Plastic sticking to bits

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This topic contains 3 replies, has 2 voices, and was last updated by Profile photo of Tom Cole Tom Cole 5 months ago.

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  • #27783
    Profile photo of Tom Cole
    Tom Cole
    Participant

    I have a single flute 1/16″ upcut end mill designed for cutting acrylic sheet. I’m cutting 3mm thick sheet running at 6mm/sec with a .8mm depth per pass at 30000 RPM. The cut is great, until swarf sticks to the bit, pretty much on the second pass.

    I can slow the RPM a bit, but not certain of exact RPM.

    I don’t seem to have this trouble with a 2 flute bit at 12mm/second feed rate with the same depth per pass.

    Anyone have any ideas why? I have an idea, but before trying I figured I’d see if someone sees any glaring issues in my setup.

    #27791
    Profile photo of Ryan
    Ryan
    Keymaster

    Plastics are temperamental. Your settings have to be spot on. I would check a cut calc for this, 1/16th is small and 30,000rpm if really fast.

    I would guess deeper per pass is going to help a lot. you need to get the chips big enough to take the heat away with them, or use coolant.

    #27819
    Profile photo of Tom Cole
    Tom Cole
    Participant

    Would a 1/8″ bit be better?

    Ok, so I’m out of tricks when it comes to feeds and speeds. I’ve been playing with this all day and it seems that the best results I got were with the 1/16″ 2 flute end mill at what I would call 2/3 power (20k RPM via redneck SWAG) The depth of cut was increased to 1.6mm and the feed rate was increased quite a bit to 20mm/sec. I switched to the 2 flute mainly because I snapped the 1 flute bit. Doh!

    This did great until the second pass on the second part. (two parts cut in same cycle) This second pass puts the bit .2mm into my waste board and the combination of MDF dust and plastic swarf makes one heck of an adhesive.

    Some fine chips that the vac misses end up in the curf and I feel that getting them out would help. So I’m going to rig a little blower to blow out the chips, hopefully toward the vac nozzle. Maybe this focussed air jet can aid in cooling too.

    #28031
    Profile photo of Tom Cole
    Tom Cole
    Participant

    I have finally cut 5mm lexan successfully, but made a huge mess! Used a 1/8″ 1 flute upcut at 20k RPM and 25mm/sec feed at a depth of 1.8mm. Success came when I followed the bit as it was cutting with a blower from my air compressor. I blew swarf everywhere! Looked like it snowed in my shop. I now have the beginnings of my 2nd 3D printer!

    This appears to have done two things to make the cut successful. First, it cleared the swarf out of the curf so it never had a chance to melt back, and second, high volume compressed air focussed on the bit acted as a coolant.

    So I’m going to design something to focus 3 independently tunable jets of air at the tool bit, hopefully blowing the swarf right into the vac nozzle. I found that the jet pressure is not nearly as important as a precise aim.

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