KEVOS® MAKEOS · Manufacturing
Drilling Fixture Clamp Check (Drill Torque, Clamp Force to Stop Rotation, Strap Clamp Screw)
When drilling a part held by strap clamps, what torque does the drill put on it, how much clamping force stops it spinning, and are the clamp screws strong enough?
Check of the clamping for a drilling operation: spindle speed, cutting and motor power, drill torque and thrust (as the drilling power tool), the tangential force the torque applies at the effective friction radius of the clamped faces, then the total clamping force by friction at the clamps and locators with a safety factor, the force on each strap clamp screw, its tightening torque and tensile stress (as the fixture clamp force tool), against the machine power and the screw proof strength.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Drill diameter | mm | Drill diameter. |
| Cutting speed | m/min | Cutting speed. |
| Feed | mm/rev | Feed per revolution. |
| Specific cutting force kc | N/mm² | Specific cutting force for the material. |
| Point angle | ° | Drill point angle. |
| Machine efficiency | % | Machine efficiency. |
| Available spindle power | kW | Spindle motor power. |
| Clamping | ||
| Effective friction radius of the clamped faces | mm | Average radius from the drill axis at which the clamp and locator friction acts. |
| Safety factor | Safety factor on the clamping force. | |
| Friction, clamp to work | Friction between the clamps and the work. | |
| Friction, work to locators | Friction between the work and the locators. | |
| Number of clamps | Number of strap clamps. | |
| Strap clamp and screw | ||
| Screw to workpiece contact distance | mm | Distance from the clamp screw to where the strap presses the work. |
| Screw to heel distance | mm | Distance from the screw to the heel of the strap. |
| Screw diameter | mm | Clamp screw diameter. |
| Screw pitch | mm | Clamp screw pitch. |
| Nut factor | Nut factor for the screw torque. | |
| Screw proof strength | MPa | Proof strength of the clamp screw. |
Method and formulas
- n = 1000 v ÷ π D; cutting power = f v D k_c ÷ 240 000; torque = P × 30 000 ÷ π n; thrust from the point angle (as the drilling power tool).
- Tangential force = torque ÷ friction radius; clamping force = SF × force ÷ (μ₁ + μ₂); the thrust presses the work onto the locators and is not counted.
- Strap clamp screw force = force per clamp × (A + B) ÷ B; torque = K F d; stress on the tensile stress area (as the fixture clamp force tool).
- Example: the drill turns the work with 25 N·m; 2,777.8 N of clamping holds it; each screw sees 32.964 MPa.
Limitations
- Friction holding only; a stop or pin against rotation takes the torque directly and needs far less clamping.
- Steady drilling; breakthrough and a grabbing drill can multiply the torque.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check clamps on a drilling fixture
- Find whether a part will spin under a large drill
- Size the strap clamp screws
Who it is for
- Fixture designers
- Machinists
- Manufacturing engineers
What you get
- Drill speed, power, torque and thrust
- Clamping force and force per clamp
- Screw force, torque and stress
Interpreting the result
- A pin or stop against rotation is far more reliable than friction for large drills.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1089–1093, 3131–3134, 1522–1532. Topic reference; no source tables or recommended settings are reproduced.
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