zeeprogrammer
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Thanks Frank. That helped a lot.
drafting symbols - what does this mean?
- Thread starter zeeprogrammer
- Start date
Help Support Home Model Engine Machinist Forum:
Pet peeve of mine.
{Peeve mode on }
When we were on BS308 for drafting there were oodles of books that laid out all the standards, then we moved onto this Geometric tolerancing mumbo jumbo and the standards were all lock up with British Standards and you have to buy a copy at 90 odd quid read about $140.
Hang on you say I have to do it this way but I have to BUY THE STANDARD to find out ??????
What's changed since BS308 came out in 19 ought plonk? We fought two world wars with everything being made interchangeable from 18 continents so it couldn't have been that bad.
China has it's own standards which are freely available in the effort to create trade, why can't the British Standard Secret Service do the same.
The biggest laugh is though that many software packages licence these standards and build them in, part of the licence deal is they can use them but nor give a menu of what they are, so some Herbert in an office somewhere decides that that symbol looks cool and stuffs it on the drawing.
You get the drawing, read it, decide it can't be made and ring up.
Conversation goes:-
"Excuse me but did you do the drawing of Widget 12345 on 38/13/200 plonk?"
"Yes" [ well at least he's decisive ]
"I'm querying the symbol attached to the face of the circlip groove on part 5678, drawing number 9876"
"Yes" [ not so sure now ]
"Could you tell me what it means? "
"Well it's put on by the program"
"You mean to say it does this automatically? "
"No"
"I though not or all the lines would have this symbol, so you have to choose this symbol? "
"Yes"
"So what made you use this symbol "
"It's a British Standard"
"you sure it's not an ISO standard? "
"Eeerrr I think it's a British standard but they might be the same" [ sound of exhaling breath ]
"But what does it mean? "
"I'll have to look it up in the British Standard"
"Hang on, you have put this on the drawing but you don't know what it means? "
"No I know what it means it's just I need the Standard to explain it correctly" [ sounds of shuffling papers ]
"Well can I save you the trouble and tell you what it means?"
[ Hesitantly ] "OK "
"Well you have specified that this 2.2mm wide circlip groove 170mm down a 40 mm bore be ground to a surface finish of 8 micro inches"
" " [ no answer ]
{End of rant }
JS.
{Peeve mode on }
When we were on BS308 for drafting there were oodles of books that laid out all the standards, then we moved onto this Geometric tolerancing mumbo jumbo and the standards were all lock up with British Standards and you have to buy a copy at 90 odd quid read about $140.
Hang on you say I have to do it this way but I have to BUY THE STANDARD to find out ??????
What's changed since BS308 came out in 19 ought plonk? We fought two world wars with everything being made interchangeable from 18 continents so it couldn't have been that bad.
China has it's own standards which are freely available in the effort to create trade, why can't the British Standard Secret Service do the same.
The biggest laugh is though that many software packages licence these standards and build them in, part of the licence deal is they can use them but nor give a menu of what they are, so some Herbert in an office somewhere decides that that symbol looks cool and stuffs it on the drawing.
You get the drawing, read it, decide it can't be made and ring up.
Conversation goes:-
"Excuse me but did you do the drawing of Widget 12345 on 38/13/200 plonk?"
"Yes" [ well at least he's decisive ]
"I'm querying the symbol attached to the face of the circlip groove on part 5678, drawing number 9876"
"Yes" [ not so sure now ]
"Could you tell me what it means? "
"Well it's put on by the program"
"You mean to say it does this automatically? "
"No"
"I though not or all the lines would have this symbol, so you have to choose this symbol? "
"Yes"
"So what made you use this symbol "
"It's a British Standard"
"you sure it's not an ISO standard? "
"Eeerrr I think it's a British standard but they might be the same" [ sound of exhaling breath ]
"But what does it mean? "
"I'll have to look it up in the British Standard"
"Hang on, you have put this on the drawing but you don't know what it means? "
"No I know what it means it's just I need the Standard to explain it correctly" [ sounds of shuffling papers ]
"Well can I save you the trouble and tell you what it means?"
