Nominal Change Decimal

[Aliffadhol]

Hi Guys.

We have several issue regarding nominal decimal precision.

We are create the program by offline.

before we called dimension that will call out in report, we already set decimal precision.

Everything going smoothly on offline.

After we transfer the CMM program to be used for checking the part (online- direct connect to the machine),

some of the nominal change.

As example:


Case 1

I set 1 dimension nominal to 3.000 ( 3 decimal) during offline programming.

But, at the report after checking the part, the nominal change to 2.99977 ( 5 decimal).


Case 2

The nominal are 3.005 ( measured from cad).
since the drawing called the dimension is 3.000, so I change the dimensional nominal to 3.000

But,
after checking the part, the dimensional are revert back to 3.005.


Is it a bug from the software?

Inspector & other engineer keep complain said that our program is wrong/ typo error.

[AndersI]

Which version of PC-DMIS?
Are you using autofeatures with FIND NOMS Active, instead of NOMINALS?
F5 -> General tab, is "Find nominals" checked in the list?
How is your alignment?
Did you search the forums for "nominals change"?

[William Johnson]

PCDMIS will use the last command that was read for parameter settings. If that last time it saw 5 decimal places that is what it will use. You program in 3 places and open up program that is 5 places.
You need to F5 dimension tab then define settings. Note that this is only 1 area of the settings that should be in the beginning of the program. Here is an example of what I have in all my programs.
This will ensure that if you change a setting in the program somewhere that is needed, when you open another program it will reset everything to your preferences.


MODE/MANUAL
PREHIT/1.5
RETRACT/1.5
CHECK/1.5,1
MOVESPEED/ 250
TOUCHSPEED/ 2
DISPLAYPRECISION/4
FORMAT/TEXT,OPTIONS, ,HEADINGS,SYMBOLS, ;MEAS,NOM,TOL,DEV,OUTTOL, ,
LOADPROBE/T2_3X20MM
TIP/T1A0B0, SHANKIJK=0, 0, 1, ANGLE=0

[Schlag]

Make sure the actual feature nominal is 3.000 and not 3.005

[louisd]

--the measured feature's theoretical nominal, as opposed to the defined nominal within the dimension output.

[Douglas]

this reminds me a little of one engineer who thought nominals on CAD models were not important when he could just edit drawing dimensions later anyway... who would even know the model is fkd up

[louisd]

The most rudimentary and absolute resolve, is to make the nominals into a formula, like 3.000+0 or 3.000-0. This locks the value in place and prevents it from changing on its own, regardless of what's causing the issue.