Need Help! BUILDING A 4 AXIS BENCHTOP CNC MILL


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Thread: BUILDING A 4 AXIS BENCHTOP CNC MILL

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    Default BUILDING A 4 AXIS BENCHTOP CNC MILL

    First off I would like to say hello to the forum, this is my first post.

    As the title says, I am looking for some advice from those who are much more experienced than I am. I'm currently a sophomore engineering student and I enjoy challenging myself with personal machining projects. I am very familiar with manual machining, I do a lot of vacuum fixturing design and prototyping for the physics department at my university. A couple months ago I replicated Steffan Gotteswinter's exchangeable anvil micrometer, after surface and tool post grinding, the mic is accurate to about 2-3 tenths over the 1 inch length, which is more then good enough for me. I'm currently in the middle of machining a aluminum rifle stock, and a fully operational scale 4 stroke engine. Although the 20-50 hour projects I have worked on are quite rewarding, I have decided to take on a more difficult challenge, something that would be useful. I'm sure anyone who has actually read this far knows where this is going.

    I want to design and build a "bench-top" sized CNC milling machine. Something relatively small but robust enough to machine aluminum without any issues. It wouldn't be a machine to do production job shop work, just something I could use to do small one offs or parts that would be tedious to machine manually. I am not concerned with efficiency, I would be okay running at the largest a .250 end mill or a max DOC of .050". Before my rambling continues any longer, I want to layout the main points I'm looking to have answered with this post.

    Overall Design:
    - I am in between a conventional style vertical milling machine and at some point adding a small 4th axis, or a PocketNC style machine minus the fifth axis. The PocketNC has a horizontal spindle, with a body made from a giant chunk of 6061.
    -I was planning on throwing an initial design together in Inventor, but figured I would try to get some feedback for this forum first.

    Size:
    -To put in perspective the overall size I am looking for, if I were to model a vertical mill, the machine table would be about 8" x 12" with 6-8" of z travel.

    Construction:
    -I have a high level of confidence in my ability to manually machine any non-lego part on the machine and I have access to several fully equipped machine shops on campus.
    -All of the "machine ways" will be made using linear rails controlled by rolled acme threads supported by radial bearings at each end and anti-backlash nuts.
    -For a spindle, I plan on purchasing a straight shank ER-20 or ER-25 collet chuck and pressing the shaft into two opposing tapered roller bearings
    -Would it be adequate to construct the table and saddle out of aluminum?

    COLUMN: I was more curious about this then anything else. With such a small machine, how picky should I be with the column constriction, I was originally thinking a 3" x 3" x 16" piece of cast iron bar stock. After doing some reading and recognizing how important it is to have a column that wont resonate the vibrations from the tool, I was looking into thick wall hot rolled tubing filled with granite epoxy resin.

    Cost: I am lucky enough to be working at a 6 month internship that pays pretty well, so I will have a steady flow of income to fund this, that being said I would still prefer to spend around 1000 dollars.



    Conclusion: I am looking for whatever help anyone is willing to give. Whether it be answers to questions asked here or general ideas and suggestions on the machine. Anyway, its 2:30 in the morning and I have to be up for work at 5:30 so I'll cut it there.

    Thank you in advance for any help anyone is willing to give.

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    Default Re: BUILDING A 4 AXIS BENCHTOP CNC MILL

    Hi there Shermama. If I may add my two cents, I'll discuss a couple of things you ought to think about.

    You ought to build the machine as big and as rigid as you possibly can with the materials, tool and methods that you have available. So you have a maximum envelope that the machine can fit in. Start with that concept to think about and then try to expand it a little. I prefer steel to aluminum because it is stronger and cheaper but there are issues with welding it.

    I am again'st benchtop machines in a small shop because they take up all the work space that you need for projects. I have a small shop and for me it is better to have a roll around machine that can be put in the corner when I am not using it. With this approach you can often build something a little nicer than a small benchtop machine and put it in it's own roll around housing
    that can allow for coolant if wanted.

    Often just by letting the machine be a little bigger you can have something that performs really well. Also, you may want a mill that is something more like a hybrid vertical mill and router which will allow you to mill a wider variety of things then just small parts. I have been studying and designing some CNC projects for couple of years but I am still collecting and building manual machines at this point so I have the machines to build them.

    Here are a few of my CAD designs that you might want to think about doing something similar.

    The Coffee table router is meant to be a very rigid deep plunge router that can act as a milling machine. It's about the size of a coffee table and was originaly designed to be used in a small house in place of a coffee table. The next is my full on intent to build a portable high precision vertical machining center with a tool changer.

    I started looking a small benchtop mill but decided it was not for me.

    If you decide to build a more traditional benchtop vertical mill you may wish to consider using EG (Epoxy Granite) for the base and column material. There are some really good designs out of Germany for benchtop machines. Search the EG thread in this forum and do a search for EG mill on Google.

    As for column size. Even a small benchtop mill ought to have a column at least 4 x 6 inches in size. Which makes it pretty heavy and hard to put up on the bench. This can be made with a solid piece of steel, cast iron or a steel structural member filled with concrete or EG. If it can be made entirely out of reinforced EG or concrete if it is made larger in size.

    You will see that any half decent manual benchtop mill is at least 400 pounds and the better ones are more like 500-600 pounds. You have to have a certain amount of mass and stiffness to get good cutting ability on a traditional vertical column mill. There are others ways to get stiffness without the weight but these methods are better suited for routers or enclosed gantry mills.

    You could also build something like the portable manual mill that I am in the process of building and make it a CNC mill that moves around. Mine will be about 600-800 pounds but not take up too much floor space.

    Attached Thumbnails Attached Thumbnails BUILDING A 4 AXIS BENCHTOP CNC MILL-33-x-41-inch-coffee-table-router   BUILDING A 4 AXIS BENCHTOP CNC MILL-integrated-steel-eg-roll-around-vertical-machining   BUILDING A 4 AXIS BENCHTOP CNC MILL-high-precision-manual-table-mill-assembly_7-jpg  
    Last edited by Hezz; 08-05-2017 at 12:15 AM.


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