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Thread: Drilling large deep holes on lathe with forestner dit

  1. #1
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    Drilling large deep holes on lathe with forestner dit

    This is a follow up question from a previous link Powermatic 3520b quill problem. I received the new quill and sure enough it moves in and out smooth as can be.
    So I apparently bent the old quill by attempting to drill a deep( 8") hole x3" Dia in a semi green piece of maple for a vase. I had recently sharpened the bit but the wood was hard and I was going slow with suction removing the chips as best possible. It did bind up a couple of times if I pushed too fast Deep in the hole it started to bind up whenever I tried to back out. I have to admit the wood had a very slight wobble to it and I'm blaming that for the bend, but nothing worse than I had done before.
    How do you go about drilling deep holes for vases and such? (And I like to sometimes drill an hole to proper depth before hollowing out a bowl.) Should the wood be really green and soft?

  2. #2
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    I drill them on the lathe. My lathe motor has lots more torque at low speeds than my drill press, I can hold the piece more securely, and I can gradually increase the bit size since the piece is centered. YMMV, of course.
    Grant
    Ottawa ON

  3. #3
    I was reading a post, where a suggestion was made to drill center out in a drill press. I have no experience in hollowing, I wonder if that would be better.

  4. #4
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    Quote Originally Posted by Grant Wilkinson View Post
    I drill them on the lathe. My lathe motor has lots more torque at low speeds than my drill press, I can hold the piece more securely, and I can gradually increase the bit size since the piece is centered. YMMV, of course.
    I was wondering about drilling initially with a smaller diameter bit and then moving up in size. That would certainly take some load off the larger bit. I’ve never done that so wonder if others have and any recommendations for sizes and steps?

  5. #5
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    When I use 1” and larger Forstner bits I keep lathe at or below 300 rpm and back the bit out every 1/2”. Anything faster causes heat build up. This also clears chips. I don’t feed the bit into the wood aggressively as that also causes heat build up and binding.
    Last edited by Dwight Rutherford; 09-25-2021 at 1:48 PM.

  6. #6
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    A good, sharp bit is also key. I learned about higher quality bits from folks on this forum. Generic HSS porter cable bits, despite my best efforts to sharpen them, were not doing the job on the lathe. I have upgraded to Famag carbide Forstner bits (and Freud carbide Forstner bits) and it goes much better. Freud are not as good as the Famag but the Famag get prohibitively expensive in the larger sizes.

  7. #7
    Drill in stages. This may sound counterintuitive but it works:

    Drill 1/2” deep with a 3” bit.
    Then drill 1/2” deep with 2” bit.
    Then 1/2” deep with 1” bit.
    Then all the way through with a 1/2” twist bit.

    Then widen the hole by going up in diametter from 1, to 2, to 3”. The bits have to work less hard this way and they can find their center by the first three stepped pilot holes. I do this whenever using a forstner beyond the depth of the flutes.

  8. #8
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    Green (and wet) is worse.
    Hobbyist

  9. #9
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    What I do

    Quote Originally Posted by Bernie Kopfer View Post
    … I was going slow with suction removing the chips as best possible. It did bind up a couple of times if I pushed too fast Deep in the hole it started to bind up whenever I tried to back out. …
    Instead of using suction to remove chips, for many years i’ve used a different method. I never read this anywhere but made it up:

    Force a strong stream of compressed air into the back of the Fostner bit while drilling the entire depth of the hole. This not only clears the chips and sawdust but cools the bit. With this method I've never jammed a bit on the hole. I drill deep holes by adding an extension when needed.

    Another thing, unless the hole needs to be a very precise diameter I never use high quality steel bits. They dull too quickly on deep holes. Instead, I reach for inexpensive carbide Forstner bits. The hole is not as smooth but for many applications this doesn’t matter. They often have more open space for the compressed air too.

    JKJ
    .

  10. #10
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    As far as I am concerned, forstner bits are not for hollowing vases. Especially a 3" one that makes it nearly impossible when boring deeply and also to keep it from spinning in the drill chuck. I drill a 1/2" hole and then bring in the hollowing tools. For what you've spent on a 3" bit and a replacement quill, you'd have spent about half what you need to get into hollowing. I make my own hollowing tools, so I got into it for a fraction of the cost of a 3" drill bit.

  11. #11
    I'm with Richard on this.
    A reasonable sized pilot hole is all that's required. Green wet wood hollows quickly but can be more difficult to drill.

  12. #12
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    Sometimes I step through it. Drill a shallow hole with the bigger diameter for alignment later when drilling deep. Then fall back to a smaller diameter bit, drill in some reasonable distance. Step up the diameter and drill almost to the same depth of the previous bit. Rinse and repeat. Stepping deeper across all diameters until the final depth is reached with the smallest diameter. Then step through the bits until the final diameter is reached.

    But hollowing tools can be faster.

  13. #13
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    Quote Originally Posted by Prashun Patel View Post
    Drill in stages. This may sound counterintuitive but it works:

    Drill 1/2” deep with a 3” bit.
    Then drill 1/2” deep with 2” bit.
    Then 1/2” deep with 1” bit.
    Then all the way through with a 1/2” twist bit.

    Then widen the hole by going up in diametter from 1, to 2, to 3”. The bits have to work less hard this way and they can find their center by the first three stepped pilot holes. I do this whenever using a forstner beyond the depth of the flutes.
    I follow Prashum plan but only do about 1/4" depth, enough to register the smaller bit using the center of the larger bit. Sure makes a big difference using smaller bits to depth first just enlarging from there, especially as bits get a little dull and cutting endgrain. You can pick some unused sizes that still give a range of diameters and not be held to the standards. I often will use a 7/8 amd 1-5/8" as example instead of 1" and 1-1/2" since the actual size is not important until the end.

  14. #14
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    I'd use a bowl gouge to remove 90% of the waste then the forstner to clean it up. To be honest I'd probably forego the forstner at that point and just finish it with a gouge and NRS, but if you need the square corner and flat bottom of the drill for your design then the drill may be the right way to go. Even so, a tearout-free surface from the drill is a lot to ask.

    Edit: Didn't notice how deep you were going, edit to say I'd use a hollowing tool to remove most of the waste and then the Forstner. 8" is a big reach with a bowl gouge!
    Last edited by roger wiegand; 09-26-2021 at 9:37 AM.

  15. #15
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    I don't have any issue with drilling a 2.5" hole 12+" deep. You need to back the bit out every 3/4" or so to clear the shavings once you get the drill chuck inside the piece, otherwise it will get stuck. I loosen the tailstock lock and slide the whole assembly out to clear the shavings.

    You also need to make sure you've got a full-sized tenon (max tenon length with flat shoulder to fit the chuck at the minimum diameter that the chuck will close around snugly).

    A steady rest will help as well.

    This process takes less than 10 minutes to set up and get to a full 12" depth.

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