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  1. #1
    Join Date
    Jun 2024
    Posts
    3

    Need help for engraving a brass

    Hello i am new to the world of engraving . I get a CNC from Stepcraft ( m700 ) and i take it to engrave brass ( wax stamp ) .I use a 3.175 mm . I using cutters like the ones that i attached. My main problem is that the cutters are broken everytime . I want to engrave like the attached photos . The wax stamp is 2.5 cm perimeter . Can someone tell me another cutter for such a detailed job ? The cutters i used are for hard material . Can someone help me with this ? I am using 12.000 rpms till now .Thank you in advance .

  2. #2
    Join Date
    Oct 2007
    Posts
    1041

    Re: Need help for engraving a brass

    this may not be the right section for your question, I do not use the cnc machine to engrave brass but do use the 100w mopa fiber laser to engrave brass

    see here https://youtu.be/5iPip7nR4Z4

  3. #3
    Join Date
    Jun 2024
    Posts
    3

    Re: Need help for engraving a brass

    You are right. i did it by a mistake.

  4. #4
    Join Date
    Apr 2004
    Posts
    5770

    Re: Need help for engraving a brass

    It sounds like your basic problem is that you're trying to do metal engraving on a router designed for cutting wood. The Stepcraft M700 https://toolstoday.com/stepcraft-m-700-cnc-system.html would probably be adequate for making wooden signs or even carving duck decoys, with that long Z axis, but it's not rigid enough to engrave brass with. The amount of chatter at the tool tip is going to break those fine engraving tips every time, as you've discovered. Changing the bits isn't going to help, I'm afraid, and there aren't any engraving bits made that are going to be able to tolerate deviating more than their tip radius while attempting to plow a path forward. You need to do this sort of thing on a dedicated engraving machine, or at least a milling machine with a fast spindle.
    Andrew Werby
    Website

  5. #5
    Join Date
    Nov 2013
    Posts
    4666

    Re: Need help for engraving a brass

    Hi,
    I use these for making circuit boards. They are 60 degree types. avoid the narrower 15 degree, 30 degree and 45 degree tips, they are just TOO tender and will break.
    Second is to get a reasonable tip radius. 0.1mm will last fractions of a second before breaking. 0.2mm or bigger is what you want.

    I spin them at 24000 rpm and have a low runout (<5um) spindle. Spindle runout (20um >) will break these tools instantly. Last thing is to engrave only 0.1 to 0.2mm at a time. If you want a deeper
    cut you have to go over it several times.

    Craig

  6. #6
    Join Date
    Apr 2018
    Posts
    143

    Re: Need help for engraving a brass

    Moderator note: Two similar threads have been combined, and the result moved to this location.

  7. #7
    Join Date
    Jun 2024
    Posts
    3

    Re: Need help for engraving a brass

    Thank you for your replies. I am making some wax stamps till now but the result is by luck eveytime( some times i am destroying 5 cutters , some 1 cutter ) . I will try to make the spindle to 20.000 rpm. For sure i will change the cutter angle ( till now i am using 30 degrees or 20) . So i will take now to try 45 and 60 degrees as you told me ( Craig ). My problem is ..will those angles, make the detailed job i want ? The depth i used to make is 0.7mm . So you tell me to try to do it 2-3 times ( 0.2mm everytime) . Last i didnt understand the runout that you refered ... The spindle i use can go till 25.000 rpm .

  8. #8
    Join Date
    Apr 2018
    Posts
    143

    Re: Need help for engraving a brass

    Here is a page from Tormach that has details about 'runout': https://tormach.com/articles/measure...ol-life-killer

  9. #9
    Join Date
    Nov 2013
    Posts
    4666

    Re: Need help for engraving a brass

    Hi,
    the tip diameter of these engraving cutters is small, typically less than 0.3mm. Thus you should spin them as fast as you can.

    Imagine an endmill 0.2mm in diameter, spinning at 25000 rpm. The surface speed is:

    0.0002 x PI x 25000=15m/min!!!!

    Which is way WAY WAY slow. Ideally you'd be up at at least 100m/min or 160,000rpm!!!!

    Last i didnt understand the runout that you refered
    Runout referes to how much the end of the spindle wobbles back and forth as it turns. Good quality spindles are <5um while cheap rubbishy spindles are >20um or more. Any wobble will
    severely test the strength of the tip.

    So i will take now to try 45 and 60 degrees as you told me. My problem is ..will those angles, make the detailed job i want ?
    Yes, the wider angle will limit the amount of detail, especially if you want to cut down to 0.7mm. You'll have to find a balance.

    I make some circuit boards that have a vey thick copper layer (top and bottom), 420um or 0.42mm. It is specialist circuit board for high current applications.

    The problem is that if I use regular 60 degree engraving tools the slope of the sides reduces the width of the circuit traces unacceptably.
    Thus for these boards I use 0.5mm two flute endmills, and I can assure your they are way WAY more tender than engraving tools. The first pass, a 'slotting' toolpath I take half the copper,
    ie 210um or 0.21mm, and then another pass to get to the full depth of 420um or 0.42mm. Thereafter I take full depth passes (420um/0.42mm) but at 25% stepover (12.5um/0.0125mm).
    I use flood cooling, especially to clear the copper chips, but with this strategy I can get eight to ten hours per tool.

    Craig

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