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Using a round over router bits on CNC?

Discussion in 'CNC Projects' started by Award, Mar 28, 2019.

  1. Award

    Award Veteran
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    Hello,

    I'm making some handles/slots for a wooden box I'm making and I would like to use a round over router bit on my CNC machine to round over the edges however the one I have has a bearing on the bottom for "normal" cut by hand use. This makes it tricky to calculate the offset for the tool path. Ideally I would have a round over bit that was a pointy end with no bearing like a v bit but I don't know if they exist?

    Has anyone got any experience of doing this or am I coming at this from the wrong angle and should just do it by hand or is there a different type of endmill to use?

    Thanks

    Adam
     
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  2. Alex Chambers

    Alex Chambers Openbuilds Team
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    Hi Adam, many router bits have the bearing attached with a screw - just undo the screw and remove the bearing.
    Alex.
     
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  3. Aussie58

    Aussie58 Well-Known
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    I thunk Adam is asking about the issue of having the shaft of the bearing guide in the way and how to make allowances for it in his setup.
    Stick with the challenge Adam, it will make you a better operator..
     
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  4. Award

    Award Veteran
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    Sorry guys - I didn't realise what the bits were called when I posted this. So having just Googled "pointy round over bits" I can see there are lots (also known as decorative beading bits apparently) Apologies
     
  5. Alex Chambers

    Alex Chambers Openbuilds Team
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    My bearing guided router bits don't have a protruding shaft once the bearing is removed. The centre of the bit is half the diameter of the bearing from the cutting edge.
    Alex.
     
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  6. Giarc

    Giarc Master
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    I bought a chamfering bit for some plates I was making. I kind of got it figured out using Estlcam, but by the time I did a tool change and re-zeroed the Z axis I found it quicker and easier to just use a bit with a bearing guide in my router table. I know this doesn't really help, but in this case, it may be the more efficient tool.

    Also, to chamfer both sides required a semi-complicated cutting procedure whereas the router table was just a simple flip of the plate.
     
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  7. Christian James

    Christian James Journeyman
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    Indeed, there will always be a place for the router table in the shop.
     
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  8. David the swarfer

    David the swarfer OpenBuilds Team
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    I would either just reference off the bottom of the cutter blade, assuming that a clearance slot is already cut for the bearing support to travel in.
    Or I would carefully measure the bit after removing the bearing. Once you know exactly how long and wide it is figuring out the offsets is not hard.
    Fusion360 would allow you to draw the custom tool and then it can calculate offsets for you. Tricky though.

    I put a chamfering calculator in SketchUcam but it won't work for this as it assumes a straight edge and always uses the center of the cutting edge.

    roundover1.png
    This is how I would figure it:
    for this 6mm radius roundover I would measure the diameter of the small end, in this case 8mm (same as the bearing).
    Cut depth is the same as the roundover radius, 6mm
    The offset we want from the edge is 4mm, so we can set the tool as 8mm diameter.
    if there is a pip/shaft on the end where the bearing would be we need to be sure that it is shorter than the remaining stock depth so it does not hit the table.

    Slot width: I think it would be better if the roundover bit only cuts on one side so I would do an extra outline cut 6mm deep to make sure that there is a 14mm wide (8 + 6) slot all the way around the part to give clearance.

    Also note that this is a relatively deep cut so maybe a few passes at difference depths are needed.
     
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