[ Hesitantly ] "OK "
"Well you have specified that this 2.2mm wide circlip groove 170mm down a 40 mm bore be ground to a surface finish of 8 micro inches"
" " [ no answer ]
{End of rant }
JS.
Rant on
A old boss of mine said if you want the shop to hit it with a file, then write "Hit with file" Great advice.
Working definition of Geometric tolerance, Three people sitting at a table arguing.
I have done a test sending out the same part to 9 vendors dimensioned 3 different ways. mill work, qty 1 and 5
Geometric tolerance with the tolerance set to the bigest of the drawings. (circle of .006)
Conventional point to point dimensions set at +/- .005
Ordinate dimension with the 0-0 at a logical starting point for the mill tolerance +/- .002
Every time the ordinate dimension is cheepest, then the point to point, the geo is last.
This is true even after I show them all 3 drawings and tell them what I want.
Rant off
Frank
A old boss of mine said if you want the shop to hit it with a file, then write "Hit with file" Great advice.
Working definition of Geometric tolerance, Three people sitting at a table arguing.
I have done a test sending out the same part to 9 vendors dimensioned 3 different ways. mill work, qty 1 and 5
Geometric tolerance with the tolerance set to the bigest of the drawings. (circle of .006)
Conventional point to point dimensions set at +/- .005
Ordinate dimension with the 0-0 at a logical starting point for the mill tolerance +/- .002
Every time the ordinate dimension is cheepest, then the point to point, the geo is last.
This is true even after I show them all 3 drawings and tell them what I want.
Rant off
Frank
rake60
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- Jul 8, 2007
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So many of those symbols are, well... UNNECESSARY!
Let me bore you with another one of my shop stories.
I was given a print that showed a radial dovetail groove in the face of the part
encircling the bore. The groove depth was to be .257 ±.001 the side angles
of the dovetail were shown as 5° ± 30' The required surface finish was 16RMS.
I took that print to the person who was in charge of the job and told him straight
out, This manual machine is not capable of holding those limits.
He laughed at me! He said that groove was just an O-Ring Groove.
The angles were to retain the O-Ring when it was popped in, and the cover plate
the O-Ring would be sealing against would never move once tightened up so the
finishes were not critical. A square radial groove .230 to .260" deep with a 125 RMS
finish would be just fine....
:rant:
In another case, the young man I worked opposite of spent 10 hours trying to make
a tiny boring bar to bore holes in cylindrical parts. The print said the bores were to
be .628" +.002 -.000" with a 63RMS finish. That morning the man in charge of that
job came to me fuming MAD! I explained the young man was having a difficult time
holding the tolerance and getting the finish. The he went ballistic!
"It's a @%#&*(%@ SPACER that needs to slide over a 5/8" rod!
Drill a 41/64" hole in it and call it done!"
I politely showed him the print and he was off to Engineering and Drafting to
discuss the problem.
:fan:
Better stick to those prints!
Rick
Let me bore you with another one of my shop stories.
I was given a print that showed a radial dovetail groove in the face of the part
encircling the bore. The groove depth was to be .257 ±.001 the side angles
of the dovetail were shown as 5° ± 30' The required surface finish was 16RMS.
I took that print to the person who was in charge of the job and told him straight
out, This manual machine is not capable of holding those limits.
He laughed at me! He said that groove was just an O-Ring Groove.
The angles were to retain the O-Ring when it was popped in, and the cover plate
the O-Ring would be sealing against would never move once tightened up so the
finishes were not critical. A square radial groove .230 to .260" deep with a 125 RMS
finish would be just fine....
:rant:
In another case, the young man I worked opposite of spent 10 hours trying to make
a tiny boring bar to bore holes in cylindrical parts. The print said the bores were to
be .628" +.002 -.000" with a 63RMS finish. That morning the man in charge of that
job came to me fuming MAD! I explained the young man was having a difficult time
holding the tolerance and getting the finish. The he went ballistic!
"It's a @%#&*(%@ SPACER that needs to slide over a 5/8" rod!
Drill a 41/64" hole in it and call it done!"
I politely showed him the print and he was off to Engineering and Drafting to
discuss the problem.
:fan:
Better stick to those prints!
Rick
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