Full Chisel Blog

May 25, 2008

Now Things Get Twisted

Filed under: Drilling,Uncategorized — Stephen Shepherd @ 3:52 pm

At some point in the eighteenth century someone came up with the idea of putting a twist to a bit in order to help extract dreck from the hole as it is being drilled.  Most bits require you extract the bit occassionally to remove the dross left over from drilling.

The theory of the twist bit is that it could extract the shavings and drill deep straight holes and not wandering like the center bit.

The first person credited with this innovation is a fellow named COOK, and here is one of his pattern drill bits.  Mercer dates this style to the 1770’s

Cook patent

This particular Cook auger is intended for a cross or T handle, I have one 7/8″ tanged bit in this pattern.


The date is 1851 and that is about 4 years or so before Gedge got his patent for his bit pattern.  Incidently Gedge filed for his patent 2 weeks ahead of Russell Jennings, the latter became the industry standard.


The unique curved cutting edge looks like it will not make a good entry hole, but the opposite is the case, it makes the cleanest entry hole of almost any bit.  And unlike the Jennings and much later Irwin patterns the Gedge can be used to drill holes at very steep angles unattainable by the other twist auger bits.

There is another type of twist bit that was developed during the very early nineteenth century by L’Hommideau which consists of a piece of metal twisted around a mandrel to produce a hollow twist with a cutting bit on the end.  Some had pivots (plain or threaded) but many had no pivot and required an excavation in order to get the bit started.  Number 10 in the lower illustration.

Drill bits and their holes

1. Button Bit

2. Center Bit

3. Counter bore center bit

4. Twisted Gimblet (gimlet) bit

5. Gouge bit

6. Nose auger

7. Pod auger (straight gimblet bit)

8. Spoon Bit

9. Duck Bill spoon bit

10. L’Hommideau bit

11. Twist bit

12. Twist bit, Jennings pattern

13. Irwin bit

The lower illustration shows the holes that the various bits produce.  I shall discuss the care, repair and sharpening of bits later and I still have to discuss the gimblet bit and my theory about these bits.

Manufacturers offered these bits in 4 ‘grades’, spur pivot point (no threads), coarse threaded for softwoods, medium threads and fine threads for hardwoods.

I believe the Jennings pattern has been in constant manufacture, and new ones are available, however the Cook/Gedge pattern is NOT being reproduced.  I think tool manufacturers are making a big mistake by not reproducing these bits as they would be a boon to chair maker’s who find this pattern bit particularly useful.



  1. No Comments?

    Alright then I will add something. Twist bits are marked in 1/16″ increments starting at 3 for 3/16″ to 16/16 which is one inch. Over an inch and the markings can continue or are marked like the one below which is stamped 1 1/8′. This is a Cook Pattern as it was made by Marples in England.

    Cook Pattern Twist Auger with square tapered shank


    Comment by Stephen Shepherd — May 26, 2008 @ 7:26 pm

  2. Stephen
    I think you meant L’Hommedieu?

    Bob, following your excellent blog entries on auger bits 🙂

    Comment by Robert Demers — May 26, 2008 @ 9:22 pm

  3. Hi Stepgen,

    You’re right, I cant’t imagine that these bits make good holes. Could You show a hole? :o)

    Owning a lot worn out Jennings, would it be possible to file them down to this pattern? There’s a lot material in them.

    Kind Regards

    Comment by Pedder — May 27, 2008 @ 4:12 am

  4. Bob,

    You are correct, the spelling checker didn’t know what I meant either. Thanks for the correction.


    I will drill a hole today and post a picture. Yes I think old Jennings and other worn out twist augers could be made into this pattern bit.


    Comment by Stephen Shepherd — May 27, 2008 @ 6:17 am

  5. Stephen,

    Thanks and please excuse the wrong spelling of your name.

    Kind Regards Pedder

    Comment by pedder — May 28, 2008 @ 2:37 am

  6. Pedder,

    Thanks for your reply and I kind of like Stepgen, almost has a glottal stop. I know I have at least one old worn out Jennings pattern I might try a conversion myself.


    Comment by Stephen Shepherd — May 28, 2008 @ 6:23 am

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