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  1. #1
    Nick's Avatar
    Lives in East Yorkshire, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 1-2 years. Has a total post count of 5.
    Right so I've started on an large cast iron/EG mill build. Plan is to use several cast iron surface plates I have bought on ebay and embeded in epoxy granite, the hope is this will give me a flat surface to mount the linear rails to.

    This is the current design in fusion

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    Travel: X 400mm, Y 250mm, Z 400mm
    Total weight 600-800kg
    Rails: 20mm hiwin clone rails
    Ball screws: Generic rolled Chinese ball screws, with a plan to upgrade in the future.
    Spindle: Initially: 2.2kw water cooled spindle. The plan would be to upgrade to a BT30 and 1.8kw servo from AliExpress if I can get this made and then integrate ATC
    Electronics: UC400 ETH, Initially steppers, with upgrade to 400W AC servos.

    Epoxy granite: Silimix 282 + west systems epoxy 105/206 10% by weight, 0.25% black iron oxide


    Cast iron:
    Iíve got one 36 x 16 inch plate

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    Along with four of these 18x12x2in plates

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    The large surface plate is reasonably flat, however the smaller plates are out by about 0.05-0.15mm. I am planning on trying to hand scrape them flat.

    Issues:
    1. I have got to cut one of the cast iron plates into four for the column mounting blocks, Iím not sure how I will do this as they're 2 inch's thick, I think I will try with a cutting disc
    2. The column and table will consist of more than one cast iron piece, Iím not quite sure what the best way to keep alignment is, I think I will have to use a flat surface, possibly the big surface plate to cast against and an angle plate.


    I've got the epoxy and Silimix. I have made the mould for the base and I think I will cast this first to check that the epoxy granite doesn't warp the surface as it sets. I'll post back with the results!

  2. #2
    Hi Nick
    Thanks for posting, will be following with interest.
    Mike
    Last edited by mekanik; 2 Weeks Ago at 09:58 AM.

  3. #3
    Nick's Avatar
    Lives in East Yorkshire, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 1-2 years. Has a total post count of 5.
    Right so Iíve casted the base. I started by preparing the surface plate, I cleaned the underside with a wire wheel and then drilled and tapped several holes for M6 and M10 bolts, so the epoxy would anchor.

    The surface plate had a hole drilled in the top when I got it, I thought this might be helpful to run wiring/pipes through, so I routed some PVC pipe to the back of the surface plate. Before I decided to cast the surface plate in epoxy, I did briefly try and cut it, I sealed this cut with silicone. I also drilled two pairs of holes in each side and passed pvc pipe through, this will let me pass some chains through to lift it.

    The mould was made of melamine "furniture" board I got from wickes, sealed with silicone and then three applications of wax were applied (three was necessary in testing, it's a huge pain when it sticks). The surface plate was lowered with an engine crane face down into the mould.

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    Mixing the epoxy granite was the hardest part, it took ages. We did it in 25kg batches, with one person packing the mould while the other used a hand held mixer. We also had a bench grinder attached to the mould, with an eccentric weight, but it quickly ripped itself free of its base. It took just under two hours in total and I managed to add some steel plate to act as mounting points later on and a small section of steel as a future motor mount.

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    I let it cure for about 48 hours before removing the melamine mould.

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    There are some areas that haven't fully combined and some air inclusion, this is worse on the side away from the bench grinder and I think related to poor vibration. But overall i'm fairly happy with how it turned out. As a very crude test, I've put a tenth indicator on a 30cm extension and jumped up and down over the base, I can't really get it to deflect. It weighs about 220kg now.

    I was also concerned that the curing epoxy would warp the surface, so I tried to map out the base with a indicator, there is very little movement (apart from the end I cut which shows about 2 thou of deviation). I also used a 2 foot straight edge, I can't pass a 0.02 mm feeler gauge under it. I don't think its warped significantly.

    Next step is to scrape all of the cast iron inserts for the column, I've started to do this, its slow work, but I think will be possible. I'm going to have to think of a way to level the end of the base, my surface plate isn't big enough so i'm not entirely sure how to do this?

    Nick

  4. #4
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,186. Received thanks 85 times, giving thanks to others 54 times.
    Following.

    How big is the area you need to get flat? I had similar challenges so had to be inventive with my own concrete build.

  5. #5
    Interesting project. I was thinking about building a dedicated milling machine the other day but priced up the off the shelf bits (motor spindle rails screws etc ) and talked myself out of it for now.
    You have a nice set of parts lined up so should make a great machine. Looking forward to watching your progress.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  6. #6
    Nick's Avatar
    Lives in East Yorkshire, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 1-2 years. Has a total post count of 5.
    The area to flatten is 900 x 400mm and my surface plate is 600x600.

    Yeah I talked myself out of it a few times. I'm not sure its going to be very economical, the BT30 spindle itself is a substantial cost.

    Chaz, I found your concrete build very interesting and I've thought about a moglice/DWH approach. I'm lacking a big enough reference surface though, any ideas on how I could overcome this?

    I'm starting to wonder if I will have to leave the base as it is. If I could be confident in the way I was measuring it and I was sure it was flat to say 0.02-0.05mm I would probably be happy and just shim/scrape it later. Does anyone a good way to measure how flat a surface is that's bigger than your reference surface?

  7. #7
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,186. Received thanks 85 times, giving thanks to others 54 times.
    Quote Originally Posted by Nick View Post
    The area to flatten is 900 x 400mm and my surface plate is 600x600.

    Yeah I talked myself out of it a few times. I'm not sure its going to be very economical, the BT30 spindle itself is a substantial cost.

    Chaz, I found your concrete build very interesting and I've thought about a moglice/DWH approach. I'm lacking a big enough reference surface though, any ideas on how I could overcome this?

    I'm starting to wonder if I will have to leave the base as it is. If I could be confident in the way I was measuring it and I was sure it was flat to say 0.02-0.05mm I would probably be happy and just shim/scrape it later. Does anyone a good way to measure how flat a surface is that's bigger than your reference surface?
    I bought a hollowed out 'reference' block from someone. Its around 900 x 600 x 600 and might be good enough for what you need. It has slots in it and few holes / marks but its what I used to lay my Y rails, then later X and Z from that.

    Where are you based? Might be worth a chat, PM your number if you think its worth discussion via phone.

  8. #8
    Was just trawling through some older "subscriptions" and think this might be your "reference box" Chaz :

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    From http://www.mycncuk.com/threads/10480...growing-nicely
    Last edited by AndyGuid; 1 Week Ago at 09:22 AM.

  9. #9
    Chaz's Avatar
    Lives in Ickenham, West London, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,186. Received thanks 85 times, giving thanks to others 54 times.
    Quote Originally Posted by AndyGuid View Post
    Was just trawling through some older "subscriptions" and think this might be your "reference box" Chaz :

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    From http://www.mycncuk.com/threads/10480...growing-nicely
    Yep.

  10. #10
    Nick's Avatar
    Lives in East Yorkshire, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 1-2 years. Has a total post count of 5.
    Chaz, that might work, how much does it weigh? I am based in Yorkshire, where about are you based?

    Just changed jobs, making very slow progress on the build at the moment.

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