Z-axis movement design


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    Talking Z-axis movement design

    I've been researching diy cnc machines for the past few weeks, readying myself to design and then make a cnc router and have noticed something common in the designs, which has raised a question which I'm hoping someone might be able to answer.

    All the cnc router/milling machines used for cutting varying materials I have seen so far have had a static gantry height with a single Z-axis screw moving the physical router/milling bit itself, up and down. I've mainly worked with 3D printers which usually have 2 Z-axis motors on each side, so they move the whole horizontal bar up and down rather than just the print head up and down.
    Why is a gantry design like I described first, common practice? The first reason I can think of is potentially the two vertical ball-screws/precision screws on either side holding up against the weight of the gantry may be to much?. The other I thought of is possibly issues with force in the y direction, but I'm not sure how much force is exerted when cutting wood, plexiglass, aluminium etc...?

    The machine I am planning to make I am hoping will cut pieces of material 1.2m x 1m or less, I'm not sure what "size" a machine that would be considered. From relatively similar sized machines I've seen I can probably get around 200mm of Z-axis height.
    The main reason I am looking at 2 Z-axis motors on either side is to vary height more. In being able to vary Z-axis height more, it does potentially open up the potential to do "more than average" sized 3D printing by switching out the router motor for a print head module.

    Also another question, in terms of not being restricted to just wood, plexiglass and thin aluminium sheet material, what changes would I need to make in order to also work with thicker aluminium? Is that just down to the "drill motor and bit" or would the machine have to be more rigid/absolutely solid to do this?

    Any insight is appreciated
    Thanks

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    Registered KH0UJ's Avatar
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    Default Re: Z-axis movement design

    Z-axis movement design-htb1gppqjxxxxxxhxvxxq6xxfxxxj-jpg

    A D-I-Y CNC machine such as like this do have 2 variable Z axis, one is automatic then the other one is manually configured, that involves loosening the 2 allen bolts then (reposition) lifting up the spindle motor itself and lock again, you can cut any material on this type of CNC, anything softer than the carbide bit is doable, aluminum is just a breeze on this machine, on my experience I cut a whole block of aluminum 80mm thick and shape it according to the customer`s preference, but that involves programming a custom CAM because the bit I used is only 1/8 single flute carbide, it can get a job done precisely and perfectly just like any other professional CNC machine but it needs time, let`s say a professional CNC machine can achieve that job within just 30 minutes, but on a D-I-Y CNC machine it took me 3 hours, same on everything but on a different time span, aluminum 1-3mm no questions asked it gets the job done quickly, you can even print your own picture in half 3D in the aluminum material using only a carbide V-bit, medals on brass, gold, silver, aluminum, high carbon steel if you want hehe it can do the job. for as long as the hardness of the material does`nt exceed on the hardness of the bit you`re using then it`s OK, another question will be raised, on a high carbon steel can it cut like 1mm per pass? absolutely NO! on harder materials you need to program the CAM @ 0.1 or 0.05mm to make it work without worrying about the bit getting dull. cabide bits can cut/engrave harder materials for days without getting dull, for as long as there`s cooking oil in it you`re good to go hehe, im not really using a coolant (I cant afford it) I use whatever is in my reach.



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    Community Moderator ger21's Avatar
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    Default Re: Z-axis movement design

    I have seen a few machines (2-3) where the entire gantry moves up and down.
    There are a few issues with this design.
    1) It's more expensive to build.
    2) The chance of it being less rigid are high.
    3) You're moving a lot more mass up and down, so it will likely be much slower.

    Also keep in mind that the more Z axis travel you havem the less rigid the machine will typically be.
    And a router does not make a good 3D printer, as it will be much slower than a lightweight printer.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Z-axis movement design

    Here is mine I looked at a lot of machines and thought this was as ridged as I could get .the front plate that holds the spindle does two things the brackets for the spindle when locked up make the plate stronger then the lineal rails are screwed to the plate making it a little more ridged along with the 4 lineal bearings with a travel of 180 even at it's lowest point it still is very accurate and not a lot of vibration.
    Z-axis movement design-cnc-jpg



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    Default Re: Z-axis movement design

    Quote Originally Posted by InMesh View Post
    Here is mine I looked at a lot of machines and thought this was as ridged as I could get .the front plate that holds the spindle does two things the brackets for the spindle when locked up make the plate stronger then the lineal rails are screwed to the plate making it a little more ridged along with the 4 lineal bearings with a travel of 180 even at it's lowest point it still is very accurate and not a lot of vibration.
    Z-axis movement design-cnc-jpg
    Well that`s a very tough looking bracket you got there sir, nice job

    But on my opinion, I hope I dont offend anyone here, a strength of a human hand holding a pencil grinder can carve, cut, slice any material he wants, with that small amount of force he can cut anything, so basically I dont really need a rigid CNC, working with metal materials on the CNC router only requires code mastery, familiarization of the CNC`s optimum speed, sharpening of the bit used, that`s why I program CAMs on lines because I want to control the spindle itself to where to go first, how thin to cut, where to zero and so on and so fourth, even if I use a wooden frame CNC I can still work on it as accurate as the original mold or part, just dont ask about the time because it will eventually be slower because I cannot let the spindle go full depth cut without vibrating the whole machine, so it will run on a feather touch on the material to maintain stability and accuracy of the part being cut.



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