Datum(s) on formed tube
Datum(s) on formed tube
(OP)
Is there a recommended method for specifying datums on formed tubing, such as formed hydraulic tubing or formed exhaust tubing. I care about the profile along the length of the tube and I care about the location of the ends with respect to each other.





RE: Datum(s) on formed tube
Look up ASME Y14.5M 1994.
Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP1.1 / PDMWorks 05
ctopher's home site
RE: Datum(s) on formed tube
Best Regards,
Heckler
Do you trust you intuition or go with the flow?
RE: Datum(s) on formed tube
It delt with assigning points on the tube, like "Position 0" for starting end, Position 1 for first bend, etc. It also mentioned Bend Angles, straight length dimensions, direction of rotation (CW or CCW) before next bend, etc.
"I think there is a world market for maybe five computers."
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RE: Datum(s) on formed tube
There are also good reasons for orienting the part relative to one end, or the extreme tangent of one end, which is what I think you need in order to program a CNC bender.
Third choice, sometimes the least awful, is to use the coordinate system of the assembly into which the tube fits as your datum coordinate system. This can get messy fast because in the general case every important point requires three linear dimensions and three angles.
The best datums, IMHO, are not imaginary like centerlines, and not arbitrary like tube walls at particular planes, but are the actual features at which the tube touches the remainder of the world, e.g. flange faces and holes in hanging features.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: Datum(s) on formed tube
If it were me, I would use one end diameter as my primary datum, the end face as the secondary datum, and a point out on the tube somewhere to control rotation.
How are you going to inspect this thing? A sketch of your inspection fixture might tell you how your datums should work.
I do not think there is a recommended procedure anywhere here beyond making sure your part is constrained in six degrees of freedom, and that your datums are some sort of functional feature if at all possible.
JHG
RE: Datum(s) on formed tube
Does anyone use true position to control tolerance between the two ends of a formed tube?
Don Peckham
RE: Datum(s) on formed tube
Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP1.1 / PDMWorks 05
ctopher's home site
RE: Datum(s) on formed tube
RE: Datum(s) on formed tube
I wouldn't use total runnout you would never get good parts. I would use a profile tolerance providing your datum scheme is thoughtout.
Just remember the part has to be manufacturable and inspectable.
Best Regards,
Heckler
Do you trust your intuition or go with the flow?
RE: Datum(s) on formed tube
A positional tolerance sounds good to me. You want the other end of the tube located somewhere, and the positional tolerance defines that. I am sure there are other ways to do this, but I would not spend any time worrying about it.
If I were inspecting your drawing, the primary thing I would look for is your tolerances. If they are not loose enough, the fabricator will assume you do not know what you are doing. Bending tubes cannot be a very accurate process. This thing will be somewhat flexible, right?
JHG
RE: Datum(s) on formed tube
We are using SAE J2551 (Recommended Practices for Fluid Conductor Metallic Tubing Applications)recommended total true position tolerance for hydraulic tubes so tolerances should be loose enough.
In the past, we specified true position tolerance at the "B" end of the tube and IMPLIED that the tolerance was with respect to the "A" end of the tube.
It is my understanding of ASME Y14.5M that "Location" tolerances must specify the datum. Therefore, I need to identify end "A" as a datum, and reference the datum in the position tolerance.
I think this will work.
Don Peckham
RE: Datum(s) on formed tube
Runout is used to define parts that spin on an axis. Either in usage or when being manufactured.
If you would describe how the part functions I can suggest the best datums to define it. The most important features which mate or aling or both are the best datums according to the standard. Not adhering to this basic principle causes no end of confusion.
RE: Datum(s) on formed tube
Thanks for your comments.
The tube is 1/2" diameter and has ORFS fittings on both ends. The tube is "U" shaped with the "A" end connected to a straight fitting on the side of a transmission. The tube runs horizontal to the left, vertical, and then horizontal to the right and about 5 degrees toward the rear in a horizontal plane. The "B" end connects to a 90 degree fitting on top of the transmission.
For this particular tube there are no clearance problems along the length of the tube. However, we need good control of the location of the ends.
I welcome your suggestions.
Don Peckham
RE: Datum(s) on formed tube
Those ends are the datums. This is a rather unusual part but the logic still applies. Since this part is probably flexible then it's the usual practice to simulate how it's restrained in use and replicate that in the fixturing to check this part for acceptance or not to the tolerance.
I still can't clearly comprehend this part. Have not a clue what those fittings look like. Are they brazed onto the tubes for instance? If they are then I suggest the detailed drawing consist of the finished assembly and not the tubing alone. This way the fixturing is simple just simulate the mating fittings in the gauge to a gauge tolerance.
RE: Datum(s) on formed tube
Thank you for your comments.
The tube ends are flared and the contact surface is on the flare. The "ORFS FLANGE" figure on page 1 at the following link shows an example. htt
The three straight lengths are 9" to 12" long and this is a 1/2" diameter tube.
Don Peckham
RE: Datum(s) on formed tube