Need Advice - New CNC flex problems


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    Default Need Advice - New CNC flex problems

    Hello,

    I finally finish my CNC project after several redesigns in order to make it rigid. I didn't save any money considering the rigidity and the quality of the mechanics but I still got a flex on the indicator when I push my motor with fully retracted Z axis. I am using Bosch Rexroth PSK60 linear modules with two long blocks each. This modules are precise one with 5 micron backlash and 5 micron position accuracy. They are made from steel and I am way in the permissible loading and momentum for the bearings but whatever I do I still got flex. For the X axis I used THK KR33 module with single long carriage without balls crew to reinforce the x-axis. Y axis is with two motors that are external synced with timing belt in order to secure the gantry squareness. So my problem is that when Z is fully retracted and when I push it by hand I can deflect it with 0.2mm in X direction and with 0.1mm Y direction. I am planning to mill aluminium. My spindle is German made 0.8kw/24000rpm. Is this acceptable deflection considering that I want aluminium milling with tool diameter not bigger than 6mm and accuracy if possible bellow 0.1mm. I have big Z stroke (25cm) in order in the future to convert the machine in 5D CNC and also to make it support 3D printing. This is why I choose top-gantry crane design. Please advice if you see something wrong in the mechanics that I can improve. Need Advice - New CNC flex problems-img_0394-jpgNeed Advice - New CNC flex problems-img_0395-jpg

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  2. #2
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    Default Re: Need Advice - New CNC flex problems

    It looks like the basic structure of your machine is weak. Using those bolted-together aluminum extrusions is a good way to make lots of things quickly, but it's not the most rigid way to construct a cage that's not supposed to flex. If you don't want to start over again, you might think about how you could introduce some triangular bracing to all the corners.

    [FONT=Verdana]Andrew Werby[/FONT]
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    Default Re: Need Advice - New CNC flex problems

    Hi
    I am not an expert in these matters but have built a CNC myself. That z-axis is extremely long. Its needs to be supported further up the length of the z. Shars a Chinese importer
    has cheap 90-degree angle plates.They have very good prices and should be accurate enough for your application because they're a machinist product..Remove the support bracket you have and add a taller version. I believe that will help. Here is the link.
    shars.com - Angle Plate & Sine Plate

    I would recommend in the future taking pictures from different angles and having them as large as the CNC zone will allow. But again. I have no idea from the pictures how rigid the rest of your machine is. If the rest of the machine is not rigid adding a support bracket may only marginally enhance rigidity. From my experience I believe we tend to overestimate the strength of metals.They flex to a surprising degree.

    Regards Barry
    Wood Solutions Home



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