1. #1
    Hi,

    After a bit of CNC hiatus, I am back on track with funds all ready to go. I am aiming for a small machine (around 40cmx30cm cutting area) for mainly wood and some plastic (if it cuts thin alu at all then great but not important…I am planning to make toys, games, and light-based gadgety design items).

    I have no workshop and live in a tiny flat so minimal machining is required (as it will all have to be paid for at silly london prices).

    Any general advice would be great before I go too far with my current design and I also have a few specific questions.

    I have attached some images of the design as it stands (still a work in progress but think one can get the idea).

    The base is two 700mm lengths of 60x60 series 6 profile extrusion sitting on three 600mm pieces across. Then sbr16 bolted straight on to this with plates (all plate in machine to be 20mm ecocast) at front and rear to provide mounting for motors and screw supports and reinforcement.

    The gantry is a 600mm length of 120x60 series 6 with a 140mmx600mm plate stuck on the front, plates at sides to reinforce, sitting on bearing plates.

    So…

    How bad is it to mount the Y rails on front of gantry rather than top and bottom (more concerned by mechanics rather than exposed screws and bearings issues) ? It seems to make the z axis so much simpler.

    With regards to z axis, should I have the y bearings outside of the z bearings (as it is currently) or should I swap around?

    I plan on snipping off any excess on the gantry sides once I have added in holes for motor and screw supports. Is it worth trying to save weight elsewhere (e.g. few holes in either of the z axis plates)?

    Fitting metal parts together…at the moment I have a couple of bolts on either side connecting the 120x60 extrusion directly to the bearing plates and then the gantry sides are also bolted to both the extrusion and the bearing plates. Can one use finger joints or similar to attach plate parts at right angles to each other (as well as bolting)? I have had a little read about interference fits etc…I can see issues in trying to build a precision machine that requires a hammer to put it together. Maybe just a reasonably close fit so it assists a bolted joint?

    Was planning on using 1605/1610? ballscrews all round, twin x, nema 23s. Is it possible to have a versatile machine without use of belts?

    I could ramble on for a while but think that is enough to hopefully get the ball rolling. As always, any advice is much appreciated. I know the machine is full of compromise but such is life.

    Notes:
    The spindle was grabbed from 3d warehouse…I will go for something which protrudes less if possible.

    Need to resolve positioning of gantry sides in relation to ballnut mount (can only attach one or the other but not both at moment!)

    I will start enquiring about prices for getting the plate parts done. If I get them milled then I will create pockets for bearings (left it all flat for now as one possibility is a university nearby that does waterjet cutting).
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Was up all night thinking about my requirements...i'd like to throw alu back in the mix.

    Thinking of a steel base, welded or bolted. Can i still use sbr16 or would i have to go up to 20? I don't have the budget for anything better.

    Few more questions...

    Can you use nuts instead of threading?

    Do you have to use brackets or can you bolt the box section directly (less holes to drill and tap)?

    If you are bolting 2 pieces of section together, one on top of the other, do you bolt from outsides (i.e. the bolt running through 2 walls of each piece) or the inside (1 wall of each piece) and if through 2 of each then do you put some kind of spacers inside?

    If I kept the base design the similar but moved to steel, can i get away with only 2 pieces running the width of the machine? This would allow me to keep to 3m of steel and also it would leave the option of working on slightly wider pieces if required (feeding my material in from the side rather than the end).

    My gantry...do i need the 120x60 piece running behind the 20mm plate or can i streamline that a little (reduce either the plate or the extrusion)?

    Also toyed with the idea of making the whole thing out of plate. Was looking at the lumenlab machine...would this suffer badly from sagging? (was explaining to the gf..a little bit of sag is ok and is inevitable)

    p.s. I know i got the spindle mount the wrong way round in my pics...

  3. #3
    Quote Originally Posted by andy586 View Post
    Thinking of a steel base, welded or bolted. Can i still use sbr16 or would i have to go up to 20? I don't have the budget for anything better.
    Yes makes no difference and don't rely on the rails to provide strength.

