jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on Feb 4, 2016 23:26:53 GMT
i think perhaps each to their own. we all bring something different to the model engineering table. and it is a big broad table!
machining big lumps of metal frightens me silly every time because i have no engineering background or training. smaller stuff im much happier with.
so far as fits are concerned, and getting back 'on topic' there are all sorts of terms and phrases which we get used to or pick up. in miniature loco work, you do have to have a degree of knowledge of fitting and fettling and where a good fit matters and where it doesnt. ive seen brake rigging made to toolroom standards that doesnt work, and non-toolroom valve gear parts i would have thrown in the bin if i could!
cheers, julian
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
Posts: 2,269
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Post by smallbrother on Feb 4, 2016 23:39:55 GMT
On one construction site I worked on in the 1970s, the pipelaying gangerman's terms of measurement were 'a big bit' (about a metre), 'a bit' (about half a metre), 'a small bit' (about 100mm) and 'a small little bit' (about 10mm) When levelling concrete shuttering too far away to be heard above machinery, we used a man's height as 1". So to raise the shutter 1/2" you would point upwards and then point to your waist. The knees were 1/4" and the chest 3/4". As you may deduce, 1/8" was about the limit of accuracy! Pete.
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Tony K
Elder Statesman
Posts: 1,573
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Post by Tony K on Feb 5, 2016 8:19:33 GMT
When levelling concrete shuttering too far away to be heard above machinery, we used a man's height as 1". So to raise the shutter 1/2" you would point upwards and then point to your waist. The knees were 1/4" and the chest 3/4". As you may deduce, 1/8" was about the limit of accuracy! Pete. Nice one Pete. Was there one for the stomach - or was that too variable?
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"bare"
Feb 5, 2016 8:31:28 GMT
Post by ettingtonliam on Feb 5, 2016 8:31:28 GMT
Before we had mobile phones or even radios for on site communication, we used hand signals a lot for distant communications. There's still a set of accepted hand signals for communication between the slinger (banksman) and crane driver. Bearing in mind that the normal tolerance in shuttering work is 6mm or so, Pete's method at intervals of 1/4" was probably as good as needed except for really special stuff.
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"bare"
Feb 5, 2016 10:11:18 GMT
Post by ejparrott on Feb 5, 2016 10:11:18 GMT
I'm a slinger and I know a set of hand signals, interestingly they don't appear to be standard. I had my training at Morris Cranes in Loughborough, next to Brush' works but I've worked with some machine movers who've used different signals.
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Post by chris vine on Feb 5, 2016 12:18:13 GMT
When I was an apprentice at Rolls Royce Aero Engines, in 1980, the instructor, in the training dept, Jim Millman, had a lovely expression.
when he wanted me to make something which was a snug, push fit, he called it a "Honeymoon fit". Very descriptive!
Chris.
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"bare"
Feb 5, 2016 12:32:02 GMT
Post by ettingtonliam on Feb 5, 2016 12:32:02 GMT
I'm a slinger and I know a set of hand signals, interestingly they don't appear to be standard. I had my training at Morris Cranes in Loughborough, next to Brush' works but I've worked with some machine movers who've used different signals. I've only ever worked in the construction industry, and as far as I am aware, there's one set of 'official' signals. Maybe 'indoor' crane operators use a different system, I don't know.
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jackrae
Elder Statesman
Posts: 1,333
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"bare"
Feb 5, 2016 19:42:42 GMT
Post by jackrae on Feb 5, 2016 19:42:42 GMT
One of the courses I did at uni, some 50 years ago was on the subject of "tolerancing" The course instructor's classic example was the design of the component parts for a Lee-Enfield 303 rifle Basically for any single design of rifle, any barrel must fit to any stock, any bolt must fit to any barrel, any trigger etc etc. After a collection of randomly selected components have been assembled, the finished article has to perform to specification. If components were "married" to produce a "perfect fit", then a serviceable rifle could not be assembled from say a couple of damaged ones ,or the replacement of a damage component from the quartermaster's store might not fit correctly, - both a necessity on the battlefield.
It's relatively easy to make one-offs to fit and work together (as we model engineers invariably do) but specifying dimensional tolerances for the manufacture of hundreds of thousands of "identical" components by possibly numerous manufacturers truly is a science.
