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Thread: CNC milling machine - 2nd attempt

  1. #1
    Registered bob^'s Avatar
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    Default CNC milling machine - 2nd attempt

    My first attempt at building a CNC router was a simple MDF one that can be seen in my display pic.
    I had a couple of issues with it, the machine wasn't rigid enough, and there was too much variation in the table movement.
    So all this lead to machine number two, which more resembles a milling machine.
    I am using linear guides (HSR20) this time as opposed to stainless steel rod with linear bearings. I am also using machined ball screws instead of the rolled ones.
    Buying 2nd hand off ebay certainly has been a little hit and miss, especially with the guides. The ones I am using for my Z axis came off a machine that was lucky to travel 30mm. In turn, some of the balls are worn more than the others so movement can be a little notchy.
    The guides for my X and Y are spot on and were definitely a bargain!

    Travel is 100mm in the Z axis, 160mm in the X (capable of 220mm with a longer ball screw), and 300mm in the Y.
    Here are some pics:

    Old machine







    I will be paying particular attention to any movement in the y axis due to the way the bearing blocks are mounted so close together. If worse comes to worse, I will space the blocks further apart and lose some travel.
    Mounting the spindle so far from the uprights is also another concern of mine, but you never know until you try, so I will give it a go and then see what improvements need to be made from there.

    The base plate is 16mm mild steel, as well as the plate that joins the X and Y axis. Both have been machined parallel.
    The extruded aluminium has a wall thickness of 8mm and will have the surface on which the guides sit on milled parallel also. That will be one of the last steps after building the machine to make sure I am happy with the design, before spending more money on machining.
    For a spindle, I am unsure what I am going to use yet. I have a high speed spindle almost finished but it will only be good for engraving as it only uses radial bearings and not thrust.
    I have been looking at those cheap Chinese spindles on ebay though with quite a bit of interest.
    I also plan on building a low speed spindle with some beefy bearings.

    My main use for the machine will be PCB milling, but machining aluminium is also a high priority as I am into radio controlled buggies (especially customising them!)

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    Gold Member jalessi's Avatar
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    Thumbs up

    Bob,

    You wont have any problems with the rail spacing the way it currently is setup and it will be as rigid as a Sherman tank.


    Jeff...

    Patience and perseverance have a magical effect before which difficulties disappear and obstacles vanish.


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    Registered Drools's Avatar
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    That looks really well built! I recently completed a gantry style router with movements in the range of X30-Y20-Z5 inches. It is nice but a little big for the desktop where I do my PCB work. I'm thinking of building a smaller unit just for PCB work, with movements in the range of X12-Y12-X2 inches. Your model looks like a path to follow.
    What Linear rails did you use? It looks like you used 8020 but I'm not able to make out if it is the thick or thin wall verity.
    Very nice job so far!

    Here is a picture of a completed through hole board I did with my present router.

    Attached Thumbnails Attached Thumbnails CNC milling machine - 2nd attempt-dscf0028-jpg  


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    Man thats looking good. Very similar to size and design I am woking on.
    What type spindle and axis motors/drives do you plan to use?



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    Registered bob^'s Avatar
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    Thanks for the kind words fellas.



    That's the basis of my high speed spindle mount (ignore the little bit of paint inside where the bearing goes!). It is an ER11 collet.
    The plan is to build the same thing, but with larger bearings as well as angular contact bearings, for the low speed stuff.
    Spindle drive will be via a brushless motor out of a radio controlled helicopter.

    The linear rails are THK HSR20's. As for the 8020, I am not quite familiar with what that is, I only know it is a type of extrusion similar to what I use.

    http://www.linearbearings.com.au/Por...ofiles%201.pdf That is a link to the stuff I'm using. I am using Profile 8 heavy (the 40x40 heavy, and 40x80 heavy). The wall thickness is 8mm. What is the thickness of 8020?

    With the motors and drives, for now I will use my existing motors for the X and Y, but I can't remember the specs. I don't think they will have adequate torque though.
    For the motor drives, I have some from the old machine that I built up which performed great.
    http://secure.oatleyelectronics.com/...161af4f034f5bd - that's the drive
    http://secure.oatleyelectronics.com/...161af4f034f5bd - that's the power supply to go with it.
    I am running them off 35V.

    The control box


    The power supply


    Drools, that PCB turned out really well. What sort of cutter do you use?



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    Registered Drools's Avatar
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    I like that spindle! Looks like it will have next to 0 runout.
    That board was cut using a 45degree carbid bit from dertsap (Curt) He sent me a few to test. The board is 1oz copper on FR4 from digikey. After that board I did another board same bit and layout but the PCB material was 2oz copper on something other than FR4 and wow what a difference the extra copper makes! There are lots of threads in the PCBMilling section http://www.cnczone.com/forums/pcb-milling/
    I have ordered a few Professional PCB milling bits from PreciseBits and I will post some results when I get them.
    I'm really interested in your spindle project! I would really appreciate it if you would document your building of it. At the moment I'm using a Wolfgang spindle and it works great for PCB only but I cannot vary the speed without jumping through some electronic hoops.
    Good work!



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    I was trying to use a Dremel to mill my circuit boards and due to the runout, the finish wasn't the greatest. That's where I'm hoping this spindle will work well.
    It was never intended to have much load on it, hence the simplicity of the design.

    You should try a brushless motor out of a radio controlled vehicle. Combine that with a speed controller and you will have full electronic speed control. You can pick them up quite cheap.

    http://cgi.ebay.co.uk/Mini-ER11-exte...4.c0.m14.l1262 that is a link to the collet and shank.



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    I like the steel end caps all around. Are you having them cut with a water jet?



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    Do you mean the plates on the end of the aluminium? Nah my local laser cutter cut them to size. I was getting him to put the holes in also, but the heat was warping the plates too much so now I just get him to cut them to size, and then I do the necessary machining to it.



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    Now that's how you get'er done! Nice job. Looking forward to seeing more of your build.



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    Any new updates on this one?



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    Nah no updates so far on this, I have been way too slack!
    I go through phases of getting stuck right into it, and then it sits in the corner of the workshop under a cover



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CNC milling machine - 2nd attempt
CNC milling machine - 2nd attempt