Cylinder

**Wes Cisco** · 06-20-2006, 10:10 AM

I use axis start point as a standard, with that start point being the datum face if applicable. I believe this is correct by the ASME Y 14.5M. (And KBOTTA will correct me if I am wrong.) If the engineer is concerned about the rest of the hole he has other tools at his disposal, most notably and commonly used is perpendicularity. HTH

**gsepan** · 06-20-2006, 10:14 AM

Wes,

Makes sense when checking a hole but how about a stud with no perpendicularity callout? Bottom of the stud may be in location but the top might be off?

**#2#** · 06-20-2006, 10:28 AM

It seems to me that TP specifies every point of a feature must fall within the zone. So to be 100% correct you would need to TP the entire length of the cylinder (hole or stud). In most cases TPing the top and bottom would be adequate and I would report the worst case scenario. If you are too worried about it you could measure multiple circles in/around the cylinder and TP them all.

**Wes Cisco** · 06-20-2006, 10:29 AM

Ok, I have a long running program at the moment, so I consulted the spec. I was wrong in my last post

, unless otherwise specified true postition covers the entire diameter length. But with the demon you can only report one location. You could report both the start and end of axis, (have two dims for each cylinder) or you could measure two circles and report each. I have done this on some parts where I reason to suspect there was drift. Also so, if there is a projection on the trueposition you can use the "reference length" box in the true postion window. If you only want one dim per stud, I would use axis average. If anyone else has a better idea, I would love to hear it. HTH

**Paul Sarrach** · 06-20-2006, 10:38 AM

I make a itersectpoint of the cylinder( which I usally create two circles, then create a line) and the plane where the TP is called out to.

**Paul Sarrach** · 06-20-2006, 12:22 PM

Who did not like the way I do my TP? And why the bad Rep? If you are going to give bad Rep, at least be a man and say why you disagree and who you are. And if you think I am wrong, correct me. What is wrong with my method? I personally don't like using the auto cylinder feature.

**gsepan** · 06-20-2006, 12:55 PM

OK, here's what I did and I'm still not sure which is the right answer... I measured the stud as a cylinder and asked for the true position at worst case. Then I measured two arcs at different heights and something just isn't right about my results.... If my worst case senerio is 1.91MM TP at 280MM in the "X" axis and then I check an arc @ 315MM (Same distance as my last arc measured for the cylinder) and it checks 2.33MM TP... which is right??? The "Master Cylinder" strikes again!!! Or is it possible I'm not understanding it correctly?

