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How to align a portable gantry milling machine


A few weeks back, we published an overview of portable gantry milling machines that explained the main machine components and the different types of milling rail available.

This time we go a stage further and explain the fundamentals of setting your machine up with laser alignment.

Applications for a portable gantry mill vary, but typical uses can include the machining of metal bases for pumps, turbine bases and skids (used in petrochemical and power generation plants).

Machine foundations can also twist and move over time, which may affect their operation and efficiency. In these situations, the on-site machinist armed with a portable gantry milling machine can come to the rescue.

Assembling the sub frame

No matter how accurately the milling rail and gantry rails have been manufactured, if the assembly is not installed correctly the results will be inaccurate and potentially hazardous.

Each job is unique, but in all cases the gantry will need to be fixed securely. This may be to the job itself, the working area surface, or onto a sub-frame. The gantry kit is provided with mounting plates which can be used in a number of different ways; such as with Rawlbolts (for fixing into a concrete floor), by bolting through suitable holes in the job, tack welding, or by using switch magnets.

If extension rails are used to create a larger working envelope, these are butted up and bolted together. (If a rack feed rail is being used, a special block and G-clamp is used to align the teeth on the rack).

When the rails, tie-rods and drive link are assembled the whole unit should be checked to see if it is square before the bolts are fully locked up. Now the milling rail can be bolted onto the gantry frame.

Laser Alignment

A typical laser alignment kit will include 3 or more modules using Bluetooth technology to communicate with each other.

  • THE LASER TRANSMITTER – A rotating unit which creates the laser
  • THE TARGET/DETECTOR – This is moved around the job to record various positions.
  • THE DISPLAY UNIT - A hand held device, which can connect to a computer or save data direct to a USB.


Many useful accessories are also available, including an angular prism used for deflecting the beam at exactly 90 degrees.

The Laser Alignment Process


Only when the whole assembly is in-situ should the alignment be checked.

  • The ‘laser transmitter’ should be positioned off the job. If the gantry is mounted horizontally on the floor, place the transmitter on any firm stable object at a suitable height.
  • The detector should be positioned on 3 selected measuring points and the values registered. These are then set to zero and the other points are recalculated for the newly created reference plane.
  • The measurement values at the other points on the frame will show the deviation from the ‘zero’ plane.
  • In addition to checking the gantry frame you may also need to place the detector on the top milling rail to ensure everything is aligned.
  • The jacking screws in the gantry mounting plates are adjusted to level the whole assembly. Various positions should be re-checked after each adjustment until the assembly is confirmed as level.
  • It is also recommended that you take more readings after the first cut, to make sure the assembly has not moved.

You can find out more about the Mirage range of milling machines here, or why not download our buyers guide?

Download the Linear and Gantry Milling Machine Buyer's Guide

If you have an on-site machining challenge and cannot find the right product to help, it may be possible for us to develop a bespoke machine for you. Please get in touch get in touch with your regional contact here to find out more.

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