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  1. #1
    Join Date
    Jun 2012
    Posts
    182

    Specifying V-Grooves

    I'm designing a part with two v-grooves in which shafts will rest. The bottom of the v-groove will be relieved with a straight bit (similar to a standard v-block). Drawing the part in my CAD program is no problem, but when the drawing is converted to gCode, how do you specify the tool height and path relative to the contact point between the shaft and the groove?

    Another way to ask the question is, how do you set the toolheight of a v-bit when you don't know how fine the point is?

  2. #2
    Join Date
    Sep 2012
    Posts
    1195
    If you are going to relieve the bottom of the "V", I think I would make that cut first, the cut the "V". That way, the point doesn't really make any difference. All you would need to know if the angle of the "V". If it's 90 degrees (45 degrees from shaft axis each way) and you want a .250" wide "V", you would set it to a .125" depth. If it's a 60 degree angle (30 deg from shaft axis) and you want .250" width, the depth would be set to .217". From the angle, you should be able to calculate the needed depth. The tip may not get all the way down to a point, but the width will be correct at the surface. If you're relieving the tip out anyways, that won't matter.

  3. #3
    Join Date
    Jun 2012
    Posts
    182
    As an example, I have a half inch v-groove router bit and the web on it is about 30 thousandths wide. If the tool height is set to the tip of the bit, the cut will be 15 thousandths too deep. How is this usually handled in the CNC world? Do you just make trial cuts until the virtual height is found?

  4. #4
    Join Date
    Sep 2012
    Posts
    1195
    Depends a bit on the CAM software I suppose. In Bobcad V24, which is what I use currently, the bit geometry can't be input for a tapered bit, so I just have to know the correct cutting depth (Bobcad uses the material top surface as the point of reference and you input the depth of cut from that plane). This can be figured out by trial and error, by getting the exact specifications from the manufacturer of the bit, or by measuring the bit and drawing up the expected cut in cad to determine how deep the cut should be. The last option is really only feasible if you have a really good dial indicator and a solid holder to make the measurements. Unless you have a dial indicator with .0001" increments, I'd say you'll get better results from the manufacturers specifications. You'll probably get the least accurate results from trial and error since it can be difficult to measure the exact width of a v-groove, but if you don't need to be closer than +/- .005", then it would be fine.

    In some software, you can input the actual geometry of the bit (again by either measuring or from manufacturer's specs). The software would then take into account the bit shape and fit is accordingly if the part is modeled in 3d. For 2d profiling and engraving, I suspect that you would still be entering the depth of cut relative to the top surface of the material, but there may also be software that uses the material bottom as the reference plane.

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