STUD_LOCATION =AUTO/CYLINDER,SHOWALLPARAMS = YES,SHOWHITS = YES
THEO/280,522,293.65,1,0,0,19,35
ACTL/280,521.06,293.48,0.9991251,0.0190992,0.0372058,19 .05,35
TARG/280,522,293.65,1,0,0
THEO_THICKNESS = 0,RECT,OUT,CIRCULAR,LEAST_SQR,ONERROR = NO,$
AUTO MOVE = NO,DISTANCE = 50,RMEAS = None,None,None,$
READ POS = NO,FIND HOLE = NO,REMEASURE = NO,USE THEO = NO,$
NUMHITS = 6,NUMROWS = 3,INIT = 0,PERM = 0,SPACER = 3,PITCH = 0,$
START ANG = 180,END ANG = 360,DEPTH = 7,$
ANGLE VEC = 0,0,-1
MEAS/CYLINDER
HIT/BASIC,287,521.67,303.14,0,-0.03,1,287,521.67,303.27
HIT/BASIC,287,516.26,301.22,0,-0.6,0.8,287,515.9,301.69
HIT/BASIC,287,512.94,296.52,0,-0.95,0.3,287,512.16,296.77
HIT/BASIC,287,512.94,290.78,0,-0.95,-0.3,287,512.22,290.54
HIT/BASIC,287,516.26,286.08,0,-0.6,-0.8,287,516.01,285.73
HIT/BASIC,287,521.67,284.16,0,-0.03,-1,287,521.67,284.21
HIT/BASIC,301,521.67,284.16,0,-0.03,-1,301,521.7,284.73
HIT/BASIC,301,516.26,286.08,0,-0.6,-0.8,301,516.36,286.2
HIT/BASIC,301,512.94,290.78,0,-0.95,-0.3,301,512.63,290.67
HIT/BASIC,301,512.94,296.52,0,-0.95,0.3,301,512.26,296.74
HIT/BASIC,301,516.26,301.22,0,-0.6,0.8,301,515.75,301.89
HIT/BASIC,301,521.67,303.14,0,-0.03,1,301,521.65,303.79
HIT/BASIC,315,521.67,303.14,0,-0.03,1,315,521.64,304.31
HIT/BASIC,315,516.26,301.22,0,-0.6,0.8,315,515.6,302.08
HIT/BASIC,315,512.94,296.52,0,-0.95,0.3,315,512.39,296.7
HIT/BASIC,315,512.94,290.78,0,-0.95,-0.3,315,513.06,290.81
HIT/BASIC,315,516.26,286.08,0,-0.6,-0.8,315,516.72,286.67
HIT/BASIC,315,521.67,284.16,0,-0.03,-1,315,521.71,285.26
ENDMEAS/
COMMENT/REPT,-------------------------------------
,PEDAL ATTACHMENT STUD C/C, U/D (DSM)
,TRUE POSITION: 1.4MM
,CHECKED AS A CYLINDER
,REPORTING WORST AXIS
,-------------------------------------
DIM D16= LOCATION OF CYLINDER STUD_LOCATION UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH
AX NOMINAL +TOL -TOL MEAS DEV OUTTOL
X 280.00 0.50 0.50 280.00 0.00 0.00 ----#----
Y 522.00 0.50 0.50 521.06 -0.94 0.44 <--------
Z 293.65 0.50 0.50 293.48 -0.17 0.00 --#------
D 19.00 0.10 0.10 19.05 0.05 0.00 ------#--
END OF DIMENSION D16
DIM D10= TRUE POSITION OF CYLINDER STUD_LOCATION USE AXIS=WORST (START PT) REF LENGTH=0.00 UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH DEV PERPEN CENTERLINE=ON DISPLAY=DIAMETER
AX NOMINAL +TOL -TOL BONUS MEAS DEV DEVANG OUTTOL
X 280.00 280.00 0.00
Y 522.00 521.06 -0.94
Z 293.65 293.48 -0.17
TP RFS 1.40 0.00 1.91 -90.00 0.51 -------->
END OF DIMENSION D10
CIRCLE-01 =AUTO/CIRCLE,SHOWALLPARAMS = NO,SHOWHITS = NO
THEO/315,522,293.65,1,0,0,19,35
ACTL/315,521.73,294.78,1,0,0,19.06,35
TARG/315,522,293.65,1,0,0
COMMENT/REPT,--------------------------------------------
,CIRCLE-01 C/C, U/D
,LOWER CIRCLE USED FOR CYLINDER CONSTRUCTION
,--------------------------------------------
DIM D15= LOCATION OF CIRCLE CIRCLE-01 UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH
AX NOMINAL +TOL -TOL MEAS DEV OUTTOL
X 315.00 0.50 0.50 315.00 0.00 0.00 ----#----
Y 522.00 0.50 0.50 521.73 -0.27 0.00 --#------
Z 293.65 0.50 0.50 294.78 1.13 0.63 -------->
D 19.00 0.10 0.10 19.06 0.06 0.00 -------#-
END OF DIMENSION D15
DIM D11= TRUE POSITION OF CIRCLE CIRCLE-01 UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH DEV PERPEN CENTERLINE=ON DISPLAY=DIAMETER
AX NOMINAL +TOL -TOL BONUS MEAS DEV DEVANG OUTTOL
X 315.00 315.00 0.00
Y 522.00 521.73 -0.27
Z 293.65 294.78 1.13
TP RFS 1.40 0.00 2.33 -90.00 0.93 -------->
END OF DIMENSION D11
CIRCLE-02 =AUTO/CIRCLE,SHOWALLPARAMS = NO,SHOWHITS = NO
THEO/287,522,293.65,1,0,0,19,35
ACTL/287,521.21,293.74,1,0,0,19.07,35
TARG/287,522,293.65,1,0,0
COMMENT/REPT,--------------------------------------------
,CIRCLE-02 C/C, U/D
,UPPER CIRCLE USED FOR CYLINDER CONSTRUCTION
,--------------------------------------------
DIM D14= LOCATION OF CIRCLE CIRCLE-02 UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH
AX NOMINAL +TOL -TOL MEAS DEV OUTTOL
X 287.00 0.50 0.50 287.00 0.00 0.00 ----#----
Y 522.00 0.50 0.50 521.21 -0.79 0.29 <--------
Z 293.65 0.50 0.50 293.74 0.09 0.00 -----#---
D 19.00 0.10 0.10 19.07 0.07 0.00 -------#-
END OF DIMENSION D14
DIM D12= TRUE POSITION OF CIRCLE CIRCLE-02 UNITS=MM ,$
GRAPH=OFF TEXT=OFF MULT=10.00 OUTPUT=BOTH DEV PERPEN CENTERLINE=ON DISPLAY=DIAMETER
AX NOMINAL +TOL -TOL BONUS MEAS DEV DEVANG OUTTOL
Y 522.00 521.21 -0.79
Z 293.65 293.74 0.09
TP RFS 1.40 0.00 1.60 -90.00 0.20 -------->
END OF DIMENSION D12

