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    Default Re: Y Gantry Twist

    Quote Originally Posted by OneWound View Post
    In regards to sag over a 10' span..I was plan on using a 25mm lead screw, you think that would sag under its own weight?

    Also, would there be concern for sagging over a 2" 5' 1566 linear shaft (under its own weight)?

    To everyone else, I hope to have a CAD model sometime this weekend...I've been busy the last few days
    Sure, if your gantry is on center of the 10' span maybe you'll have no problems. I foresee however as you move to either extreme of the table there will be issues with sag. And whip - if you want 500ipm consider how fast the screw must spin. Especially if you want .001" accuracy. If you use a C7 rolled ballscrew the lead variation is about .002"/ft. I think at those speeds and that length you'll have issues with whipping and potentially wind-up. You could use a 25mm lead, but then you'll have to deal with back-driving, meaning you'll need bigger motors.

    My guess is that you'll have problems with the round linear rod. I think structurally this is the number one problem that had plagued many earlier build threads as well as inexpensive import machines. And these are smaller machines, 24" spans, with 3/4" unsupported rod. Not only will they flex up and down but your Z axis will act as a lever and twist as well. Each rod alone will weigh about 60lbs, not including your Z axis assembly, spindle, leadscrews, all bearing blocks, motor, cable chain... I think even mounting two 1" supported linear rail to a rectangular aluminum tube would work better.



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    Default Re: Y Gantry Twist

    Quote Originally Posted by louieatienza View Post
    Sure, if your gantry is on center of the 10' span maybe you'll have no problems. I foresee however as you move to either extreme of the table there will be issues with sag. And whip - if you want 500ipm consider how fast the screw must spin. Especially if you want .001" accuracy. If you use a C7 rolled ballscrew the lead variation is about .002"/ft. I think at those speeds and that length you'll have issues with whipping and potentially wind-up. You could use a 25mm lead, but then you'll have to deal with back-driving, meaning you'll need bigger motors.

    My guess is that you'll have problems with the round linear rod. I think structurally this is the number one problem that had plagued many earlier build threads as well as inexpensive import machines. And these are smaller machines, 24" spans, with 3/4" unsupported rod. Not only will they flex up and down but your Z axis will act as a lever and twist as well. Each rod alone will weigh about 60lbs, not including your Z axis assembly, spindle, leadscrews, all bearing blocks, motor, cable chain... I think even mounting two 1" supported linear rail to a rectangular aluminum tube would work better.
    In regards to the round linear rod, how do suggest mounting the linear rails as accurately as possible? That's one thing I've struggled with, and why I wanted to use linear rods. It's hard to fight a 5' piece of extrusion that is flat. The only thing I could think of would be mic6, even than I'd have to order a HUGE piece of mic6 and have it waterjet (which is within the realm of possibility) to get it close to dimensions. From there, it'll still have to be machined flat

    The above post comes from the mind of a mechanical engineer student. You are warned.


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    Quote Originally Posted by OneWound View Post
    In regards to the round linear rod, how do suggest mounting the linear rails as accurately as possible? That's one thing I've struggled with, and why I wanted to use linear rods. It's hard to fight a 5' piece of extrusion that is flat. The only thing I could think of would be mic6, even than I'd have to order a HUGE piece of mic6 and have it waterjet (which is within the realm of possibility) to get it close to dimensions. From there, it'll still have to be machined flat
    Exactly why we've tried to make the point that building a machine to your desired specs is not as trivial as you make it out to be! Mic-6 already ground flat within .005" or less, I would think the supported rail mounting would absorb any imperfections and give you a reasonably straight installation. With your budget you should be able to find a nice steel tube and have it machined.



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    Default Re: Y Gantry Twist

    Quote Originally Posted by louieatienza View Post
    Exactly why we've tried to make the point that building a machine to your desired specs is not as trivial as you make it out to be! Mic-6 already ground flat within .005" or less, I would think the supported rail mounting would absorb any imperfections and give you a reasonably straight installation. With your budget you should be able to find a nice steel tube and have it machined.
    So if I have a machine with a big enough X movement to machine a mic6 plate in one operation (machine waterjet cuts, fly-cut the top, dowels to help locate position, and mounting holes for two linear rails), I should be able to get that precision down to +/- .002, correct? Or is my thinking flawed due to the enormity of the piece?

