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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Eldon_Joh View Post
    Z axis rails should be as far apart as the Y axis rails.. no reason to make one more floppy than the other.
    Seems like a good point at first glance. A few observations though.

    1. The Y axis needs to be wider because it supports the weight of the saddle and the table+vise+workpiece which can travel from one end to the other. In other words these can be large momenta twisting the saddle, so you need need wider base. The weight of the Z axis on the other hand is directed down so column torsion would only be created by cutting forces.

    2. Commercial vertical milling centers do not seem to generally follow this rule. Some have almost the same spacing for Y and Z rails while others do not, like the one bellow:
    Large Epoxy Granite Vertical CNC Mill-nfv-skeleton-big-jpg

    I have a little wiggle space for the column, it is currently 10" wide at the top, I can make that 12" add add 2" between the rails. Another option is to make the head a little wider than the column so the rails can be moved further away from each other.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Voyager77 View Post
    1) A wider base could be beneficial to mate with the base / stand and reduce vibrations
    Well, the mill is already very heavy, heavier that the Tormach PCNC 1100, so it will have to stay the way it is.

    Quote Originally Posted by Voyager77 View Post
    2) The hollow column could be difficult to make. Keep in mind you need to vibrate the mold to compact E/G. Consider a face-down approach that is either solid or adds a mold-lid with profile that is added last to add recesses into the back of the column. You could also cast a tube inside the column for cables, air hoses, etc...
    I will probably still go with the hollow column but increase the wall size to 2.5". Hoses and cables can be passed through the middle.

    Quote Originally Posted by Voyager77 View Post
    3) Consider getting the head made from solid steel. In effect this could be a precision ground plate with mount for a spindle. I don't see E/G adding benefit in this particular application, more a limit on what spindles you can install.
    My idea, and this will sound crazy, is to cast the head around the spindle, forever bonding the spindle in. This will have the greatest strength and vibration absorption. I don't think I will ever want to replace the spindle, at least not with the same one I have which I'm very unlikely to find another.

    Quote Originally Posted by Voyager77 View Post
    4) Consider making the Y axis saddle from steel. I would also flip this around to create a smaller cross plate with a bigger table on top. This would give you more space on the table for clamps, vices, etc and hide / protect the ballscrew on the underside.
    I seriously thought about making it from steel as well. The weight would be crazy though, so I opted instead for EG with a serious internal skeleton made out of steel.

    Flipping the saddle is a no go. Every vertical machining center is designed this way for a very good reason. It provides the maximum support for the saddle at all positions, improving rigidity. In a reverse arrangement (like in a Bridgeport-type mill) when you move the table to one end its whole weight is creating a torsion momentum that acts on the rails/slides. This can lead to bending of the entire table severely limiting precision.

    The table size is made only slightly larger than the travel of the machine on purpose. This is so I can use the machine itself to mill the top of the table flat and cut the T-slots into it. I do not want to use any tool (less a machine shop!) that I don't already have in my garage. I also like the idea of using the machine to build itself!

    Quote Originally Posted by Voyager77 View Post
    5) Allow ample space for oiling system, cables for way switches, chip guards. You don't want this to look like an afterthought.
    Yeah, its hard to design these ahead of time, too much crap to think about. There is plenty of space between components so hopefully switches, cables, oiling hoses, way covers could be installed in a decent way after the main structure it in place.

    Quote Originally Posted by Voyager77 View Post
    6) In theory, to maximise the E/G benefit, you would want vibrations from the head & column to transfer into the base via a wide mating surface. I like how you have tucked away the Y axis motor but this reduces the mating surface of the two major E/G components.
    Yeah, this makes sense. Commercial castings vary greatly on what kind of bearing between the column and base they use. None has a single large contract plane because of two factors I think: 1. Hard to machine such a large surface to the tolerance needed for good contact and 2. The weight would be too large. What I should do though is to make the bottom part of the column beefier by lowering the recess between the two legs of the column.

