Deep drilling GD&T
Deep drilling GD&T
(OP)
Question regarding GD&T for deep drilling / boring drawing. What is the common practice for tying down an internal bore, taking into account straightness, cylindricity, and 'wander' from start to finish of the bore?
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RE: Deep drilling GD&T
Chris
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)
RE: Deep drilling GD&T
As the OD of the initial stock bar will be turned to a finished diameter, I have usually specified a drift of 0.001" per 1.0" depth. As the OD is sufficiently oversized, the total 'wander' of say 0.144" is not outlandish.
My feeling is to define cylindricity on the bore itself, and then perpendicularity to one of the ends.
The finished diameter (after turning the OD) would then be controlled by way of concentricity to the original internal bore (difficult to check though)...
RE: Deep drilling GD&T
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RE: Deep drilling GD&T
The ID of the bore (though entire length) is 2.125"
Depth of bore (thru' all) is 12 feet.
Hole will be bored, stock OD will be turned down to finished diameter 2.875".
As there is sufficient stock OD to work with, it should be relatively straight forward to bore the hole, then use the bore's axis as the datum to turn the OD. As long as the bore does not wander excessively, and remains straight (or cylindrical) relative to itself along all 12 feet.
RE: Deep drilling GD&T
You can use projected tol or total runout.
If the part is assembled to mating parts only on the ends you can call out a tighter tol on the ends.
You can use the I.D. as the datum, that is will it will be chucked for turning the O.D.?
Chris
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 10-27-06)
RE: Deep drilling GD&T
What is the function of the tube?
RE: Deep drilling GD&T
All I am really after is the tolerancing required for the first step in the deep boring operation, which is to drill the hole straight though the bar. All the finishing is handled by another drawing. I just want to have a drawing that is easily understood and can be inspected with minimal difficulty for the first boring op.
My thoughts have been somewhat mixed, including: perpendicularity of a cylindrical tolerance zone (specifying an allowable deviation of the axis per unit length) to the entry or exit plane. Also cylindricity appeared to be somewhat sensible, but prohibitive to inspect.
I can see runout being useful on the finishing drawing, but not necessarily of any use on the initial operation as a means of putting a bound on the allowable drift.
Someone out there must do deep hole borings for a living and have this done to a fine art!
RE: Deep drilling GD&T
As such without knowing the effect on the finished part & assy it can be difficult to answer a question like this.
If all you really want to do is maintain a minimum wall thickness for later machining why not consider positional?
RE: Deep drilling GD&T