Extrusion Twist GD&T Specification

[sljames]

Does anyone have a slick way of calling out twist on an extrusion? I can't find any GD&T standard to address twist. The twist I'm speaking of is a general roll of the material as it leaves the extrusion and is pulled through the rollers. Perhaps degrees/feet?

 

[CheckerHater]

Well, judging from using feet you are American.
There is no American standard for twist.
German DIN 1748 covers aluminum profiles and that's about it.
If significant area of your part should be flat in perfect "untwisted" state you may try to use Flatness.
There isn't much more to say given the information you provided.

 

[drawoh]

sljames,

Do you want twist, or are you trying to eliminate it?

Flatness tolerances can be applied per-unit length if you wish. I do not know about profile tolerances. This would be worth looking up.

Your extruder will cut his extrusions into twenty foot pieces, right?

JHG

 

[drstrole]

There is an Aluminum Extrusion Manual from the aluminum extruders council that I use. This gives expected tolerances, including twist.

Drstrole
GDTP - Senior Level

 

[sljames]

Yes I am in the US. I would be fine to list the requirement any way that is proper. The extrusion is a multi-lumen polymer based tube. The twist is critical because the lumens will need to remain in the same orientation at the end as at the begining. I can tolerate about 15 degrees of rotation per 4 feet but that's about it.
I want to spell it out on the print but haven't been able to find the proper callout for twist.
I'll check out the Aluminum Extrusion Manual to see if that fits.

 

[KENAT]

Does 14.8 the casting/molding spec have anything that could be applied to this application? I don't think it explicitly covers extrusions but does address thing like mold mismatch so might give some ideas.

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