[AT] Getting water out of a gearbox/now bearing life

[jtchall at nc.rr.com]

Over toleranced parts is not an American problem. I daily work with German, 
Dutch, and Japanese prints that are ridiculously toleranced. Some of it is 
so closely engineered you need to manufacture in a tightly controlled 
temperature setting and do the assembly in a clean room. The funny part is, 
everybody wants crazy tolerances, but none want to pay for them. We've been 
dealing with variables in raw materials for years. Anything from plastic to 
stainless steel, you never know for certain what you are going to get. One 
batch machines like it should, the next cuts horribly. At least at my work 
we have been trending toward tighter tolerances and better finishes for 
quite some time---a lot of it is absolutely unnecessary.

John Hall


-----Original Message----- 
From: macowboy at comcast.net
Sent: Monday, June 08, 2015 8:59 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Getting water out of a gearbox/now bearing life

I have been reading this topic with great interest. For the past 15 years I 
have been involved either on the supplier side providing components to the 
big automotive assembly lines or on the OEM side for the medical device 
industry. I have been to most of the major automotive assembly plant across 
the country and a few of the big truck manufacturers too. One things that 
was made clear to me that todays vehicles are designed to last 150,000 
miles. This is straight from the engineers at the assembly plants. I don't 
know where this number came from but this is what I was told. The Japanese 
do a much better job with design and assembly. They use a practice called 
Probabilistic Design where they take the variability of each component in an 
assembly and determine what the process capability(defect rate) will be. If 
it is less than a zero defects, back the drawing board. I have found that 
the American manufacturers tend to design in the electronic world(CAD) and 
do not take into consideration the manufacturing capability of the process 
they have selected. What happens is that when a certain combination of 
tolerances occur in a assembly, you will have failures. The design guys will 
tend to put very unrealistic tolerances on their drawing as it makes their 
jobs much easier. The DFMEA that was talked about earlier is more of a paper 
work/regulations requirement rather than a good tool to use. Most engineers 
that do this conduct a top down DFMEA where they look at the assembly as a 
whole. A better way to do this is a bottom up DFMEA where you look at each 
requirement on each component. One engineering manager did this and his 
final product was as close to flawless as possible. BTW, as far as 
components go I can say the electronics(PCB's) are the worst followed 
closely by raw materials/chemicals for failures.


Jim Thomson
macowboy at comcast.net