Squaring a Power Route (and reasonable expectations)

[riotonthebay]

I'm going through the process of squaring & tramming my Power Route and I'm curious about methods of doing so and reasonable expectations to have for how precise I can get. I'm the kind of person who really wants something done right, so I'm willing to put in a lot of effort to get that last little bit of accuracy even if I don't really need it. 

To test how square the gantry is, I milled bored four 1/4" holes in a square such that the diagonals were 24.02" apart. I put precision dowel pins in the holes and a known 24" rule (a large square) between them, then used a feeler gauge to measure the remaining gap. This lets me compare the difference in diagonals, and it looks like I'm about 0.015" out of square on those diagonals. So, a couple questions:

1) For someone with more experience, what would you consider an acceptable level of squaredness? Maybe 15thou over that distance isn't so bad — I really have no point of reference.
2) What is the right way to square a Power Route further? I've already messed with the anti-racking cables as much as I'd like to, I don't want them to be dramatically different tensions and I don't want them to be overtight. What other places should I look at for further squaring the gantry?

Thanks for the help!

[Derek the Admin]

You can get it closer. The antiraxkint cable does pull one side as you add tension, but it also has to do with how the gantry is mounted and the squareness of everything else. Consider that the holes all have free fitment for the bolts, so it’s possible tomoubt one rail further up or further back. That will be one source of adjustment.

[blinsc]

Would it be possible to get a more in-depth guide for squaring the machine? For instance, when Millright assembles a machine in the shop for testing, what procedures are taken to ensure that it is square? I'm still waiting on a replacement Z-probe/Z-limit switch since the one I got is apparently for a newer version of the control board box than was shipped to me. In that time I'd like to try to square the machine up or at least know what the procedures are because I'm guessing the chances of getting the diagonals exactly right on the first try are pretty slim.

[Bruce]

Check out this thread:
millrightcnc.proboards.com/thread/1468/tram-spindle-on-cheap

[blinsc]

I appreciate the link to that thread but I'm talking specifically about squaring the router - making sure the X- and Y-axis are square to each other and that the diagonal measurements on a rectangle match.

Since I can't really cut anything yet (can't fully home the machine), I've just been jogging the router around and marking points with a fine-tip marker loaded in the collet. The closest I've been able to get it is about 1/16th, but then when I change the tension on the wires, it doesn't seem to change much, and I don't know exactly how much tension to put on the wires before it's too much. The assembly manual simply says "musical note".

To the OP: Did you have any success getting your router dialed all the way in, and if so, what methods did you use?

[Bruce]

Which machine do you have?
The other thing that could be checked is the movement accuracy. millrightcnc.proboards.com/thread/35/fine-tuning-machine
You can check the squareness of your machine with a square on the corners.

[Derek the Admin]

You can actually cut without homing. A portion of our customers don't even own homing switches and certain competitors do not even offer them. I do recommend them, but it's not required and wont lock out use without a homing cycle like on some cobtrols.. Check out the video on work coordinate systems and you will see how to use G92 to just create a zero.

To square everything you just build it so things match up on each side. For instance, there is a bit of free fitment in the holes of the plates. If the X rail on the gantry is mounted to the extreme back on the right side and the extreme front of the holes on the left side, it will be slightly out of square. The same applies to every other axis. Understanding that and using a square while you set up things like the frame get you 95% of the way there. Then you run a square cut and measure everything to see how it came out. From there you can make adjustments if necessary.

[blinsc]

My problem wound up being the alignment of the gantry on the Y-axis linear bearings. Here's a tip: if you know your frame is square, you can send the gantry all the way to the back, then measure from the underside crossbeam (the one that connects to the ballscrew nut) to the rear frame crossbeam on each side, and if they're the same, you're probably in pretty good shape. Before realigning the Y-axis bearings, I was about 3mm off side to side.  I loosened the Y-axis bearings (as well as the ballscrew mounts underside) and twisted the gantry slightly to get it aligned on the bearings.

In terms of squareness, I'm probably within 0.010" now, literally the width of the little hashlines on my ruler square. I'm not sure if I'm going to try to chase down that last little bit as when I cut a 200mm wide symmetrical part that had an assortment of 3-, 4-, and 5mm clearance holes, I was able to flip it over and have it still fit.