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  1. #11
    In my journey so far, you lot... you know who you are... have already warped my thinking to such an extent... thank Thor... that for now I intend using the following components/concepts:

    - 20mm supported-rail on X
    - 20mm profile-rail on Y,Z
    - RM1610 ballscrews on X,Y,Z
    - Gear+Belt drive on X and Y, and suppose this may well be used on Z as well... in for a penny.... but this aspect probably worries me more than anything else!

    I am now feeling very comfortable with SKP/SketchUp, and how I wish I had used such a tool when designing the odd thing in the past!

    I'm starting to make good progress with the design... I think... so have included two SKP pics of my design so far for feedback.

    The structure is mostly to be formed out of 6"x2"x3/8" aluminium angle which the Aluminium Warehouse website converts to 152.4x50.8x9.53 mm but let's call it 152x51x9.5 which is what I used in SKP. There are two other materials used so far:

    - Blue = 100x50x5 rectangular tube
    - Yellow = 45x45 extrusion from KJN

    More research is needed before I complete the drive for the X and Y, and do the Y-carriage and the entire Z axis.

    Am trying to do the build with standard components, but already need a ballscrew-mounting for Y to be machined and think more will come out of the design of the Y-carriage and Z.

    The ballscrew lengths... between bearing blocks... are about 1060 on X and 707 on Y.

    When I move on from the touring caravan in the future, this machine will be mounted on a rigid frame with an adjustable bed, so the obviously limited depth below the cutting point is temporary to allow me to get to grips with getting the thing working. Bracing the base of the frame... particularly behind the cutting point is still to be included in my SKP pics.

    Please "holler" about the problems... I'm that thickskinned that I cannot recall ever having taken offence at anything!

    Thanks,

    PS. Is 5mm aluminium sufficiently thick to make a M6/M8 tapped thread reasonably strong?
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  2. #12
    Quote Originally Posted by WandrinAndy View Post
    Please "holler" about the problems... I'm that thickskinned that I cannot recall ever having taken offence at anything!

    Thanks,

    PS. Is 5mm aluminium sufficiently thick to make a M6/M8 tapped thread reasonably strong?
    Ok I'll holler first but not too much. . Lol

    45x45 extrusion is pretty weak so I would consider going larger.!

    5mm in aluminium is NOT enough. M6 = 1mm pitch so only 4 full threads M8= 1.25mm pitch so 3 full threads no where near enough and it will strip.!!

  3. #13
    Quote Originally Posted by JAZZCNC View Post
    Ok I'll holler first but not too much. . Lol

    45x45 extrusion is pretty weak so I would consider going larger.!

    5mm in aluminium is NOT enough. M6 = 1mm pitch so only 4 full threads M8= 1.25mm pitch so 3 full threads no where near enough and it will strip.!!
    Thanks Jazz.

    I had thought that the heavy version of the 45x45 would be strong enough as it is bolted along the back of it's whole length to 9.5 plate. I will look at replacing the top section with 45x90 then. Do you think this will be enough?

    I'm hoping that tapping into 9.5mm plate... 90% more threads.... is just ok then?

  4. #14
    Quote Originally Posted by WandrinAndy View Post
    I had thought that the heavy version of the 45x45 would be strong enough as it is bolted along the back of it's whole length to 9.5 plate. I will look at replacing the top section with 45x90 then. Do you think this will be enough?
    Nah even the heavy version isn't has strong as you think.!! The 45x90 will be better but I'd put it top & bottom and have the wide bit flat.
    This way it ties into the sides better and gives more resistance to bending in lateral cutting directions.! It doesn't Add much to the vertical up & down strength plunging will inflict but the 10mm plate will help here and plunging should be avoided if at all possible anyway.! Most of the time the machines cutting and the forces are lateral.!!

    10mm is just about ok for threading in Alu.

