Thru To Bore Note

[aardvarkdw]

With the change to symbol based hole notes does anyone know if the note "Thru To Bore" is still the accepted way to describe the depth of a hole that intersects another hole but does not go all the way thru?

 

[ctopher]

Also, your dwg shows the holes going a depth in hidden lines. It is confusing since you indicate thru to bore. There could be a question from the machinist. I prefer THRU ONE WALL.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-05)

 

[ringman]

aardvarkdw,

I just did look and your drawing and was wondering what and how you are tolerancing the patterns.

 

[EngJW]

A designer I knew would call out the depth to the centerline of the intersected hole. I don't know if that was his standard or a company standard, but it sounds workable and doesn't depend on which hole is put in first. We had inspectors that would pick with nits, but it never came up as an issue.

 

[ctopher]

I think it would be a lot of work for the machinist to drill to the centerline of the intersecting hole. Seems like personal preference for your designer.

Chris
Systems Analyst, I.S.
SolidWorks 06 4.1/PDMWorks 06
AutoCAD 06
ctopher's home (updated 06-21-05)

 

[KENAT]

I tried opening the link to the drawing but had trouble.

I agree that giving a depth as anything other than reference makes no sense as you can't inspect it. A ref dimension to the centre of the hole you're going to might be a good idea tho'.

I was always taught that hidden detail is non preffered and sections are better but I know in some situations hidden are still useful.

Still in any situation where defining the hole using standard methods/callouts is awkward I tend to put a section.

Would wording like 'Thru to ØX.XX hole' be a way of clarifying it? Especially if accompanied by a section and reference dimension.

 

[wgchere]

Would wording like 'Thru to ØX.XX hole' be a way of clarifying it?

That would be clearer, but now you have another problem. If the large bore ever changes size you have to remember to change all the dimensions that have that diameter referenced in them.

 

[MechNorth]

The question of how to call out the depth is answered indirectly in ASME Y14.5M-1994;
"Section 1.8.9 Round Holes: ... Where it is not clear that a hole goes through, the abbreviation THRU follows a dimension." In other words, where the geometry is clear, further detailing is not required. In this case, the section clearly shows a tapped hole from the outside wall to the inside bore, so specifying the pre-drill and tap size is all that's required. Machinists should know how to read an engineering print, so they would see the intersection, note the position and size of the cross-bore and do the math to ensure that the holes fully intersect. Adding notes such as "Thru to Bore", "To Bore", "One Side Only" are redundant at best if the drawing shows the geometry correctly in section or in phantom lines, and may confuse inexperienced machinists at worst.

The only inspection to be done on the depth of a hole thru to the bore is visually verifying that it completely intercepts the cross-bore and does not enter the opposite face of the bore. It wouldn't be an issue in this sample because there is another bore on the other side.

SoapBox time: I would be concerned saying that this drawing somehow conforms to Y14.5M-1982. There are no datums, no positional tolerances, no general size tolerances to cover the non-toleranced dimensions... Without a positional tolerance on the tapped hole, the feature could be significantly out of position which would theoretically allow the tapped hole to nick the tangent of the cross bore and exit the other side of the outside diameter. Sounds "impossible", but "legally" that part would pass inspection.
Stating that a drawing conforms to Y14.5M (any edition) sets a legal precedence that can bite you if the engineering isn't correct. End SoapBox.



Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

 

[aardvarkdw]

Jim,
The drawing orignialy had a general tolerence block and such but it was removed along with notes and title block at the request of my company prior to posting. It was simply an illustration (albeit a bad one) of a note in context that I had a concern about.

That being said, I agree with you. If the hole is shown in section a note specifying depth would be redundant, but in cases where a clear section veiw is not an option the reference depth dimention that was mentioned earlier would be the best option.

 

[MechNorth]

Tks Aardvarkdw. I was a little concerned there.

Jim

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

 

[ewh]

MechNorth,
I agree with your post with the exception of "specifying the pre-drill and tap size is all that's required". The only tapped hole information required is the actual thread designation and depth of thread (as req'd), except for special situations such as where the pilot depth is critical. The drawing should not tell the fabricator to tap, or what size pilot drill to use, as these are per existing specifications and would be redundant on the drawing. Every machinist should have access to the Machineries Handbook.

 

[MechNorth]

Fair enough, ewh. I don't have ANSI Y14.6 or Y14.6aM (the standard for specifying and dimensioning screw threads) onhand. I've usually used the tap call-out and depth (as needed) as directed by company stadards. Specialty taps like SpiraLok typically need a pilot drill called out or the taps may be easily broken (from experience).

tks
Jim

Jim Sykes, P.Eng, GDTP-S
Profile Services
CAD-Documentation-GD&T-Product Development

 

[ewh]

You're right that this rule is not set in stone, as there are situations where more detail is involved. As a general rule though, the machinist should know how to proceed. It is just a pet peeve of mine, as I always seem to be bleeding on drawings because of it (and other similar mistakes). I've had one designer brag that he had never taken a drafting course in his life. He was a good designer, but often said "that's the way we did it at (insert any previous employer)" when it came to drafting.

 

[KENAT]

Finally got the drawing to open and you’re right that with the cross section you don’t really need the ‘thru to bore’ or variation there on, the cross section is my preferred way of doing it from my knowledge of the standards.

I'm with ewh on only calling out the thread, not how to create it/tap drill size but have also been guilty of giving more details on 'specials'.

One case I can think of though (which comes up quite often here in pneumatics) is where the thread only goes down part of the length and then the ‘tap drill’ dia continues on down to intersect with another bore or something.

We have a problem here because by default our CAD system only has the nominal and minor dia data for screw threads in it. So the tap hole ends up being the diameter of the screw thread minor diameter, not the true tap drill size. To do it properly you end up creating 2 separate holes which then leads to other problems, but there you go.

Can I just say that after looking at various engineering news boards & talking to CAD users etc it’s refreshing to come across a group of engineers that actually know & care about standards etc. I knew they existed but sometimes they seem few and far between.

Ken