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How to Use a V-Block for Drilling Round Stock

Guide · Updated October 28, 2026

Cross-drilling a shaft for a pin needs the hole through the exact center of the round. V-blocks hold the shaft square to the table and keep its centerline in a predictable place, so you can find center and drill straight through.

Check center height

Set center height with gage blocks under an indicator if needed. The free Gage Block Calculator builds the stack.

Step by step

Clean the V-blocks and table: Burrs tilt the part.
Clamp the shaft: Use the V-block clamp or a vise with the V-blocks.
Find center in Y: Edge find both sides of the shaft and split the difference, or indicate the top.
Locate along X: Set the hole position along the shaft.
Spot drill: Spot on the crown so the drill does not walk off the curve.
Drill: Drill through; peck for deep holes.
Check: Measure from each side of the hole to the shaft surface.

Worked example

A 1.000 in shaft in a 90° V-block. Edge find the front side at Y = −0.700 in and the back side at Y = +0.300 in (with a 0.200 in edge finder, already corrected). Center = (−0.700 + 0.300) ÷ 2 = −0.200 in. Centerline height above the V contact points: for a 90° V, the center sits R ÷ sin 45° = 0.500 ÷ 0.7071 = 0.707 in above the V apex. Spot drill at the crown, drill 1/4 in through. Check: wall thickness each side of the hole should be (1.000 − 0.250) ÷ 2 = 0.375 in; a reading of 0.380 and 0.370 in means the hole is 0.005 in off center.

Why spot drill on a curve

A drill point on a curved surface sees uneven forces and walks. A spot drill makes a flat cone to start in.

Common problems

Off-center holes: center not found or drill walked. Angled holes: V-block not square or part tilted on a burr.

Tips

V-blocks: V-block with gage blocks.
Edge finding: edge finder basics.
Drilling: drill on a mill.

Quick shop check

To cross-drill a 1.000 in shaft on center, the V-block centers the shaft automatically on the V axis. Locate the drill over center by indicating both sides of the shaft or using a center finder, then center drill and follow with the final drill. For a 1/4 in hole, use about 1,200 RPM in mild steel (≈80 SFM with HSS).

FAQ

How do I cross-drill on center?

Hold in V-blocks, find center, spot drill and drill.

How do I find center?

Edge find both sides and split the difference.

Why spot drill?

So the drill does not walk on the curve.

Center height in a 90° V?

R ÷ sin 45° above the V apex.

How do I check the hole?

Measure the wall thickness on each side.

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