    Quote Originally Posted by andy586 View Post
    Can you use nuts instead of threading?
    Yes if you can access the nuts but threading is easy and less messing around. Why not thread.?

    Quote Originally Posted by andy586 View Post
    Do you have to use brackets or can you bolt the box section directly (less holes to drill and tap)?
    Not exactly sure what your meaning but brackets are mostly used to provide strengthening rather than hold together.

    Quote Originally Posted by andy586 View Post
    If you are bolting 2 pieces of section together, one on top of the other, do you bolt from outsides (i.e. the bolt running through 2 walls of each piece) or the inside (1 wall of each piece) and if through 2 of each then do you put some kind of spacers inside?
    Yes if going thru 2 sides then you'll need crush tubes. If bolting and you don't want to have crush tubes but can't access the material, IE in middle of long length, then just drill a larger access hole on the outer wall for a socket to pass thru. Bosch Holes saws are good for this and easily cut steel.

    Quote Originally Posted by andy586 View Post
    If I kept the base design the similar but moved to steel, can i get away with only 2 pieces running the width of the machine? This would allow me to keep to 3m of steel and also it would leave the option of working on slightly wider pieces if required (feeding my material in from the side rather than the end).
    Again not sure were or what your meaning with the access from side.? . . But if it's the bed supports then NO. If anything you want another one not taking away.!! Don't compromise the machine for sake extra £20 it's the foundation and any weakness here will pass to the finished result. IE Shitty finish.!

    Quote Originally Posted by andy586 View Post
    My gantry...do i need the 120x60 piece running behind the 20mm plate or can i streamline that a little (reduce either the plate or the extrusion)?
    Drop the 120x60 and use Steel box, Often box section comes in 7.5mtr lengths so I'd source a local steel supplier and ask the price you may find it's not much more for full length than 3mtr off the net. Chances are they will even cut it up for you.?
    This will then give you enough for gantry and to beef the frame up more, the steel for the whole machine will cost less than the price of just the 120x60.

    Now regards previous post and you saying going to use Eco cast then don't bother has it's not required if your using SBR rails. The rails them self will have more error than the plate so it's waste of money. Only really need Eco cast if using Profiled rails so Just buy 5 series cut plate and it will be more than good enough. In any case you only really needed Eco cast for the important areas like bearing plates, Z axis etc Gantry sides and other things like general plates etc could all come from cheaper rolled plate lengths.

  4. #4
    Many thanks for the reply Jazz. Will definitely save me a few quid using 5 series instead of ecocast where i can, and i will be ditching the big extrusion in favour of steel box.

    I've hit a bit of a problem...I realised that I was massively optimistic when sizing my machine in relation to the actual space i've got. I could fit the machine but would have only a few millimetres clearance between the wall and access will be a nightmare. Therefore I have to reduce the width of the machine and position it elsewhere.

    I can see 2 ways of doing this...

    Type 1 : moving the x screws to above the x rails. This means the y rails will always now be that extra bit higher and the whole machine looks a bit less solid. I tried running the x screws threw the space between the y rails but then it becomes even more tall as i've obviously got to consider the y screw and motor positioning.

    Click image for larger version. 

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    Type 2: moving the x screws inside the x rails. i thought i could actually then use the machine in 2 configs. config 1 with a bed above the bearing plates when i need full width of machine.

    Click image for larger version. 

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    Then config 2 when i need strength and want to cut below the x rails instead of above. When using config 2 I would lower the piece of plate which the y rails are attached to (sorry..haven't done that in sketch).

    Click image for larger version. 

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    which do you think would be the best way to go?

    if i went with type 2, when i lower the plate with y rails on them, would this be a major hassle each time for set-up? i thought i could use a few other pieces to hold the gantry sides relative to each other, unbolt the y plate and then bolt back in lower down.

    p.s. these sketches are just to consider the 2 options and obviously there are loads of things missing.

    as always, any replies much appreciated.

  5. What about a fixed gantry and moving bed ?

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