Tapered vs. Straight Drill Bits - FineWoodworking

Hey all! Amateur woodworker here in need of some guidance. I’m not sure if I should be using a tapered or straight bit and for the life of me can’t find an answer. I have a handy dandy Wood Screw Pilot Hole Size chart that tells me for a #8 wood screw pilot hole I should use a 11/64 tapered bit or a 1/8 straight bit for hard wood and 5/32 tapered bit or a 7/64 straight bit for soft wood.

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I don’t understand the purpose of a tapered bit. I have an 11/64 tapered bit but when I hold it next to the screw, the bit is wider at the end of the taper than my #8 2 ½ screw. How can this work? It would make the pilot hole larger than the screw.

I’m going to guess and presume that the tapered bit would correspond with a tapered screw and that I should use a straight bit for my pilot holes.

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Which leads me to my next question. Are tapered screws used for specific purposes or is it just a matter of preference over straight screws?

 

Please advise. Thanks in advance.

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Please excuse what are probably very elementary questions. I have inherited several drill bits and reamers. Instead of having a straight cut off end many are tapered with a tang on the end. The bits are various sizes ranging from approx. .125 to 1.0 inches. The smaller drills have a No. 1 morse taper. The medium and large drills are either No. 2 or No.3 morse taper. There are also several reamers, both cut off straight and tapered shank, 1, 2 and 3 morse taper. The reamers are designated either hand reamers, chucking reamers or taper pin reamers. I would like to use these in my lathe (Enco 9x20) which has a 3MT spindle and a 2MT tail stock.

Questions

1. Does MT and morse taper mean the same thing? Is this an American or international design.

2. If I want to put a 3MT or 1MT drill bit or reamer in the 2MT tail stock, can I buy and adapter for this?

3. Conversely, if I want to put a 1 or 2MT drill bit or reamer in the spindle, is there an adapter.

4. Is there a serious downside to using adapers (if available).

5. What is the difference between a hand reamer and a chucking reamer? Is the hand reamer ONLY used manually and ONLY very low speed?

6. What is a taper pin? What is a taper pin reamer?

7. Why are some of these tools cut off straight while others have tapered shanks.

8. My only drill press is a Delta with an ordinary key type drill chuck (1/2-inch capacity). Can I get an adapter so I can use the tapered shank drill bits and reamers?

Thanks in advance,

Frank ) 1. Yes. The design is standard.

2, 3, and 4. Yes there are adapters to go to different sizes. If going from a larger machine taper to the smaller bit taper it will be in the form of a bushing. If going from a smaller machine taper to a larger bit taper it will be in the form of an unwieldy extension. Downside is you lose a decent amount of space when using this type. Also tapers are friction fits. Stack enough together in the form of adapters and you have a higher chance of spinning especially if there is no tang.

5. Hand reamers have a square end to accept a tap handle or wrench. Most hand reamers are for specific tasks or adjustable. IE. handy mans reamer, taper pin reamer etc. Can they be used in a machine, possibly, but I wouldn't. Chucking readers have a round end and are meant to be used in a Jacobs type chuck.

6. Taper pin is an old form of joining things to shafts. As it's name implies it is a round tapered pin. A taper pin reamer is used to make the holes in the parts you wish to join tapered to accept the pin. You will find these a lot on your lathe especially southbends.

7. Different applications. Tapered shanks are more stout because you are not holding them in a Jacobs chuck. They are more common in larger sizes that would require a reduced shank to use in a drill chuck.

8. Unless your drill press spindle is a morse taper then no. Any adaptor you could make to fit in a Jacobs chuck will require too much room. You also wouldn't see any benefit over a standard bit.