9 Replies Latest reply on Jul 19, 2017 4:55 AM by Chris Berry

# GD&T Perpendicularity on end face of square extrusion.

A supplier for my company make 40mm x 40mm aluminium extrusion beams & we specify what lengths to cut them to. However, sometimes when they cut the beams, the cut face is not perpendicular to the main extrusion. Now I could control the perpendicularity by placing a datum on one of the 4 faces but that only controls it to that one face and could be out on the remaining 3 faces. Placing a datum on each of the four faces would work but that’s messy & doesn’t look (or feel) right.

Is there a best method on controlling the cut on the end face?

btw, The four faces of the extrusion are assumed to be straight.

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

I guess it depends on what you want.

How long is the finished cut piece?  What's the tolerance for that cut length?  The tolerance zone for perpendicularity is 2 parallel planes at whatever distance you give it.  For example, .005 (i'm using english numbers) would mean that the finished plane of the cut would need to fall within the 2 parallel planes .005 apart.

Another way...

Do you have an axis down the middle the extrusion?  If so, make that your Datum A and then the flat cutoff face (I'm assuming) would be perpendicular to that datum axis.

HTH

Steve C

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

Length can vary as we make several different sized frames from several different lengths. The length isn't really an issue, as this is controlled via a toleranced dimension (+/-0.25mm). The problem arises when a section is bolted to a face of another beam & if the end isn't perpendicular it wants to go off at an angle. Usually we only get one of two 'duff' ones per batch, but the manufacturer doesn't want to take responsibility as its not stipulated on the drawing. The cut is 'assumed' to be perpendicular but is not checked or controlled, I would like to change this.

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

Ok, so on your drawing you'd have Datum A (one of the 4 faces of the square) and Datum B (one of the other 2 faces that is perpendicular to A) and then the end face would be perpendicular to Datums A and B within 0.25  The supplier might have to change his fixturing a bit but should be able to hold those numbers.

Steve C

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

I would say that doing this would be the best way to control the perpendicularity of the end face. Thanks.

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

BTW Chris, I use and work with ISO standards on a daily basis and have a question for you.  If the length of the cut piece varies, doesn't/wouldn't the overall tolerance expand as it gets bigger?  I'm referring to ISO 2768-mK as that is what I use in most cases and for most of us who grew up with imperial tolerancing ideas, is still hard to grasp in some cases.

Steve C

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

I know where you are coming from with regards to tolerance vs length.

The manufacture is happy with the standard one we use (0.25mm) for the lengths we want. They range from 1700mm down to about 350mm.

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

Are you happy with my explanation?  If so, make it as the answer, please.

Steve C

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

Chris,

I think you have a good direction for the answer to your original question.

As a job shop, my opinion is more on what happens next. If we had a part like your first run with no parallel callout, it is a basic cut and check length job.(Which means I can put a saw operator on it) Quoted at that price point.

If you added an inspection for parallelism we would have to set up an additional inspection along with piece part sets of inspections this would add cost to the original quote as well as the project.(And all further runs).

This job may require someone above a saw operator level depending on their skill level who can check and fill an inspection report.(Again adding cost)

I am not saying that you are off base, but depending on the amount of rework or issues you are seeing the cost of additional inspections on a part may not offset the cost of doing business. So to speak.

• ###### Re: GD&T Perpendicularity on end face of square extrusion.

Yeah, we know about the additiional costs that might be involved by adding in the inspection aspect. We are probably going down the path of getting the beams rough cut to length & then being finished on a miller in order to get the accuracy.