    The above post comes from the mind of a mechanical engineer student. You are warned.


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    Default Re: Y Gantry Twist

    I can't remember the link, but I saw a CNC with a positional accuracy of .001 and .005 of repeatability.
    I think you have that backwards. Repeatibility is usually better than positional accuracy, as it doesn't depend on the precision of the components.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Y Gantry Twist

    It's great you're exploring alternate gantry designs and drive systems.

    It sounds like you've only done a little research so far. There are some techniques gain expertise, and this is essential to pull off a machine of this scope. I'd suggest using Q&A to resolve the harder or unclear issues, and verify what you've learned already.

    On R&P, for example, try a search like this:
    https://www.google.com/search?q=rack...n+vs+ballscrew

    Here's shaft whirling/whip in action -- it's a resonant phenomena, so worst at certain frequencies.


    If you recall from Mechanics of Materials, beam deflection is proportional to Length^3 or Length^4. This is why it's difficult to make a ballscrew work at long lengths, and also unsupported round rod.

    On linear guide/shaft/rail, for example:
    https://www.google.com/search?q=linear+shaft+vs+rail
    And see the archives for thousands of posts why unsupported rail is flexy.

    When starting in a field, one of the hardest parts is knowing what keywords to choose, and of course google results are highly dependent on keywords. A good strategy is to search on what you know, then read mainly to gather better keywords, then search on those new keywords, and repeat. The best designers are sponges for good information.

    As Gerry noted, repeatability is necessarily always better than accuracy.

    A practical problem with a 3" thick solid gantry is it can't even manage its own weight. Let's say it has 0.005" bow (fore-aft) in the installed orientation, but we didn't know that and haven't measured it. Now lay it flat. It's self weight will pull it flat to the mill table. We put feeler gauges under it and detect nothing, so we think it's sitting pretty. Then we skim the rail mounting surfaces. Then we stand it upright again: 0.005" bow returns. You can run the beam deflection equations to verify. A big tube will be much more stable because it has much higher I and J, and much less weight/foot. Sure, we could indicate the solid bar before laying it flat, then shim it, but why work so hard when there are better designs.

    Closely study the industrial routers: TechnoCNC, Multicam, Onsrud, Thermowood, etc. What do they do for gantry design, linear guides, drive systems, etc? Try to find a ballscrew on an axis longer than 5' -- that is very rare, and if so, big diameter ($$) for the reasons mentioned. As a rule, when one is not an expert in a new field, it's wise to assume that the standard designs are standard for good reasons, and that non-standard designs will probably have problems.

    There are some general guides out there on DIY CNC, e.g.:
    Official Home Page of the Roman Black
    Mostly correct: Homemade CNC Router The Builder's Guide (FREE!)

    David Malicky


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    Default Re: Y Gantry Twist

    The ballscrews on our Morbidelli are 32mm diameter. Not sure of the pitch, but they are multistart, so don't spin fast.
    The gantry has a 72" screw. The X axis screw is about 14', but uses a spinning nut, and there's a spring loaded support in the center.

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Y Gantry Twist

    Check this article out:

    Go long: The pros and cons of rack-and-pinion systems | Linear Motion content from Machine Design

    Wittenstein also had a really nice white paper on this. I cannot find it anymore online. I archived it but cannot find the PDF. But basically rack-and-pinion, all things considered, is probably the most efficient method of converting rotary motion to linear.



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    Default Re: Y Gantry Twist

    Quote Originally Posted by dmalicky View Post
    It's great you're exploring alternate gantry designs and drive systems.

    It sounds like you've only done a little research so far. There are some techniques gain expertise, and this is essential to pull off a machine of this scope. I'd suggest using Q&A to resolve the harder or unclear issues, and verify what you've learned already.

    On R&P, for example, try a search like this:
    https://www.google.com/search?q=rack...n+vs+ballscrew

    Here's shaft whirling/whip in action -- it's a resonant phenomena, so worst at certain frequencies.


    If you recall from Mechanics of Materials, beam deflection is proportional to Length^3 or Length^4. This is why it's difficult to make a ballscrew work at long lengths, and also unsupported round rod.

    On linear guide/shaft/rail, for example:
    https://www.google.com/search?q=linear+shaft+vs+rail
    And see the archives for thousands of posts why unsupported rail is flexy.

