KEVOS® MAKEOS · Maintenance
Jackbolt Turns and Flats for an Alignment Move
How many turns and head flats of the jackbolts at the front and rear of the machine give the side-to-side moves my alignment calls for?
Jackbolt moves for horizontal shaft alignment as the handbook works them: one full turn advances the bolt by its pitch (1 ÷ TPI for inch threads, or the metric pitch), one flat of a square head by a quarter of that and one flat of a hex head by a sixth, so the turns are the move divided by the pitch and the flats the turns times the number of flats, rounded to the nearest flat.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Jackbolt thread | choice | Whether the jackbolt has an inch or a metric thread. |
| Threads per inch (inch thread) | TPI | Threads per inch of an inch jackbolt, e.g. 11 for 5/8-11. |
| Pitch (metric thread) | mm | Pitch of a metric jackbolt, e.g. 2 mm for M16. |
| Jackbolt head | choice | Square heads have four flats and hex heads six. |
| Move needed at the front jackbolt | mm | Side-to-side move at the front jackbolt from the alignment calculation. |
| Move needed at the rear jackbolt | mm | Side-to-side move at the rear jackbolt from the alignment calculation. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Jackbolt thread
- What it is
- Whether the jackbolts have inch threads or metric threads.
- Units and format
- Choose one of 2 options from the list: Inch (threads per inch); Metric (pitch in mm).
- Example
- The form opens with “Inch (threads per inch)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Chooses threads per inch or the metric pitch.
- Get it right
- Check the bolt designation, e.g. 5/8-11 is inch and M16 is metric.
What this means: Threads per inch (inch thread)
- What it is
- Number of threads in one inch along an inch jackbolt.
- Units and format
- Enter a number in TPI: threads per inch. The form accepts 0.000001 TPI to 80 TPI. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 11 TPI as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The advance per turn is 1 ÷ TPI inch.
- Get it right
- Read it from the designation, e.g. 11 for 5/8-11 UNC.
What this means: Pitch (metric thread)
- What it is
- Distance between threads along a metric jackbolt.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The advance per turn equals the pitch.
- Get it right
- Read it from the designation, e.g. 2 mm for M16 coarse.
What this means: Jackbolt head
- What it is
- Number of flats on the jackbolt head, square or hex.
- Units and format
- Choose one of 2 options from the list: Square head (4 flats); Hex head (6 flats).
- Example
- The form opens with “Square head (4 flats)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- More flats give a finer move per flat.
- Get it right
- Square heads have four flats and hex heads six.
What this means: Move needed at the front jackbolt
- What it is
- Side move needed at the front jackbolt from the alignment calculation.
- Units and format
- Enter a number in mm: millimetres. The form accepts -100 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.6256 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Divided by the pitch to give the turns at the front.
- Get it right
- Take it from the rim and face or reverse indicator result, with its sign.
What this means: Move needed at the rear jackbolt
- What it is
- Side move needed at the rear jackbolt from the alignment calculation.
- Units and format
- Enter a number in mm: millimetres. The form accepts -100 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.3114 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Divided by the pitch to give the turns at the rear.
- Get it right
- Take it from the rim and face or reverse indicator result, with its sign.
Method and formulas
- Advance per turn = pitch = 1 ÷ TPI (inch) or the metric pitch.
- Advance per flat = pitch ÷ 4 (square head) or pitch ÷ 6 (hex head).
- Turns = move ÷ pitch; flats = turns × number of flats, rounded to the nearest flat.
- The sign of the move gives the direction; push from the side the machine moves away from.
- Example: the front jackbolt needs 0.704 turn (3 flats) and the rear 1.001 turn (4 flats).
Limitations
- The advance assumes the bolt bears straight on the machine foot with no take-up of slack or bending.
- Back off the jackbolts on the opposite side before advancing, and take a final set of readings after the move.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Turn the side-to-side moves from an alignment into jackbolt turns
- Choose square or hex jackbolts for fine moves
- Check how close a whole number of flats gets to the move
Who it is for
- Maintenance fitters
- Millwrights
- Reliability engineers
What you get
- Advance per turn and per flat
- Turns at the front and rear jackbolts
- Nearest whole number of flats and the move it gives
- What is left over after the nearest flat
Interpreting the result
- Heavy resistance while turning means a mechanical bind, not a rusty thread, as the handbook notes.
- Remove and store the jackbolts after the alignment is complete.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2631–2632. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · KEVOS® original book
Making the moves
In Shaft Alignment by the Numbers
What it covers: How to combine readings and thermal growth into cold shim corrections, choose shims, make the vertical then horizontal moves against indicators, and confirm the running result.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Jackbolt Turns and Flats for an Alignment Move calculator