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  1. #1
    Well I posted in General as an introduction but didn't even get a 'Forget It' comment. So I will try again.

    I have need of a machine to cut Ply and MDF from 8X4 Sheets. I am thinking an Extrusion based build using a Kress spindle. 20mm Aluminium Plate for Gantry Sides, Rack and Pinion for the long (X?) axis and Lead Screws for the Y(?) and Z. Or possibly one Lead screw positioned centrally under the bed (prefered option)

    One end open to facilitate loading would be necessary. Here comes the Interesting (but not original idea) I would like to build in a 4th Axis across the machine for spindle work. If it's not feasible then I will find a Lathe instead.

    Suggestions for Min/Max Extrusion sizes and appropriate linear bearings eg Hewin or supported Rail (I am concerned there may be too much dust/debris for Hewin type Bearings) would be much appreciated.

    Questions about motors etc can wait but I will again be looking for any help I can get.

    A Workshop (read Shed) is being built to house the beast as we speak and will be ready by the time I have collected all the bits and pieces needed (I hope).
    Tim G-C

    I disapprove of what you say, but I will defend to the death your right to say it.

    (attrib. Voltaire but written by Evelyn Beatrice Hall "The Friends of Voltaire" 1906)

  2. #2
    'Forget it' is not a bad start but I'll stick my neck out and give it a go.

    First it's a big machine for a first build, not impossible but just saying.
    For spindles most use the 2.2kW or 3kW water cooled ones, make 2.2kW your minimum size.
    20mm plate sounds good for a lot of the parts.
    Not sure about using extrusion as I've no experience with it but a lot of people use it. Steel would be cheaper, for the frame at least, but you'd need to weld it.
    Rack and Pinion is not the first choice but it might be okay for your size machine and application.
    Ball screws are what you need for Y and Z. If you use these for X also, then one centrally mounted is a definite NO NO, you need two, one each side.
    4th axis integration is fine, it just means the machine will be longer to accommodate it.
    Hiwin or similar rails are much preferred over round supported rails but are more expensive.

    Wait for more people to chip in then using that information knock up a drawing. Unless you already have some CAD software, 'Sketchup' is commonly used because it's free and easy to use
    Look through the build logs and get ideas there. http://www.mycncuk.com/forums/253-DI...ter-Build-Logs
    Last edited by EddyCurrent; 15-10-2014 at 04:24 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  3. #3
    Okay thanks for that ... I'll look into spindles. I can weld (in a fashion) so I'll look at steel pricing. I've just had a lightbulb moment (don't laugh) If the bed was correctly stressed I could mount the ways for the 4 th axis into the bed. Just remove a section of bed to reveal the space. The centreline of the 4th axis does not need to be higher than the bed. I have an unused Wood lathe I can use for the ways and tailstock, a Stepper/belt to drive the Headstock assembly.
    Tim G-C

    I disapprove of what you say, but I will defend to the death your right to say it.

    (attrib. Voltaire but written by Evelyn Beatrice Hall "The Friends of Voltaire" 1906)

  4. #4
    The links I posted here might be of interest ?

    http://www.mycncuk.com/threads/7960-...2243#post62243
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  5. #5
    Is Mild Steel box 100 X 50 X 3mm okay for frames or would I be better using 5mm
    Tim G-C

    I disapprove of what you say, but I will defend to the death your right to say it.

    (attrib. Voltaire but written by Evelyn Beatrice Hall "The Friends of Voltaire" 1906)

  6. #6
    Well I used 50x50x3 and 100x50x3 albeit on a smaller machine. These sizes were ideal and provided the design is right there should be no flexing of the structure. You do though have to consider that the 3mm thickness is not much if you intend making threaded holes in it, and you will for the X rails at least. In my case I glued a piece of 30x6 flat strap inside to beef the threaded thickness to 9mm.
    I think you should go with the 5mm thickness
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  7. #7
    First let me say for a first machine this will be challenge so don't go rushing into it without carefully researching and drawing up a detailed design.

