I’ve been trying to come up with a way to determine how straight the 1/2" EMT rail is on my LR3. Does anyone have a good technique with typical shop tools?
I am using unistrut, and I fenced the drill press when creating the holes. But each rail clip does have some play. I spent a fair amount of time squaring the machine to within about 0.5 mm over a 1524 mm length. Beyond that I found that my eyeball and tape measure had diminishing returns.
I’m just about to the point where I can install the spoilboard and tram the router. However, I started contemplating how to assess the rail before I finalize. Bye eyeball it looks good, but my eyeballs are old.
Left to my own devices, I’m going to tension a string along the table from end to end, then point a V bit at the string and move the router along it to see how well it follows? Just making stuff up at this point.
For adjusting all 4 corners to be on the same plane (but not necessarily level…) could use a Mason Line String similar to ~24:15 in Neat! - #248 by azab2c ? Guessing sag in middle of two equally tensioned mason lines crossing over each other (‘X’ pattern) shouldn’t be much, and probably won’t matter even if they’re both sagging the same amount? Could do this for some janky MacGyver barely above the sloped garage floor setup?
A look from near in line with the rail will show you changes in the line you would be hard pressed to measure with a machinist straight edge. As long as you don’t try it in 100+° weather, where the air starts to add shimmer to things, this is as accurate a measure as you should need for anything that isn’t 100% fully captured.
The rail being straight is important. It being 100% parallel to the edge of the table? I think this is less important, so long as it’s close enough that the machine stays on the table, while the beam is maintained perpendicular to the rail.
Now I have to see how straight my rail is. I put some straight edges I had against it and it was good to the eye…hmmm. That would be funny if it was curved.
You can use a simple method with basic tools. First, tension a string along the table from one end of the rail to the other. Then, use a V bit on your router and move it along the string. If the router follows the string smoothly without veering off, the rail is likely straight. This method helps you ensure accuracy before installing the spoilboard and tramming the router.