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Thread: Large Epoxy Granite Vertical CNC Mill

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    Default Large Epoxy Granite Vertical CNC Mill

    I've been planning to build a serious vertical CNC mill for a while now. I have a Sieg X2 which is pretty useful but every time I use it I have to deal with the small table, small travel, low rigidity, adjusting gibbs, imprecise z-axis positioning, low power, etc, etc. The new mill is designed to eliminate all of these problems as much as possible. The design considerations are as follows:

    • massive bed and column made of epoxy granite to improve rigidity and dampen vibration
    • move on linear guide rails on all axes (20mm or larger, no more gibbs!)
    • driven by ball screws (20mm diameter)
    • and large stepper motors (Nema 34)
    • much larger working envelope (~250 x 500 mm)
    • full size cat 40 vmc spindle (6000rpm)
    • powerful DC spindle motor (3hp)
    • pneumatic actuated draw bar
    • CNC as well as manual operation


    Here are some drawings of the design I've come up with.

    Large Epoxy Granite Vertical CNC Mill-1-png Large Epoxy Granite Vertical CNC Mill-6-png Large Epoxy Granite Vertical CNC Mill-9-png
    Large Epoxy Granite Vertical CNC Mill-4-png Large Epoxy Granite Vertical CNC Mill-3-png Large Epoxy Granite Vertical CNC Mill-2-png
    Large Epoxy Granite Vertical CNC Mill-7-png Large Epoxy Granite Vertical CNC Mill-5-png Large Epoxy Granite Vertical CNC Mill-8-png
    The z-axis head is not fully designed yet, the spindle motor and pneumatic cylinder are roughly placed!

    All brown-ish colored parts will be made of epoxy-granite cement with internal steel reinforcements. Grey-colored components are steel or aluminum.

    To give you an idea of the size, the vise sitting on the table is a standard Kurt 6" angle lock.

    The base is ~ 250 x 460 x 880 mm with a weight of about 150kg.
    The column is ~ 305 x 460 x 1090 mm and weighs also around 150kg
    The saddle is ~ 95 x 240 x 820 mm and weighs about 50 kg.
    The table is the same size as the travels, that is ~250 x 500 mm and will be made of solid steel.

    The exact dimensions of the mill are given by the sizes of the linear rails and ball screws that I happened to have in my "collection"!

    I will keep adding more posts as I make progress on the mill.

    Any comments, suggestions or questions are welcome!


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Looks like a really interesting build. Any reasoning behind the hollow core in the column? It looks like one complex mold to build, you'd have to cast the entire column from top to bottom to maintain that hollow core, instead of laying it on it's back like what is more commonly seen. You maybe thinking of cost savings but it sure looks like a headache! Also, I'm not quite sure how well you could consolidate the EG from the the top down. I couldn't see it filling those webs near the mounting bolts. Also, what's the hollow core in the head for?

    Also, what are you going to mount the rails to? You may want to consider adding some sort of machinable bar stock into the mold so that a true, flat and parallel surface can be machined afterwards. Don't count on the EG being 100% flat and true right out of the mold.

    Just my 2 cents though..

    Devin



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Those are some good points.

    1. The holes in the column and head are simply to reduce weight while at the same time not affecting rigidity too much. My plan was to cast the column sideways. Put some epoxy granite then simply insert a styrofoam core, then continue pouring on the side of it and the top. The styro will stay there or can be dissolved out.

    2. The rails will be bolted directly to the EG face and the bolts will screw into anchors inserted into the mold before casting. The surface of the EG casting can be "ground" using diamond coated metal surfaces (i.e. lapidary discs). The plan is to use a reference straight edge (and/or surface plate) to check and guide the grinding process.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    To make such large epoxy granite (EG) castings one needs a LOT of epoxy... And here it is, freshly delivered from US Composites in Florida (I live in California).

    Large Epoxy Granite Vertical CNC Mill-dsc_0001-jpg

    And after un-packaging you have a lot of thin, slow curing epoxy and hardener in 1 gallon bottles. White is the epoxy and yellow is the hardener. They are to be mixed in a 2:1 ratio, 2 parts epoxy and 1 part hardener.

    Large Epoxy Granite Vertical CNC Mill-dsc_0004-jpg

    The bottles are very well capped and covered with Scotch to make sure they will not leak during shipping which as you imagine would be a disaster inside the UPS truck!



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Nice build! Will definitely follow this closely! How much did those boxes cost you?



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Some more thoughts:
    I like the idea with hollows but you know normal consumer styrofoam cannot handle epoxy. It will dissolve and most likely destroy your casting. You need to find an alternative that is suitable for epoxy. Have a look at Divinycell, it's made for epoxy.

