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Dimensioning slots

Dimensioning slots

What is the "standard" method for dimensioning slots? We have for years located the slot by the geometric centerlines and described the slot size by note. For example: "SLOT 9/16 X 1". Some of us are wanting to locate the slot with the longitudinal centerline in one direction and by the ends of the slot in the opposite direction. I haven't found any conclusive ANSI discussion.

RE: Dimensioning slots

There are 3 ways to dimension slots or oblongs.

1) Long axis of slot, center-center length and outside width, and radii.
2) Outside length and outside width, and radii.
3) Centroid of slot, and outside length & width, and radii.

"The attempt and not the deed confounds us."

RE: Dimensioning slots

This may be a company standard rather than any "official standard", but we dimension it by the centerlines also, and use a leader note to call out the dimensions as you stated: "SLOT 9/16 X 1".  The radii dimension is redundant because it is half the width of the slot.  
Our sheetmetal fabricators can enter these numbers into the program on the punch press.  To check it they can get a calculator out.
If the critical dimension is from the edge of a part to the inside edge of a slot, then exceptions would be made on how it is dimensioned.  


RE: Dimensioning slots

I made a mistake in my above posting, you do not have to call out the end radius of any of those methods, unless the radii is not a true radius.

"The attempt and not the deed confounds us."

RE: Dimensioning slots

As much as it pains me to say...

Slots are best dimensioned for their manufacture.


Locate from the center for a stamping/die cutting process.  (Some manufacturing programs will actually use this data to make the part.)

Locate from the first diameter center or edge for a milling op.

Dimensioning to the first dia ctr is easier for manual milling.
This is also easier to calculate if the slot is long enough.

The main benefit of dimensioning for manufacture is the programmer or machinist does not have to recalculate everything.  

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RE: Dimensioning slots

On the job shop end it is best to dimension the slot at the extremes and not tie the machinist to a radius unless it is critical, or apply a large tolerance to the radius.

Have fun make money.

have fun make money

RE: Dimensioning slots

Hello all, I'm *new* here, but not new to engineering :)

Good info on the dimensioning of a slot, but how would one apply a positional tolerance on it? Any GD& T wizards out there? Thanks in advance.


RE: Dimensioning slots

My preference....

Dimension to the edges of the slot, and then dimension the length and the width of the slot as two seperate dimensions.

Coupla comments in response to the above posts...
1. Dimensioning to the edges (without GD&T) gives more opportunity for excessive tolerance stackup.
2. I don't care whether the hole is punched, drilled and milled, laser cut by Buzz Lightyear, or 'Shot Out' by Annie Oakley at 50 yards with a double-barreled shotgun so long as that hole ends up where and how I want it, so I dimension to the edges as edges are what causes the interference - not the centers.
3. In most cases, I prefer dimensioning the length and the width of the edges of the slot as two seperate dimensions rather than a note. The slot mentioned in previous posts was 9/16" x 1", but if I have a 1/2" x 5/8" slot drawn at 1/4 scale with a leader dictating '1/2x5/8', it gets foggy pretty quick as to whether the slot should be cut hertical or vorizontal (pun intended).  


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