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Depth of a CB hole on a incline
2

Depth of a CB hole on a incline

Depth of a CB hole on a incline

(OP)
Hello all,

I am looking for standard definition of depth of a CB hole on a inclined surface.

For e.g., I have a triangular gusset. I have a CB hole on the inclined surface parallel to the base. So the depth of the CB hole varies from a min. value to a max. value. So when I do a hole callout annonation in a drawing for a CB hole what should the depth be? Min. value, max. value or value at the center? What is the standard manufacturing practice?

And is there any standard that defines this and what is it? Any help would be really appreciated.

Regards,

RE: Depth of a CB hole on a incline

I dimension this type of hole in a section view so that I can reference a surface from which to measure.

RE: Depth of a CB hole on a incline

I agree with ewh. You can dim from a surface or a defined point. The min, max, etc is up to you.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

(OP)
ewh and Chris,

Thanks for the quick replies. Section view makes sense.
So a regular CB hole callout using a CAD software would be ambiguous and incomplete?

If not how is the machinist going to interpret it?

Regards,

PS: I have used "a" instead of "an" before an vowel in my previous post. Sorry, it was a typo smile

RE: Depth of a CB hole on a incline

Quote (GunT):

So a regular CB hole callout using a CAD software would be ambiguous and incomplete?

If not how is the machinist going to interpret it?
Can you clarify? How can it be ambiguous and incomplete using CAD?

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

(OP)
As explained in my above example, I have created a CB hole using SolidWorks hole wizard and made the drawing of the part. And called out the CB hole using "Hole Callout" Annotation of the software.

The callout is as follows:

<dia sym>hole thru
<CB sym>CB hole <depth sym> depth of CB head.

The depth you obtain is the max depth by default(If no subsequent operation is performed on HW hole).

But some machinists I talked to say that the depth should have been "Value @ Center of CB" not min or max.

Hope this clarifies.

RE: Depth of a CB hole on a incline

It should be a nom depth by default. Then dim it on the dwg with tol.
But, depending on your design, it could be called out as min or max. I don't know what the CB is used for.
Create your holes, make a sect view, then dim dia and depth.
Your callout looks good to me. Draw a centerline thru the center of the hole on the dwg. The machinist should never have a problem with it.
I hope I understood you correctly and I made sense.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

The problem with measuring from the center is that the center point no longer exists when inspecting.  The machinist may want to machine it that way, but I would get the opinion of an inspector as to how it should be called out on the drawing.
This is one of those situations that are not always covered by today's cad packages.

RE: Depth of a CB hole on a incline

Look at your application to determine how to best dim the CB... for example

1. The CB is for a socket head cap screw, and you do not want the head exposed,  well then, a Min Depth will be your guide.

2. You are using the CB to fit a bushing. You don't require an amt lenght of bushing, but you must maintain a minimum wall thickness on the machined part... then you should specify a max depth, and trim the bushing.

there are numerous examples where only experience will tell you which way to go... but hey, that why we get paid the Big Bucks right?

Wes C.
------------------------------
When they broke open molecules, they found they were only stuffed with atoms. But when they broke open atoms, they found them stuffed with explosions...

RE: Depth of a CB hole on a incline

(OP)
I am sorry if I created any confusion by calling min. and max. depth. I am not talking about "Tolerances". And I definitely understand " Design Intent" and know how to accomplish it.

My question relates to a depth callout of a "Variable Depth CB hole" and how does one interpret it.

I have obtained 3 different answers and unable to find a standard definition of depth in case of a variable depth hole.

Here are the three answers:

1. Depth is measured from the point where a full cylinder of the feature is defined aka Min Value of the depth ( Not tolerance).

2. Depth is measured from the center of the CB hole cause it is to where the location of the hole is measured.

3. Depth is measured from the point the probe makes initial contact aka Max value of the depth.

So my questions are "If I specify the CB depth (of a variable depth hole)o n my print how is the machinist/inspector going to interpret it? Min value, Max value or the Mean value. Or the callout incomplete without a section view? And what standard defines it and where can I find it?"

I appreciate the discussion guys. Thanks a lot.

RE: Depth of a CB hole on a incline

If you use a section detail of the hole as ewh stated there is no room for misinterpretation.

"I think there is a world market for maybe five computers."
Thomas Watson, chairman of IBM, 1943.
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

RE: Depth of a CB hole on a incline

The logical way is to use the section view, and dimension not to the angled surface, but to the feature behind the hole that's most likely to be used to support the part while milling the cbore.  That way the quill stop depth setting doesn't have to change for parts with variations in location of the angled surface.

Mike Halloran
Pembroke Pines, FL, USA

RE: Depth of a CB hole on a incline

(OP)
MadMango,

I agreed to it already. I am asking about the scenario where the section view was not created. How does one deal with such situation?

Is the callout completely illegal without a section view or section view just adds clarity to drawing. IMO both are completely different scenarios. And I am looking for Standard which addresses the issue.

Regards

RE: Depth of a CB hole on a incline

You can not call out a variable depth CB. If you did, you could get anywhere from a spot face to a thru hole. Call out one depth with a tol.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

I agree with Mike Halloran, easy to understand and everything you need to know, what could be easier?

RE: Depth of a CB hole on a incline

Okay, you _could_ adopt a _local_ standard saying, e.g.,  the depth of the cbore is measured from the theoretical intersection of the hole axis and the surface that it penetrates.

One problem becomes apparent immediately, even beyond the nonexistence of your datum:

- The usual tools for measuring cbore depth intrinsically assume the existence of a datum surface normal to the hole axis.

The problem gets worse if your angled surface is also nonplanar.

