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  1. #11
    Ok, there's a few things you need to look at. How are you going to get to all the bolts to fasten on the bearings to the gantry and Z axis?

    Are you welding everything, if so how are you planning to take the inevitable distortion out if the frame, gantry and Z axis? Epoxy? Shims?

    The Z axis with the back plate does nothing for stiffness, think of a cornflake packet with the top and bottom cut off, and only makes it harder to align everything as adds more complication.

    What thickness steel are you using? There's no problem in using steel but it will need bracing to stop it bending and twisting.

    On an all steel machine (if thats what yours is?) you'd be best connecting the steppers to the ballscrews with belts and pulleys, this will stop any resonance from feeding back to the stepper motor.

    Can't comment in the plasma thing as no experience with them, I'm sure a dual machine could be built but as with anything that doesn't do just one thing, there will be compromises.
    Neil...

    Build log...here

  2. #12
    all good questions , ill attempt to bluff my way through
    ......
    Quote Originally Posted by njhussey View Post
    Ok, there's a few things you need to look at. How are you going to get to all the bolts to fasten on the bearings to the gantry and Z axis?
    gantry - steel tube 3mm, drill and tap thread , or weld threaded rod to tube ?
    x carriage - aluminium plate and angle bolted togeather, rails bolted through
    z axis - maybe thicker plate 20mm ?

    Quote Originally Posted by njhussey View Post
    Are you welding everything, if so how are you planning to take the inevitable distortion out if the frame, gantry and Z axis? Epoxy? Shims?
    i worried about this, maybe only weld below y rails and shim them out to put y rails on then above this bolt together
    Quote Originally Posted by njhussey View Post
    The Z axis with the back plate does nothing for stiffness, think of a cornflake packet with the top and bottom cut off, and only makes it harder to align everything as adds more complication.
    so better just to have stiffer plate ? and forget sides

    Quote Originally Posted by njhussey View Post
    What thickness steel are you using? There's no problem in using steel but it will need bracing to stop it bending and twisting.
    3mm , lots of jigs and clamping
    Quote Originally Posted by njhussey View Post
    On an all steel machine (if thats what yours is?) you'd be best connecting the steppers to the ballscrews with belts and pulleys, this will stop any resonance from feeding back to the stepper motor.
    very good suggestion, my current machine has no issues like this as it is so sloppy no resonance builds up !
    Can't comment in the plasma thing as no experience with them, I'm sure a dual machine could be built but as with anything that doesn't do just one thing, there will be compromises.
    thanks for persevering with my somewhat undeveloped project ,
    cheers
    ben

  3. #13
    Quote Originally Posted by outtastep View Post
    all good questions , ill attempt to bluff my way through
    ......
    That's all I do

    gantry - steel tube 3mm, drill and tap thread , or weld threaded rod to tube ?
    x carriage - aluminium plate and angle bolted togeather, rails bolted through
    z axis - maybe thicker plate 20mm ?
    3mm is not thick enough to tap, unless you're using M4 bolts, you'll either need to use thicker section or glue a strip behind and drill and tap into that. Whilst steel Z axis can be done (see Boyan Silyavski's builds) it's far more common practice on here (not saying it's correct, but just what gets done on here as it works!) to use a 20mm plate for the Z axis, both for the back plate and the front.


    i worried about this, maybe only weld below y rails and shim them out to put y rails on then above this bolt together so better just to have stiffer plate ? and forget sides
    Welding the frame is fine. You can, with a bit of thought, weld sections that bolt together which then allows for shimming to get the frame square. You can also file/scrape/fill the steel to get it flat or use the epoxy method and either use metal putty to set the steel rail supports at the correct height or pour slow setting epoxy on the top of the rails (like I did) and this (should) then be a flat surface to put the rails onto. Have a good look through the build logs and see what others have done, this should give you some ideas and will show how others have overcome the issues they encountered.


    3mm , lots of jigs and clamping
    Again 3mm isn't much good for tapping holes into, it's too thin so you won't have enough thread engagement.

    very good suggestion, my current machine has no issues like this as it is so sloppy no resonance builds up !
    Can't comment in the plasma thing as no experience with them, I'm sure a dual machine could be built but as with anything that doesn't do just one thing, there will be compromises.
    thanks for persevering with my somewhat undeveloped project ,
    cheers
    ben
    Keep the changes coming, if you see my build from what I originally planned and drew to what I ended up with you'll see how all this questioning and re-drawing is good!!
    Last edited by njhussey; 25-11-2015 at 12:22 PM.
    Neil...

    Build log...here

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  5. #14
    My suggestion is forget Plasma the cost is too high and by that I don't mean cost in money but strength/performance/hassle.
    The high Z axis will cripple this machine for anything but light duty cutting. Plasma is messy, smelly and expensive to do right. Your electronics will need to be geared towards it other wise you'll have potential for major hassles from EMF and is area where taking short cuts or cost cutting will bite you quickly.
    Plasma and Routers just don't play well together and best kept separate. Also Plasma machine is basic in strength requirements and building required so easy enough to build a low cost stand alone frame to do the Job. Just make the Electronics interchangable with Din plugs and have Plasma profile Setup in software.

    Having a High Z for 4th axis is also costly in performance/accurecy terms but often desired thou seldom used in practise so why cripple the machine for something you'll maybe use 5% of the time.?
    This doesn't mean you can't have 4th capabiltys just design the machine in such a way that the 4th axis is off the machine. Either at the side or on then end then design the gantry or frame so you can reach it.!

    No harder to build really just different but with no compromise in strength or accurecy as router.

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  7. #15
    thanks Jazz,
    appreciate the advice re. plasma
    with the high Z, I know what you mean it is a real weak point- ill reduce this
    I would however, like to keep the option of having large material fit under the gantry, (300mm)

    if i reduce z travel by 100 mm and bring material up with a raised bed do you think the machine is more solid or still compromised by gantry height?

    cheers ben

  8. #16
    Quote Originally Posted by outtastep View Post
    if i reduce z travel by 100 mm and bring material up with a raised bed do you think the machine is more solid or still compromised by gantry height?
    Yes provided you keep the Distance or Z axis extension short then you won't have a problem. But this is still a slight compromise on overall machine stiffness because you still need to create that height in the first place which weakens the machine to some degree compared to short stubby design but it is the lesser of two evils I suppose.!

    For machines like what you want then having a moving bed is best option because it gives the best of both worlds but keeps the machine stiff compared to just packing the Bed up.

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