    Quote Originally Posted by Voyager77 View Post
    7) Have you made test casts yet? Any plans for a vibration table?
    I will use a motor with an off-center weight that will be bolted straight to the bottom of the mold.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Don't forget to design in provisions for lifting the parts. Some have eyelets and some have through holes for inserting a pipe into and the ends are used as lift points. Tow straps can always be used, but they are not very elegant.

    Lee


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Yes I understand the reasons you gave for the Y axis saddle to be wider than the Z axis but you aren't machining the rail mounting surfaces to a tenth, so any error in the rail position is amplified by the narrow rail spacing.

    unless you intend to use this machine to resurface 500 pound anvils, the weight is of no practical concern, from your drawings it looks like the center of mass is still inside the rails, even with the table fully off to one side, if the bearing blocks are supposidly good to.. what? 20 kilownewtons or 4000 pounds? i think mine are only 30mm long so there is only 20 x 1/8th inch dia balls touching the rail at any given time, so its only good to about 1000 pounds.

    Anyhow my experience has been that when you bolt the rail down to the epoxy you're going to get a wave in the rail of about half a thousanth minimum, simply due to the epoxy surface imperfections compressing under the rail.

    anyway for the Z axis i would put the rails as far apart as the distance between the spindle is to the column minimum.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Nice idea you have there petruscad. I think you're crazy though for not wanting to go with solid base, column, and head! Do the cavities really save much money? Increased rigidity, damping, stability, and casting simplicity must surely outweigh the $$$?

    I know nothing about mounting rails straight to E/G but surely processing steel plates cast into the frame would be easier than E/G with inserts... The steel should also spread the forces from the rails to the E/G more evenly doing away with the problems Eldon_Joh expressed.

    Where are you getting the 40 taper spindle from? And what's it costing you?

    Cheers, Fenza



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Fenza CNC View Post
    The steel should also spread the forces from the rails to the E/G more evenly doing away with the problems Eldon_Joh expressed.
    and much more work to scrape the surface to fit.. although you could buy some free machining steel with lead in it.. that stuff cuts like butter lol.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    I learned through experience that linear rails are not straight, even the precision grade ones. I had to show my boss to make him believe me. The hardening process for those rails naturally makes them warp slightly. For way precision, you should consider anchoring steel plates with rail guides to the epoxy for mounting rails. Mounting the rails directly to the epoxy will result in a lot of headache trying to align everything straight. Rail guides are extremely important. Take a look at reference in link

    https://tech.thk.com/en/products/pdf/en_a01_432.pdf#1

    I understand why you would want the mount the table on a long saddle, however with proper setup, most inverted long tables can achieve accuracy within 0.001" which is good enough for many types of work. Most small sized VMC like HAAS use that setup too. Usually large VMC like the one in your picture or precision die making versions use the supported approach. I guess it depends on what level of accuracy you are trying to achieve and what you plan to do. Re:Eldon_Joh, I did a calculation back years ago on THK linear guides, and in order to make one slider deform 0.001" you need to apply the weight of a small car and this is on C2 grade clearance which is basically minimum preload. I don't know what kind of Hiwin rails you got there, but unless they are worn, they should perform similarly.

    You can buy a new table from sources like grizzly or others and basically drill your own holes for rails or search ebay religiously. either way having a good table that you know is flat is one less thing to consider when things don't line up during assembly.

    If you want to strengthen the column a bit, you can make the bottom recess between legs of the column an arch instead of a rectangular cutout or simply give it more fillet.

    To know if the z axis rails are at a good distance go the THK website and use their calculators with estimated load of 500lbs. Just make sure that the 2 sliders on the same rail is further apart from each other than the distance between two rails.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Eldon_Joh View Post
    Yes I understand the reasons you gave for the Y axis saddle to be wider than the Z axis but you aren't machining the rail mounting surfaces to a tenth, so any error in the rail position is amplified by the narrow rail spacing.
    I agree with the broad comment, however most linear guides compensate somewhat for the imprecision of their mounting surfaces. So if the mounting surface dips .0004" in the middle, you will only see .0002" with the linear guides installed. You just have to make absolutely sure that the mounting surface uneven surface is within the tolerance of the precision grade of linear guides.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Something you can do... with the internal steel tube... Fill it with concrete. concrete is cheap, and it will most CERTAINLY deaden your structure. Not to mention it will have different resonance then the EG, which I have read can have 3 different resonances (depending on the aggregate) so this will add more weight and rigidity. Oh, did I mention concrete is cheap? A square steel tube suspended in the EG will fill easy enough for a few dollars.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Weight is your friend. The more mass your mill has, the less it is affected by vibration and chatter. A heavy structure also helps if you want to drive your axis with powerful motors and achieve higher speeds. You can pick up a 2t pallet jack cheaply to move the mill around in a garage if necessary. I would not want a machine that is convenient during 1% of its service life but falls short during the remaining 99%.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    What aggregate are you planning to use in your polymer concrete? Will you be buying a pregraded, optimised commercial aggregate like Silimix 262, or making up your own?