    When starting in a field, one of the hardest parts is knowing what keywords to choose, and of course google results are highly dependent on keywords. A good strategy is to search on what you know, then read mainly to gather better keywords, then search on those new keywords, and repeat. The best designers are sponges for good information.

    As Gerry noted, repeatability is necessarily always better than accuracy.

    A practical problem with a 3" thick solid gantry is it can't even manage its own weight. Let's say it has 0.005" bow (fore-aft) in the installed orientation, but we didn't know that and haven't measured it. Now lay it flat. It's self weight will pull it flat to the mill table. We put feeler gauges under it and detect nothing, so we think it's sitting pretty. Then we skim the rail mounting surfaces. Then we stand it upright again: 0.005" bow returns. You can run the beam deflection equations to verify. A big tube will be much more stable because it has much higher I and J, and much less weight/foot. Sure, we could indicate the solid bar before laying it flat, then shim it, but why work so hard when there are better designs.

    Closely study the industrial routers: TechnoCNC, Multicam, Onsrud, Thermowood, etc. What do they do for gantry design, linear guides, drive systems, etc? Try to find a ballscrew on an axis longer than 5' -- that is very rare, and if so, big diameter ($$) for the reasons mentioned. As a rule, when one is not an expert in a new field, it's wise to assume that the standard designs are standard for good reasons, and that non-standard designs will probably have problems.

    There are some general guides out there on DIY CNC, e.g.:
    Official Home Page of the Roman Black
    Mostly correct: Homemade CNC Router The Builder's Guide (FREE!)
    I appreciate the comments in regards to the ballscrew, and I'll look into it more. I'll probably keep the ballscrew on the Z axis, however.

    In regards to having a huge mic6 plate weighing a lot, pockets could be machined in such an orientation it won't bend due to its own weight, as well as the weight of the Z assembly. Am I wrong in my thinking or?

    The above post comes from the mind of a mechanical engineer student. You are warned.


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    Default Re: Y Gantry Twist

    Certainly, machining can be done to lighten a solid Mic-6 plate. Consider 2 things, though:
    - Mic-6 is dead soft, so it's gummy to machine.
    - Pocketing will reduce weight and bending stiffness in ~equal proportions, so there will be no net gain in its ability to manage its own weight. I.e.:
    I = (1/12) * b * h^3
    Weight = density * length * b * h
    Pockets remove b from both terms. So both go down equally. And J (torsional) will go down faster.
    A horizontal mill could remove the mid-portion of the beam while it is oriented upright (so it doesn't sag due to self-weight); this could make an I beam which would be stiff and light for vertical bending. But I beams have horrible J, and mediocre I in the other orientation.

    There are only 2 ways to lighten it and preserve J:
    - Bore it out from each end. I.e., make it into a tube. (not a serious suggestion for something this big)
    - Mill out a triangulated pattern, as sometimes used in (clever) cast-iron lathe beds: http://www.lathes.co.uk/nuttall/img2.jpg
    But doing that on a vertical mill leads to even more bending deflection due to its own weight. Those diagonal webs are pretty good for torsion but not as effective for bending in the vertical orientation. A horizontal mill fixes that problem, but it's just a machining exercise, since a tube is far easier and stiffer for the important loading modes (Ixx, Iyy, J).

    David Malicky


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    Default Re: Y Gantry Twist

    Quote Originally Posted by dmalicky View Post
    Certainly, machining can be done to lighten a solid Mic-6 plate. Consider 2 things, though:
    - Mic-6 is dead soft, so it's gummy to machine.
    - Pocketing will reduce weight and bending stiffness in ~equal proportions, so there will be no net gain in its ability to manage its own weight. I.e.:
    I = (1/12) * b * h^3
    Weight = density * length * b * h
    Pockets remove b from both terms. So both go down equally. And J (torsional) will go down faster.
    A horizontal mill could remove the mid-portion of the beam while it is oriented upright (so it doesn't sag due to self-weight); this could make an I beam which would be stiff and light for vertical bending. But I beams have horrible J, and mediocre I in the other orientation.

