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How to Set Up a Horizontal Mill
Guide · Updated October 28, 2026
A horizontal mill drives cutters on an arbor supported at both ends. It removes metal fast with slab, side and form cutters, and can gang cutters to cut several surfaces at once.
Set straddle widths
Set spacers to width with gage blocks. The free Gage Block Calculator builds the stack.
Step by step
- Clean the arbor and spacers: Dirt on spacers bends the arbor.
- Mount the arbor: Seat and draw it in.
- Place cutters: Put cutters close to the column.
- Fit the arbor support: Mount the overarm and support near the cutter.
- Tighten the nut last: Only with the support in place.
- Set speed and feed: Calculate rpm and feed.
- Choose direction: Conventional unless the machine has a backlash eliminator.
Worked example: speed and feed
A 3 in HSS slab mill, 8 teeth, mild steel at 80 SFM: rpm = 3.82 × 80 ÷ 3 = 102 rpm. At 0.004 in per tooth: feed = 102 × 8 × 0.004 = 3.3 in/min.
Straddle milling
Two side mills on one arbor, spaced by spacers to the width. Set the spacing with gage blocks.
Climb vs conventional
Most manual horizontals need conventional milling because of table backlash.
Common problems
Chatter: support too far. Bent arbor: tightened nut without support. Wavy finish: dirty spacers.
Tips
- Speeds: milling speeds and feeds.
- Backlash: backlash.
- Gears: cut spur gears.
Worked example: arbor and cutter speed check
A 4 in diameter HSS side-milling cutter on 1018 steel at about 90 SFM runs at RPM = 3.82 × SFM ÷ D = 3.82 × 90 ÷ 4 ≈ 86 RPM, so pick the nearest lower spindle step. With 18 teeth at 0.004 in per tooth, feed = 86 × 18 × 0.004 ≈ 6.2 IPM. Mount the cutter as close to the column as the work allows and put the arbor support as close to the cutter as possible to limit arbor deflection.
Common problems: chatter usually means the overarm support is too far from the cutter or the spacers are dirty; a cutter that wobbles means a burr on a spacer face or a bent arbor. Indicate the arbor near the support, aiming for no more than about 0.001 in TIR, before cutting.
Quick shop check
Common problems: arbor nut tightened before the overarm support is in place can bend the arbor. Install the support first, then tighten the arbor nut. Check that keys are in the cutter keyways.
FAQ
What is a horizontal mill?
A mill with cutters on a horizontal arbor.
Climb or conventional?
Conventional on most manual machines.
Why tighten the nut last?
To avoid bending the arbor.
What is straddle milling?
Two cutters cutting both sides.
How do I find feed?
rpm × teeth × chip load.
Related guides and calculators
- Milling Speeds and Feeds
- Leadscrew Backlash Basics
- How to Cut Spur Gears with a Dividing Head
- How to Use a Dividing Head
- How to Cut a Keyway
- How to Use Toe Clamps and Strap Clamps
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- All free machinist calculators
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