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  1. #1
    Wal's Avatar
    Lives in Stockport, United Kingdom. Last Activity: 30-03-2023 Has been a member for 9-10 years. Has a total post count of 491. Received thanks 71 times, giving thanks to others 29 times.
    Hello again,

    It's been a while since I first posted and I've had plenty of time to think (and re-think) my design...

    I thought originally that it would be cool to have something capable of cutting aluminium, but the reality is that to build a machine than will do that 'properly' is a different project altogether... The primary goal for this project is to be able to cut hard/soft woods and be accurate/repeatable in doing so.

    Specs so far:

    Cutting area maximum 5'x3'.

    X Axis driven by 2x 20mm ball-screws with a lead of 5mm driven by a NEMA34 motor connected by cam-belt/pulleys.

    Y Axis driven by a 16mm ball-screw with a lead of 5mm driven directly by a NEMA23 motor mounted to gantry side-plate.

    Z Axis driven by a 12mm ball-screw with a lead of 2mm driven directly by a NEMA23 motor.

    All linear bearings will ride on supported rails.

    Main gantry to be constructed from 15mm 6082 aluminium plate.

    So, here are my ideas so far:

    This clip shows how I propose to build the main gantry:



    In order of appearance:

    1. The first plate will act as a mount for the linear bearings riding on 20mm supported rails (TBR20 from Zapp) mounted to 80mm aluminium extrusion and will also act as a brace for the...

    2. ...vertical cross piece, which also has 20mm supported rails mounted to its front to accommodate the z-carriage. The hole in the arm that drops to either side will accommodate the ball-nuts. There will be a ball-screw on either side of the bed driven by one motor via a belt/pulleys to move the gantry on it's X. The ball-screw for Y motion will run in between the two supported rails and be directly driven by the motor which will be mounted to the...

    3. ...side-plate which, when bolted to the other 2 pieces, will hopefully add to the overall rigidity of the structure.

    Some questions so far.

    I'm using 15mm 6082 aluminium plate for this build. I'm hoping to use M8 35mm hex socket head cap screws to bolt this all together, which means the screws will bite 20mm of the thread I'll tap into the plate edges. Does this depth sound robust enough? Is M8 too big for the edge of 15mm plate?

    To allow for a bit of adjustment I'll be making the holes in the face of the plates 10mm in diameter so there will be a bit of slop to play with before torquing everything up once it's all aligned. Does this sound okay?

    Where there are slots cut for plate to pass through (the arm which passes through the side-plate, for example) - rather than cut this slot to be exactly 15mm wide, should I make it slightly wider (say 15.25mm) to ensure that the plate passes through okay? .25mm too much?

    Obviously there won't be any internal right-angles because the end mill will have a radius. Where there's a square edge that fouls a radius, I'll manually chamfer off the corner to make it fit (see pic below).

    Click image for larger version. 

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    Now on to the bed that the gantry sits on:



    In order of appearance:

    1. C channel which connects the 2 X rails.

    2. Spacers to fill the gap between the C channel and the spoil-board.

    3. L section which adds rigidity along the Y-axis and connects to the machine frame.

    4. 25mm x 25.4mm aluminium spacers. Hole-sawing them at the mo - Pff, long and dirty job...

    Click image for larger version. 

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    5. 25mm thick plywood spoil-board.

    6. 6mm plate. Ball-screw bearing blocks will mount directly to this.

    The T-bolts that secure the aluminium extrusions to the top plate will pass through the top-plate, spoil-board spacers, L section c-channel before being fastened with a nut/grip-washer to the underside of the c-channel.

    A general and straight-forward question here. Is this viable?

    I have some ideas about how this is all going to connect to the frame, but I'll leave that for now and get a diagram together in the near future... Same goes for the Z-carriage. Meanwhile here are some pics of the adjustable feet I made... First time welding and also had a go a bluing the mild steel plate, didn't come out too bad...

    Click image for larger version. 

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    Is there anything here that represents an alarmingly bad design decision? Or could this actually work?

    (Bear with me on the wooden legs, all will be explained...)

    Cheers!
    Last edited by Wal; 22-12-2012 at 01:09 PM. Reason: Pic links fixed.

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