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How to Use a Vertical Milling Attachment

Guide · Updated October 28, 2026

A vertical milling attachment bolts to the column face of a horizontal mill and drives a vertical spindle from the horizontal spindle through gears. It lets one machine do end milling, drilling and boring as well as horizontal cutting. Like any vertical head, it must be trammed.

Tram with an indicator

Check your indicator with gage blocks before tramming. The free Gage Block Calculator builds the stack.

Step by step

  1. Clean mating faces: Wipe the column face and attachment flange.
  2. Mount and engage drive: Bolt it on and engage the drive with the main spindle.
  3. Check the speed ratio: Some attachments run at a different speed from the main spindle; read the plate.
  4. Tram: Sweep an indicator in a circle on the table and adjust the head.
  5. Lock: Tighten all bolts and recheck.
  6. Install tooling: Use the attachment taper and drawbar.
  7. Cut: Light cuts to start.

Worked example

Sweep an indicator on a 6 in diameter circle. Left reads +0.0015 in, right reads −0.0005 in, so the head tilts 0.002 in over 6 in. Adjust until left and right match, then check front and back. If the attachment ratio is 1.5:1 and the main spindle is set to 400 RPM, the cutter runs 600 RPM.

Rigidity

Attachments are less rigid than a dedicated vertical mill; take lighter cuts.

Common problems

Poor finish: head not trammed or loose bolts. Wrong speed: forgot the ratio. Gear noise: drive not fully engaged.

Tips

Worked example: tramming the attachment

Mount a test indicator on a swing arm about 3 in from the spindle centerline (6 in sweep diameter). Sweep the table front to back and left to right. If the readings differ by 0.0006 in over the 6 in sweep, the head is out about 0.0001 in per inch, which leaves a slight step on wide face cuts.

Adjust in small moves, retighten the clamp bolts in sequence and re-sweep, because tightening often shifts the reading. Aim for 0.0005 in or less over the sweep for general work.

Second worked example: drilling at 45°

With the head tilted 45°, feeding the quill 0.500 in moves the drill 0.500 × sin 45° = 0.500 × 0.7071 ≈ 0.354 in vertically and 0.354 in horizontally. To reach a hole depth of 0.250 in measured vertically, feed 0.250 ÷ 0.7071 ≈ 0.354 in along the spindle.

At 30° from vertical, the vertical component is cos 30° = 0.866 and the horizontal is sin 30° = 0.500. A 1.000 in quill feed then moves 0.866 in down and 0.500 in sideways. Spot the hole with a center drill first so the tilted drill does not walk.

Quick shop check

Common problems: a head that keeps losing tram usually has dirty mating surfaces or unevenly torqued bolts. Clean the faces with a stone, then tighten bolts in a cross pattern.

FAQ

What is a vertical milling attachment?

A head that mounts on a horizontal mill to add a vertical spindle.

Do I need to tram it?

Yes, every time it is mounted.

Does it change spindle speed?

Often; check the ratio plate.

Is it as rigid as a vertical mill?

Usually not; take lighter cuts.

How do I tram it?

Sweep an indicator in a circle and adjust.

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