**Wes Cisco** · 06-20-2006, 01:18 PM

Well, with out a print, and only partial data, here is what I see:
1) You measure the cylinder from 180 to 360, you should measure the full 0-360 unless you cannot get to it, or it does not exist.
2) You are reporting all three axis in the trueposition, you should only report 2. Based on the 1,0,0 vector I would not check the y axis box when setting up the truepostion dim.
3) Because you are only using 180 degrees of arc, I would have more faith in the cylinder than the circles because there is more data for the software to calculate the form from. If you want to report two locations, use start and end of axis, (instead of worst).

There may be other stuff I am overlooking, someone else will catch, but that should give you some ideas to work with. Remember that the software is using an algorythem to construct the circle/cylinder from the actual hits, the large the arc and more hits the more accurate the construction will be, up to a point of diminishing returns of course. HTH

**Paul Sarrach** · 06-20-2006, 01:37 PM

I am seeing the same thing about the 3 axis. If you are going to do it that way, use deviation PerpTo Centerline. A TP unless other wise stated is always reported in 2d

**gsepan** · 06-20-2006, 01:48 PM

Thanks for you input Wes... The "X" axis should be turned off for true position but because I didn't take sample hits I show no surface deviation and some will argue that surface deviation indeed will change the location especially if on a compound vector. Due to fixture constraints I could only check the stud to 180 degrees but I have been told that that is a minimum for accurate readings. Was I misinformed?

**Wes Cisco** · 06-20-2006, 02:29 PM

Well, when you get to less than 180 degrees of arc you begin to have trouble. I have done some experimenting and found that if I can get three levels with at least 5 hits each level I can get fairly accurate with as little as 60 or 70 degrees of arc, ***BUT*** "fairly accurate" is a purposefully vague term. Each time I do something like that I am taking into account the entire project: what I am trying to measure, do I know the function, what are the print tolerances, am I just looking for size or size and location or profile? You get the idea. This is grey area stuff at best. When working with circles instead of cylinders, I would not trust any measurement with less than 180 degrees of arc. But especially with circles, I always try to measure as much of the arc as possible. If I can get to 270 I will not settle for 180. Depending on the application, I sometimes index the head and use individual vector points to build my circle, cylinder, cone. Again, it depends on what I am trying to acheive and the degree of accuracy, (tolerance), I need to hold.

I almost never take sample hits, ***BUT*** I work with precision machined parts, not castings, not stampings, not sheet metal. . .

HTH

**gsepan** · 06-20-2006, 03:32 PM

Thanks Folks!

I think I'm gonna stick to just checking the upper most portion and the lower most portion of the stud as a circle and True Position both. Both should fall within the tolerance boundaries if manufactured properly. I think it also gives the engineers more info on exactly what's going on with the stud whether it's off location and/or if it's not perpendicular to the cad surface as mentioned by Goodluck. I'm just not sold on the cylinder thing yet... especially when the stud pins on the gage, the gage checks good and when I measure using cylinders it checks bad....

**Paul Sarrach** · 06-20-2006, 03:53 PM

Thats why I stated I do not like cylinders. And I also agree with you TPing both circles, Why I was asking about the print, is where they want the trur pos? It could of been a projected, could be at the base at the tip, and by creating that line you could also use it for the perpindiculaity call out, if there is one. And you usally see both, if TP is good at the end where they ask for it, the Perpindicularity call out controls that the rest of the cylinder is in TP.

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