  5. #15
    Quote Originally Posted by JAZZCNC View Post
    The 45x90 will be better but I'd put it top & bottom and have the wide bit flat.
    This way it ties into the sides better and gives more resistance to bending in lateral cutting directions.! It doesn't Add much to the vertical up & down strength plunging will inflict but the 10mm plate will help here and plunging should be avoided if at all possible anyway.! Most of the time the machines cutting and the forces are lateral.!!
    I would have thought that my design as pictured already provides lateral resistance roughly equivalent to what you're suggesting, as a cross-section of the bottom of the gantry consists of 45x45 bolted close to the backwards pointing 51mm leg of the 9.5 angle? And the 9.5 angle extrusion is bolted to both the base and the uprights of the X-carriage hopefully creating a very rigid joint?

  6. #16
    Quote Originally Posted by WandrinAndy View Post
    I would have thought that my design as pictured already provides lateral resistance roughly equivalent to what you're suggesting, as a cross-section of the bottom of the gantry consists of 45x45 bolted close to the backwards pointing 51mm leg of the 9.5 angle? And the 9.5 angle extrusion is bolted to both the base and the uprights of the X-carriage hopefully creating a very rigid joint?
    OK then go for it.!

  7. #17
    9.5mm is definitely fine for M6 since none of the forces on this small machine will get anywhere near the rating of an M6 bolt. I'd advise using threadlock to make sure any bolts don't vibrate loose.

    Quote Originally Posted by WandrinAndy View Post
    - RM1610 ballscrews on X,Y,Z
    Good choice for X and Y but there's no need to use 10mm pitch on the Z-axis. Keep the resolution by using RM1605 on Z.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  8. #18
    Thanks for the feedback guys.

    Last query on the limits of thread in 5mm thick aluminium... When attaching the supported round rails on top of the beam on the X-axis is it then necessary and best to run a length of thicker flat bar through the box section to take the bolts?

    I've decided to go with Jazz's GREEN design for the Y-beam..... It's a great KISS solution... can't for the life of me recall why I dropped the idea in the first place! Have attached updated pics.

    Although my gantry end plates are only made from 9.5mm angle-section.... it helps makes the design compact and build easier what with my current limitations... I'm hoping that with the end plates and gantry being relatively squat, this will be rigid enough. Or should I include some bracing to the angle?
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  9. #19
    Quote Originally Posted by WandrinAndy View Post
    Last query on the limits of thread in 5mm thick aluminium... When attaching the supported round rails on top of the beam on the X-axis is it then necessary and best to run a length of thicker flat bar through the box section to take the bolts?
    To be sure then Personally yes I would.! . .BUT. . If you use M5 bolts then with smaller pitch and keeping the centres closer together with the higher quantity of bolts you could get away with it.?
    I've done this with steel 4mm box section and it's worked ok.! . . It's just with softer Ali @ 5mm could be marginal.?

    At the worst you can just add the thicker bar through at a later date if it doesn't feel right or causes problems.?

    The Angle gantry sides should be ok because of the squat nature and the fact it's driven from both sides.! The thing to watch out for is that the Angle both internal and external are close to 90deg.? The round rail bearings will handle some discrepancy but you don't want too much.!! . . . Bracing will help absorb any resonance and can only help.

    I've noticed from the pics you have 2 plates on the bearings and cutaways in the gantry sides for what looks like access to the bearing bolts.?
    If you use 2 plates then you don't need access to the bearing bolts and can bolt the top plate direct to the bearing plate so no need for access slots. The beauty and point of 2 plates means it makes gantry squaring easier without having to worry about bearing bolt access.

  10. #20
    Quote Originally Posted by JAZZCNC View Post
    I've noticed from the pics you have 2 plates on the bearings and cutaways in the gantry sides for what looks like access to the bearing bolts.?
    If you use 2 plates then you don't need access to the bearing bolts and can bolt the top plate direct to the bearing plate so no need for access slots. The beauty and point of 2 plates means it makes gantry squaring easier without having to worry about bearing bolt access.
    Splendid... I wasn't looking forward to "hacking" out those cutaways, but thought I had read somewhere that one should allow access to the bearing bolts... and now know that's to allow for gantry squaring.

    It will be so much easier doing it the way you suggest. I had already included four bolts (M8?) holding the plate and angle together, so will maybe tweak these to be a tad closer to the bearings and add two in the middle for good measure and just drill holes in the angle to accomodate the bearing bolt heads.

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