Circularity of Holes

[gregfox]

After reading so much gd&t stuff, it has become apparent that no vendor is capable of accurately drilling a straight hole with a single diameter, what are commonly held tolerances to be applied to holes that are:
drilled
drilled and reamed
made with an endmill

Or is it only for pocketed recesses in turned parts.

And does circularity also apply to tapped holes?


Fox Manufacturing Group

http://foxmfggroup.com/Home.html

 

[powerhound]

The appropriate course of action would be to state what tolerances are required and let the machine shop figure out how to achieve them.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[gregfox]

Maybe a better question is what are the common capabilities (tolerance)of each method to hold what degree of circularity.

If I just want a drilled hole, what tolerance should be called out. I ask, because in the past, I would have just dimensioned a hole of size with a given +-, and did not use circularity, assuming some common value for the process. If I wanted it tighter, or with a better finish, I would have made the size tighter and assumed reaming, but still no circularity. But with gd&, I feel bullied into using circularity, but don't know how to tolerance it or rather by how much.

Obviously a super precise application for a feature would dictate the circularity, but I'm at a loss when it comes to specifying it for common features made by simple standard processes.

Fox Manufacturing Group

http://foxmfggroup.com/Home.html

 

[powerhound]

Per rule #1 the circularity is limited to the size tolerance. It then depends on the actual size of the hole. Let's say .5" +/-.005". You have a total of .010" of circularity error if the hole is actually made at .505". If the hole is made at .5" then you can have up to .005" of error. If the hole is made at .495" the you can have no error in circularity. Perfect form at MMC is the paraphrase for rule #1.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[powerhound]

I'm assuming you are working to the ASME Y14.5 standard. If not, then rule #1 does not apply.

"If I just want a drilled hole, what tolerance should be called out."
What you really want is a hole. It should not matter how it gets there. Function should determine tolerance and the machine shop determines how to put the hole in based on the tolerance and other specifications.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II