W.A. Clark Expansive Bits by Eric Brown

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W.A. Clark expansive bits by Eric Brown

Clark, William A. (Bethany, Woodbridge & New Haven, CT.)

  1. William A. Clark invented what is known as the “Clark” standard for expansive bits that use dovetails, a screw, and a clamping plate, to hold the movable cutter. William A. Clark, R.H. Brown, and maybe Convalco, were the only “genuine” makers of “Clark” bits. After the patents ran out the design was copied by many others and they are known as “Clark Pattern” bits. The original design has a spur on the head and the fixed cutter on the head is on the opposite side from the movable cutter (135+ degrees). In addition, where the head and shaft meet, there is a twist in the head to aid in chip removal. Some later copies eliminated the fixed spur, and the fixed cutter is roughly 90 degrees from the movable cutter to lower manufacturing costs, and is called “Clark Modified Pattern” in this list. Also, many of the movable cutters look alike, but some makers shifted the markings on the cutter and they may also have different dimensions making compatibility a challenge.
  2. William A. Clark, based on his patents, lived in the towns of Bethany, Woodbridge, and New Haven, all in the county of New Haven, Connecticut. His company was first located in Westville and then later in New Haven.

Clarks Patent # 20,192 May 11, 1858 Bethany, CT. (His original expansive bit patent)
Clarks Patent #21,597 Sep. 28, 1858 Bethany, CT. (1st Improvement patent)
Clark opened his plant in Westville, CT. before the Civil War. (The building was constructed by Wales French in 1848, for the manufacturing of augers and bits on the site of an old paper mill.) During the Civil War the plant was used by William Blake to manufacture bullet molds for Colt.

Civil War lasted from 1861 to 1865. Did William A. Clark enlist, move his business, or what?

Pictures of early Clark expansive bits with two patent dates. Note both bits have the square tang flat in orientation with the head. Also, on the larger bit, the screw point is a fine straight taper and the clamp plate is flatter and thinner than later ones. Note: The clamp plate screw may have been replaced and the cutter has been shortened to two inch.

Clarks Patent 20,192 Reissued as RE3,516  Jun. 22, 1869  Bethany, CT. (Original patent)

Clarks Patent 93,808  Aug. 17. 1869 Woodbridge, CT. (Hollow Auger)

Clarks Patent 20,192 Reissued again as RE3,733 Nov. 16, 1869  Woodbridge, CT. (Original patent)

Clarks Patent 20,192 Reissued again as RE4,668 Dec. 12, 1871  New Haven, CT. (Original patent)

Clark patents Extended in 1872 until expiring in 1879.

Clarks Patent #141,324 Jul. 29, 1873 New Haven, CT. (2nd Improvement patent) No examples known.

3. Picture of two large bits marked with “WM A. CLARK – CAST STEEL” and “PAT’D MAY 11, 1858-PAT EXT’D”
Note: Screw points are now bullet shaped and clamp plates have thicker bevel shape. Square tangs rotated 45 degrees

4. Picture of two small bits marked with “WM A. CLARK – CAST STEEL” and “PAT’D MAY 11, 1858-PAT EXT’D”   
Note: Top one has older (flat) orientation of the tang

5. The William A. Clark patent #20,192 (May 11, 1858) showing the development of the dovetail edges and clamping plate.  Source: Patent.

6. The William A. Clark patent #21,597 (SEPT. 28, 1858) improving on his earlier patent, showing how his dovetailed cutter could be incorporated into a single twist bit.  Source: Patent.

7. The William A. Clark patent #141,324 (July 29, 1873) improving upon his first two patents, showing the development of the movable cutter set further into the head.  Source: Patent.

8. Peter Sarafans bit marked “GENUINE CLARK EXPANSIVE BIT”. It is 9 ½” long. Shaft is a shade under 7/16 over the entire shaft. Note the difference in the clamping plate, the lack of a twist where the head meets the shaft, the “Wm” in the name and the square tang is rotated 45 degrees to the head


This small bit has “CLARKS EXPANSIVE BIT” put on the shaft diagonally. The head is missing the twist where it meets the shaft.

This large bit has “CLARK EXPANSIVE   USA” stamped around the shaft.

 These two bits are marked “CLARKS PATTERN” and were probably made by IVES. Note: There is no clamping plate. Instead the cutters are held by a screw in the back. Ives also made a similar bit with their trademarked “MEPHISTO” brand name.

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