X-Y axis Square: How square is square enough?
I recently had opportunity to work on squaring a 4'x8' table from a reputable manufacturer. It appears that the machine was never, from the manufacturer setup, very square to begin with. The owner doesn't use it for very exacting purposes so probably never noticed. But I expected that it would be square from the initial setup to within a few thousandths. The thing is, when speaking with tech support from the manufacturer, they suggest using a tape measure to check large square diagonals. I can't see how you can get it square into the single digit thousandths with a tape measure and simple marks on the spoil board. Am I expecting too much? Is it common to be 0.020" or more out of square (offset between one side of X vs the other) on a commercial grade machine of this size?
Re: X-Y axis Square: How square is square enough?
.020 is unacceptable in my opinion. I squared up a 4 x 8 router and was able to square it to within .005 over 48." The only challenge is getting a large square to use as your standard.
Re: X-Y axis Square: How square is square enough?
"Commercial Grade" means different things to different people.
Is this a $20K machine? $50K? 100K?
The more expensive the machine, the better the chances that it will be square from the factory.
As for square enough? If it's affecting the quality of your work, then it's not square enough.
Re: X-Y axis Square: How square is square enough?
Thanks Ger21 and warrenB.
To follow up to Ger's comments...
Let me rephrase/clarify my questions:
A) On a $50k machine, how many thousandths of "squareness error" would you expect to see?
B) On a $50k machine, what techniques would you expect to use to determine and/or adjust for squareness?
Re: X-Y axis Square: How square is square enough?
Quote:
Originally Posted by
chmedly
A) On a $50k machine, how many thousandths of "squareness error" would you expect to see?
B) On a $50k machine, what techniques would you expect to use to determine and/or adjust for squareness?
We have a 4-axis woodworking router in that price range. The gantry squareness was adjusted by checking the diagonals with a tape measure (within 0.5mm or so). This is perfectly adequate for the parts we are making. It would be foolish for us to spend extra time and money chasing the unneeded "precision".
Re: X-Y axis Square: How square is square enough?
Quote:
Originally Posted by
chmedly
I recently had opportunity to work on squaring a 4'x8' table from a reputable manufacturer. It appears that the machine was never, from the manufacturer setup, very square to begin with. The owner doesn't use it for very exacting purposes so probably never noticed. But I expected that it would be square from the initial setup to within a few thousandths. The thing is, when speaking with tech support from the manufacturer, they suggest using a tape measure to check large square diagonals. I can't see how you can get it square into the single digit thousandths with a tape measure and simple marks on the spoil board. Am I expecting too much? Is it common to be 0.020" or more out of square (offset between one side of X vs the other) on a commercial grade machine of this size?
90° is square enough. ;)
Re: X-Y axis Square: How square is square enough?
Quote:
Originally Posted by
chmedly
A) On a $50k machine, how many thousandths of "squareness error" would you expect to see?
B) On a $50k machine, what techniques would you expect to use to determine and/or adjust for squareness?
A) Depends on how you are measuring, but I'd expect it to not need any adjustment, if it comes ready to run.
B) I'd cut large squares, and make a jig to compare diagonals. How you actually make adjustments depends on how the machine was designed.
Re: X-Y axis Square: How square is square enough?
Since Gerry won't be pinned down, I'm using the other posts to confirm my suspicions. :wave:
First of all, I'm trying to talk about squareness in terms of the offset between the 2 sides of the gantry at the rails. I call this the rail-rail offset. This kind of thing could also be defined in terms of angle from square which might be a better way to discuss it from a geometry stand point. But in terms of measurements and in-machine correction, offset between the rails makes more sense to me.
I don't think it's reasonable to measure tighter than about 0.020" with a tape measure across 4' diagonals. I think this is especially true if it takes 2 people to do the measurement (one at each end of the tape). If the machine rails are 60" apart then that means a rail-rail offset margin in the vicinity of 0.017". btw, I think this machine was off over 0.050" before I started.
Certainly, 0.020" (0.5mm) amount of squareness across the entire width of the machine is fine for many kinds of parts. But for a machine that measures repeatability in the range of 0.001", I would expect overall positioning accuracy to be better than 0.020". Perhaps in the range of 0.005"? Conversely, 0.005" of accuracy over 96" of travel does seem quite impressive.
Since I'm hoping to soon cut a new project on this machine where I want the absolute best squareness I can get, I have a different technique in mind for measuring the diagonals. I plan to cut (4) 1/4" diameter holes in a 44" square pattern. I'll insert precision 1/4" pins in each hole. I have a 60" ruler with a hole in one end. I'll lay the hole over one pin and lay the ruler out towards it's diagonal counterpart. Then I'll use a 6" caliper to measure the remaining few inches between the end of the ruler and the pin. I think this will allow me to measure with accuracy in the range of a couple thousandths. To be clear, I'm not talking about measuring an absolute length. I'm simply looking for the difference in length between the 2 diagonals. That's what I'll be able to measure with significant accuracy. I think.
Re: X-Y axis Square: How square is square enough?
Quote:
I don't think it's reasonable to measure tighter than about 0.020" with a tape measure across 4' diagonals.
That's why I suggested making some type of jig, which would make it easy to compare the dimensions. You don't need to know how long the diagonals are, just the difference between them.
Re: X-Y axis Square: How square is square enough?
The importance of being square is dependent on what you are making. Signs and cutting boards can be a long way out of square before it matters. Clock gears are a lot more important to be square, unless you want oval shaped gears.
The typical 4x8 machine probably has two 8' rack and pinion gears on either side. Both travel together to move the gantry. Getting them square involves moving one side independently from the other until it is square with the gantry. There may be a routine in Mach3 to calibrate this using some precision limit switches to detect square.
Steve
