1. #1
    robump's Avatar
    Lives in Harrogate, United Kingdom. Last Activity: 14 Hours Ago Has been a member for 4-5 years. Has a total post count of 12.
    Hi Everyone,

    I have been lingering in the background here for some time looking with envy at all the different build logs.

    I have decided that i am going to have a go at building one and am looking for some critique and advice on a design that would work.

    I unfortunately dont have a milling machine so was originally going to convert a milling machine to CNC to assist with the building of the router but they seem to be going for quite a lot 2nd hand so i thought i would go straight for the router.

    I was thinking that i would use ali extrusion for the base of the router for the accuracy of the extrusion, but after reading up about using auto leveling resin to mount the rails on i have considered switching back to 100x50x5mm steel box section.

    I plan on using a standard 2.2kw spindle but have yet to design the z axis, i was hoping to get the base and the gantry sorted before considering the z designs.

    I plan to use the router to cut mdf and plywood but also to engrave acrylic and pcbs.

    I am thinking about using SBR20 rails on the X axis but not yet sure about Y and Z, possibly linear guide rails but looking for a bit of advice on this.

    In terms of ball screws i was thinking of using 1605's but again would appreciate some advice on this.

    I haven't decided for certain about the size of the machine yet but think that a 1000x610mm working area, being half a 6x4ft standard sheet size. Does this seem reasonable or am i being a bit optimistic?

    I have had a play on sketchup and come up with the following designs, any advice would be greatly appreciated!

    Thanks

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  2. #2
    Hi Welcome.

    Well your needs are small and they fit with each other well. This focused group of materials all need relatively high feed rates with the exception of PCB which needs high accuracy and low/medium feeds.(Don't do much PCB so not my strong point)

    So starting with feeds then really you'll be better with RM1610 has they will offer good feed rates and resolution. Also if you connect motors to screws with belts then you have the option of gearing 2:1 and increasing resolution and torque for more demanding or resolution orientated work.
    Your design suits having both screws being connected with timing belt which will work out cheaper and IME much better than slaved motors.

    Your design could use a few small tweaks but it's very close. Size wise I'd maybe increase length to suit 1250 has sheet sizes tend to be 8x4 rather than 6x4. That said if you can live with 1000 then keep it shorter has it helps with screw whip at higher feeds.

    #1 Add more supports for the base and cross brace to keep square and add strength.

    #2 Gantry is a bit low and by time bed surface and then spoil board you won't have much clearance so I'd place some raiser blocks between bearing plate and gantry.

    #3 Gantry sides don't need to extend past ballscrews and can go on inside of screws. This will put ball-nut mounts on outside and make alignment and setup bit easier, it will also make gantry and bearing plates narrower and that bit more ridged.

    #4 Regards the rails then if you can stretch to profiled linear rails then do so has they are so much better than round and if you plan on doing high accuracy work like fine engraving or small PCB work they will pay dividends. If mostly wood work then round rail will be ok but they need more attention/maintenance and wear out much quicker.

    Like I say small tweaks but quite beneficial to good machine.

    Regards the Z axis then make it strong, use 20mm plate no less and Rm1605 ball-screw again connected to motor with a timing belt. Timing belts really help with resonance and make for smoother running motors plus they give flexibility of gearing if required.

    Hope this helps.

  3. #3
    As for your ball screw mount, the amount of material used in trying to get it hang on the side of the side of the box section will almost be the same as putting the ball screw and rails next to each other.
    Have a quick look at my build log and you'll see what I mean.

    It will also make it easier to align.

  4. #4
    Quote Originally Posted by jcb121 View Post
    As for your ball screw mount, the amount of material used in trying to get it hang on the side of the side of the box section will almost be the same as putting the ball screw and rails next to each other.
    Have a quick look at my build log and you'll see what I mean.

    It will also make it easier to align.
    Not sure what you mean here JCB.? It looks very similiar to your drawings in this thread. http://www.mycncuk.com/forums/router...-mark-2-a.html

    I don't like ballscrews running along side of rails on flat horizontal surface because they become chip traps. With screws on side chips fall away and it's easy to put a chip deflector cover and help keep clean. . . . Alignment isn't much harder. It also means orientating top rail in it's wider weaker position which means more supports so there's actually more material needed.!

  5. #5
    robump's Avatar
    Lives in Harrogate, United Kingdom. Last Activity: 14 Hours Ago Has been a member for 4-5 years. Has a total post count of 12.
    I have just had a 30 min go on sketchup to try and implement some of the more simple suggestions for your gantry design, is 50x50x5mm aluminium box strong enough or should i be using a solid alu billet for the riser off the linear rails?

    Now going to look at strengthening the base and working out the cutting area.

    Thanks once again.

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  6. #6
    Quote Originally Posted by robump View Post
    is 50x50x5mm aluminium box strong enough or should i be using a solid alu billet for the riser off the linear rails?
    I'd go for something stronger.

    Quote Originally Posted by JAZZCNC View Post
    I don't like ballscrews running along side of rails on flat horizontal surface because they become chip traps. With screws on side chips fall away
    If moving the ballscrew doesn't comprimise the strength of the axis, then I agree you should try to avoid letting chips collect on them. However, as I mentioned in this build log, it's very easy to just put 15mm rubber shaft seals either side of the ballnut and they'll take care of the chips.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  7. #7
    Quote Originally Posted by Jonathan View Post
    If moving the ballscrew doesn't comprimise the strength of the axis, then I agree you should try to avoid letting chips collect on them. However, as I mentioned in this build log, it's very easy to just put 15mm rubber shaft seals either side of the ballnut and they'll take care of the chips.
    Yes I've tried that before but they only last for short while then chips start getting thru.!!. . . Better if chips don't get there at all or better still do both.!

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