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  1. #11
    No casting is good enough to use straight out the mould they all need machine prep work to be used and this is where the time and money comes into affect to make accurate surfaces etc.!!

    Would make a good Kit for someone with access to milling machine but for a Kickstarter and to be useful straight out the box I don't think they'd be cheap enough to produce and be attractive.?
    Last edited by JAZZCNC; 06-06-2014 at 07:47 PM.

  2. #12
    I don't see why you would want to cast a gantry. The open back structure significantly limits stiffness.

    If you compare it to a simple 80x160x4mm steel RHS section you would need to make the cast aluminum 'C' shape gantry have web and flanges of 60mm thick to match the bending and torsional stiffness.

    Makes much more sense to cast the end connection down to the bearings blocks and ballscrew, with a neat interface to say a 160x80 RHS steel gantry.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #13
    Quote Originally Posted by routercnc View Post
    I don't see why you would want to cast a gantry. The open back structure significantly limits stiffness.
    But we're not limited to just one beam, so you could get the torsional stiffness by casting two beams in one piece. I'd go for something similar to the gantry design on my last machine:

    Click image for larger version. 

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    The Y-axis rails may have to be moved and it would take a fairly big milling machine to mill the rail mounting surfaces.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #14
    Still haven't finished the gantry pattern as I'm flat out with work but I'm doing bits in between jobs.
    I do know about shrinkage in casting, rule of thumb is 1/4" per foot,my alloy is 1-1.3%. It's accounted for in the pattern.
    For anyone asking why? Here's why, I just want to cast it to see if it can be done and work.

    The price of doing it in aluminium plate is crazy compared to casting it and once a pattern is made for casting you can repeat over and over. It'll all be one piece so no marking out, cutting and bolting plate together.
    I can cut this to length, machine the ends then top and bottom for the rails and wherever parts are to be mounted. I might even bolt 2 castings back to back and make an "I" beam from them.

  5. #15
    Watching with interest. G.

  6. #16
    Quote Originally Posted by jrcast View Post
    I can cut this to length, machine the ends then top and bottom for the rails and wherever parts are to be mounted. I might even bolt 2 castings back to back and make an "I" beam from them.
    Don't bother with the I-beam idea - rubbish torsional stiffness.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  7. #17
    Quote Originally Posted by Jonathan View Post
    Don't bother with the I-beam idea - rubbish torsional stiffness.
    True, but to pick up on your initial idea of twin beam arrangements you could arrange them like this:

    [] instead of ][

    [] has similar vertical stiffness to ][, slightly better fore/aft stiffness, and massively better torsional stiffness. If you cast it then you can include baffle plates at intervals so long as you also bolt through these as well.

    A simpler alternative is to do |] where ] is the cast part (with optional internal baffles or ribs) and | is a simple closer plate.

    Still lots of effort all round but they are possible configurations and much better than just ].
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  8. #18
    Quote Originally Posted by jrcast View Post
    Hi all,
    I'm starting a build thread for my machine and I'll see what you all think of it. I run a small aluminium foundry and a cnc router is something that'll be useful for making patterns for me.
    I'm going to be casting a lot of the parts for it and I haven't seen another one like this on here so I hope you'll enjoy.
    I've bought the rail, ballscrews and a 2.2kw spindle and VFD, here's the shopping list so far.

    SBR20-300/600/1000mm linear slide guide shaft (6 fully-supported rails+12 SBR20UU bearing blocks)
    Anti backlash RM1605-350/650/1050/1050mm-C7(4ballscrews+4ballnuts+4endmachinings)
    4 sets BK/BF12 bearing end supports with locknuts and circlips
    4 pcs 6.35mm*10mm(motor*RM1605) couplers
    I got exactly the same kit for sale !!! you would of saved a few pounds lol
    Casting alloy parts would work well, i was looking at casting my z axis assembly until i realized it would need machining to to get the finished parts !!
    I cant wait to see this build take shape it will be pioneering at its best !!
    Last edited by Steel; 17-02-2017 at 08:16 PM.

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