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  1. Something to be aware of, I was using 6mm wall Al box section from Aluminiumwarehouse.co.uk. It was pretty straight, but slightly twisted. so that in 1m, on a 50mm box one side was about 0.5mm off the supported round rail. At the moment I have just built the thing, which I will probably regret later, though it is not the worst issue with the machine.

  2. The Following User Says Thank You to daveshorts For This Useful Post:


  3. #32
    Quote Originally Posted by daveshorts View Post
    Something to be aware of, I was using 6mm wall Al box section from Aluminiumwarehouse.co.uk. It was pretty straight, but slightly twisted. so that in 1m, on a 50mm box one side was about 0.5mm off the supported round rail. At the moment I have just built the thing, which I will probably regret later, though it is not the worst issue with the machine.
    Thanks for that - definitely something to keep in mind. I'm currently intending to use 80mm, 3mm wall, box section. Maybe that's not the best of ideas.

    Thinking about it if the box section is twisted then with a rail on either side they will still be the same distance apart so should run smoothly. In an extreme case I suppose it would mean the Z axis wouldn't remain perpendicular to the bed and would get slightly translated at the cutter tip - pretty negligible for 0.5mm though I think?

    The number of times I change my mind on this because of all the advica I get/ ideas I have is getting ridiculous!

  4. My impression is that the rails will resist torsion better than the box section anyway. I certainly don't have any issues with binding with supported round rail.

  5. #34
    To my mind, mounting a profiled rail to this slot slightly to the right or left of centre may result in the rail ending up rotated with respect to the plane or possibly twisting slightly along its length.
    im thinking that it might be a bit of a pain if your using 15mm rails and a little less so with 25mm rails... either way make sure you buy the groved slot nuts and your rail should sit pretty close to central then do your best to centralise before swinging on the cap heads ... the camber is suposed to act as a locking device and will pull out under tension so if your on 25mm rails there shouldnt be any twist at all

  6. #35
    ecat's Avatar
    Location unknown. Last Activity: 08-02-2014 Has been a member for 6-7 years. Has a total post count of 157. Received thanks 5 times, giving thanks to others 8 times.
    I don't pretend to understand much of this but precision aluminium profile (and box? it is extruded) apparently conforms to DIN 17615:

    DIN 17615
    Outer Dimensions: Depending on size, 0.2 to 0.4 mm
    Straightness Deviation: Max. 1.5mm/2m
    Flatness Deviation: Max. 1.5mm/2m

    http://www.maytec.org/technische_daten_e.htm
    and
    http://www.drivesystemsgroup.com/PDF...ue%20(DSG).pdf

    also this is an interesting read, or would be if it wasn't so late
    http://www.easy-conveyors.fi/materiaali/NTS_GB2002.pdf

  7. #36
    Some interesting reading there certainly...

    Somewhere it says 'For one manufacturing set-up the variation within one profile is 0.0004 inches'. That's roughly 0.01mm which is negligible. So even if the 80mm dimension is +-0.45mm as it says in your first link, the actual dimension should be stable.

  8. #37
    ecat's Avatar
    Location unknown. Last Activity: 08-02-2014 Has been a member for 6-7 years. Has a total post count of 157. Received thanks 5 times, giving thanks to others 8 times.
    That's where I became totally confused Jonathan

    if the 80mm dimension is +-0.45mm as it says in the first link and the actual dimension varies by about 0.01 then where do the straightness and flatness deviations per meter fit in? Also the 1.5mm/2m is not necessarily a gradual change along the full length, it could be bumps or waves or??? I don't know.

  9. #38
    ecat's Avatar
    Location unknown. Last Activity: 08-02-2014 Has been a member for 6-7 years. Has a total post count of 157. Received thanks 5 times, giving thanks to others 8 times.
    Brain is starting to fry, again!

    This guy had problems with the concave surface of his ali profiles...
    http://www.cnczone.com/forums/showpo...7&postcount=33

    ... his fix was a mix of long t-nuts and epoxy to flatten the face, but the area he was dealing with was quite small.

    This got me thinking, could epoxy be used to to flatten all mounting surfaces on steel box and smooth over the dimension issues with ali profile? The above thread makes for good reading and at some point leads to this build...
    http://oneoceankayaks.com/madvac/madvac_index.htm

    This epoxy is amazing stuff, the two linked builds make heavy use of it to ensure the joins in the steel frames are true.

    So, with enough epoxy, a precision level and a thick sheet of glass do you think it possible to true ali profile? The end result must be better than building with 1mm irregularities?

    Two big problems:
    1) The cost of ali epoxy, http://uk.farnell.com/araldite/arald...0ml/dp/1759545, need to add in the cost of a dispensing gun too, I think.
    2) The fact that even with surface prep the special epoxy is not a guaranteed strong, long lasting join.

    Since all I'd be using the epoxy for is to make the filling between two lumps of metal is it necessary to use ali epoxy? And indeed, am I obsessing over trivial detail ?

  10. #39
    Not got time to look at those links now - about to go into school to make a few bits I can't do at home :)

    Try this site for epoxy:
    http://www.ecfibreglasssupplies.co.u...k/default.aspx

    Maybe reinforce it with some of there glass/carbon fibre?

    I've sortof assembled mine with just the box section as it is...and it seems ok. I'll have it assembled properly later on today, then we'll see!

  11. #40
    Quote Originally Posted by ecat View Post
    Two big problems:
    1) The cost of ali epoxy, http://uk.farnell.com/araldite/arald...0ml/dp/1759545, need to add in the cost of a dispensing gun too, I think.
    2) The fact that even with surface prep the special epoxy is not a guaranteed strong, long lasting join.

    Since all I'd be using the epoxy for is to make the filling between two lumps of metal is it necessary to use ali epoxy? And indeed, am I obsessing over trivial detail ?
    Hopefully you shouldn't need much epoxy, where you need to fill anything over a few tenths of a mm you could put glass fibre cloth in the space. It will be better to use a thixotropic or fairly viscous variant than the west system stuff which is designed to wet out composites and is a pretty thin liquid. I don't think you need to worry too much about bonding if it's trapped in a clamped interface - using epoxy to actually make the join is another matter and you would need very good surface prep and glue / material selection in that case.

    I've a length of 3" square 1/4" wall aluminium that I'm intending making my router out of but I haven't had chance to do any measuring on it. I'm hoping it will be close enough that I can just use a thin layer of epoxy on the interfaces and by initially clamping the rails down very lightly until the epoxy sets ensure that they are not deformed by the box section. It'll be at least a couple of months before I get to that stage so I'm looking forward to reading how you get on

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