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Thread: Large Forstner bits?

  1. #1

    Unhappy Large Forstner bits?

    I have been using a 2" (Chinese) Forstener bit at my slowest drill press speed (~600rpm?) to drill through 3/8" thick woods.
    Things are OK with Teak, Walnut is easy, but Maple is something else again.

    With Maple, the drill doesn't want to penetrate. It is slow going with lots of fine dust, and some smoke if I don't pause often. The wood doesn't burn though. If I press a little harder the bit bites into the wood and stalls the drill press (belt slipping - I hope). The only cure is to raise the bit and start over.
    It takes WAY too long for a 3/8" hole.

    I have tried sharpening the bit slightly with a diamond file, but don't see any improvement.

    Is this just a case of too much speed for the hard wood, or should I be looking at better Forstner bits?

  2. #2
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    Can you clamp your piece in place and then step drill the hole with different sizes so you take less material at once?

    I do not know the best speed for drilling like, will be interested in what others have to say.

  3. #3
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    Hardwoods should be run at maybe half of that speed... for a 2" bit, I'd probably be in the 200rpm range for that.
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  4. #4
    +1 on 200 - 250RPM for that size Forstner. The lack of bite indicates a sharpening problem; probably the angle of the wide portion of the cutter.

  5. #5
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    My song is going to be a little different. First, you speed is too high for THAT bit, it just isn't sharp enough or designed well enough to clear chips at that speed. The short answer is better bits. My solution has sticker shock associated with it so read at your own peril. The only two forstner bits I will use (except for sizes above 2.5" because neither make them) are Colt Maxicut or Famag Bormax, with the former being a little better than the latter. Even at 600 rpm they both would drill 2" holes like there is no tomorrow, they both recommend 500 rpm for 80mm bits and it isn't like the Germans are engineering slouches. The slower speeds we often see listed for forstner bits are based on what I consider inferior bits. If you want to see what a forstner bit should look like drilling check out:

    http://www.youtube.com/watch?v=j1zOGmuMM1I


    The rotostop Colt system is very cool but again pricey. If they are more than you are willing to pay there are several threads with lower cost forstner bit options that people have had good luck with. If the packaging doesn't have specific recommendations for speeds use the standard speeds mentioned Dan and Glen mentioned.

  6. #6
    Van - that Colt bit is impressive. You got to love the German technology.

  7. #7
    First of all, thanks to everyone for the prompt comments.

    I realize thet 600 rpm is too fast, but that is as slow as my drill press will go.

    I have no problem with paying for good tools, and will look into better Forstener bits. Thanks, Van, for your suggestion.

    For 1" and less, my Freud Forsteners are fine.
    The Chinese bits go from 1" to 2-1/4", and generally work OK for softer woods, but for real wood, I'm going to replace them with real bits (probably one-at a time).

    Any and all recommendations are appreciated.

    Thanks again for the prompt response!!!

  8. #8
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    Here's a handy chart I found recently that lists cutting speeds: http://www.woodmagazine.com/woodwork...s-speed-chart/

    I'm relatively new to Forstners, but having had a set of cheap and dodgy Eastern ones and more recently a set of Famag Bormax that perform very well (the Colts while hugely impressive judging by the demo videos were just a bit too expensive) - it seems to me that a common problem with the cheapies may be inaccurate grinding of the cutting edges.

    That's not to say that they won't anyway wear out fairly quickly due to poor materials or hardening, but in my case some actually cut very well - while others wouldn't cut without far too much feed pressure. (if at all)

    There's quite a bit going on in a Forstner - in that there's a lot of cutting edges. My set seemed to include instances of either the wrong angles (especially no proper clearance angle in the zone immediately behind the cutting edge), wrongly placed bulges in e.g. the rim, and small unground sections of cutting edge.

    My guess from looking at the cheap ones is that they probably start as not very accurate forgings, and are ground by hand - and that the result is consequently pretty inconsistent. The grinding was pretty coarse too, with heavy wire edges. I was able to sort out one or two relatively easily with a file, but eventually binned the whole lot and ordered the Bormaxes.

    Chances are that with a bit more persistence, getting the right tools and information and putting in more time I could probably have rescued most of the set. I wasn't really prepared to risk this against the possibility that the material was anyway poor though.

