NDR - why does a round drill sometimes make a triangle hole?

Charlie S and Titan

Charlie S and Titan

Well-known member
I guess the whole question is there... Why do I ask? I was drilling some aluminum for a transom plate for a boat and I noticed that I got triangular (not really triangles, but the general shape) rather than round holes. Why?

Thanks!

Charlie
 
Because of the geometry of a standard drill bit, a mechanical resonance can cause the tip to walk, especially when using dull bits in a hand drill, often making a hole with three sweeping arcs, and not round. Usually only a problem in sheet metal, but deep holes you’ll see it too until the helix begins to cut. Use a center drill (which has a different start) to drill a pilot hole, or if you don’t have a set of center drills, drill a small pilot hole first with a smaller bit. Also there are sheet metal bits which incorporate a center drill design at the tip. They work best for drilling sheet metal.

Hitch
 
Also, interesting color difference in our dogs... Titan is a chocolate lab too - he looks a lot darker though. Might be sunlight vs inside pictures, but I never noticed that much color range before. Neat!

Charlie
 
Boy he is a dark chocolate. Probably means he has more class :) Good lookin dog!

Hitch
 
since we are talking drill bits here --- has anyone used that drill docter sharpening tool --- does it work or is it a waste of money
 
The sheet metal will also deflect depending on how well supported the metal is, as the drill begins to cut into the metal and pressure on that portion of the "hole" is relieved it begins to lift so the drill begins to cut on 3 different planes almost instantly.

Kyle

Try a sharper bit, higher speed and lower pressure.
 
George,

I can't give you a first hand review of the product but I'll pass this along. I work in a tool and die shop for a living and we sharpen all our own drills. We do this on a choice of three different grinders depending on the size of the drill.

The Drill Doctor is set up much the same way as two of our grinders as far as the actual sharpening process. I make this statement based on my casual in the store observations of the Drill Doctor. The big difference besides cost ( ours run $3500.00 to $5500.00) is the materials the grinder and drill holders are made from. Drill Doctor uses plastic parts and a commercial unit uses metal parts. Plastic parts are not always a bad thing but in this case the plastic will not hold your drill quite as securely or accurately as the commercial one will.

In the thirty years I've been in the business, we have not always had these sharpening machines. Standard twist drills were sharpened freehand using an open bench grinder. A skilled craftsman can sharpen a drill to cut quite well, it just takes more skill and time to do it freehand rather than with a machine. A machine ( Drill Doctor included) can also sharpen to what is called a "split point". This is basically thinning the web to a point, at the cutting edge, to reduce drill pressure (forward thrust) and walking of the drill bit when drilling.

After all this rambling, I'll answer your question by saying; I think the Drill Doctor is worth the price asked. I would buy one if I didn't have the advantage of being able to use the machines at work to sharpen my own personal drills from home. Again I stress that I (obviously) don't own one but they seem to look OK in the store. I would not expect for them to have as much power and speed as the commercial grinders that I'm used to, but should be fine for the home owner looking to touch up his drills at home.

If you do decide to get one there is one thing to keep in mind, sharpen often. It is a lot easier to take just a few thousands off, to renew a cutting edge, as opposed to have to grind back a very dull tool. If you are faced with this, try to hand grind the drill bit on a standard bench grinder first, prior to finish grinding in the machine. This will save your diamond wheel (in the machine) and it will last a lot longer.

Hope this helps some.
 
thanks for the input -- as a hobbiest i do not use drill bits daily, and would probably not stress the plastic parts in a drill doctor for many years -- just never talked to anyone who used one and am always skeptical of what looks too good to be true

it may make a good fathers day gift - (hint-hint) if only my son read this site - sigh!
 
I am pleased with my Drill Doctor. Home Depot had a very good offer on them a couple of years ago and I have trouble passing up a deal. I have re sharpened a large collection of old drill bits that were kicking around that I had inherited from grand father, father and an uncle. Some of them could have been pushing Dave Parks age. What I found on my model was that it did a very good job on bits that were 3/16" and larger. The smaller ones were both too short and didn't control as well. Maybe with some practice I will be able to push that down a bit. Once sharpened these tool steel bits drilled easier and cleaner than the almost new cheap Asian set that I have.

How long it will hold up? Obviously I don't know but I bet I have heavily sharpened (re-established the full cutting edges) around fifty drill bits to 1/2" dia. and it's going strong. I suspect it will hold up to my dozen or so uses a year. I feel it paid for it's self in the first batch of sharpenings. My big advantage was that I had a drawer full of bits to sharpen right off. It allowed me to figure out what I was doing and left me feeling like I had my money's worth immediately.

Talking old drills and bits, are the old braces and bits worth anything yet. I have a drawer full of the old wood drill bits with the tapered square ends. Some are wicked long. Even have a couple of the old drills to go with them.

scott
 
I think Scott hit something on the head there...usually bit's smaller than 3/16 are so inexpensive that I wouldn't waste the electricity to re-sharpen them..where it shines is with the bigger bits. I don't have one but several of our contractors do and they think it's the best thing since cordless tools.
 
sounds like i got nothing to lose then in purchasing one -- thanks for all the input regarding the drill dr -- sorry for taking your thread in another direction
 
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