1. #1
    Hi I am working on milling some foam, about 130mm deep.

    The longest cutter I have is about 120mm in total. Can anyone recommend a good cutter for foam, prefferably something around 20mm in diameter.

    So far the only cutter I can find long enough is this carbide insert cutter from APT but im not sure how well the carbide inserts will cut foam.

    BAP300R-16-200-C16 End Mill for APMT 1135 Inserts 16mm dia 16mm shank 200mm long Associated Production Tools
    CNC routing and prototyping services www.cncscotland.co.uk

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  2. #2
    I've just had a quick look on aliexpress, but not come up with much:

    1X3flutes 20mm HRC50 Fine powder tungsten steel alloy cutter for aluminum milling-in Milling Cutter from Industry & Business on Aliexpress.com
    Wholesale New HRC 60' High Speed Milling Long Shank A2~4S 8 150 2,4 Flutes Micro Grain Carbide Square End Mill Cutter-in Milling Cutter from Industry & Business on Aliexpress.com
    6*101*140mm lengthened 2 flute end mill, customized wood milling cutter, carbide spiral router bits, for foam acryl cnc machine-in Milling Cutter from Industry & Business on Aliexpress.com

    Maybe you'll find something with a bit more searching, or you could ask the last seller to make one as the ones he's listed appear to be specially made? For foam I expect a low number of flutes would work better.

    Remember the deflection of a cutter is roughly proportional to its length cubed, and inversely proportional to the diameter raised to the power 4. You therefore should always use the shortest cutter you can, with the largest diameter. That's why the 6mm diameter 100mm long cutter is probably only going to be able to cut foam - e.g. with the same cutting force it would deflect about 110 times further than a 25mm long cutter the same diameter, or 18 times more than the 16mm cutter from APT (assuming 120mm and 170mm unsupported length respectively).
    Having said that, you're only cutting foam so the cutting forces are tiny which means you can get away with a lot.

  3. #3
    Probably easier to make an extender - with 20mm dia you've plenty of room to hold a 1/4 inch shank 20mm router bit in a 19mm shaft.

  4. #4
    Quote Originally Posted by FatFreddie View Post
    Probably easier to make an extender - with 20mm dia you've plenty of room to hold a 1/4 inch shank 20mm router bit in a 19mm shaft.
    That's a good way to do it, depending on how deep he needs to cut. If this cutter needs to cut the surface of a tall face perpendicular to the bed, then a cutter with long flutes will get a better finish.

  5. #5
    Hi Gav

    Be careful if you extend the shaft that you do not reach the "critical speed" at which point there will be greatly increased vibration. Particularly if you are using a Chinese high frequency spindle. that can push 20,000 RPM.

    The shaft can bend to and suffer catastrophic failure. If it flies off and hits a person you can imagine the damage it could do.

    Regards
    John
    Last edited by John McNamara; 08-11-2013 at 03:50 PM.

  6. #6
    Try searching for "frog tools " if I remember right, they do long foam bits. Not cheap tho !

  7. #7
    I ended up using the apt tool with the indexable tips. I went with the alu inserts because they had a nice sharp edge. Diameter 25mm total length 200mm cutting flute 12.5mm.

    worked great, only real down side was the small cutting flute. Those frog tools solve that problem but way too much cash. Anyway the majority of cutting time was spent 3d profiling and the frog tools can't help with that. So overall I would recommend using an indexable tool like this for milling insulation foam.
    CNC routing and prototyping services www.cncscotland.co.uk

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