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  1. #1
    knoba's Avatar
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    Drill bits for plastics

    Tip angle 60°, flat 4° rake, clearance angle 12°






    Page link: https://knoba.wordpress.com/2015/04/...s-for-plastic/

    Thanks Ken!

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    kbalch (04-10-2015), Paul Jones (04-12-2015)

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    Thanks knoba! I've added your Drill Bits for Plastics to our Miscellaneous category, as well as to your builder page: knoba's Homemade Tools. Your receipt:


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    knoba (04-11-2015)

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    Content Editor DIYer's Avatar
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    School me on this, please. Would the reprofiled bits prevent jagged edges? Cracking? I just use metal bits when I need to drill through plastic.

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    Yes, those bits are used to avoid ("prevent" is probably overstating their efficacy) chipping and cracking. I used special plexiglass bits with similar profiles to drill the canopy on my airplane.

    Ken

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    DIYer (04-13-2015)

  8. #5
    knoba's Avatar
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    As Ken said.

    You can use metal bits but it's wise to take some special precautions;
    Use an undrilled area of a sacrificial backing piece (wood) for each hole.
    Avoid using pilot holes if process permits.
    Clamp the plastic down.
    Use slower rpm speeds.
    Slow feed pressure down on break-through.

    hth

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    DIYer (04-15-2015)

  10. #6
    Paul Jones's Avatar
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    I wish I had these for drilling Plexiglas parts. Have you also ground special drills for drilling brass?

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    I'm gonna give this one a try. Recently drilled a panel of plexi, lots of hairline cracks.

  12. #8
    knoba's Avatar
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    Quote Originally Posted by Paul Jones View Post
    I wish I had these for drilling Plexiglas parts. Have you also ground special drills for drilling brass?
    Hi Paul,

    You do some very nice work, btw!

    No I haven't reground a set for brass. Do you mean; once the bit grabs into brass it starts pulling itself through without much coercion from the operator?

    I would have thought the best geometry for brass drill bits would be to back-off the "lip relief" shown in the following diagram as "x";



    hth.

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    Hi Knoba,

    Thanks for the compliment. I have similar trait to Ken's toolmaker mentor concerning "finishing the areas that no one else will ever see".

    For years I have been temped to reduce the lip relief for some larger nominal sized import drills I use for drilling brass with the tailstock in the lathe. A few times I had 3/4" drills pull the tailstock chuck out while drilling out brass or bronze round stock prior to boring. No serious accidents but something to avoid. I found rolling a small section of printer paper in between the chuck and tailstock Morse tapers seem to make it hold better but doesn't fix the root cause.

    Thanks, Paul

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    knoba (04-14-2015)

  15. #10
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    Quote Originally Posted by knoba View Post
    As Ken said.

    You can use metal bits but it's wise to take some special precautions;
    Use an undrilled area of a sacrificial backing piece (wood) for each hole.
    Avoid using pilot holes if process permits.
    Clamp the plastic down.
    Use slower rpm speeds.
    Slow feed pressure down on break-through.

    hth
    Great advice, knoba! Thanks!

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