Lowrider with 1.9m x 2.8m bed area

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This topic contains 12 replies, has 4 voices, and was last updated by  Jeffeb3 1 month ago.

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  • #114431

    Stanley
    Participant

    Hello,

    I was wondering if anyone has tried a longer x axis with the lowrider 2?

    Stock boards here come in 1830mm x 2745mm so to get the extra 630mm I figured a thicker walled stainless steel tubing would work?
    or is it the flex and strain on the printed parts that’s the limiting factor of the gantry distance?

     

    Thanks for the help,

    #114436

    Barry
    Participant

    It would probably be alright.  It might still flex a bit in the center though.

     

    Keep in mind thicker tubes mean more weight, so you’d need to adjust your speeds.

    • This reply was modified 1 month ago by  Barry.
    1 user thanked author for this post.
    #114450

    frosty
    Participant

    Extending the usable width from 48″ to 72″ will increase the deflection seen at the center by ~2.75x. To put this in perspective an 80″ long, 1″ diameter tube with .092″ wall thickness will deflect an extra 1″ at the center when loaded with 5lbs of weight (2m, 25.4mm, 2.35mm, 25mm for the metric types). And that is on top of whatever sag there is in the pipe just from its own weight. A thicker pipe will reduce the deflection from the router/carriage, but the extra weight will add to the sag so I don’t know if you will end up winning or losing if you make that trade.

    The “proper” solution would be to move up to a larger tubing size. Increase the diameter from 1″ to 2″ (25mm to 50mm) would reduce the sag by 8x and only increase the weight by 2x but that would require a redesign of a lot of parts.

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    #114468

    Jeffeb3
    Participant

    There was a mondo build a while ago. There was significant sag in the middle, and he figured out Marlin’s mesh levelling, so if you were try to cut straight across, the Z would actually move up in the middle to keep it closer to level. It’s going to be tough at that size no matter what.

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    #114469

    Jeffeb3
    Participant
    #114474

    frosty
    Participant

    I still need to put together a test apparatus to prove/disprove my sag-combatting internal support scheme detailed in that thread. I have all the bits, just need the time/space…

    1 user thanked author for this post.
    #114478

    Stanley
    Participant

    Thanks Jeff and Frosty,

    Frosty, the correct way as you pointed out may be for a later point, but might be achievable with just doubling the scale of everything and sourcing some larger bearings. Not sure how the motors would cope with lifting that extra weight. I plan on building a few iterations including one with geared steppers so that could end up in one of them.

    Jeff, mesh levelling does seem the way to go to be absolutely certain with the cuts, I’ll look into it once the other half of my end stops arrive, will certainly help me with the finer details in carving.

    Frosty in your link inside the post Jeff mentions, there’s a bit of confirmation for 2 ideas of reducing sag that I was thinking of implementing after a walk around the workshop.

    Firstly, inside the tube, epoxy a length of 2-3mm flat bar vertically to act like an I beam, eliminating Z axis sag without much weight gain and still allowing for cable runs.

    Secondly, the aluminium angle used for the vacuum hose, printing a second pair of supports a second channel can be fitted to stiffen the x and y axis to some degree. I found an aluminium 50x50x3 extrusion in the workshop today with ridges to increase rigidity but also reduces weight comparatively, a test bend of the 3.0m ( just under 10′ ) long stock I had showed about at 5-8mm deflection on the edge/angle and nothing noticeable when bending from the sides.

    any thoughts?

    Sorry about all the metric I’d try convert to inches but I’m not sure what the standard fractions or equivalent stock is so the result would be laughably wrong no doubt.

    • This reply was modified 1 month ago by  Stanley.
    #114497

    Jeffeb3
    Participant

    Carving on a rig that size seems nearly impossible, even with mesh leveling. You don’t want to carve anything nearly that big, do you? That would take weeks.

    1 user thanked author for this post.
    #114524

    Stanley
    Participant

    No I don’t intend to carve that large off the bat, main purpose of the machine is going to be cutting flatpacks as well as cutting the more involved joints in sets of hardwood.
    Once I’ve got that up and running properly I figure it can’t hurt to try a few of the crazier ideas, though like you point out machine time (and with that, the bits potentially wearing down during the job) would be a major factor even if I could get the required accuracy.
    The carving idea is just a bit of running before I’ve learnt to walk.

    #114529

    Barry
    Participant

    One more thing to keep in mind.  Due to the sag, your endmill won’t be perpendicular to the bed, so your cuts are going to be a little wonky.  It will always point a little bit to the closest side.  Might not be enough to make a difference, but keep this in mind.

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    #114531

    Jeffeb3
    Participant

    The angle the z bit would have would be based on the sag at each end of the 611 plate. Since they are only 6″ apart, there won’t be anywhere on the span where it would be that much different. Something like:

    tan-1((sag(X)-sag(X+6″))/6)

    To be off by 1 degree, you’d need 0.1″ difference in sag over 6″.

    1 user thanked author for this post.
    #114533

    Stanley
    Participant

    Thanks Barry, will keep it in mind, hopefully the I-Beam will limit that sag enough for it to not be noticeable.

    And thanks Jeff, I’ll run the numbers once I’ve got it built up, then I know what I’ll have to account for in my cuts.

     

    Maybe I’ll offset any sag with some bracing on the 611 plate if it turns out significant enough, some aluminium angle offcuts should do the trick.

    From the roughing you’ve made to get a 1 degree deviation I think I’d be still have to be fighting with the sag to be effected on any noticeable level.

    • This reply was modified 1 month ago by  Stanley.
    #114538

    Jeffeb3
    Participant

    But, even if the sag in the middle is 5″, the difference between the middle and 6″ from the middle won’t be 0.1″.

    I was arguing that it would be no big deal.

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