Autodesk Inventor

[#1]

While trying to create a custom Heli-Coil Hole templet setting in Inventor 2011 for the Hole subroutine, I discovered an interesting quirk? If you examine Thread.xls the spread sheet that has all the thread data, you'll find that for a tapped hole Inventor uses the Minor Diameter value when it puts a hole into a part. Example, in sheet, "ANSI Unified Screw Threads", row 38, a 4-40UNC screw has a nominal body diameter of .112 and under the "U" column marked "Tap Drill" you'll find the standard ANSI drill diameter of 0.089, yet in a model, the value of the hole that is put into the part is the MINOR Diameter of .0849 (cell O38). This is uniform for any hole placed in a part, does anyone know WHY? If I send my model to my vender to use to profile the part for CNC, technically they would receive the wrong hole data. I was asked by my CAD Supplier would a 0.005 delta difference matter, and depending on the material that one is going to machine the part from it would. Aluminum isn't terribly finicky but if the material was 17-4 stainless or Kovar, it would matter. Since the table has the correct tap drill listed, why is that not used for the hole in the model? In the 2d drawing that is created, the ‘hole note’ can be modified to list the correct tap drill, why is the model different? When I get the Heli-Coil spread sheet worked out, I’d be happy to share it with anyone who’d like a copy.

[#2 · Accepted solution]

Open a model, go to document settings, under the modeling tab you can chose tap drill.

[#3]

John, Thank You (and to coin a phrase 'DUH!') although, when I change that setting (and why is that NOT in the hole feature itself...?) I get the following error message 'Drawing Manager thread representations are generated correctly only when Tapped Hole Diameter is set to "Minor". ' Any idea what that means?

[#4]

Don't have a clue.  You will have to try it and see. 

[#5 · Accepted solution]

Basically what that means is that if you set the Tapped Hole Diameter to display as Major, then the hidden lines representing the threads will not be visible in idw drawing views, so they will look like unthreaded holes. Ridiculous in this day and age, but it is what it is.

[#6]

I can understand if you had set the model to display the tapped holes as 'major', My question is 'why would you? As I stated in my original post, if I send a model to my vendor to fab, he's going to put drill hole in for the tap, not the major or minor diameter, so why not give them the right information to begin with? It is all about getting designs right the first time but I guess its a matter of preference, it just seems really odd.

[#7]

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PeteMiller wrote:

I can understand if you had set the model to display the tapped holes as 'major', My question is 'why would you? As I stated in my original post, if I send a model to my vendor to fab, he's going to put drill hole in for the tap, not the major or minor diameter, so why not give them the right information to begin with? It is all about getting designs right the first time but I guess its a matter of preference, it just seems really odd.

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Right off, I can think of two possible scenarios for using the larger diameter in the model:

1. To visually verify that the tapped holes aren't too close to another feature or edge, etc.

2. To eliminate perceived interference of threaded fasteners when doing assy interference analysis.

There is or was an effort to standardize imbedded mfg information , such as threads, finish , etc. into 3d models, but I don't know what became of it.

You'd think the Inventor team could come up with a way to:

A. Make all pertinent geometry of threaded holes visible in the model simultaneoulsly.

B. Always generate the threaded hole properly in the idw, regardless of what model display is chosen.

oh , and C. Make the warning messages understandable.

[#8]

I agree Paul, those are valid reasons/concepts, I guess I've never had issues with holes being so close that I couldn't percieve of interference/fit problems before hand, perhaps just lucky I guess...

[#9]

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PeteMiller wrote:

I agree Paul, those are valid reasons/concepts, I guess I've never had issues with holes being so close that I couldn't percieve of interference/fit problems before hand, perhaps just lucky I guess...

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For the 'interference' bit, I was refereing to the Inventor Assy Inference analysis tool, which will interpret threaded fasteners as 'interfering' with their holes unless 'Major' diameter display is selected, IIRC.

[#10]

Ah (chuckles) yeah, I had missed that one. actually when I do an interferance analysis, I prefer to know that the treads/hardware interfere, as I expect them to. If they don't then I feel I have other problems