True Position HELP!!

[shays]

This is a tough one, I will try to write this so it makes sense ha ha:

I am having trouble with a true position spec - I have a 12mm diameter, with a bolt hole pattern of 3.7mm diameters in a 19.05mm diameter around it. The 12mm diameter is lBl. The back wall of the feature thru which the 12mm & bolt hole pattern diameters are located is lAl.

The true position callout is from each of the (3) 3.7mm diameters, to lBlAl.

In my alignment, the wall lAl is the Y origin, and the 12mm dia lBl is the X origin.

Per the engineers in charge, this callout relates lAl to the diameters as perpendicularity of the axis thru the 3.7mm diameters to the plane that is lAl, rather than a linear distance. It appears, however, that PCDMIS (3.7) is calculating this as linear.

What would I need to do, possibly in the geometry of my constructed features, so that PCDMIS relates, in a TP callout, a line thru the axis of a diameter perpendicular to the plane?

Thanks for any help on this!

[Cumofo]

Well, the holes must first be measured as Cylinders. If the datums are properly used as your alignment features, you shouldn't have a problem.
1) Datum A, level to YPLUS
2) U need to decide which feature, or feature sets you will use that are perpendicular to DATUM A to establish axis of rotation. Mabey one of the holes in the pattern is daum c?

oK neXT?

gABRIEL

[shays]

Hi Cumofo, and thanks for the info.

I have constructed lBl as a cylinder, and used this feature as rotational Y plus around Z plus. The plane for lAl is leveled to Y plus.

I have constructed one of the 3.7mm diameters as a cylinder. When I dimension this 3.7mm dia as TP to lBlAl, my nominals are showing as X: -4.725 (which is correct) and Y: -.6377 (which would be correct as the center point of the Cylinder, if I were looking for a linear distance.)

I am still stuck :-(

[tking]

shay,

Wouldn't you consider those to be the nominals for a true position callout for the hole? TP includes perpendiularity because your cylinder has to be within the true position callout top to bottom.

TK

[Cumofo]

ohh,
Use the X axis and the Z axis as reported AXIS. Also you may need to use polar coordinates, if you dont have the cad or are lazy with ur trig!

Gabriel

[Cumofo]

ohh,
Use the X axis and the Z axis as reported AXIS. Also you may need to use polar coordinates, if you dont have the cad or are lazy with ur trig!

Gabriel

[shays]

Thanks for the info guys. I am still working on this one.....

tking - I understand what you say about the perp being included in true position, but am curious - how is the actual perp value (or deviation) shown in the "results" area of true position in PCDMIS?

thanks again!!

[tking]

Thanks for the info guys. I am still working on this one.....

tking - I understand what you say about the perp being included in true position, but am curious - how is the actual perp value (or deviation) shown in the "results" area of true position in PCDMIS?

thanks again!!

shays,

Technically it's not. Simply put if the c/l of the feature is in position from top to bottom it meets the implied perpendicularity requirement. If you want the actual perp deviation from 0 to display you would have to do a perp check and report it, I would report actual only (this is not a 2x calculation as TP is).

TK

[shays]

This is what I have suspected, from what I am seeing in my results.
Thanks for the explanation, this helps me out a LOT.
shays