"In line" tolerance?

[handleman]

I'm dimensioning a weldment part (picture attached) that has a couple of H7 toleranced dowel pin holes for alignment of a linear guide component. The component has a datum edge that will be "bumped up against" two dowel pins in the H7 holes before being tightened down with screws into the four tapped holes. If it matters, this is for a piece of one-off equipment, so only one of these parts will ever be made. I don't really care at all about the absolute position of the holes in the face, but I do want to make sure that the two H7 holes are "vertical" to one another with respect to the bottom surface, so that when the bracket is assembled to a base plate the linear motion component will be vertical. My supervisor told me to just draw a dimension/extension line between the two hole centers and specify perpendicularity between that line and the bottom surface. While that does seem to communicate what I really want, I (think) it's totally wrong. How can I tolerance this part without adding a bunch of unneccessary cost?

Thanks!

-handleman, CSWP (The new, easy test)

 

[KENAT]

aardvarkdw

Yes I believe you. The excuse of 'not wanting to confuse the machine shop' and similar excuses will be the death of clear, unambiguous, well toleranced drawings at this rate.

Great, we've made it clear for this one specific operator in this one specific machine shop, now what if any of this changes. Or what if it comes in wrong and there's a legal dispute over the ambiguity of the drawing.

If only there was some national/industry spec that laid all this down...

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[geotol]

Here is one way to accomplish what you need, see attachment. You want to control the tol zone (2 par planes)between the two holes to be both perp to mating face and bottom surf with some location from side surf.

Mike Lacroix
GDTP-S-0355

 

[axym]

I like Mike's suggestion, except that I would omit the reference to Datum C. That way it will control the zone's orientation relative to Datum B, without controlling the zone's location relative to Datum C.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca