ASME B94.32-1954 (1971) — Circular and Dovetailed Forming Tool Blanks

🔩 ASME B94.32-1954 (1971) is a classic foundational standard in the B94 cutting-tool series, originally titled “Circular and Dovetailed Forming Tool Blanks and Associated Mounting or Clamping Elements for Holders Used on Automatic Screw Machines.” It was first published in 1936 by Technical Committee No. 10 (Forming Tools and Holders) of the ASA (now ANSI) Sectional Committee B5, revised in 1943 and 1947, approved as an American Standard on August 24, 1954, and subsequently maintained by ASME through the 1971 reaffirmation. Its core purpose is to standardize forming-tool blanks and holders across the various makes of automatic screw machines, providing interchangeability and eliminating the uneconomical situation in which a tool could be used only on the machine for which it was designed.

1. Subject and Scope 📌

The Standard covers two classes of forming-tool blanks for automatic screw machines plus the associated holder mounting and clamping elements:

• Circular forming tool blanks: disks with a centrally located mounting hole, plain or threaded, with a number of adjusting holes on one side (Fig. 1). They are used to make forming and cut-off tools by machining the periphery to the required product form; a notch is ground into the periphery to provide a cutting edge.
• Dovetailed forming tool blanks: square or rectangular blocks with an external dovetail machined on one side over its whole length for clamping in the holder (Fig. 3). The dovetail is slotted to provide adjustment; the formed profile is machined in the side opposite the dovetail, and its top forms the cutting edge.
• Circular forming tool holders: devices that hold circular cutting tools in the proper relation to the work as they are actuated back and forth on the tool slide of an automatic screw machine; a center bolt and a hook bolt generally clamp the tool (Fig. 2 and Table 6).
• Dovetailed form tool holders: devices that clamp the dovetailed portion of the forming tool; a collar-head screw or a hook bolt provides vertical adjustment of the cutting edge (Fig. 4).

2. Machine Classification and Group Numbers 🏭

To cover the widest range of machines with the fewest blank sizes, screw machines are classified by capacity (Machine Classification, Table 1), and group numbers relate blank sizes to the machines in which they are used:

Group numbers are arbitrarily assigned to identify the size of the tool with the machines in which it is used, so new machine models can be introduced into their respective groups without disturbing the standardization of tool blanks.

3. Blank Dimension System and Key Requirements 📏

The Standard provides complete dimension tables for finished blanks (e.g., Table 2):

• Circular tools are designated by basic outside diameter and width — for example, 3 1/2″×1/2″, 4″×1″, 5″×1 1/2″ — with maximum/minimum outside-diameter tolerances (e.g., 3 17/32″ to 3 33/64″).
• The threaded mounting hole is made to Unified and American Standard Class 2B and chamfered 35° at both ends (dimension E).
• Six adjusting holes are equally spaced on the diameter-C circle, with a minimum depth of 1/4 in (deeper holes optional); the adjusting-hole diameter D and the locating-circle diameter C carry tolerances of ±0.002 in. Blind holes are on the face opposite the one containing the counterbore H.
• Blanks made of high-speed steel are stamped “H.S.” for material identification.
• All dimensions are given in inches.

4. Holder Mounting and Cutting-Edge Adjustment 🔧

The Standard specifies how holders mount blanks and how cutting edges are adjusted:

• Group 1 circular blanks have no adjusting pin holes; a friction plate may be provided to adjust the cutting edge to the center of the work (Fig. 2).
• Holders for the larger machines provide a positive means of adjustment: a plate with a pin engages one of the six holes on the side of the circular tool and raises or lowers the cutting edge; the movement is transmitted through the adjustment mechanism.
• Dovetailed holders use a collar-head screw or a hook bolt for vertical adjustment of the cutting edge (Fig. 4).
• Circular-tool holders use a center bolt and a hook bolt to clamp the blank so it maintains the correct relation to the work as it is actuated back and forth on the tool slide.

5. Engineering Practice Essentials 📋

• 🔍 Selection workflow: identify the machine make and capacity → look up the group number in the classification table → choose the blank outside diameter from the forming width and required rigidity → verify holder compatibility (center hole, adjusting holes, dovetail) → order to the Standard’s size tables.
• 🔧 Material marking: high-speed-steel blanks must be stamped “H.S.” to distinguish them from carbon-steel blanks and prevent mixed lots with inconsistent life and quality.
• 📏 Tolerance control: enforce Class 2B on the threaded hole, ±0.002 in on adjusting holes, and ±0.002 in on the locating circle in both procurement and receiving inspection.
• 🔨 Maintenance: resharpening is done on the periphery (circular) or the top face (dovetailed); after resharpening, reset the cutting edge to the work centerline.

6. Frequently Asked Questions ❓