My opinion is it's a wonderful metal for proper applications. Easily heat treated, even at home. I've worked it all through my machining career, although never in quantity. I've turned it on a lathe, which is less than fun, especially drilling or reaming. It's not uncommon to have a reamer seize in a bore and have to be machined out to recover the reamer. I've made (flat) springs from it on many occasions, some of which I still have in my spares box. They were for use in tooling in the aero-space industry.
The toxicity is such that at one of my customer's facility, where they made various tooling components from it (the source of the tools I built), the company policy was for machinists to machine it for a maximum of 90 days, then never work it again. Apparently it accumulates in the body.
If you have a specific question in mind, ask away. If you're looking for someone to tell you that you should start casting it, and machining it in the future, I'd suggest you forget it at your young age unless you have a specific need. No sense risking your health for no good reason.
I once said in here something to the effect that if a part must be aligned to .001", then it should only be aligned to .001 and no further (too expensive).
Ed Huntress perked up and said that this attitude was exactly what was wrong with the automotive industry (sorry if I have a foggy memory, Ed.)
This is bullshit.
I make parts to the tolerance on the drawing. If there is no tolerance, I cannot make the part.
It is not my fault if the designer/draftsperson places an incorrect tolerance on part which would prevent it from functioning. These days, prints are explicit. I would be surprised if you could find a hole without a tolerance specification (of some type) on an automotive part.
Actually it would, and I'm sure we have lawyers who would make that determination (if you ship an OEM a defective part/module that prevents the car from being assembled, they make you buy the car).
Under toleranced drawings are the fault of the designer/draftsperson
You and I come from different worlds. I can imagine that in certain industries, there are problems with inexperienced designers not dimensioning parts for function or for manufacturability. These days we cannot afford to guess (our prices are not allowed to increase - in fact they must decrease each year, for the same part).
Again, different worlds. If the part matches the specification, it's right. Time is a very serious issue in automotive.
Because they build for fuction, which is not wrong. GD&T is designed for assemblability and manufacturability. It normally allows for greater tolerances than can be specified normally and it makes products cheaper.
Yes. Built for function (exactly what else is there?) While the number on the pricetag for our dies is pretty large, that doesn't mean there is time to double drill or ream screw holes. This doesn't mean the dies are faulty or of poor workmanship - it just means that we're producing the highest possible quality at the lowest possible price.
They are all critical to funtion - it's just that most aren't hard to make.
It would under ANSI Y14.5, which is the most widely accepted drafting standard in North America. This page very closely paraphrases what Y14.5 says regarding general tolerances.
*********************** Tolerances may be expressed in one of the following ways: · As specified limits or tolerances shown directly on the drawing for a specified dimension. · In a general tolerance note, referring to all dimensions on the drawing for which tolerances are not otherwise specified. · In the form of a specific note referring to specific dimensions.
**************************
Y14.5 also allows referencing other documents for specific features or processes. This would allow a reference to, for example, some mil standard which is what I assume you're talking about.
I also have a copy of the NASA Glenn Drafting Standard. It incorporates Y14.5 by reference with no exceptions.
It seems probably quite a few have considered the question. Back in the 'good old days', holes were spec'd as ... 1/4 drill thru..... Nowadays, it is more likely to be spec'd as .... .25 thru... with a corresponding part of the drawing labeled "tolerances" specifying how much deviation (tolerance) is allowed as to two, three, four place decimal numbers. The same tolerance block would perhaps carry the notation "unless otherwise specified, tolerances must meet xxxxxx, whether it be mil spec's, or the company's own spec's.
I once had the occasion to check on "parts out of tolerance". The drill press operator showed me in black & white, "drill #30 thru". And of course he had correct drill, but it was so badly worn, it was drilling way undersize.... But, according to print, he was not at fault.
As you well know, the first place any machinist looks on a drawing is the tolerance block, or for any other applicable spec's. A lot of drawings even carry notation of "generally accepted good machine shop practice".
Years ago before "ma bell" was forced to break up, I had the opportunity to examine a print for "tooling" required for one of their components. EACH & EVERY HOLE for dowels, bolts, etc. were completely toleranced as to size and location.
As for me, I went to work for an independent, and most drawings were hand sketches on note paper. Product was various die sets for lots of precision stamping & forming of small sheet metal products.
Where I was trained, he would have been. That's the point. Unless otherwise specified, there were standards to which we had to drill holes.. QC made sure we did. Do keep in mind we worked to MIL specs, however. We were engaged in building a missile. The tolerance block on the print did not apply to drilled holes aside from location. Hole size was dictated by a standard with an ever increasing tolerance, according to hole size, and it was far more restrictive than the block tolerance. It made sure that a hole could not vary by going much undersized, and was relatively tight for oversized. To me, it made sense. In today's throw away society, with a bar that has been lowered below ground level, perhaps it no longer does.
All of this prompted me to look into _Machinery's Handbook_, and what I find is the following (in part).
"Normally the diameter of drilled holes is not given a tolerance; The size of the hole is expected to be as close to the drill size as can be obtained. The accuracy of holes drilled with a two-fluted twist drill is influenced by many factors, which include ... "
And a table -- derived from measurement of 2800 holes drilled in steel (which suggests near 467 holes per size):
Oversized Diameters in drilling (inches)
Drill Average oversize, Inch
Dia Av. Max Mean Av Min. ================================================ 1/16 0.002 0.0015 0.001 1/8 0.0045 0.003 0.001 1/4 0.0065 0.004 0.0025 1/2 0.008 0.005 0.003 3/4 0.008 0.005 0.003 1 0.009 0.007 0.004
This is from page 855 of the 25th edition of _Machinery's Handbook_, and would seem to define what can be expected from single drilling.
You have to remmeber, AT&T was famous for documenting every aspect of the business so that two workers on opposite ends of the continent would do things the same way, even if they were each doing it for the first time and without supervison. I remember a 20 foot wall with 7 foot tall bookcases filled with Bell Standard Practices. That was not all of them.
It was actually possible for a tech with general training to grab a book and fix just about any of the hardware at the company (given enough time).
I agree! - My dad was tasked to write one manual - a mere 250,000 page monster that described to the device a Radar system that involved three parallel processing computers, 2 floors of disk drives, one of tapes, and then the special and custom hardware. It cost him 2 years of putting off his planned retirement.
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