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"bare"
Feb 5, 2016 20:57:53 GMT
Post by goldstar31 on Feb 5, 2016 20:57:53 GMT
Jack
One book is/was Statistical Quality Control in the McGraw Hill Series.
I used it for setting manufacturing limits. If you look up at some suspended acoustic ceilings with funny wavy indentations ( made with an arc welder ) and a lot of old fashioned whisky corks and closures on coffee caps and pickle - guilty as charged, me lud!
Cheers- and a lot of plastic tiles. I'd forgotten.
Regards
Norman
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"bare"
Feb 6, 2016 4:15:14 GMT
Post by runner42 on Feb 6, 2016 4:15:14 GMT
One of the courses I did at uni, some 50 years ago was on the subject of "tolerancing" The course instructor's classic example was the design of the component parts for a Lee-Enfield 303 rifle Basically for any single design of rifle, any barrel must fit to any stock, any bolt must fit to any barrel, any trigger etc etc. After a collection of randomly selected components have been assembled, the finished article has to perform to specification. If components were "married" to produce a "perfect fit", then a serviceable rifle could not be assembled from say a couple of damaged ones ,or the replacement of a damage component from the quartermaster's store might not fit correctly, - both a necessity on the battlefield. It's relatively easy to make one-offs to fit and work together (as we model engineers invariably do) but specifying dimensional tolerances for the manufacture of hundreds of thousands of "identical" components by possibly numerous manufacturers truly is a science. When I worked for a Defence Quality Assurance organisation one of the first things that we had to ensure that both product and functional interchangeability were satisfied. This required that any part when integrated into a system would work identically to any other part. When parts deviated from specification and a concession was sought to use as is, the concession form required that interchangeability be addressed, non-interchangeable items were invariably downgraded for training or dummy use only. To ensure that this is achieved tolerances were specified for all important parameters. Having operated on this basis I was a little confused when entering into the ME field to find that no tolerances were called up on drawings and being new to the hobby had difficulty in determining that if I made a part that was not spot on (within the limits of my measurement accuracy) how much deviation was acceptable before the part was scrap. Knowing this is part of the learning curve, or make every part exactly to the drawing requirements. A proviso is that not all parameters are critical to the functioning of the item, some the designers don't care and specify for ease of manufacture only. I thought maybe incorrectly that bare fitted this criterion.
Brian
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tim
E-xcellent poster
Posts: 236
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Post by tim on Feb 6, 2016 12:31:15 GMT
I've yet to make this part for my bogie side control springing and was pondering over the "bare" term. I was beginning to think it meant nominal as I cannot see what difference any kind of small tolerancing would make on the 1/16" dimension. Tim.
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"bare"
Feb 6, 2016 12:52:59 GMT
Post by bambuko on Feb 6, 2016 12:52:59 GMT
Thank you Tim, for bringing this thread back on topic!
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weary
Part of the e-furniture
Posts: 290
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Post by weary on Feb 6, 2016 13:42:43 GMT
"Fulls and Bares"
...... I ..... am just referring to a letter received from a brother who used to be Inspector of Fitters in a Naval dockyard. He wants to know why I don't give definite measurements, instead of referring to full and bare dimensions; ......
First of all, the terms "full" and "bare" are regularly used in everyday engineering practice. Our dockyard friend contends that they may mean anything from half-a-thousandth to one-eighth of an inch or more. They might, it is true, but they don't when used with the meed of common sense possessed by all the good folk who indulge in engineering pursuits, either as a living or as a hobby. If you read in these instructions, for example, that in order to make the end of an axle a drive fit into a 5/16" hole in a wheel boss, you first of all turn it to 5/16" full, and ease it with a file to start it, you wouldn't be such a ninny as to imagine that "full" meant anything larger than the merest fraction over the 5/16". But you can imagine the effect on a raw tyro, beginner, L-card merchant, or whatever you like to call him, who has never read a "mike" in his life and couldn't read one if he had it, if I told him in these notes to turn the end of the axle to a diameter of .3135 if an inch! ......
"L.B.S.C."; Shops, Shed and Road; Model Engineer Magazine, Vol.76, No.1864, January 28th 1937, page 89.
Regards, Phil
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"bare"
Feb 6, 2016 14:04:14 GMT
Post by bambuko on Feb 6, 2016 14:04:14 GMT
At last... a sensible explanation with a source quoted :-) Thank you Phil, you are gentleman and a scholar ;-)
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