What's the correct drill bit?

Questions about tools and jigs you want to buy/build/modify.
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Mark Wybierala
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What's the correct drill bit?

Post by Mark Wybierala »

I need to drill 1 inch diameter hole through four inches of walnut in line with the grain. I'm thinking that a spade bit will not be up to the task due to the grain orientation. This is for the shoulder of a harp and I'm building three of them. I also need drill the same hole through three inches of walnut going across the grain which I could see a spade bit doing okay but not one that is worn out. I do have a decent drill press with a 1/2" chuck. Looking at McMasterCarr, 1" bits can get expensive. There are Forstner bits for under $40. DO you agree that a spade bit is not going to be up to the task? Is the Forstner bit what I need or should I go up to the higher priced HSS conventional drill bit?

Bob Hammond
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Re: What's the correct drill bit?

Post by Bob Hammond »

I would go with a Forstner bit, equipped with a shank extension to reach the four inch depth. If you clamp it up securely on the drill press, you could possibly hog out most of hole with a smaller bit - e.g. a 1/2" or 3/4" bit, and then without disturbing the setup, chuck the extended Forstner and finish up. You'll need to 'woodpecker' the hole for frequent chip removal. If you have compressed air available, a blow gun can be used along with a vac, to clear the chips from the hole.

And of course, a practice run on scrap is always a good idea.

Brian Evans
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Re: What's the correct drill bit?

Post by Brian Evans »

My experience with forstner bits is they really need the nib in the middle engaged to keep the bit centered. If you are heavily clamped to a sacrificial piece you can drill right through with minimal tearout. A lot depends on the configuration of the wood, if it's flat, if you have access to both sides, etc. I would personally do this with an end mill in a Bridgeport, but then I have such a beast. If you think about what would a guy do 150 years ago, he would use a brace and spiral bit, well sharpened.

Brian

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Barry Daniels
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Re: What's the correct drill bit?

Post by Barry Daniels »

I think a sharp spade bit would work fine, just go slow.

Be cautious of normal twist bits in large sizes. They can dig in and self feed which will normally result in some kind of disaster. Spade bits cut with a scraping action so they don't self feed.
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David King
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Re: What's the correct drill bit?

Post by David King »

I would also recommend the spade bit which you should touch up the edges on to get it razor sharp.
Drilling into end grain sucks no matter how you go about it. My best drill for deep straight holes is an antique self feeding auger bit designed for a bit brace that I cut the tapered square drive off of and can chuck in my power drill. It has a polished, high angle flute and can be honed to perfection so that it can easily drill oak or cedar and everything in between.

I know that Freud makes carbide tipped Forstners that are supposed to be the cat's meow.

Rick Milliken
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Re: What's the correct drill bit?

Post by Rick Milliken »

Might consider a Brad point bit. You get the chip removal of a twist drill, but less of the downsides mentioned earlier. I use them in hardwood a lot for pen barrels and tool handles (smaller diameter obviously)

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Barry Daniels
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Re: What's the correct drill bit?

Post by Barry Daniels »

While we are on the subject of drill bits, one thing I am doing is taking a dremel grinding disc and flattening the cutting edge of my twist drills so that there is a zero angle rake. This makes the bit take a scraping cut and prevents the self-feeding issue I mentioned earlier. The bits definitely cut better in brass and steel, and even seem to work better in hardwood. Drilling softwood is the only material that I use that seems to suffer from this treatment.

This seems to work really well on the larger bits but I even do it for bits down to 3/16" diameter.
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Bryan Bear
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Re: What's the correct drill bit?

Post by Bryan Bear »

Barry Daniels wrote:While we are on the subject of drill bits, one thing I am doing is taking a dremel grinding disc and flattening the cutting edge of my twist drills so that there is a zero angle rake. This makes the bit take a scraping cut and prevents the self-feeding issue I mentioned earlier. The bits definitely cut better in brass and steel, and even seem to work better in hardwood. Drilling softwood is the only material that I use that seems to suffer from this treatment.

This seems to work really well on the larger bits but I even do it for bits down to 3/16" diameter.
I'm having a hard time visualizing what you mean in three dimensions can you snap a picture? I think you are saying that when you are done the bit is flat but I'm sure I'm just missing it. . .
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Clay Schaeffer
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Re: What's the correct drill bit?

Post by Clay Schaeffer »

Another possibility would be a shell auger if you could find one. Trevor Robinson describes how to make one in his book " The Amateur Wind Instrument Maker ".

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Barry Daniels
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Re: What's the correct drill bit?

Post by Barry Daniels »

Bryan Bear wrote:I'm having a hard time visualizing what you mean in three dimensions can you snap a picture? I think you are saying that when you are done the bit is flat but I'm sure I'm just missing it. . .
Can't do a picture now. But no, the bit is not flat.

Normally, the cutting edges have an approximate 60 degree rake which pulls the bit into the cut. After alteration, there is a zero (or 90 degree) rake angle to the cutting edges which makes the cutting face parallel to the axis of the bit. It is only necessary to grind a little bit off to create a flat face on the leading edge.

Edit: I found a picture online that shows the rake angle on a normal bit.

http://www.giangrandi.ch/mechanics/shee ... rill.shtml
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Alan Carruth
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Re: What's the correct drill bit?

Post by Alan Carruth »

When I ran drill presses in a machine shop we would always break back the edges of drill bits for brass. Basically, this consisted of touching the edges to the side of the grind wheel such that a small flat was generated parallel (more or less) to the axis of the bit. Unless you do this any bit larger than, say, about 1/4" will dig it's way into brass in a hurry, often deeply enough to jam the bit. The piece/jig spins around a few times until the unbalanced load causes the bit to break, flinging the whole thing across the shop. You sit there sucking on your cut finger while everybody else in the shop cusses you out. DAMHIKT The chip tends to end up as small conic pieces rather than long shavings. They have very sharp points, and get into your socks....

Another caution on drilling brass is the favorite phrase of my foreman: "Let the tool do the work". If you push a bit too fast in brass the hole can wander out of perpendicular by a surprising amount. It would not surprise me at all to find this happening in hard woods, particularly in end grain.

David King
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Re: What's the correct drill bit?

Post by David King »

For the 0º rake mod you can watch this very short video.
https://www.youtube.com/watch?v=pAngKHIZgyA

Todd Stock
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Re: What's the correct drill bit?

Post by Todd Stock »

Wood Owl auger bit...very smooth cutting and the depth will work.

http://www.toolplanet.com/product/7308/ ... gLScPD_BwE

Mark Wybierala
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Re: What's the correct drill bit?

Post by Mark Wybierala »

A total of 3 holes, each four inches deep holes cutting into the end grain of 2X3X4" blocks. One of them was through a block of Black Walnut and the other two were through blocks of African Mahogany. I really over-thought about this. A new Irwin brand "Speed Bore" spade bit from Lowes ($4.95) did all three holes without beginning to smoke. I purchased two bits because I didn't have faith that the bit would survive cutting through that much hardwood endgrain. The inside of the holes is not a refined finished surface but it doesn't need to be. My clamping consisted of only a length of 1X2" clamped to the side of the block and resting against the pillar. The linear alignment result was more than adequate. I don't regret making the post because there is never a dumb question on a forum as friendly as this one.
Much thanks brothers and sisters.

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