1. #1
    This isn't quite a build log as I want to wait until I'm making lots of consistent progress - few things are as annoying as a log that looks great for two posts and then goes silent for a year :confused:

    I had the opportunity to catch up with John S in his workshop this week. He's a gentleman, a scholar and and all-round good chap I left* a little poorer in pocket, but richer in knowledge and with a pile of materials to put to work.

    Click image for larger version. 

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    My original plan was to use 80x40 (or more) for weight and surface area, but I think the 40x40 will make a good building and learning exercise. It's also like Lego, but for adults! The great thing about it is that I could knock together a few ideas and see them take shape in front of me, rather than have everything on paper or screen. I also get to poke, prod and wobble things to see how they act. Before any aluminium gets cut I want to have a clear idea of how I want it to go together.

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    Dimensions are "off" because I'm approximating the structure but to be honest I could do most of this with very few cuts - also known as "less chances to bugger something up" - if I would accept something bigger than planned. The only problem is that it would also need increasing the size of other more expensive components. The example here is dimensionally fairly close to what I want, though (i) the gantry is far too low and (ii) the distance from the gantry to the far end of the router is too long, requiring those components to be trimmed at some point.

    The pieces of alu that run along the inside of the "wall" are for a mounting location for the rails, though I'm still considering how to do this effectively.

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    I'm thinking that using alu plate as sidewalls will help brace the structure and improve rigidity. What I don't really know is whether there is a minimum plate thickness to make it worth adding in the first place - 500mmx500mmx5mm would work out as 19+VAT per side, but would it be sufficient? Going up to 10mm doubles the price, but does it give double the value for my purposes? I simply have no experience or frame of reference for answering those questions, which is one of the reasons why I throw myself on the mercy of the wise members of this forum!

    So, in summary, I've got some new bits to work on and that brings me a step closer to the goal. Brace yourselves for lots more annoying questions. Thoughts and input always welcome!

    * eventually. Actually, I completely forgot to watch the time and my wife rang me up to tell me off and suggested I get a move on :whistling:

  2. #2
    hi Rogue,
    Have a hunt round for a post which has a very good spreadsheet attached, (sorry can't find it or I'd post the link) you can put in info about the thickness and material of the gantry sides and see the difference it makes to the rigidity etc... and lots of other stuff to suck away the hours LOL...

    (I'm rather envious of those who have already GOT something to play with! I'm still awaiting my first "delivery" :-(

  3. #3
    Quote Originally Posted by mocha View Post
    Have a hunt round for a post which has a very good spreadsheet attached, (sorry can't find it or I'd post the link)
    Here it is:


    It's a useful spreadsheet, but it wont give useful results here as you're adding the side plates mainly to counter forces parallel to the Y-axis, not X. Since the force is parallel to the plate the plate does not need to be very thick at all - 5mm would be fine, so long as it doesn't bend - so stiffen the plate if necessary.
    Last edited by Jonathan; 17-11-2011 at 12:37 AM.

  4. #4
    Intriguingly enough, the follow design works with only two cuts needed to get the internal rails to the right length. It gives me (by a scrape) enough travel for a 300mm work area on the Y, plenty (up to about 400mm) on the X and approx 160mm on the Z.

    Click image for larger version. 

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    I think I'll eventually take the plunge and cut some profile to length in order to extend the back section. It feels unbalanced as it is and I'd like that the angle to be slighty shallower.

    Someone came up with the rather interesting idea of replacing the side plates and front gantry plates originally planned with a single piece folded around the frame. The idea is that it would form a more rigid structure and could also work with thinner plate - the suggestion was to use 3mm, presumably to assist in forming cleaner sharper bends? If memory serves, this would be similar in concept to a monocoque design as the walls provide structural strength? Let's see how that would look (but with 5mm because I forgot to change the numbers)...

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    ...and the flattened sheet...

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    This piece of plate in 5mm comes in around $42 + VAT, 4mm at 34 + VAT, so material-wise it isn't a significant price difference from the original bracing idea. The issue is cutting it out cleanly, then finding a local fabricator to bend it for a reasonable price!

    A key piece of the puzzle remains the gantry. Another interesting idea that came up is mocked up below (again not dimensionally accurate)...

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    The ballscrew and motor were to be internal, with a slot in the front of the panel allowing the ballscrew to connect to the sled for the Z axis. Pulleys were to be external for ease of changing (note motor shaft and ballscrew sticking out the side).

    I presume the idea could still be achieved by doubling up on the ganty supports, to reach a depth of 80mm - which would accomodate NEMA 23, while a cut-away section would be needed to accomodate NEMA 34.

    I'm not particularly planning to try and implement this, but there's something about the idea I liked so I thought I'd share it :)

  5. #5
    Thanks for the replies, I wasn't ignoring them, I've just been writing that post for more than an hour with lots of interruptions!

  6. #6
    Folding the sheet seems like a good plan combined with the original extrusion.

    Quote Originally Posted by Rogue View Post
    which would accomodate NEMA 23, while a cut-away section would be needed to accomodate NEMA 34.
    You will not need Nema 34 for this size machine so don't worry about it. The 3Nm nema 24 that lots of people use will be plenty.

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