    There are only 2 ways to lighten it and preserve J:
    - Bore it out from each end. I.e., make it into a tube. (not a serious suggestion for something this big)
    - Mill out a triangulated pattern, as sometimes used in (clever) cast-iron lathe beds: http://www.lathes.co.uk/nuttall/img2.jpg
    But doing that on a vertical mill leads to even more bending deflection due to its own weight. Those diagonal webs are pretty good for torsion but not as effective for bending in the vertical orientation. A horizontal mill fixes that problem, but it's just a machining exercise, since a tube is far easier and stiffer for the important loading modes (Ixx, Iyy, J).
    I've never had experience with Mic-6 being gummy. In fact, I've found it makes nice small chips, not long and stringy like some other aluminum. For "gummy" aluminum I try to use a low helix endmill to aid with chip-breaking.



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    Default Re: Y Gantry Twist

    Quote Originally Posted by dmalicky View Post
    Certainly, machining can be done to lighten a solid Mic-6 plate. Consider 2 things, though:
    - Mic-6 is dead soft, so it's gummy to machine.
    - Pocketing will reduce weight and bending stiffness in ~equal proportions, so there will be no net gain in its ability to manage its own weight. I.e.:
    I = (1/12) * b * h^3
    Weight = density * length * b * h
    Pockets remove b from both terms. So both go down equally. And J (torsional) will go down faster.
    A horizontal mill could remove the mid-portion of the beam while it is oriented upright (so it doesn't sag due to self-weight); this could make an I beam which would be stiff and light for vertical bending. But I beams have horrible J, and mediocre I in the other orientation.

    There are only 2 ways to lighten it and preserve J:
    - Bore it out from each end. I.e., make it into a tube. (not a serious suggestion for something this big)
    - Mill out a triangulated pattern, as sometimes used in (clever) cast-iron lathe beds: http://www.lathes.co.uk/nuttall/img2.jpg
    But doing that on a vertical mill leads to even more bending deflection due to its own weight. Those diagonal webs are pretty good for torsion but not as effective for bending in the vertical orientation. A horizontal mill fixes that problem, but it's just a machining exercise, since a tube is far easier and stiffer for the important loading modes (Ixx, Iyy, J).
    I have machined mic6 before, and it produces good chips. When I was referencing pockets, I was thinking of designs similar to bridges to allow for a better strength to weight ratio. As far as machining it, it will be easiest to toe clamp the mic6 plate to a CNC machine for all of the machining. While it may take a couple of setups, ie relocating toe clamps so you don't machine them, it will be much better than a vice. (Note: While the mic6 plate won't be 100% parallel to the machine X/Y axis, it can be taken care of by measuring the angle offset and executing a G68 command). This will also allow for a single setup (Pocketing can be completely done if they put a piece of shim stock under the mic6 plate), and the rest can be milled peripherally.

    The above post comes from the mind of a mechanical engineer student. You are warned.


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    Default Re: Y Gantry Twist

    Quote Originally Posted by dmalicky View Post
    Certainly, machining can be done to lighten a solid Mic-6 plate. Consider 2 things, though:
    - Mic-6 is dead soft, so it's gummy to machine.
    - Pocketing will reduce weight and bending stiffness in ~equal proportions, so there will be no net gain in its ability to manage its own weight. I.e.:
    I = (1/12) * b * h^3
    Weight = density * length * b * h
    Pockets remove b from both terms. So both go down equally. And J (torsional) will go down faster.
    A horizontal mill could remove the mid-portion of the beam while it is oriented upright (so it doesn't sag due to self-weight); this could make an I beam which would be stiff and light for vertical bending. But I beams have horrible J, and mediocre I in the other orientation.

    There are only 2 ways to lighten it and preserve J:
    - Bore it out from each end. I.e., make it into a tube. (not a serious suggestion for something this big)
    - Mill out a triangulated pattern, as sometimes used in (clever) cast-iron lathe beds: http://www.lathes.co.uk/nuttall/img2.jpg
    But doing that on a vertical mill leads to even more bending deflection due to its own weight. Those diagonal webs are pretty good for torsion but not as effective for bending in the vertical orientation. A horizontal mill fixes that problem, but it's just a machining exercise, since a tube is far easier and stiffer for the important loading modes (Ixx, Iyy, J).
    I thought you were referencing round tube...not rectangular tube (thanks louie).