    Forget driving gantry from centre and really forget using ballscrews for the long axis unless your prepared to get into rotating ballnuts etc. Rack & pinion is the way to go for the long axis. Using R&P brings it's own challenges but they are much easier and cheaper to solve than ballscrews and mostly just means choosing the correct motors and ratio's.

    Profile is fine and easy to work with but it's very expensive compared to steel. For a machine this size then you'll want minimum 80x80x5 steel.
    Build it in such a manner that you don't really have gantry sides, make the sides of the machine high and sit the gantry directly on the bearings. There are several builds here that use this setup so just look around the build threads.
    Hi-win style profiled linear rails are what you need so forget round rails and they easily handle the debris, infact much better than round rail does.


    Regards a 4th Axis then if your wanting to use like a Lathe then forget using a stepper motor.! They just don't spin fast enough or have enough torque.
    Even if you want just a rotary axis for 3D work then I'd look at using a Rotary Axis converted with a Stepper motor.? Reason being is the Resolution. Steppers connected to pulleys don't give enough ratio so the resolution is low and for better or more detailed work then much higher ratios are preffered.

    Make the Axis rails longer than the bed and put the 4th axis on the end has messing around with removing portions of the bed will soon become a pain. Also if the 4th axis is below the bed this means the Z axis is over extended giving much greater chance of flex and poor finish. Having the 4th axis on the end higher up makes much stronger giving better finish quality.
    Another reason for the top rails extending past the end other than 4th axis is that you can machine the edges or ends of panels or cut dovetails etc this is very useful in many ways.

    Like I say this will be a very big challenge for a first machine but it is do-able but not if you rush into it so go carefull, be patient and ask questions.

    Oh and forget Kress spindles they are toys. Like eddy recommends 2.2Kw or larger is the way to go.
    Last edited by JAZZCNC; 15-10-2014 at 10:58 PM.

  8. #8
    Thanks for the pointers.

    Okay, let me get this right. Minimum 80X80X5 steel box ... Build frame with bed set to give max Z needed directly off the top of the frame (I haven't worded it very well but I know what you mean).

    R & P for X and Y with Lead/Ballscrew for Z. Hewin rails on all Axis. 15 or 20mm or what?

    Rails mounted on face of Gantry or top and bottom, which would keep Z close to Gantry?

    I thought thick Ply for the bed with replaceable MDF as a spoil board.

    The machine will only be used to cut Ply, MDF(Ugh!!!) and natural Timber.

    Good thinking re running the gantry past cutting area for edging etc.

    I already know the maximum dimensions/diameter that the 4th axis work requires so maybe I can build it into the walls of the frame parallel with the Gantry(the work is not complex or detailed, imagine an egg timer but with a spheroid shape of smaller diameter instead of a narrow neck with a tenon and slot at each end They are the upright supports of the Rocking Horse frame).

    Is there a way to work out what size motors/ gearing I will need to get good accuracy/repeatability/resolution?

    Tim
    Last edited by Wobblybootie; 16-10-2014 at 12:48 AM. Reason: Grammar, Spelling
    Tim G-C

    I disapprove of what you say, but I will defend to the death your right to say it.

    (attrib. Voltaire but written by Evelyn Beatrice Hall "The Friends of Voltaire" 1906)

  9. #9
    20 mm rails minimum, forget 15 they are a pain to grease for one thing, I would never use that size again.
    Gentry Y rails top and bottom keeps Z close to gantry
    I use ply for the bed 2 x 18mm birch glued together and bolted down, plus spoil boards. It's strong but will flex under load if not well supported by frame cross members underneath.
    The 4th axis is great but you could machine the supports in 2.5D as two halves you glue together lengthways.
    I think Jonathan posted something about motor sizing, use the forum search box.
    Last edited by EddyCurrent; 16-10-2014 at 08:29 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  10. #10
    I think Dean was suggesting R & P for the long axis only with ball screws for the other two. ..Clive

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