Mike Halloran
Pembroke Pines, FL, USA

RE: Depth of a CB hole on a incline

Dimension in a section view.  Specify depth at either maximum or minimum depth.  Keep tolerance such that one can check with a scale (nearest +/-.015" should do), as it is likely a caliper or depth mic will give an erroneous reading due to the incline and curvature.

RE: Depth of a CB hole on a incline

(OP)
Initially what MikeHalloran said in his first post looked like a great solution. But it does not address the issue in all cases.

What if I take away the vertical surfaces i.e. that if I have a part shaped like a rhombus or a parallelogram then my problem surfaces again.

Also if ones dimensions like MikeHalloran asks, then one can accumulate the tolerances! And you will loose design intent.The problem is not just restricted to CB holes but can include tapped holes also.

Whats scary is that I was not able to find a theoritical definition of the depth of the CB hole anywhere in the literature so that I can extrapolate.

Yes I can make my "Local standard". But the problem is it will be not be interpreted like that in all cases and I have to communicate the standard each and every time. And that really baffles me cos this should be part of the standard literature somewhere. I don't think this is a trivial issue. And I really appreciate the discussion.

Regards,

RE: Depth of a CB hole on a incline

It isn't covered in the literature to any depth (no pun intended) because putting a counterbored hole in an inclined surface kills your manufacturability.  You can't use a standard counterbore, piloted in the through hole, because the side loads will break the tool; you have to mill the counterbore.  Which I guess makes it a milled pocket, not a counterbore at all.

Why would anyone devote any effort to producing a standard for a bad practice?

Mike Halloran
Pembroke Pines, FL, USA

RE: Depth of a CB hole on a incline

(OP)
So a CB hole on an inclined surface need to be milled and is no CB any more. I never knew this. I am taking your word for it.

But what about a threaded hole. Is it still called a threaded hole?

Thanx for the info  

RE: Depth of a CB hole on a incline

MH is correct. It really would not be a CB. It would look like one, but not made like one. Which goes back to thd beginning of this thd. Make a section view and dim the dia and depth. This way it is up to the machinist and inspectors how they want to interpret it.
For a threaded hole? A thd is a thd. Yes, it is a threaded hole. It can be tapped or turned, but is still a thread.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

I would disagree, it is still a counter bore, if the angle/ surface is near to flat then a counter bore can still be used at a reduced feed rate until full contact is achieved, failing that just spot face the surface prior to counter bored or better still counter bore before machining the top surface/ angle.

I have seen a lot of steels that have full 3D form on the top and counter bores are always dimensioned from the bottom face (I have no idea if this is a correct standard) but it is very easy for the machinist to use the flat bottom face as a datum.

Now what about the chamfer around the counter bore? winky smile

RE: Depth of a CB hole on a incline

GunT,
Can you show us a pic of your CB? Maybe it would clear up for most of us.
thanks

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

I would dimension that hole depth from the vertical surface opposite the entry point.  It would define the length of the hole rather than the depth of the CB.

RE: Depth of a CB hole on a incline

(OP)
MH already pointed that out. My question was what happens when that vertical surface is not available as in the case of a rhombus or parallelogram.

Regards

RE: Depth of a CB hole on a incline

I was responding to the picture provided.

There are no hard and fast proceedures for dimensioning this type of hole.  You need to find a feature from which you can relate back to the hole.  In the case of a rhombus where the hole is not normal to any side, I would dimension from the intersection of two sides, using both linear and angular dimensions.

RE: Depth of a CB hole on a incline

I agree with ewh.
If the shape is different...it depends on your design. If it is important where the screw head is in relation to the outer surface, you need to find a point or surface to dim from to the bottom of the CB.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

(OP)

Quote:

There are no hard and fast proceedures for dimensioning this type of hole
.
Probably this is what I was looking for. Some standard hard and fast procedure to dimension this type of hole. And it does not exist.

I really appreciate all your help. Its been very illuminating.

Regards,

RE: Depth of a CB hole on a incline

Okay, you could use a counterbore, at vastly reduced feedrate, if you needed one part real fast and you didn't have an endmill.  In that circumstance, you'd give the machinist a sketch of what you wanted, or do it yourself.  You wouldn't make a drawing.

Counterbores are really intended to be used in something like a turret drill, at cycle times governed by how fast the operator can cycle the turret, and feedrates governed by how hard (s)he can lean on the handle.




Mike Halloran
Pembroke Pines, FL, USA

RE: Depth of a CB hole on a incline

But for a CB, like any feature, you don't specify on a dwg how do make it...you just dim it.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

Chris is correct.  You dim the cb and tolerance it.  The tolerance will indicate (to the shop) the method they will use to produce the feature.  If you wanted to, you could dim/tolerance the cb such that the shop would cut the cb first and then shape the outside of the part indexed off the cb.  

RE: Depth of a CB hole on a incline

(OP)
Where did I ever say that a CB hole should be produced using CounterBoring process only? I am talking about a CounterBore Hole with a "U" like symbol.

Am I missing something? I am confused.

Regards,

RE: Depth of a CB hole on a incline

You are correct, use that symbol...with either the depth symbol or a dim to the btm CB surface from somewhere.

Chris
Systems Analyst, I.S.
SolidWorks/PDMWorks 05
AutoCAD 06
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

RE: Depth of a CB hole on a incline

If I was dimensioning this and was concerned about someone not understanding the intent, I would draw in phantom lines that decribe the missing edges of the cb. I would then dimension from your flat surface, that is perpendicular to the hole cl, to the top of your cb. This gives your machinist a height off of the table to begin cutting at, and then dimension the depth of the cb in your hole note.  

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