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Thread: Large Epoxy Granite Vertical CNC Mill

  1. #61
    Member nateman_doo's Avatar
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    Default Re: Large Epoxy Granite Vertical CNC Mill

    The week just won't go by fast enough will it?? can not wait to see this thing.



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    Default Re: Large Epoxy Granite Vertical CNC Mill



    You guys have been very patient the whole week waiting for the epoxy to solidify. I think you deserve an update.

    Here it is still sitting on the supports with some side boards removed. You can see the six steel feet sticking out. Four of them have holes for large locking pins that will locate the base onto the stand (which is yet to be built).

    Large Epoxy Granite Vertical CNC Mill-dsc_0024-jpg Large Epoxy Granite Vertical CNC Mill-dsc_0025-jpg

    Removing the side boards was easy. I just took the screws out and yanked them off in one piece. The middle boards, top and bottom, are a very different story. They are squeezed between the sides of the base so removing them was a lot harder, but with hammers and chisels and pry bars they did come out with absolutely no damage to the part. Then the two rectangles were removed they same way, slowly but surely... Anyway, here is the final result!

    Large Epoxy Granite Vertical CNC Mill-dsc_0026-jpg

    The six pipes sticking out are the holes through which the column is going to be bolted to the base. The steel plate in the middle is where the Y-axis ball screw and motor are going to be mounted to.

    The surface is pretty smooth but not entirely free of air pockets. However, I don't think that some air inclusions will be a problem. They may help dampen vibration even better!

    The next step is to make a stand on which the mill will rest and lift the base up onto it before the grinding flat can begin.





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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Looks excellent.

    Regards,
    Mark


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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Looks great- following your progress with great interest. You cast in steel feet for the bottom, how are you attaching the rails for the top?



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    Default Re: Large Epoxy Granite Vertical CNC Mill





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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Looks great!

    Skickat från min GT-I9300 via Tapatalk



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by gt40 View Post
    how are you attaching the rails for the top?
    There are some large bolts embedded in the cast just bellow the surface. I will drill the EG out to expose the top of the bolts then drill into them and tap the holes. The rail will bolt into that.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by petruscad View Post
    There are some large bolts embedded in the cast just bellow the surface. I will drill the EG out to expose the top of the bolts then drill into them and tap the holes. The rail will bolt into that.
    Um - just checking I understand...
    You mean you put large fat bolts with threads in the EG, and you will drill and tap into the middle of those large fat bolts for a smaller size bolt?
    Kinda cute.

    Cheers
    Roger



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Rcaffin i agree that's a lot of work, i would have done it differently, in hindsight since i've only done this once.... you know the tolerance you get for sending 6mm bolts through a 6mm "clearance" bolt hole in the linear rail is pretty small if all you got is a drill press and a center punch.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Your casting really looks awesome- can you share how much epoxy you ended up using for the base and aggregate



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by RCaffin View Post
    You mean you put large fat bolts with threads in the EG, and you will drill and tap into the middle of those large fat bolts for a smaller size bolt?
    Roger
    Precisely. The bolts are head down with the top about 7-8mm bellow the surface. The head being wider that the body and the threads prevent them from being pulled out easily (or at all should I say!).



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by Eldon_Joh View Post
    Rcaffin i agree that's a lot of work, i would have done it differently, in hindsight since i've only done this once.... you know the tolerance you get for sending 6mm bolts through a 6mm "clearance" bolt hole in the linear rail is pretty small if all you got is a drill press and a center punch.
    Yeah, the tolerance needed is probably ~0.1mm since the holes in the rails are 6.9mm and I will be using 1/4-20 bolts, that is 6.35mm in diameter. You also need the rails to move a little around the bolts since the rails need to be adjusted for straightness and parallelism to each other. I plan on using a fixture for the hand drill that will allow me to center the drill on top of a hole in the rail, clamp it, and move it only vertically down. The crests of the threads of the mounting bolts can also be lathed down a little (only for the part that is inside the rail) to increase the clearance if need be. With some care it should work out.



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    When I am using the CNC for both parts the clearance hole for M6 is 6.0 mm - and it works.
    If I am using a manual mill I normally use 6.5 mm for clearance, unless the holes are close together and I can use the dials.
    If I am using a hand-held drill or a drill-press - I clamp it all together and drill both parts in one go! All bets are off.

    Pedantic, pedantic, pedantic:
    > The crests of the threads of the mounting bolts can also be lathed down a little (only for the part that is inside the rail)
    If the 'bolt' has threads up to the head it is a screw not a bolt.
    Pedantic.

