Precision?

[clockworkcheval]

The time of calculating by slide rule and drawing on vellum is definitely gone for a good many reasons. However working with a slide rule gives you an ingrained feel for order of magnitude and caused me to memorize for many years the tables of 1-20 to the powers 2, 3 and 4. Nowadays I'm happy to check my estimated calculations with a phone. But I still out-calculate my grandchildren!
Drawing by hand is so time consuming that we would as often as possible start with an existing vellum and adapt that. The great benefit apart from time saved being that al the other engineering information like choice of tolerances, chamfers, surfaces roughness and material choice was already there, proven by years of previous use. I still make most of my drawings by hand, but I finally started on Fusion360 mainly because the CAD 3D assembly presentations give me a much better interference check then I'm nowadays able to do in my head.

 

[Steamchick]

Green Twin, I like your philosophy. I learned very early on that if the math says it will break, it will! Maybe not in controlled conditions, but somehow, somewhere it will meet a condition not wholly considered, and then fail! If the math says it is OK, think of something else to check!
When the brain is drained, have a sleep and think again. Check historical failures, and successes, and consider if your design can possibly fail the same way, and design it so it cannot. Ask all the old hands.... They will quickly spot the weakest link, and you will learn some more.
K2

 

[stanstocker]

Green Twin, I like your philosophy. I learned very early on that if the math says it will break, it will! Maybe not in controlled conditions, but somehow, somewhere it will meet a condition not wholly considered, and then fail! If the math says it is OK, think of something else to check!
When the brain is drained, have a sleep and think again. Check historical failures, and successes, and consider if your design can possibly fail the same way, and design it so it cannot. Ask all the old hands.... They will quickly spot the weakest link, and you will learn some more.
K2

It usually got a confused look at first, but I used to tell folks new to real (as opposed to college exercises) programming: Never test for a condition you don't know how to handle, never fail to test for a condition you must handle. Makes you think a lot deeper about what's going one. Saw quite a few hardware failures in the aerospace business as a wee nerd, so many test systems and plans focus on confirmation of expected behavior without going out to or beyond the edge / pathological conditions. "That can never happen" is a phrase I learned not to use or even let loose in my head early on.

I also am sorry that people no longer have a sense of magnitude or the learned ability to have a rough idea of expected results from a calculation. My kids would be doing homework and I'd ask them to look at an answer and they truly had NO idea what I was talking about when I asked if their answer was even close to the expected result. You couldn't live in slide rule land and not always have some idea of a believable result. At 64, I'm probably around the last of the age group that learned to use slide rules, by the time college came around calculators were fairly common. My first real calculator was a National Scientific RPN one, very fancy, programmable, and much less expensive than the HP25 that was beyond my means. Probably got that around 1977.

 

[awake]

Its like I tell people; "don't use locomotives to crack walnuts".

My version is, "don't use a sledgehammer to swat a fly."

 

[master53yoda]

The last ten years before I retired I worked as a commisioning agent in the HVACR and Electrical systems, I had to write the tests to verify that the system would work as intended(not necessarily as designed) If you want to find out if somithing will work as intended you test for the negative reaction rather then the postive. You can have a zillion postive tests and it may still fail but if you can find a negative test, it proofs that it WILL fail. The problem scientist have is that they look for all the things that agree with the theory if they are vested in the theory through education etc. They tend to take the negative and set it aside and call the negative an anomaly and don't try to modify the theory to accommodate the anomaly. What an anomaly tells us is that the theory is in error.

Art B

 

[Steamchick]

Aha! Thinking cleverly suits you well my Masterful friend. MTFBWY.
Truly, good words for May 4th.

 

[Jasonb]

The cad operator just accepts the value without trying to make a value in round numbers. In my designs I have always tried to make things in round number size. If something will works at 1 1/2 long I see no reason to make the item 1.532. To each their own.

A lot can depend on how a drawing is dimensioned. Take the example below it may seem odd that the hole is placed 0.543 from the ctr but the CAD operator could just be making it easy for the builder by giving the offset to wind the handwheel or use the DRO reading to lay out the holes on a 1 1/2" PCD rather than the builder having to work it out