Hole Depth (drill Depth)

[tomw]

Dear All,

Warning: this is a VERY basic question.

When a plan calls for a certain drilled depth of hole, at what point is that measured? Is it measured from the point of the drill bit, or from the start of the full diameter? In the drawing below, this would be B versus A.

Thanks,

Tom

 

[T Bredehoft]

Point A, the usable hole.

 

[w9jbc]

depends a lot on how the print is drawn here at work it is the total depth including point. often we use a 150* drill point to flatten the hole out for great tap/ chip clearance. but they do that so as not to break through and intersecting hole on the part.

 

[RJSakowski]

In my experience, drill depth is usually specified to the shoulder (a). SolidWorks goes to "a". My CAM program can go to either although I usually choose to go to "b".

 

[chips&more]

Back in the day, many light years ago. I recall the V bottom as total depth. In this way, regardless of the angle on the bit. The total hole depth is controlled. You don't want to be drilling where you don't belong!...Good Luck, Dave.

 

[RJSakowski]

In my experience, drill depth is usually specified to the shoulder (a). SolidWorks goes to "a". My CAM program can go to either although I usually choose to go to "b".

I should add that the reason that I go to the total depth (b) in my CAM software is that I set my tool offset to the tip of the tool, using a height gage. The tool offset table in Mach 3 goes to the tip of the tool.

 

[John Hasler]

Back in the day, many light years ago. I recall the V bottom as total depth. In this way, regardless of the angle on the bit. The total hole depth is controlled. You don't want to be drilling where you don't belong!...Good Luck, Dave.

I uglified a part the other day by getting this wrong. I carefully calculated the maximum depth not to break through and then drilled to the shoulder instead of to the point. Didn't actually hurt anything, but I meant that to be a blind hole.

You can get it wrong the other way too, though. Perhaps a bottoming tap is expected to go to the shoulder, or the hole is intended to intersect another one for an oil passage.

 

[tomw]

Thank you all for your responses. The drawing I am working off of (a steam engine kit) does not specify shoulder or full depth (A or B), so I thought there might be a convention. It seems like maybe there isn't. I guess I will go to B, and if it is not deep enough go to A.

 

[Tony Wells]

Generally, if it is DP it means total depth, if is dp it means depth to full diameter, by far the most common in ANSI drawings. Reasoning that there are so many variables in drill point angles. If this is your own project, you can do what you want. You should determine if there is a reason not to drill beyond a certain depth for pressure concerns, etc. If nothing prevents you, and you are going to tap the hole, the deeper the better.

 

[Bill C.]

It is better to ask the designer/engineer what they want. Usually the drawing will show total depth of hole. It should tell you either by image or note. Drafter sometimes can look at their drawings and forget to add notations. I have done it.

This is true of tap holes as well. One may have to use two taps to reach the designed depth. Reamed holes I usually bottom them out to the drilled depth.