General Question - Slotted Holes

[rhasell]

Hi

I have just spent the last hour scouring the internet trying to find a definitive answer to slotted holes. This one has been plaguing me for years, but I have never found an answer.

When designing a slotted hole in structural steel, is the hole dimensioned to the center or to the outside of the slot?

Example of the AS4100 standard.

I think this one is Standard independent, besides small dimension differences.

Below is an example of a short slotted hole.

Thanks

[S_May]

Hi @rhasell 

here is the german norm.

[rhasell]

Thank you for the link.

Unfortunately, it only tells me how to make and dimension a slot, but not how big to make it.

I am looking for the interpretation on the codes. They are all ambiguous, and open for interpretation, which is most frustrating.

Does the code state that the maximum slot length as Overall length or Centre to Centre length?

I have always created slots as overall length, but is it correct, can I make them bigger?

Thanks.

[swalton]

I'd pay for a written opinion from a licensed structural engineer who is knowledgeable about each code you use.  

[hosford]

Reg

Looking at ASME Y14 dimension and tolerance book, both are acceptable.

as one that has had to machine the details drawn, I prefer the method that defines the center line, there is no math required.

 

[swalton · Accepted solution]

To restate @rhasell's Question:

1. Slot dimensions are defined by a Structural Code (think Building Code).
2. @rhasell wants to know if the Code defines the slot length by
   1. The Center-to-Center dimension of the obround?
   2. The Tangent-to-Tangent dimension of the obround?

@rhasell you might get a better answer over on the Autodesk Robot structural analysis forums.  It is more likely that one of the users in that forum will be familiar with the details and standard practices in Australia.  However, I would not trust that answer to be useful in a legal dispute if the building falls down due to incorrectly sized holes.

I suspect the only way to get the correct legal answer is to ask Australia Standards (the group that wrote the code) or consult a licensed structural engineer who designs bolted connections governed by that code.  

Finally, my sense of the Code is that the Tangent-to-Tangent dimension is critical, due to the last clause of line iii.  However, I'm not an engineer in Australia. 

[dpeceMAN78 · Accepted solution]

hehe I (in Australia) was wondering the same. Thank you so much for sending this extract.

I just re-read this for 4th time and found the answer:

"where the length of the slotted hole is taken as the total length from one hole EDGE to another along the LONGEST dimension"

That means, tangent to tangent.

It also makes sense with the rest. Because, for example, when it limits dimensions of an oversize hole, talks in relation to df, and limits the outermost boundary. so, it makes sense to limit tanget to tanget (eventhough, construction wise, you need centre to centre).

[Jared_RobinsonNSBGA]

I need to refresh myself with ASME Y14 2009.  

[blandb]

Would it depend upon the process?? We used to punch out holes and slots (the name of the equipment escapes me), but the slot punch was identified as the out to out dimension (tan to tan). So on our drawings we called out to out because of that. If you are going to mill, then I would think the center to center is ideal for a programmer to set the mill path. Just a thought. Keep in mind, that company was a hybrid machine/structural company so...standards....ehhh..their standards lol.

[Jared_RobinsonNSBGA]

Not an expert but from my understanding of ASME Y14, the process shouldn't matter. I've read about similar things about ASME Y14 for example, not calling out drill bit sizes on drawings unless it's a design requirement. I normally work with machine shops outside of my company so ideally, I'll dimension per ASME Y14 unless more detail is needed.

Jared Robinson | Sr. Project Engineer

[ldutkaTUZ58]

If you have a good connection with a good steel shop, I'd ask them. They're experienced in the field and know what works for them. I used to detail in a steel shop, and the center-to-center dimensions were the standards. Good luck.

[rhasell]

Thanks

The general consensus is to design the hole outside to outside for both options, but when it comes to detailing, to detail the holes center to center.