True position

[Grobar]

Hi guys,

I am a rookie with pc-dmis so my "problem" will probably seem ridiculous. I don’t get this true position. I have measured that .437 boss, thread hole, and both lines. I don't understand how machine is doing the math so I am not sure if I am dimensioning this right. I don’t know if it is taking center point of a line for dimensioning because in that case it would depend on first and last point I took when I measured that feature. I am babbling... Anyways, I attached the drawing, so any help on this is more than welcome!

Thanks!

[Roger Kilpatrick]

Create a cylinder on the .437 dia boss and align to that cylinder then set zero in both directions to the cylinder. Compare the threaded hole to this alignment as true position (t/p), your theoreticals should be .000 - .000 for the c/l of the threaded hole and your tolerance for the t/p should be .010 at RFS. Think of it as rotating the boss with an indicator on the minor dia of the thread, you are actually measuring runout or T.I.R. from one feature to another. Oh yeah..... just to through in another little twist t/p of a thread is ALWAYS measured to the pitch cylinder, not the major or minor dia ( unless otherwise specified on the drawing ). Have fun.

[BSchwark]

check out this site for a True position calculator.

http://www.engineersedge.com/true_position.htm

Your print is hard to read. But it appears you can translate your origin (alignment) to the measured .437 boss and report the 1/4-20 diameters on both sides of your part. Use your true position for dimensioning. Nominals would be X=0, Y=0 (depands on your working plane). Should calculate it for you.
You may wish to obtain a book on Geometric Dimensioning and Tolerancing (GD&T).

Good Luck and welcome to the school of Hard Knocks

BS

[Grobar]

After a break, we're back on track. This long weekend was too short!
Thanks guys for your help, but the thing that's giving me a hard time is true position of those notches (see .343 distance between notches). How can I do that?
Any thoughts?

Thanks.

[george frick]

one way is to create a midpoint or symmetry between the .343 notch and check it in relationship to the .437 boss. in y the variation should not exceed +/-.005 and you may also use mmc from the size of the notch.

[Underspec]

Would concentricity & true position be the same thing when the datum is circle and the circle which calls out for TP is above that?

[kbotta]

post pic of your drawing?
If your FCF has a position symbol, than it is position. If it had a concentricity symbol, it is concentricity. 2 diff. things.

[Underspec]

The part I'm looking at is basically a cap that has an inner cylinder in the center. The print is calling out for the TP of the outer diameters to the inner (datum). I'm questioning because it used to be concentricity, but now there's a new print with the TP called out. Can someone elaborate why? And how it's different?

<<<< Learning noob....

[Jeffrey Lovely]

think like a gage

[kbotta]

Underspec,
Check your PM's...

It might explain why...

[Underspec]

New print = new part too. I'm saying the customer usually calls out concentricity on this type of dimension.

[kbotta]

Check your other thread, I uploaded a file from ASME for you...
KEV