    Regards,
    Mark


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Fenza CNC View Post
    Where are you getting the 40 taper spindle from? And what's it costing you?
    I bought a Mazak VQC 15/40 cat 40 spindle from eBay for $250 (including shipping). The pull stud grippper is missing though, so I'll have to machine it.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Winterwatchers View Post
    Just make sure that the 2 sliders on the same rail is further apart from each other than the distance between two rails.
    What's the rationale for this?



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by RotarySMP View Post
    What aggregate are you planning to use in your polymer concrete? Will you be buying a pregraded, optimised commercial aggregate like Silimix 262, or making up your own?
    I will use my own aggregate, I'll post the formula with pictures later.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    I have just started making a formula based on the various graded sand/pebble I can get at the hardware store, using a Fuller curve xls, from Thomas Zietl.

    Regards,
    Mark


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Alright, its time to start building something! Or, at least to start thinking of building something. The build steps/strategy is going to be like this:

    1. Cast the base of the mill
    2. Make a stand and lift the base on it
    3. Grind the base and install the Y-axis rails
    4. Cast the saddle
    5. Grind the saddle all-around and install the X-axis rails
    6. Install the saddle on the Y-axis rails: scrape mating surfaces, make housing for Y-screw nut and mount it.
    7. Buy a piece of steel, scrape it to a plane on one side and bolt it to the rails; this is (or will become) the table
    8. Make a housing for the X-screw nut and install the screw after scraping mating surfaces.
    9. Mount the Nema 34 stepper motors
    10. Wire the electronics for the X- and Y- axes and do some moves (carefully, since there are no limiting switches! Or maybe install them as well...).
    11. Cast the column
    12. Grind the column and install the Z-axis linear rails
    13. Figure out how to mount the column perpendicular to the Y-axis rails... and then do that. (any ideas how?)
    14. Cast the head around the spindle.
    15. Grind the head mounting pads until the spindle axis is parallel to them (any ideas how?). Install the head.
    16. Make a hosing for the Z-screw, scrape mating surfaces and install the screw.
    17. I may need an electromagnetic clutch on the Z-screw to prevent the head from back-driving the screw and falling down!
    18. Install Z-axis motor and electronics and play with it.
    19. Make and install the oil mist lubrication system for the spindle
    20. Mount spindle motor and make the spindle turn (oh yeah, I will need a driver for the motor).
    21. Make the gripper assembly for the spindle which is missing
    22. Install the air cylinder and get it to grip and release the cat 40 tool holders.
    23. First cuts! Push the cuts faster and deeper in aluminum and then steel to find the limits of the machine. Wait, how do I hold the material down since the table does not have T-slots?
    24. Cut the T-channels in the table with the machine itself (cover the ways temporarily with something).
    25. Surface the table top.
    26. Make way covers for all axes.
    27. Make some electronics to make it easy to use the mill in manual and semi-manual mode as well.


    Does this seem like a good plan? Are there enough steps!? Of course not all steps have to be done in this order and by the end there will probably be many more steps!

    Well, in any case the amount of work is daunting. It will probably take me several years to complete this build and this is assuming that I don't get tired of it and abandon it in the middle. The hardest thing I think is going to be the grinding and scraping of the surfaces for rail mounting and mating surfaces. And the hardest part of that is going to be deciding when to stop trying to get better precision, alignment, perpendicularity, etc. I mean without using otherworldly tools (large surface plates, cranes to lift the heavy parts to place them on the surface plates, many precision edges, large precision squares, large machining centers, etc.) there will be a limit to how much precision can be achieved in a reasonable amount of time. Under these circumstances I could see myself getting frustrated not being able to achieve perfection and then give up. I guess I'll just see how it goes...




