Need drafting advice

Tim Neumann

 I'm working on a 3D scan of a machined part that our customer wants us to create drawings from. Mind you this is not my realm of expertise since usually work on piping/structural steel stuff where tolerances are +/- 1/8". Anyways this part has a bunch of counter-bored holes on different bolt circles and orientations. What is the standard practice for drawings on something like this, especially regarding hole locations? Any insight would be welcome, see the attached images for reference - no laughing at my feeble attempts allowed!

John Gaunt

I think what you have done is fine, at least from a 'traditional' point of view.
The section line should run through holes.
It might be asked if it matters where each circle of holes starts in relation to the others, but showing one row in line with the section through them should cover that.
The steps in height/thickness might be preferred dimensioned from a datum, depending how it's machined.

Joe Dunfee

 The actual holes may be drilled using a CNC machine, and the holes just found by the software as the CAD 3D file is loaded.  So, it may not care how, or if, you dimension it. But, your dimensions on the print are for human eyes. I see a few consumers for the dimensions.  The guy who inspects your drawing, the guy making it, the guy inspecting it, and the draftsman who may need to re-draw it based on the print..

But, I think the most important is the guy who is going to make it. Ask them how they would prefer it to be notated. He may not actually care if his software is just reading the CAD data directly. Then next in line is the inspector. Perhaps he has a machine that gives him a X,Y coordinate of the hole by using  probe.  In that case he will want them dimensioned that way, probably in a hole table. 

Still, even with the hole table, I think you need to include a set of dimensions that are more typical of drafting. These show the design intent at a glance. If the holes do not all line up at one point,  I would just choose one from each bolt circle diameter, and dimension the diamter. If it does not fall at a 90deg angle, dimension its angle. Then add a leader that says "6 Holes located at ## radius, equally spaced.  Think about how you want it shown to you if you had to re-draft the drawing.

-Joe

Scott McKenzie

I would show the partial section view to give details on the profile of the part, however I would make this a full section, on this view detail the steps on the part, remove the bolt hole dimensions. Manually writing details of the hole locations on the section view could potentially be problematic, it is very easy to miss making an update or very easy to make an error; your dimensions should be on a view showing what you are detailing. To dimension the holes I  would create a hole table (or use datum dimensions), using the center of the part as 0,0 and giving the coordinates to the centers of the holes with enough precision to ensure that the holes are located as required, show bolt circle diameters on your plan view as inspection dimensions.  The other option is to fully dimension the bolt circle and clocking of the holes on the plan view, but this will quickly become an angular dimensioning nightmare. I would assume that this part will be milled on a vertical mill, so showing the x and y locations will be the best option here as that is what the operator will  input into the machine to locate the holes following the turning of the blank part on the lathe.