Depth of a CB hole on a incline 2

[GunT]

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,

 

[ctopher]

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)
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[ajack1]

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? ;-)

 

[ctopher]

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)
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[GunT]

Here is the link to the image. I hope this works.



Regards

 

[ewh]

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.

 

[GunT]

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

 

[ewh]

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.

 

[ctopher]

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

 

[GunT]

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,

 

[MikeHalloran]

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

 

[ctopher]

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
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[Kwan]

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.

 

[GunT]

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,

 

[ctopher]

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

 

[aardvarkdw]

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.