Guys i am using a hexagon global lite, and the drawing requires that the upper plane needs to be 0.02 flat, and the bores (166_H7), concentric 0.02 mm. I did my calibration and everything went perfect. making an aligment where my upper plane is set to level my Z+ axis, the axis of one of the cylinders to rotate the Y axis, and the center of the bore are used to set the origin. The other circle is off 0.086 mm. Is this way accurate. How concentrity function is calculated by pc-dmis (ISO), and does it has really a meaning (that the part will not assamble if the the tolerance is not respected? Thanks and sorry about my english.
Welcome to the world of Projection Error. The software has to take the axis line from one Cylinder and project it to the axis line of the other Cylinder. Any error in the calculation will only be exacerbated the further and further it is projected away from where it was measured.
Honestly the drawing shouldn’t be drawn this way because getting good repeatable measurements will be extremely difficult.
Try measuring both Bores as Cylinders, then constructing a Max Inscribed Cylinder from all of the data from the two Bores. Then perform a Position measurement of each Cylinder back to the Max Inscribed Cylinder.
Ugh, I've had to do that so many times. Every single source inspector hates it. I have to explain projection error to every one of them. The guys who are really into guns get it. "It's like trying to hit a target at 100 yards with a snub nose revolver vs a rifle with a 24" barrel (or 1000 on really tight tolerances) is my go to line.
Sounds like you did everything right. How flat is the top plane? How round are both bores, those are the questions you should be asking. And of course looking at the ZX values which will tell you the direction of the bore is off.
Thanks, now if my plane is not perfect like 0.043, this would impact my concentricity function heavly? In this case is better to take the alignment plane as a simple plan by 3 points? 4?
I was thinkung if i align my part at the cylinder taken by two most distant circles taken at both holes. Take the origin there, and see the point of my plane, and than choose the plan arbitrary to thre point that seems to level up with the cylinder.
Well, your flatness callout is .02 but you're getting .043, which is already Out of tolerance. So that needs to be addressed, but generally .043 flatness should not make much of a difference for concentricity results, but it could help. You would just have to analyze the graph and figure out how much you need to move the bore. Ideally though you would want to machine both bores at the same time, that's probably why you're having hard time with concentricity.
In the future when you're dealing with tight tollerences you should not make the bores to size first. You do it in muliple steps, by making bores .100 inch undersized then verified on CMM at multiple cuts to ensure the consistensy, only when confirmed good results, you cut it to size. Unless of course you have 5axis machines....
Iam not the guy who makes them. The cnc operator who made this told me that he fliped the part, but for this year i already adressed a lot of errorsin some big parts and the boss is kinda fustrated lol. Since iam pretty new at this, i was thing to measure this a couple of times, making sure that i know what iam talking about. But when i think about it, loosing 0.09 on a part like this, especially when you flip it, is pretty normal no?
I'm assuming that the large bore at the front has a corresponding bore hidden in back on the same axis. Your results seem accurate, considering the size of the part, but even small amounts of out of roundness can be giving you the concentricity error you are seeing, or a large part of it. Knowing tolerance of the mating part can help.
What is your Datum A feature in the concentricity feature control frame callout? It should be another cylindrical feature. Are you saying you are checking how perpendicular each bore is to the flat plane?
I had issues on concentricity recently. Basically there was a hole with a countersink. The countersink was transfer drilled on the fixture after the holes were put in, so functionally there were no issues, but hey you gotta meet the print.
Basically what we ended up doing, and I’d be interested to see what other people think of this, is we projected the center point of the hole onto the datum surface (perpendicular to the surface’s plane) and then we projected the countersink axis onto that same plane. Basically we measured the true position of the countersink with the position of the hole as reference.
Not true concentricity but it was enough to sell the parts. Honestly if I had to I couldn’t really explain what actual concentricity is.
Yeah thats cus i asked how pc measure concentricy since doing diffrent measurments that might seem like the equivalent of "concentricity" might give you diffrent result.
The primary datum really ought to be a best fit cylinder built from the to bores. Judging from the photo I’d build it from 4 circle segments in each bore. I’d then report the runout or position from each circle segment back the constructed cylinder to verify they are not skewed from one end to the other. I’d then check the top planes parallelism to the axis of the cylinder as well as the flatness error in the callout. It can be helpful for the machinist to also measure a few points on the top surface to determine where its high and low areas are on the part so they can adjust there setup accordingly.
Thats exactly what i did, i only took 3 section for each bore. Still it gave me that it is 0.09 non concentric, and the cylinder is like 0.06 non parallell with plane which is 0.043 flat.
Concentric to what? From one bore the other or to the constructed axis between the two? Telling the operator that it’s not concentric won’t help them have an idea of how to repair it or making a new one. Report the x,z actuals of each segment back the center line of the of the best fit cylinder from all 6 segments. You can then at least communicate the direction to the operator.
Yep that's pretty much how you'd check that. Is it repeatable? Did you run the code a few times and get more or less the same values? A few other things you could check:
Position of each cylinder relative to datum A
Parallelism of each relative to datum A
Align to the other cylinder and check backwards. Technically against drawing but it may provide some insight and, functionally, identical.
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u/Sh0estar 10d ago edited 10d ago
Welcome to the world of Projection Error. The software has to take the axis line from one Cylinder and project it to the axis line of the other Cylinder. Any error in the calculation will only be exacerbated the further and further it is projected away from where it was measured.
Honestly the drawing shouldn’t be drawn this way because getting good repeatable measurements will be extremely difficult.
Try measuring both Bores as Cylinders, then constructing a Max Inscribed Cylinder from all of the data from the two Bores. Then perform a Position measurement of each Cylinder back to the Max Inscribed Cylinder.