluminium extrusion). . You then use a contrast like engineers blue on the required surface. You then wipe the surface with board 1 until you remove the blue. You reblue and use board 2 then you use board 3. You work down the grits until you get to where you want. Along side of this you blue board 2 and wipe with board 1. You then do same with board 2 & 3 and rotate the boards. In this way the boards get flatter and the surface gets flatter. Once your happy with the surface your done. You can probably get away with 2 boards. This is how this sort of surface has been done for centuries by stonemasons and then engineers before machinery existed to do this sort of thing. Plus you use a scraper for the high spots so you don't dip the low spots. . Do the best you can with the dollars you have. Keep making. Peter
    Don't worry about the flak, mate. At least not on this thread. I am interested.

    The reason for trying less conventional methods, i.e. not machining these beds, is due to their size and the logistics of it, and the fact that I generally like to look at the less conventional / innovative ideas. Possibly a mistake in this case. But possibly not, it will work out one way or another.

    I am quite familiar with how to manually work a surface with bearing blue and a scraper, and also with various other tools. And over the years I have made very many composite patterns and molds manually (not CNC) and am very used to working with surfaces manually, not as exact as what we are talking for machine beds, but very fine surfaces nonetheless. I also researched this area earlier in the design process and from that research I determined that, not so much for linear bearing beds but certainly for sliding beds and larger tables, that hand scraping was the way. It is all depending on the skill of the operator, of course. Experience. Hand & eye, care & patience, discipline. Good measuring tools.

    From what I have done myself I feel that I can work to flatness of 0.03 or 0.02 mm over 500mm with a combination of tools and methods. But after that then my measuring tools errors probably come into play. And the time required.

    But my original post on this matter was to ask the question about what tolerances I should apply to bed flatness for medium precision/preload linear rails (face-to-face) (20mm-45mm rails)

    Jonathon Clarke
    www.solpont.com


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    Default Re: Large Format 5-Axis Gantry Router

    Hi Jono - What preload are you using in this machine? For an accurate router or mill machine bearing manufactures recommend their heavy preload spec. http://www.pmi-amt.com/en/data/Catol...EN_GW_MD08.pdf download the PMI design catalogue it has most of this data in it including parallelism, level delta, etc. Your brand of bearing should have same info. They are made to an international std so should all be the same. Cheers Peter



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    Default Re: Large Format 5-Axis Gantry Router

    Quote Originally Posted by jono5axe View Post
    But my original post on this matter was to ask the question about what tolerances I should apply to bed flatness for medium precision/preload linear rails (face-to-face) (20mm-45mm rails)
    I'm enjoying this build thread, looking forward to seeing the next update! I used HIWIN brand rails on my machine and they publish the specs in their catalog. See attached image. This should give you a rough idea, but the manufacturer of your rails should have documentation for you.

    Large Format 5-Axis Gantry Router-hiwin-rail-mounting-surface-accuracy-png

    Attached Thumbnails Attached Thumbnails Large Format 5-Axis Gantry Router-hiwin-rail-mounting-surface-accuracy-png  
    Jeremy
    http://www.diycncdesign.com/


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