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    Default Re: Large Epoxy Granite Vertical CNC Mill

    column alignment
    Principles of Rapid Machine Design
    page 83
    page 84
    http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf



    http://www.cnczone.com/forums/attach...3&d=1317502554



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    Default

    Quote Originally Posted by petruscad View Post
    Alright, its time to start building something! Or, at least to start thinking of building something. The build steps/strategy is going to be like this:

    1. Cast the base of the mill
    2. Make a stand and lift the base on it
    3. Grind the base and install the Y-axis rails
    4. Cast the saddle
    5. Grind the saddle all-around and install the X-axis rails
    6. Install the saddle on the Y-axis rails: scrape mating surfaces, make housing for Y-screw nut and mount it.
    7. Buy a piece of steel, scrape it to a plane on one side and bolt it to the rails; this is (or will become) the table
    8. Make a housing for the X-screw nut and install the screw after scraping mating surfaces.
    9. Mount the Nema 34 stepper motors
    10. Wire the electronics for the X- and Y- axes and do some moves (carefully, since there are no limiting switches! Or maybe install them as well...).
    11. Cast the column
    12. Grind the column and install the Z-axis linear rails
    13. Figure out how to mount the column perpendicular to the Y-axis rails... and then do that. (any ideas how?)
    14. Cast the head around the spindle.
    15. Grind the head mounting pads until the spindle axis is parallel to them (any ideas how?). Install the head.
    16. Make a hosing for the Z-screw, scrape mating surfaces and install the screw.
    17. I may need an electromagnetic clutch on the Z-screw to prevent the head from back-driving the screw and falling down!
    18. Install Z-axis motor and electronics and play with it.
    19. Make and install the oil mist lubrication system for the spindle
    20. Mount spindle motor and make the spindle turn (oh yeah, I will need a driver for the motor).
    21. Make the gripper assembly for the spindle which is missing
    22. Install the air cylinder and get it to grip and release the cat 40 tool holders.
    23. First cuts! Push the cuts faster and deeper in aluminum and then steel to find the limits of the machine. Wait, how do I hold the material down since the table does not have T-slots?
    24. Cut the T-channels in the table with the machine itself (cover the ways temporarily with something).
    25. Surface the table top.
    26. Make way covers for all axes.
    27. Make some electronics to make it easy to use the mill in manual and semi-manual mode as well.


    Does this seem like a good plan? Are there enough steps!? Of course not all steps have to be done in this order and by the end there will probably be many more steps!

    Well, in any case the amount of work is daunting. It will probably take me several years to complete this build and this is assuming that I don't get tired of it and abandon it in the middle. The hardest thing I think is going to be the grinding and scraping of the surfaces for rail mounting and mating surfaces. And the hardest part of that is going to be deciding when to stop trying to get better precision, alignment, perpendicularity, etc. I mean without using otherworldly tools (large surface plates, cranes to lift the heavy parts to place them on the surface plates, many precision edges, large precision squares, large machining centers, etc.) there will be a limit to how much precision can be achieved in a reasonable amount of time. Under these circumstances I could see myself getting frustrated not being able to achieve perfection and then give up. I guess I'll just see how it goes...
    It may be easier to cast some strategically placed cast iron plates into your mold and anchor them to your casting, and it would be easier to scrape those surfaces instrad of the e/g...



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by louieatienza View Post
    It may be easier to cast some strategically placed cast iron plates into your mold and anchor them to your casting, and it would be easier to scrape those surfaces instrad of the e/g...
    Yes, I will place steel plates into the EG for the ballscrew fixed support mounting surfaces and for the ballnut hosing mounting surfaces. The linear rails, though, will be mounted straight to the EG.

    Last edited by petruscad; 02-19-2015 at 02:40 PM.


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Thanks for posting this- keep the pics and updates flowing



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