    The only thing I don't like about rectangular tube is the tolerances. To be more precise, I don't like the wrapping that comes with tubing. While I understand I can always use shim stock, I feel like it would be a major PITA to get precisely straight.

    Last edited by OneWound; 04-19-2016 at 01:28 PM.
    The above post comes from the mind of a mechanical engineer student. You are warned.


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    Default Re: Y Gantry Twist

    I believe Dave is referring to rectangular tube...



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    Default Re: Y Gantry Twist

    That's good to hear you two did not have any problems with Mic 6. I didn't find it bad, but it tended to stick to tools in some ops. Probably need a better process, or maybe the Mic 6 I've had wasn't really Mic 6. Still, there are many complaints on practical machinist about it. I'd certainly use it for parts with normal machining, but pocketing 100+ lbs of it seems risky to me.

    On the gantry, yes, there are many triangulation variations to get good stiffness. Of course, they key is no 'open' faces (4-sided). So yes, milling a solid 3x8 bar into a "truss bridge" would result in a good stiffness to weight ratio, if the roof and floor of the bridge do not have open faces (real bridges often do). But it is remarkable waste of material, $, and machine time. And even Mic 6 may distort after removing so much of its volume.

    Only the rail and 'foot' mounts need to be high accuracy surfaces. As described on page 1, all commercial and DIY routers have standard solutions for tube warp. Easiest is to attach (epoxy, bolt, and/or rivet) sacrificial strips (for rails) and pads (for feet), then machine those level. Commercial and some DIY routers weld on the strips and pads, but then the gantry needs to be stress relieved. Or get a T-slot extrusion like most DIY routers -- these are straighter than normal tubes, and can be spec'd with flattened rail surfaces. The Hardwoods thread has specifics.

    Finally, this is a thread that I don't understand. For example, I haven't seen real consideration of gantry alternatives; instead the focus keeps returning to billet machining. Maybe there just isn't much spare time now to put into this project.

    David Malicky


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    Default Re: Y Gantry Twist

    Quote Originally Posted by dmalicky View Post
    That's good to hear you two did not have any problems with Mic 6. I didn't find it bad, but it tended to stick to tools in some ops. Probably need a better process, or maybe the Mic 6 I've had wasn't really Mic 6. Still, there are many complaints on practical machinist about it. I'd certainly use it for parts with normal machining, but pocketing 100+ lbs of it seems risky to me.

    On the gantry, yes, there are many triangulation variations to get good stiffness. Of course, they key is no 'open' faces (4-sided). So yes, milling a solid 3x8 bar into a "truss bridge" would result in a good stiffness to weight ratio, if the roof and floor of the bridge do not have open faces (real bridges often do). But it is remarkable waste of material, $, and machine time. And even Mic 6 may distort after removing so much of its volume.

    Only the rail and 'foot' mounts need to be high accuracy surfaces. As described on page 1, all commercial and DIY routers have standard solutions for tube warp. Easiest is to attach (epoxy, bolt, and/or rivet) sacrificial strips (for rails) and pads (for feet), then machine those level. Commercial and some DIY routers weld on the strips and pads, but then the gantry needs to be stress relieved. Or get a T-slot extrusion like most DIY routers -- these are straighter than normal tubes, and can be spec'd with flattened rail surfaces. The Hardwoods thread has specifics.

    Finally, this is a thread that I don't understand. For example, I haven't seen real consideration of gantry alternatives; instead the focus keeps returning to billet machining. Maybe there just isn't much spare time now to put into this project.
    I ran FEA testing on a new beam design, with 20"x72"x2.5". A load was applied at the CG with the weight of the beam, and a weight of 150 pounds was placed simulating the weight of Z-Axis assembly. Deflection was 6.867x10-4.

    The reason I don't want to know with extruded aluminum is due to deflection. I can build a more rigid machine if I use heavy (that term being relative) gantry, I can take deeper cuts, move faster, etc. I do understand this comes at the cost of top speed of the servo, but this is something that would be beneficial. To give a nice example of this, I'd rather be able to take 1" DOC at 250 IPM rather than .375" at 500 IPM. More efficient use of time, IMHO.

