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how do you use a 3" screw end forstner bits?

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Forum topic by distrbd posted 05-30-2015 12:36 PM 1266 views 0 times favorited 16 replies Add to Favorites Watch
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distrbd

2228 posts in 1914 days


05-30-2015 12:36 PM

I,m not a big fan of screw end forstner/saw tooth bits , the one I had to use yesterday was a 3”, I set the drill press on 500 rpm , clamped the 1” thick plywood well but as soon as the tip of the screw hit the wood it wouldn’t let go of it and screwed itself to the wood so tight that I had to turn off the drill press to stop it all.
I ended up removing the center bit(screw) and used the saw tooth bit on its own and it worked but what’s the point of having that screw in the middle of the bit?
What am I doing wrong here?lower rpm ?hand held drill?

-- Ken from Ontario, Canada


16 replies so far

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JayT

4786 posts in 1679 days


#1 posted 05-30-2015 01:18 PM

Wrong application.

Those bits are called self-feeding bits and are mainly used by plumbers and electricians for boring holes through studs, joists and other framing members to run pipe and conduit. The screw tip pulls the bit into the wood since it’s very difficult to get enough pressure behind a drill when it’s in the tight space between joists to use a hole saw. They work very fast, but not very clean—lots of blowout on the back side.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

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distrbd

2228 posts in 1914 days


#2 posted 05-30-2015 01:28 PM

What tool are these bits used with? hand brace drill maybe?
This is the set I got ,used the largest bit which is 3”:
Grizzly H5982 Forstner Bit 9-Piece Set, 1-3-Inch

-- Ken from Ontario, Canada

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gfadvm

14940 posts in 2158 days


#3 posted 05-30-2015 01:40 PM

All Forstner bits are best used in a drillpress. You could grind the threads off of those screw spurs and just grind a sharp point on a shorter spur.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

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distrbd

2228 posts in 1914 days


#4 posted 05-30-2015 01:53 PM



All Forstner bits are best used in a drillpress. You could grind the threads off of those screw spurs and just grind a sharp point on a shorter spur.

- gfadvm


I never thought about grinding the screw to get rid of the threads, I came up with another solution while typing this post, how about drilling a pilot hole a size bigger than the bit so the threads don’t grab on to the wood so tightly? but that is an extra step, I like your idea of grinding the center screw .
Thank you Andy.

-- Ken from Ontario, Canada

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ChuckV

2882 posts in 2995 days


#5 posted 05-30-2015 02:06 PM

I think that it will be hard to get a clean cut with just the one cutting edge. You probably want something like these:
http://www.leevalley.com/US/shopping/AddViews.aspx?p=45541

My set is from Rockler and I have been very happy with them.

-- “Big man, pig man, ha ha, charade you are.” ― R. Waters

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johnstoneb

2150 posts in 1640 days


#6 posted 05-30-2015 03:01 PM

JayT +1

-- Bruce, Boise, ID

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Ghidrah

667 posts in 690 days


#7 posted 05-30-2015 03:02 PM

Plumbers and electricians tend to use HD right angle drills

-- I meant to do that!

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TheFridge

5765 posts in 953 days


#8 posted 05-30-2015 03:07 PM

I drill a pilot hole sometimes. Usually if I need to use an electric drill.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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JayT

4786 posts in 1679 days


#9 posted 05-30-2015 04:47 PM



What tool are these bits used with?

- distrbd


Plumbers and electricians tend to use HD right angle drills

- Ghidrah

Yep, something like this.

-- "Good judgement is the result of experience. A lot of experience is the result of poor judgement."

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JoeinGa

7489 posts in 1474 days


#10 posted 05-30-2015 04:54 PM

I have a complete set of the same type by Makita. That screw tip center bit will unscrew to be removed from the bit. I take the screw tip out and use one that I ground down to a nib when I need to use these. It’s a bit “jumpy” at first but in the drill press it’s not too bad so long as the work is clamped down.

-- Perform A Random Act Of Kindness Today ... Pay It Forward

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jerryminer

528 posts in 909 days


#11 posted 05-30-2015 06:38 PM

Sell those bits to your local plumber and get a set of actual Forstner bits.

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distrbd

2228 posts in 1914 days


#12 posted 05-30-2015 07:20 PM

these bits are obviously not for woodworking the way they are, I don’t get why Grizzly is selling them without mentioning what their intended use is, I will however try to grind the threads and reshape the tips.

I just tried the bit with a larger pilot hole and it worked fine.
thank you all for your help,Tjay,thanks ,I learned something new today.

-- Ken from Ontario, Canada

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runswithscissors

2192 posts in 1493 days


#13 posted 05-31-2015 03:54 AM

Those big diameter bits can be dangerous used in a heavy duty low speed right angle drill. When the bit hangs up, it can break your wrist. They usually have a threaded hole in the gear head for an auxiliary handle made from a piece of pipe. Better yet, some now come with a clutch on the low speed setting, including the Dewalt, more recent Milwaukee Hole Hawg, and the old Black and Decker Timberwolf (from the days when B&D made actual industrial quality tools).

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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TopamaxSurvivor

17677 posts in 3143 days


#14 posted 05-31-2015 05:34 AM

That is definitely what we used to call a planetary bit not a Forstner bit. They are used by electricians and plumbers. They are nearly worthless without the feed screw. ;-) Putting one of those in a Milwaukee Hole Hog and hitting a nail or knot is not for the faint of heart ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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distrbd

2228 posts in 1914 days


#15 posted 05-31-2015 01:49 PM

Thank you all,I have been urged by members from another WW site to contact both Amazon and Grizzly and see if they can replace these plumbers bits with actual forstner bits.

As I mentioned before, when I ordered this set I searched for large forstner bits, found this set, I assumed they are like my smaller set made for woodworking,I never looked at the center bits in them to see if they had brad points or not. so you you know what they say about assuming anything .

-- Ken from Ontario, Canada

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