My shop has drilled and tapped more or less 1500000 6-32 holes in extrusion[6061 and 6063] in the last 15 years. When we were doing a lot of these, we would get around 3000 holes minimum out of a coated greenfield roll tap, probably average 10000. We would throw them out out of pity.


If you can't do this, he was right.

6-32's are what they use to hold down TO220 transistors among other things, so yes it is the industry standard, and cannot be swapped out in many circumstances

Engineers (I are one) come in all shapes and sizes... good ones and bad ones, experienced ones and novices. They're no different than machinists or gardeners or CEOs.

Good engineers attain that level of proficiency on the job, not in a classroom. It's as much art as science.

And like everybody else, they follow orders. In some situations they have wide latitude in their designs, while in other situations they may be rigidly constrained. Without being involved in the whole definition phase of a project, you can't know what the options are.

- Leigh

Doesn't a 6-32 have the smallest root diameter to od due to pitch? I'd much rather tap 4-40 than 6-32, it goes give fits. I work almost 100% in electronics and 4-40 is much more common in my world than 6-32.

In 1986 I was the program manager, project engineer, and electrical engineer on the Antenna relay for the B1B. It was a pork barrel contract from Rockwell, like many handed out in every state.

The Aluminum base had mounting holes with accuracy of +/- .0002".

This was in the specification from Rockwell, and we flowed the tolerances down to our drawing of the base that we out sourced to a local machine shop.

The parts came in, flunked receiving inspection, and wound up in material review board [MRB].

I was called to the factory to help disposition the parts.

I told them to return to vendor [RTV] as Rockwell would flunk our whole box if we shipped that way, even if it would work fine in the aircraft [+/- 0.0100" would have worked].

The machine shop complained that they could not hold those tolerances.

Later, I revealed all this, while I was shooting the bull with my brother, who was a piecemeal aircraft machinist at the time, earning a fortune, but under allot of stress.

He exploded at me. He always hated engineers, but it had not been pointed at me before then.

I was used to electronic technicians hating electrical engineers, but now I find out that machinists hate mechanical engineers.

I do work for a engineer that draws everything incremental. Drives me nuts I gave up incremental back in 1976 when I started to program CNC.

JB

I agree Ox I have made a bazillion of them, and never had an issue, especially in 1/4" aluminum plate ??

Bill

That's not really true. I find that most mechanical engineers are very easy to work for, and quite likeable guys.. (At least in my world.) IMHO, there are a few that are extremely arrogant and impossible to work for. (I have run most of those off.) I think that machinists and mechanical engineers are very like minded, having similar aptitudes in math and things mechanical. Engineers are able to concept and most machinists are really not, and that is the major difference. (Again, this is only my opinion.)

showing my ignorance here, what does that mean?

I think he means not using ordinate dimensioning. -
(ordinate = all dimensions from a datum feature)

Quite simple really

Imagine a 2 holes in a plate, the left hand hole is dimensioned from the edge of the plate, the right hand hole is dimensioned from the the first hole.
Which is all well and fine until you start considering tolerances and how CNC machines work (or any other kind of hole drilling machine).

So our first hole is positioned 1" in from the left edge with 1" between holes
So thats a program that would read
X+1
<drill>
X+2
<drill>
which is easy
So imagine what happens when you have to program 50 holes all dimensioned incrementally from each other.....
However the hole positions are supposed to be within +/- .001" of nominal ,the first hole goes in at .999", its in limit. the 2nd hole goes in at 2.001" its within the nominal position BUT the distance between them is 1.002" and thus out of limit.
Multiply that by 50 times for 50 different holes and you can get to see why us CNC machinists hate engineers who draft in incremental.

Boris

ahh, ok, had a brain fart. I know what he's talking about now. Thanks for refreshing my failing memory

What's the guy supposed to do if he's the engineer
*and* the machinist at the same time????

Self hate?



Jim

More like 'self love'

How about an engineer that changes the datum point with the view. I have had a couple of jobs where the dadum point changes either end to end with the change in view or from the edge of a casting to the face of a boss, a 15mm change on a 1200mm long part. My customer (not the company who made the drawing) called me when they were checking the casting to say that I had made a mistake. By the time I had pulled the drawing out (all the while thinking about how much money this was going to cost me) they called me back to say there was no error they had just noticed the datum change.

I agree. Most of the problems are from refusing to listen, or from insisting on being 'right'. On both sides. The more experienced someone gets, the more they will listen, unless their ego is insufferable. On both sides.

Pretty much, I guess. That's the scenario I find most stressful, because I wind up going back into design mode while I'm running the machine, questioning every dimension, and having my focus split between the concept and the execution. Making parts to someone else's print is much easier!