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  #61  
Old Wed 03 June 2009, 10:48
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Yes, there are some duplicate instructions, in the "notes" on the drawings.

The 6.8mm is the tapping drill size for 8mm. When steel is much thicker than the height of a typical M8 nut, you can insrease the drill size without fear of the screw stripping. Last week we tested some holes at 7.5mm and they held up - we ended up drilling 7.2mm and easily running the 8mm tap through with a cordless drill.
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  #62  
Old Wed 03 June 2009, 11:02
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The logic behind the duplicate instructions goes like this:

Drawing 10 10 246 D has to tell you everything you need to know for making the holes in part 10 10 246 D, and

Drawing 10 10 300 D has to tell you everything you need to know for making the holes in part 10 10 300,

because it is possible that you could be using two different sub-contractors for parts 10 10 246 and 10 10 300. The bloke making 246 needs to know that he must not make 13mm holes before lending his job to the other guy. The guy doing 300 is going to look for the spacing between the holes - he needs to know that he has to borrow the pilot drilled rails.

The alternative way, is to give hole spacings on both drawings with tolerances of 0.1mm and then watch the price go up 3-fold . . . .
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  #63  
Old Wed 03 June 2009, 15:54
cvriv.charles
Just call me: charles
 
New Jersey
United States of America
Ok. Well,... I was looking at all this more like steps where step 5 and 6 six are the same or atleast I think they are the same. It's hard when you are only X percent sure of what is going on. Same reason whay I asked about the 25.00043 numbers before. Wasn't sure if that was right not. have to question everything when you just dont know.
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