[he1957]

There are possibly many different ways to align and square a CNC router table gantry to get the best possible accuracy for cutting your parts. Parts that are not square can pose problems - especially if you want to do double sided machine. In this thread, feel free to add your favourite method to align, square and test your setup to share with others.

Here is a method I've found to be easy and quite reliable and does not require expensive equipment. Just a good straight rule, some pencils, pens and a few measuring tapes if needed. A piece of MDF or even large piece of paper would work but you can use the MDF to make parts after you have finished!

The alignment is not difficult, just a little fiddly.

1. Start with a straight line drawn with a spring loaded pen/pencil in the spindle on the master rail side on Y (and set X to (close to) zero)
2. Around the center of travel for Y, make a 1000mm set of marks (500 mm each side)
3. Measure and mark your 1000 mm box with a good straight edge rule using the diagonals to ensure it's square
4. Align spindle center (pen) to one line of intersections on X=0 side, move X along line to other side (X+)
5. If gantry is square to master rail, it will follow line and match at the end of line intersections, otherwise diddle the mechanicals until it is
6. Repeat to check
7. Move Y to other perpendicular line and re-check.
8. If there is a discrepancy take the difference of the two to maximise (minimise?) squareness between the allowed distance
9. If there is a discrepancy it shows the master rail is not straight and has a bow of sorts

Any measurement is OK, bigger is better, it's just our old friend Pythagoras for the hypotenuse side. In the above, a square of 1000 x 1000 mm is used with diagonals of 1414.2 mm. This is a nice value but a 500 x 500 mm square will have diagonals of 707.107 mm so as can be seen, it's a nice ratio. A rectangle can also be used. Assuming D is the hypotenuse side and A and B represent the right-angle sides, the formula is:

square_root(D) = ((A^2) + (B^2))

As mentioned in previous post, if meshing of R+P is not snug and easy for both sizes, power down and move slave side motor. The idea is to find the best full step position for meshing without power. After power on, the meshing may cause a slight movement, so again mechanical adjust if needed.

Then under power move the spindle pen around the box, for the perimeter and the diagonals to show the tracking of the lines.

[GME]

Here is easiest, most straightforward method I've found - and it's cheap. It involves drilling 4 holes, inserting metal dowels or router bits into the holes (the dowels or bits should be the same size as the holes), measureing the diagonals, and adjusting the gantry. That's the short version. The longer version follows:

1. Create a toolpath to drill 4 equal sized holes within the work envelope. The toolpath can be a square or a rectangle. For best results, the holes should at each corner of work envelope at or near the outer extremes. The holes can be any diameter as long as they are all the same size. I have 1/4" metal dowels, so I drill 1/4" holes. You can as easily use router bits (insert the shanks), as long as all 4 are the same diameter.

2. Run the toolpath and insert the dowels. router bits, or whatever.

3. Measure diagonally from corner to corner. I use the word "measure" very loosely. This isn't a tape measure type of measurement. You use bar gauges. Assuming you don't luck into a perfectly squared gantry, determine which diagonal is SHORTER and set your bar gauge such that it just kisses the inside of the dowels. Then, move the bar gauge to the other diagonal. Butt it up against the inside of one dowel and observe the gap at the opposite end. Use feeler gauges to measure the amount of gap.

4. Divide the measured gap in No. 3 above in half. 1/2 the gap is the amount you need to move the gantry on one side or the other to bring it into square.

5. Adjust the gantry.

6. Offset the toolpath to drill 4 new, adjacent holes. Still a square or rectangle. Repeat from No. 2 above

Keep repeating until it's dead on.

Which way to adjust? Assume you are going to adjust the X+ side. If the right front to left rear diagonal is longer, you need to move the right side of the gantry toward the rear. If the left front to right rear is longer, move the gantry toward the front. The amount of movement is the number derived in No. 4 above.

Here are 2 examples of bar gauges. They can be purchased or fabricated in various configurations.



https://www.leevalley.com/us/Wood/pa...513,43553&ap=1





Veritas® Bar Gauge Heads - Lee Valley Tools


Gary