    Cheers
    Roger



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    Default

    Quote Originally Posted by RCaffin View Post
    When I am using the CNC for both parts the clearance hole for M6 is 6.0 mm - and it works.
    If I am using a manual mill I normally use 6.5 mm for clearance, unless the holes are close together and I can use the dials.
    If I am using a hand-held drill or a drill-press - I clamp it all together and drill both parts in one go! All bets are off.

    Pedantic, pedantic, pedantic:
    > The crests of the threads of the mounting bolts can also be lathed down a little (only for the part that is inside the rail)
    If the 'bolt' has threads up to the head it is a screw not a bolt.
    Pedantic.

    Cheers
    Roger
    If I am not mistaken the formula for the length of threads on a bolt is (2 x D) + 1/4". Any bolt whose shank is shorter than the formula will be fully threaded.



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    Default Re: Large Epoxy Granite Vertical CNC Mill


    Alright, now the stand. The plan is to make it out of wood but strong enough to hold the >1000lb weight of the mill. Here's the design.

    Large Epoxy Granite Vertical CNC Mill-1-png Large Epoxy Granite Vertical CNC Mill-2-png

    The first photo shows how the mill will sit on the stand and the two plates that will form some sort of worktable for tools, vises and other stuff. All space in the stand will be occupied by sliding drawers (eventually!) to store end mills, parallels, indicators and other small items that every mill needs.

    The second photo shows only the "structural" part, what will actually hold the weight of the mill. The legs are 4x6 and the cross beams are 4x4. The top beams are three 2x4 planks glued to each other (I already have them dry and ready to go). The table will ride on casters, more precisely four casters per leg. Each caster is rated for 110lb which means I could put up to 1760lb on the stand.




  16. #76

    Default Re: Large Epoxy Granite Vertical CNC Mill

    Lookin' good!



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Hi Louie

    > the formula for the length of threads on a bolt is (2 x D) + 1/4".
    Wonder how that works in metric land?

    Anyhow, it seems I was at least partly wrong. A bolt goes through drilled holes and is secured with a nut. A screw relies on a thread in the hole and does not use a nut.

    Oh well.

    Cheers
    Roger



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Hi Petrus

    I used hardwood 4"x3" beams and 4"x4" uprights. Seemed quite strong enough. Two Industrial wheels and two industrial castors for moving, although most of the time the stand sits on fixed supports so the wheels don't deform over time.

    You cannot have enough bench top space around the machine. I suggest you need a fair bit out front as well as what you have at the sides - just from experience.

    Cheers
    Roger



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    haven't read the whole thread so forgive me if this is a repeat. I work with composite and generally speaking more strength can be achieved with a post cure at an elevated temperature. Have you considered that? Its easy to do, get the figures from the epoxy company, build a tent around the casting with cardboard boxes and put a small space heater inside, stick a meat thermometer through the tent in various locations to monitor temp and cook it to the new spec. Easy way to elevate the strength. If it has only seen ambient temps of 75 degrees it might be much weaker than it could be.

    Just my educated 2 cents worth, Awesome project by the way.

    jh



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    Default Re: Large Epoxy Granite Vertical CNC Mill

    Quote Originally Posted by johnh View Post
    haven't read the whole thread so forgive me if this is a repeat. I work with composite and generally speaking more strength can be achieved with a post cure at an elevated temperature. Have you considered that? Its easy to do, get the figures from the epoxy company, build a tent around the casting with cardboard boxes and put a small space heater inside, stick a meat thermometer through the tent in various locations to monitor temp and cook it to the new spec. Easy way to elevate the strength. If it has only seen ambient temps of 75 degrees it might be much weaker than it could be.
    Yeah, I read about that on some aerospace web site. They basically said that all epoxy properties are improved by a post cure since apparently epoxy does not fully react at room temperature. They were talking about very high temperatures though, like 150C, which I suppose can only be done in a vacuum chamber for obvious reasons! It will see temperatures up to 35C since the garage gets that hot in the California sun during the summer. You think just raising the temperature to 50C or 60C will improve it much more?

    Since you work with composites I have another question: the thermal expansion of EG can be pretty high compared to steel, what can be done to reduce that? This is because the coefficient of expansion of epoxy is 5 times larger than that of steel. Temperature stability seems to be the only major shortcoming of EG vs cast iron or concrete.



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