    I suspect too that much like in the case of hand tools that even in the case of good ones that there is a lot of improvement to be had with careful fine tuning and proper sharpening...

    ian

  9. #9
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    Depends on the Chinese Forstner bits. I have the big set from Grizzly and they work pretty well, but the 2.25" in a Camphor limb is a bit of trouble. I was boring a deep hole, it was easy going for the first 1.5 inches, but after that, the bit kept getting bound up and slipping the belt...

    I found that the problem wasn't the bit, or the wood, but rather the work out OEM belt... I swapped over to an AccuLink temporarily and the trouble went away... I plan on getting new belts asap...
    Trying to follow the example of the master...

  10. #10
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    Nice demo, Van... I did a quick search and found them for a decent price (relatively speaking, mind you) at Infinity Tools. Still, I don't have $500 to throw at a 20-piece Forstner set...
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  11. #11
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    Quote Originally Posted by Dan Hintz View Post
    Nice demo, Van... I did a quick search and found them for a decent price (relatively speaking, mind you) at Infinity Tools. Still, I don't have $500 to throw at a 20-piece Forstner set...
    I have never added it up but I am sure I would cringe at what I have in my set. I have I think it is 21 Colt's (all the imperial and a 35mm) and 8 or 9 Famags in the sizes up to 2 1/2" Colt doesn't make. Along with about 5 bigger sizes (Woodcraft brand) and I imagine I have around $900 in the set. Jeez, I didn't want to realize that!

    If you want to see what The Schwarz has to say about them watch this video, he also has a blog entry on them.

    http://a.blip.tv/scripts/flash/strat...%252F&source=3

  12. #12
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    Quote Originally Posted by Jim Pletcher View Post
    Any and all recommendations are appreciated.

    Thanks again for the prompt response!!!

    Its rare that I'll suggest a trip to the borg, but I've been buying freud Diablo's from the HD, they work quit well both freehand and in a drill press, and they are worth a try. They are not the ultimate forstner bit, but they cut well and are a great value. If you want to drill 10 billion holes in nasty exotics, these are not the correct bits, but for most domestic hard woods, very decent performance, and not too expensive.

    FWIW, if teak is a regular for you you need a carbide tipped bit for that. HSS or tool steel wont last long in teak due to the silica and other minerals present in the wood. That 600 RPM's is a bit fast for the 2" bits but its more likely the chinese bits are junk causing your problems. I use some cheap chinese bits at work that I consider nearly useless and they have similar lousy performance in anything more dense than butter.

  13. #13
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    Quote Originally Posted by Trent Shirley View Post
    Can you clamp your piece in place and then step drill the hole with different sizes so you take less material at once?

    I do not know the best speed for drilling like, will be interested in what others have to say.
    Step drilling with a Forstner is an exercise in futility. They rely on the brad point of the bit for centering, and even with a drill press a bit will chatter and wander without a solid center to guide it.

    For a shallow, wide hole, a circle template with a router pattern bit can do a pretty nice job.

  14. #14
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    Quote Originally Posted by Josiah Bartlett View Post
    They rely on the brad point of the bit for centering, and even with a drill press a bit will chatter and wander without a solid center to guide it.

    .
    News to me! A "true" forstner bit doesn't even have a brad point but you don't find them much anymore, the center point is there exclusively for centering. A forstner bit is rim guided, that is the reason they can drill partial, overlapped or angled holes where the center point either never touches the wood or only well after the hole is started. If your forstners are wandering or chattering there is something wrong with the bit or the press.

  15. #15
    Quote Originally Posted by Josiah Bartlett View Post
    Step drilling with a Forstner is an exercise in futility. They rely on the brad point of the bit for centering, and even with a drill press a bit will chatter and wander without a solid center to guide it.

    For a shallow, wide hole, a circle template with a router pattern bit can do a pretty nice job.
    Actually, Forstners are the cutter of choice when you can't use the center of the bit for piloting. They excel at cutting angled holes and holes that hang off of an edge. The spur in the center of my bits is to small for any thing but aiming at a marked center.

    IME the main culprit with poorly performing Forstners is misuse. The user, in an attempt to drill through the stock allows the bit to spin without cutting. This immediately burnishes the cutting edge of the bit, forcing the user to use higher speed and pressure to cut. A forstner bit should never create dust as this is an indication that the bit is merely spinning on top of the wood. Instead, it should be cutting the way a hand plane would creating ribbon like chips.
    Last edited by johnny means; 12-08-2010 at 5:55 PM.

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