Datum selection for inspection?

[ArubaBob]

We have a couple of Extrusion Mandrels used in the making of copper tubing. The existing drawings are being converted over to GD&T dimensioning. Straightness of these parts is very critical. These Mandrels extend into and through a mating die. Heated copper (1500 degrees F) is extruded through the annular gap created between these two parts to make copper tubing. If the Mandrel is not straight the wall thickness of the tubing that is produced will not be concentric and out of specification.

Firist, I am not sure the parts are GD&T dimensioned correctly.
Second, After these parts are produced they may be sent out for Nitriding or other heat treating or coating processes. They will need to be inspected again to be sure they have not warped during this treatment.

Would it be better to show the surface and not the axis of the area marked as "B" as the main datum and do Total Runnout referenced to this surface? That would make inspection easier? Would we get the straightness, etc. needed?

Another question I have is with regards to the threaded portion of the Mandrel. Is it possible to call out a runnout for these threads as I have shown? The Mandrel screws into a holder that has mating threads and matching diameters to the two shaft diameters on each side of the threads. There is a .002" to .009" clearance to these diameters.

One additional note. The center hole in the Mandrel is for a cooling water tube that is inserted into it. Water flows out the end of this small tube near the end of the Mandrel and back along it and out the end of the Mandrel. If the center hole of the Mandrel is not concentric the uneven heating of the Mandrel due to different wall thickness can cause the Mandrel to warp. In the "Part B" shown on the sketch I guess the only way to inspect this center hole would be with Ultrasonics? The same with Part A?

Thanks for any help or suggestions.

Bob

 

[ModulusCT]

Bob, I'm afraid your image doesn't work for me. It may be a problem on my end, but you might want to double check.

I'm not a vegetarian because I dislike meat... I'm a vegetarian because I HATE plants!!

 

[ArubaBob]

Thank you ModulusCT for the reply.

I will try to upload it again. It is:



Your file's link is:

http://files.engineering.com/getfil...a-4da5-9b13-29a253bcb259&file=GD&T_Sketch.pdf

 

[SeasonLee]

You may need try again, it doesn't work.

SeasonLee

 

[ArubaBob]

Trying one more time.

Please see: <a href=

http://www.filesavr.com/W602HZL9NDVAEV8><img

src=

http://www.filesavr.com/images/share_download_button.png

width=127 height=145 border=0/></a><br /><div style=font-size:9px;font-family:Arial, Helvetica, sans-serif;width:127px;font-color:#44a854;><a href=

http://www.filesavr.com/>

File Storage & File Hosting</a></div>

The URL is:

http://www.filesavr.com/W602HZL9NDVAEV8

Thanks,

Bob

 

[CheckerHater]

I will start, but may need help from other members of this forum, as you question(s) is really big.
"First, I am not sure the parts are GD&T dimensioned correctly."
The part looks pretty good, especially if you are new to GD&T. I assume you are located in "inch" country, follow ANSI/ASME standards released not earlier than 1994.
"After these parts are produced they may be sent out for Nitrating or other heat treating or coating processes. They will need to be inspected again"
Your drawing always represents the final state of the part. If necessary you can fortify it by explicitly stating things like "size applies after painting/plating, heat treatment, etc." So describe hardness required, specify process if necessary, and demand final accuracy "after".
"Would it be better to show the surface and not the axis of the area marked as "B" as the main datum and do Total Runout referenced to this surface."
Surface marked "B" is not the best choice for fixturing. Actually holding part by DIA 2.975 and controlling runout for the rest of it looks good.
"Would we get the straightness, etc. needed?"
Actually standard (ASME that is) comes with what is called the "envelope requirement". When specifying DIA 2.975 +/-.001 you create "envelope" engulfing straightness, roundness, cylindricity, etc. requirements. All of them must be less than +/-.001.
So you don't really need total runout of .005 on said diameter because it is smaller than .001 and in fact, illegal specification.
"guess the only way to inspect this center hole would be with Ultrasonic?"
You are the boss, you know how the part works and what you can and cannot do to it. For example, drill it all the way thru, control location of the hole from both ends, then plug/braze/weld the hole (if possible)
I will also try to re-submit your picture the way everybody is used to.