    I think grounding E/G is a lot harder to get a good result from than simply putting a bar of steel and have it surfaced.

    Skickat från min GT-I9300 via Tapatalk



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    This epoxy cost about $790. It's not all going to be used for the mill though, there's too much for that, some of it is actually going to be used by somebody else for another build.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Here's a bit of history as to how I got to thinking about building this milling machine.

    A number of years ago I took apart a few printers and removed from them anything that could be useful: cables, steel rods, power supply assemblys and motors. Some of those motors were stepper motors and I was wondering how can you make them move and what could I do with them? One thing led to another and I ended up building this CNC router (its not complete yet in this picture).

    Large Epoxy Granite Vertical CNC Mill-dsc02378-copy-jpg

    This machine worked and I used it for a few things but the flimsy MDF construction, the linear rails made of gas pipes and skate bearings and the acme screws with hand tapped plastic nuts did not make it a very reliable or precise machine! So I gave up on it and made another, smaller CNC mill using actual linear actuators for all 3 axes and mounted everything to a epoxy granite L shape structure.

    Large Epoxy Granite Vertical CNC Mill-dsc_0016-jpg Large Epoxy Granite Vertical CNC Mill-dsc_0014-jpg

    Here's how the base was cast. First the mold was filled with EG from the side, then it was covered up, turned vertically and filled completely. The car tire there is the "vibrating table", there is a motor with an excentric weight under the wood board, in the middle of the tire.

    Large Epoxy Granite Vertical CNC Mill-dsc_6129-jpg Large Epoxy Granite Vertical CNC Mill-dsc_6178-jpg Large Epoxy Granite Vertical CNC Mill-dsc_6205-jpg


    This worked much more reliably than the MDF one. Here it is with a 4th axis mounted to the table and engraving graduations on a dial for a rotary table! It could also do a little more serous cuts in aluminum (not too serious though!).



    But, this machine is tiny with its 4"x9" table and not much head to table distance, especially when the 4th axis is added. It also cannot take a 1" deep cut in steel easily... or not at all.

    And this is why I "need" a much larger CNC mill !


    Last edited by petruscad; 02-11-2015 at 05:13 PM.


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    For the hollow column section, you should consider using a inner steel tube and attach the steel-reinforcement bars in the epoxy matrix to it. This will allow the torsion force to be transmitted to the more rigid inner tube. Also this will simplify mold making since now you have a reference inner mold that you don't have to remove after curing.

    Just curious, did you go through the whole epoxy granite mega thread. I sort of given up on a epoxy granite frame because all the effort seems too much for me. I opt instead on steel tubing filled with easier to prepare epoxy mix and even non-expanding cement since epoxy can get expensive especially for the dimensions that you are going for. Also care to share what your mix is going to be?



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Winterwatchers View Post
    For the hollow column section, you should consider using a inner steel tube and attach the steel-reinforcement bars in the epoxy matrix to it. This will allow the torsion force to be transmitted to the more rigid inner tube. Also this will simplify mold making since now you have a reference inner mold that you don't have to remove after curing.

    Just curious, did you go through the whole epoxy granite mega thread. I sort of given up on a epoxy granite frame because all the effort seems too much for me. I opt instead on steel tubing filled with easier to prepare epoxy mix and even non-expanding cement since epoxy can get expensive especially for the dimensions that you are going for. Also care to share what your mix is going to be?
    I was thinking that too. either a 3x3 steel tube, or maybe a 4x4 wooden post in the middle?

    oh... and lol @ "giant mega thread"



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    but you know normal consumer styrofoam cannot handle epoxy. It will dissolve and most likely destroy your casting.
    Epoxy does not dissolve foam. Polyester resin does.
    WEST SYSTEM - Projects - The "lost foam" method of composite fabrication

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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Hmm, I did not think about using a square tube as an "internal skeleton" but its definitely a good idea. I have to calculate the weight and cost of that steel vs. just filling the whole space with EG. If it ends up similar I may just make it solid EG!

    Yeah, I did go through the EG thread! Well, I didn't actually read the whole thing but mostly looked at pictures and aggregate formulas to see how they came out. The main information could be extracted out of that thread and it would be less than a page!

    Your're right, epoxy is expensive and the aggregates can get very fancy and expensive too. Actually, people make too much fuss about the properties of aggregates, their composition (zeospheres, precision grain size, etc), proportion of epoxy resin, frequency of vibration, degassing, etc, etc. In practice, in your garage, you're never going to stress that casting to its maximum failure point, so a cheaper, simpler, saner formulation and method works quite fine. I will share my formula once I get closer to casting the base.



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