How to square up the gantry?

There has to be a more sophisticated way of getting the rails installed. I have tried multiple times by securing one side, running the machine from the back to front while securing the other side. I always end up with rails 1/16 out and I cannot get this thing to cut square.

Did you try following the directions precisely from the setup instructions? Specifically after you’ve secured the right side, don’t use the diagonal screws on the left; run it past the ends to the back, secure with only the vertical screws as you jog forward. It’s very easy to get the machine out of square with the angled fasteners.


yes, I followed the instructions precisely. I have the machine mounted on a torsion box which is very flat. I even bought a bit extender so I could predrill for the screws. If I secure the right side and then jog the machine, I always end up with a 1/16" larger space between the two front feet than the two back.

If I hold a framing square against the gantry, there is a 1/4 gap over 24 inches.

I am a carpenter by trade, and I find this very frustrating. I ended up cutting a “sandwich block” to the fit between the feet, so that I could gently squeeze the rails to match. I then used a framing square and squared up opposite feet. After making a test cut, the results were better, but on a 6" square piece I am still out 1/16.

The V shape of the gantry and rails makes measuring angles extremely difficult. I wish there was a simple solution. Following the directions doesnt even land me a parallelogram. Not sure what to do.

@joekorman When you say that on a 6" square piece, you are out by 1/16", do you mean that you run a job on the Mill that is a 6" square and, measuring the diagonals, you are out by 1/16"?

What is the “sandwich block”, and how are you using it? From your description, I’m thinking that it is a piece of wood that fits precisely between the two back feet when they are tightened. Then you move it to the two front feet, squeeze them until the block precisely fits between the front feet, then tighten the front feet. I am thinking, though, that I am missing something, since doing only this would guarantee that the Z rails are parallel to each other, but it would not mean that they were square to the X gantry.

Now you have me wondering if my machine could be out of square; my test cut was a simple 1"x1" square which did come out perfect but I’ll cut a 6" one tonight and measure. I can’t imagine why you’re having such difficulty and my leading hypothesis would be that your angle aluminum is not straight; do you have a way of verifying that your rails are true?

@joekorman this was a comment I found from Stephen Allan on our FB group on how he found a way to resolve squareness issues:

Had the same problem. fully assembled according to instructions and out of square by 1/2" , so you end up with a slight parallelogram instead of a square. Still works but everything you cut will be skewed. I ended up by fastening front and back feet on the right side first. then I put a wooden straight edge for reference butted up to the right front leg support and using a framing square fasten it to the table. Move the gantry almost to the very back, leaving just enough space to insert the screw in the left back leg. Before screwing in make sure the front left leg support is butted tight to the wooden straight edge you just fastened to your table. Put in the screws in back left support. If the gantry does not butt evenly at the very back at this point, hand screw the threaded rods until both sides of the gantry are tight against both back leg supports. At this point you should be able to move the gantry along the tracks and insert the remaining screws in the left side. When you are done the setup should be square to your table. An easy check is to put a v bit in your router and cut a shallow inverted L the width and height of your work surface. Check this with a square to make sure everything is square.

The discussion thread can be found here: LongMill and Mill One User Group : Working with Chris Thorog, we determined my v-wheels I received were too large

Most times the basic assembly will be quite close for the majority of individuals who assembly their LongMills but sometimes it’s not enough. Let me know if this process works for you, and if so I’ll work to amend it to our assembly instructions for those who want to guarantee near-perfect squareness after assembly :+1: