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How to Ream a Hole
Guide · Updated October 28, 2026
A reamer takes a drilled hole to a precise size and a smooth finish. It follows the drilled hole, so location comes from spotting and drilling; the reamer gives size and finish.
Check the hole
Check reamed holes with a plug or pin gage, or a bore gage set from a ring or gage blocks. Check it with a mic you've verified against gage blocks; the free Gage Block Calculator builds the stack.
Step by step
- Spot and drill: Spot drill, then drill undersize so the reamer has the right amount of stock.
- Leave the right stock: Leave roughly 0.010–0.015 in on diameter for a 1/2 in hole; less for small holes, more for big ones.
- Hold it true: Ream in the same setup as the drill so the reamer follows the hole.
- Slow down: Run about half to two thirds of the drilling RPM.
- Feed more: Feed about twice the drilling feed; too light a feed rubs and work hardens.
- Use oil: Use cutting oil or coolant and keep the reamer turning forward.
- Withdraw forward: Pull out with the spindle still running forward; never reverse a reamer.
Worked example
0.500 in hole in 1018 steel with an HSS reamer: drill 31/64 in (0.4844 in), leaving 0.0156 in on diameter. Drilling at 80 SFM is about 610 RPM; ream at about 300 RPM and 0.006 in/rev, about 1.8 in/min. Check it with a 0.5000 in go pin; a plug gage confirms go and no-go.
Oversize or bell-mouthed holes
A hole that comes out big usually means the reamer is not following the drilled hole, the spindle runs out or a built-up edge is on the reamer. Use a floating holder on a lathe, check runout and clean the flutes.
Rough or chattery finish
Too little stock, too slow a feed or a dull reamer. Leave more stock, increase feed and use oil.
Tips
- Start from reamer speeds and feeds.
- Spot first: center drilling and spot drilling.
- Check with a plug gage.
- Deep holes: peck drill before reaming.
FAQ
What size drill before reaming?
About 1/64 in under for 1/2 in holes; aim for roughly 0.010 to 0.015 in on diameter.
How fast should I ream?
About half to two thirds of the drilling RPM, with about twice the feed.
Can I reverse a reamer out of the hole?
No; reversing chips the edges and ruins size.
Why is my reamed hole oversize?
Runout, misalignment with the drilled hole or a built-up edge.
Hand reamer or machine reamer?
Machine reamers for the mill or lathe; hand reamers have a long taper lead for starting by hand.
Related guides and calculators
- Metric dowel pin chart (ISO 8734)
- Reamer Speeds and Feeds
- Drilling Speeds and Feeds
- How to Center Drill and Spot Drill
- Peck Drilling Basics
- Plug Gage Basics
- How to Use a Dial Bore Gage
- How to Bore on a Mill
- Countersink and Counterbore Basics
- How to Drill on a Mill
- How to Sharpen a Drill Bit
- How to Use a Keyway Broach
- How to Use a Boring Head
- How to Hone a Bore
- How to Use a Rotary Broach
- All free machinist calculators
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