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How to Use a Spin Indexer
Guide · Updated October 28, 2026
A spin indexer holds a 5C collet on a spindle that turns by hand. A 36-hole plate and pin give you 10° steps, and many have a vernier for finer angles. It is a cheap way to drill bolt circles, mill hex or square ends, and grind radii on a surface grinder.
Set heights with gage blocks
Touch off radii and centerline heights with a gage block stack. The free Gage Block Calculator builds the stack.
Step by step
- Mount it: Clamp the indexer to the table or vise with the spindle parallel to an axis.
- Indicate the spindle: Indicate a ground pin in the collet along its length and across it; shim or tap the base until it reads true.
- Load the part: Clean the collet and tighten the drawbar firmly.
- Set the start: Lock the index pin in hole zero, or set the vernier at zero.
- Cut the first feature: Lock the spindle brake before cutting.
- Index: Release, rotate the required number of holes (10° each on a 36-hole plate), pin, lock and cut again.
- Check the result: Measure across flats or the bolt circle before removing the part.
Worked example
Grinding a 0.2500 in convex radius on the end of a punch held in a spin indexer whose centerline sits 2.0000 in above the chuck. The wheel bottom must touch at 2.0000 + 0.2500 = 2.2500 in. Wring a 2.2500 in gage block stack (2.0000 + 0.2500 blocks), touch the wheel to it with a paper feeler, then move over the part and swing it back and forth while feeding down until the wheel just reaches that height.
Indexing math
On a 36-hole plate each hole is 10°. Six holes per step give a hex (60°), nine give a square (90°). Angles that are not multiples of 10° need the vernier or a dividing head.
Common errors
Forgetting to lock the brake lets the part creep. Not indicating the spindle gives tapered flats. Grinding a radius without a known centerline height leaves the radius off center.
Tips
- Fixed blocks: using a 5C collet block.
- Grinding: using a surface grinder.
- Stacks: building a gage block stack.
FAQ
What is a spin indexer?
A hand-turned 5C spindle with an index plate for dividing and holding work.
How many degrees per hole?
On a 36-hole plate, 10° per hole.
Can I grind radii with a spin indexer?
Yes; set wheel height from the centerline with gage blocks.
Spin indexer vs dividing head?
The spin indexer is simpler and faster; a dividing head handles odd divisions.
Should I lock the spindle while cutting?
Always.
Related guides and calculators
- How to Use a Dividing Head
- How to Use a Surface Grinder
- How to Build a Gage Block Stack
- How to Use a Rotary Table
- Magnetic Chuck Basics
- How to Use a 5C Collet Block
- How to Cut a Hex on a Mill
- How to Cut a Square on a Mill
- All free machinist calculators
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