    I don't quite understand how Mic 6 will distort as you say. Since Mic 6 is stress relieved, and it is machined on a flat surface (with no edges of the Mic 6 hanging off a table), how could it bend? Also, the Mic 6 would be nice to waterjet the main "truss" sections out, leaving .050 cleanup for a machining company to clean up. When the machining company cleans up the pocket, they can drill and tap all holes required for mounting to the X axis gantry. One benefit of this is that the pockets of Mic 6 can be reused for other components in the design.

    Let me also discuss as to why I want to stick to using huge pieces of stock. If I were to go with rectangular tubing, I have this feeling in would be a major PITA to level the danged thing. We, we being the people who will eventually assemble this, will probably take a couple days to make it perfect (or as close to it as we can). If I were to machine it, it would be think enough for deflection to be a worry. Another issue I find with rectangular tubing would be the outer radius on the square. While I understand they most likely will be well within their spec, betting on a component to be within tolerance and not mess up the assembly process seems like a bad idea in general. I wish we could cast a y-gantry base, but that is not feasible. Besides the issues of having to find a company to do a mold that big, edges would also have to be machined to get rid of the casing surface. This sounds worse than machining the Mic 6. Are there any fallacies that I am assuming in the above paragraph?

    While you are correct that I don't have as much free time as before, work will still continue. I'm trying to find a solution that most people within this forum mostly agree to a solution to the Y-Gantry & a design for the CNC, while not all ideas may take form in CAD, discussion (or telling me I am wrong as it should be) still helps the continual design process for this CNC.

    The above post comes from the mind of a mechanical engineer student. You are warned.


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    Default Re: Y Gantry Twist

    That's good you've run a simulation. 20" x 2.5" is not a strategic cross-section for the loading a gantry experiences. Gravity load is the easiest and should be of little importance, once the machine has been made stiff. The vector load at the cutter is what matters. Generally a square cross-section is the most strategic use of material for the gantry, for the bending and torsion loads it experiences. A rectangular section is also reasonable, if it is no taller than a 2:1 aspect ratio. I suggested a T-slot extrusion because there is indeed one option from Misumi that should be stiff enough for your machine. But all of that is in the Hardwoods thread -- you need to do some independent research to understand the problem you are trying to solve. There's little value in designed or running FEA when the mechanical requirements are not well understood.

    Mic 6 has very low residual stress, but I don't know if we can count on it to be Zero. Even a temp variation during clamping would be enough to generate thermal stress when machining. And machining itself creates residual stresses on every machined surface. Normally all of these are tiny and can be ignored, but 0.005" over 72" is similarly tiny, and you're planning on massive machining, so these effects could be important. A efficient hollow cross-section with very high I and J, requiring minor machining, is just more likely to stay stable, and it is a proven design and method. The current gantry design is in new territory -- it may work just fine, but since it is new it has intrinsic risks.

    Waterjet is indeed much smarter for the process, but triangular scrap tends to not be so useful.

    It's clear you have a strong opinion about tubing. I don't know why you feel it would be such a pain to level the important surfaces. I've already described the standard methods that everyone else does -- and we don't consider it a pain.

    I'm not following the concerns on "If we were to machine it.... deflection to be a worry", "outer radius on the square". Or how a cast base is important to this question.

    David Malicky


  18. #58
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    Default Re: Y Gantry Twist

    I think there's too much worry about splitting hairs. If you took your Mic-6 plate, and got supported linear shafting, the support base is aluminum as well, and you'll likely "even out" any irregularities when mounting it, at least enough for practical purposes. You wouldn't even need to surface Mic-6 (it's already Blanchard ground) so unless you have access to a Blanchard grinding machine it'll be tough to duplicate. Just drill the mounting holes for the rail supports. You can make all your attachments referenced off the face of the Mic-6, even the gantry legs, thus removing one variable from the equation.

    I wouldn't even worry about weight. If you use rack and pinion you can enjoy a high mechanical advantage and run the gantry as fast as you want. CarveOne built a large table with a heavy gantry and ran it with NEMA23 steppers. Changed out only because the shafts on the cheap steppers snapped off.

    Here's an older build but classic! He uses expensive ground ballscrews however that would blow your budget today. Also, he was able to attach his linear rails without the aid of CNC.
    MadVac CNC - home made 4'x8' cnc precision gantry router



  19. #59
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    Default Re: Y Gantry Twist

    Interesting thread this, not that it bares much relevance to me as I never plan to build my own machine.

    Did this ever get finished?



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