Thread. xls - Incorrect Tap drill callouts?

[jparks_79]

Has anyone else noticed that the tap drills for the NPT hole callouts are not consistent with any conventional standard?

Am I just not reading the table right? Or am I referencing some old standard tap drill table?

1/4-18 npt calls out a .422 in tap drill
I am finding that .4375 in is the correct drill size

3/8-18 npt calls out a .5468 in
I am finding that .578 in is the correct drill size

These are just two for example. Anyone else have any comments on this?

Thanks,
Jeremy

[karthur1]

In R2008, here is what I have changed my table to. The ones shown in red were changed to met the values shown in any tap-drill chart that you can pick up.

I don't have R2009 in front of me, so I can't check that. I was hoping that got corrected.

[mcgyvr]

NPT holes are typically tapered.
Autodesk seems to put the minimum size.
Just change the excel table to meet your companies needs.

[jparks_79]

Yes. this what we ended up doing. But if you only update the tap drill diameter, the feature doesn't display properly on the drawing or model. It shows the threads to be really short. You have to change the other parameters to match the change in tap drill diameter. We did not do this, of course. that would be a huge waste of time. So we just changed the taper angle to 2 degrees. Just so that drawing view displays something close to reality.

But, where did these values come from? I am new to inventor. Has this problem been around for several releases, or was it just this one?

[Anonymous]

The latest "Machinists Handbook 27th edition" call for a minor dia of .438
without reamer and .422 with reamer for 1/4" NPT.

Page 1868 table 8

--
Dell 670 dual Xeon - 3.2
3gb memory, SCSI320-15k
XP-Pro, sp2
Quadro FX3400: Driver: 169.61 Direct3D
IV2008-pro sp2,
SpacePilot Rel V: 3.5.6 Dvr V: 6.5.5 Firmware 3.12

wrote in message news:5895412@discussion.autodesk.com...
Yes. this what we ended up doing. But if you only update the tap drill
diameter, the feature doesn't display properly on the drawing or model. It
shows the threads to be really short. You have to change the other
parameters to match the change in tap drill diameter. We did not do this, of
course. that would be a huge waste of time. So we just changed the taper
angle to 2 degrees. Just so that drawing view displays something close to
reality.

But, where did these values come from? I am new to inventor. Has this
problem been around for several releases, or was it just this one?

[jparks_79]

Yes. I see how that value can be seen as correct. But what about the others. Am I just overlooking something?

I don't have 27th. I have the 26th edition. It has the same table

[kstate92]

You might also checkout this web page (watch for word wrap):

http://www.precisiontwistdrill.com/techhelp/help_pages/tap_projection_minor_diameters.asp

It's not definitive and many companies have slightly differing drill size suggestions. The biggest factor is the material you're drilling and tapping: softer steel, smaller hole; harder steel, bigger hole. Plus, there's the whole to taper ream or not to taper ream question.

BTW, I hate pipe threads - I almost wish they were illegal But I think companies still make products with pipe threads because the pipe fittings are cheaper than SAE fittings.

[Anonymous]

NPT would be cheaper than JIC or ORB, only involves the drill and thread, no
machined face to seat/seal against.

--
Dell Precision 690
Dual Quad Core E5320 @ 1.86GHz
4Gb DDR SDRam - 667 Mhz, ECC
SAS 146Gb - 15k rpm
Quadro FX3500 256Mb - Driver: 169.61 Bios: 5.71.22.55.08
XP Pro Sp2 - AIP 2008sp2 - D3D
Space Explorer USB 3.5.6
wrote in message news:5895700@discussion.autodesk.com...
You might also checkout this web page (watch for word wrap):

http://www.precisiontwistdrill.com/techhelp/help_pages/tap_projection_minor_diameters.asp

It's not definitive and many companies have slightly differing drill size
suggestions. The biggest factor is the material you're drilling and
tapping: softer steel, smaller hole; harder steel, bigger hole. Plus,
there's the whole to taper ream or not to taper ream question.

BTW, I hate pipe threads - I almost wish they were illegal But I think
companies still make products with pipe threads because the pipe fittings
are cheaper than SAE fittings.

[MaxU77]

BTW, there is another problem with threads:

Let take ISO metric standard.

We have one assembly where M20x1,5 thread goes through couple of parts (manufactured at assembly itself)

Both parts do already have plain 18,5mm dia holes (as supposed).

Inventor (up to release 2012) refuses to build thread in the assembly (the feature didn't change the number of faces...) unless diameter be <=18.376mm (even so Tap drill diameter is 18,5mm).

Isn't that something that should be improved?

[powerdraft]

We use feature recognition software here, and when inventor refuses to model something correctly, we are forced to hand-program (when we catch it) the feature for our CNC's.  Pipe threads are typically used here for grease zerks and some other lubrication features.  This is a very frustrating flaw in Inventor.  Even modifying the thread.xls file is difficult; The parameter(s) that drive the feature are absolutely ludicrous.

     After changing values in the thread table, one column at a time, and re-starting inventor repeatedly (to purge the cached thread table), I have finally identified the parameter that needs changed when you correct the tap drill diameter.  If you change this value by the same amount as the tap-drill change, it appears to properly generate the feature in the model.  I have only done the 1/8 NPT so far (as that is the one I  need on this model), but I'm sure this will help those others having this same issue.

I used a slightly tweaked "wrench makup diameter" then described above so the bottom of the taper is  nearly the same diameter as the tap drill.

why would "Wrench makeup" have anything to do with modeling this feature.  Do I have some ignorance that's preventing me from seeing the correlation?  If this is the case, please, someone fill me in.

It's unfortunate that Most Machine Designers are not computer programmers/and computer programmers are not machine designers.  This is fairly evident in inventor.

[cadcamm99]

where is the table located?

[Mark.Lancaster]

@cadcamm99

By default: C:\Users\Public\Documents\Autodesk\Inventor <version>\Design Data\XLS\en-US

[mcgyvr]

---

@cadcamm99 wrote:

where is the table located?

---

@cadcamm99 Its located in the XLS folder where your design data/style library stuff is..

[Mark.Lancaster]

@mcgyvr  Too slow today...

[mcgyvr]

---

@Mark.Lancaster wrote:

@mcgyvr  Too slow today...

---

@Mark.Lancaster 

But thats not where my thread file is.. and many others I'm sure.. 

Lets be like power rangers and combine to be one super power..

Mark..

By default: C:\Users\Public\Documents\Autodesk\Inventor <version>\Design Data\XLS\en-US

+ Me

Its located in the XLS folder where your design data/style library stuff is..

+ A little extra

That can be found by looking at your project file settings..

= Super Answer... 

[cadcamm99]

The thread taper however still wants to go to the .422 dim making the thread length small.  According to Inventor the taper length should be .395.  But after changing the drill size to .4375, the length is smaller even though Inventor shows it at .395.