Drawing Standards

[richardandtracyParticipant @richardandtracy]

Mark,

The company I work for makes boxes. Fancy boxes for satellites & such, but they are boxes. We are not foundry specialists, which is why we go to a foundry so they can overlay their expertise on our finished shape. We do not expect the foundry to treat our finished parts as the pattern. Having cost the company thousands due to delays in testing and delivery, it's not a mistake that we are going to permit twice.

Edited to add: Also, how much shrinkage is there on the new EN version of AB2? I have no idea & it's not quoted in any standard we have. We need the foundry to put their experise in here as well as where to put the sprues.

Regards,

Richard.

Edited By Richard Williams 7 on 02/06/2013 17:39:27

[Mark CParticipant @markc]

Richard,

Was not having a go at you, it just appears that if both parties (you obviously understand the shrinkage issue especially if you are doing molds) knew there would be shrinkage, someone ought to have asked the question – has shrinkage been allowed for, can we use the model as is, do we just need to add the casting features etc.? It sounds like they might have been doing it for the first time also, or had not long taken the technology on.

It still sounds like communication and it is a shame that the technology will not be adopted especially if you are making expensive, fast turnaround tooling as it would speed things up considerably and probably drive down cost as well.

Mark

[Nigel Graham 2Participant @nigelgraham2]

BS who? 🙂

 

I was the materials storekeeper and cutter for several years in the 1980s, for a company that designed and made its own range of industrial printing-machines; though simply by capacity many of the parts still had to be manufactured by the then-many, local subcontract engineering companies.

The company bought a CNC lathe and later, two CNC mills, but this was in the days the setter/operator had to know tuning or milling and programme the machine, which used punched paper tape. Otherwise it was all conventional machine-tools, about twenty of them.

My task on receiving the drawings was to select the correct materials, mainly aluminium-alloy, mild steel and stainless-steel, and issue it as appropriately sawn blanks or lengths to the machinists. I’d also send requests to the Purchasing Department where we needed buy more.

The only hint of any formal specification I ever saw on any drawing was something like “HS30”, sometimes after merely the word “ALUM”. I don’t suppose Aluminium Sulphate is very easy to machine….. I think I came to know metals specifications better than the machinists, thanks to trade catalogues and a big MacReady’s chart in my store, above my simple but effective card-index stock-control system.

.

“Wouldn’t a computer help you?” the Purchasing Manager once asked. Confusers were just beginning to appear in offices, probably still in MS-DOS and BBC Acorn days.

“Will a computer unload ten-foot lengths of grease-clartered three-inch steel bar from a lorry in the pouring rain, and lug them through the building to my store?”

He admitted I had a point…

…

I, or rather the firm, came unstuck on “specifications” only once.

One component was a flat mild-steel plate about 12 X 8 X 1/4″, obtained as sawn pieces. Then the designers changed it to gauge-plate. Fine, I thought – fill in the Purch. Req. to buy that instead. Gauge-plate for a couple of years then one morning, the drawing clearly called for “Mild Steel”. Odd, I thought, not gauge-plate? No, mild-steel is what it said.

“Why have you supplied the wrong material!!!???” They demanded after the machinist had queried what I’d issued, with the workshop manager.

“I haven’t”, I replied, “Look at the drawing! That’s what the Drawing Office issued. I can’t know the designer’s intentions!”

They retreated, muttering. I duly received the modern copy of the drawing and filled in a PR for sawn Gauge-Plate.

 

And not a single BS, DEF-STAN, En…, ISOxxxx,  in sight; yet the company thrived, and still does. Though as now part of a much larger firm, and assembling the machines from components all made by outsiders, I suspect its drawings these days might carry more strange numbers and arcane squiggles than actual part outlines and dimensions.

[howardbParticipant @howardb]

I can only recall my own intro to the CAD X & Y world in the mid 1960’s as follows:-

During my time as an apprentice, having done the tour of the machine shop, shaper – 4 months – big Herbert horiz borer 5 months – Colchester mastiff 6 months – I was posted to the DO – Drawing office, probably as I had a grade 3 metalwork/ tech drawing pass at O level from school.

No overalls – clean – lots of girls – What’s not to like I thought ?

My first task was to start the recalculation of some of the existing machining drawings from angles and radiuses to  X & Y coordinates as the company had just installed a 2 axis cnc machine –  a rare thing in the 1960’s to produce a rationalised machine frame which would ensure the profitability of the company for the next 50 years ( it didn’t – that’s another story)

So from day one,  I sat there with a set of log/sin/cos/tan tables cranking out dims for the revised machining drawings, and entering them on a film copy, that were then input into the “digital” departments punch cards.

[Speedy Builder5Participant @speedybuilder5]

GT&D and Wikipedia

Just for clarification- Question.  The hole in this drawing has an allowable tolerance of 0.02 from either or both faces A,B.  But no tolerance of the hole itself or even diameter. Would that be my understanding and If so, how would you add diameter, hole tolerance etc to the drawing.

[Martin ConnellyParticipant @martinconnelly55370]

Is it a hole? Could be a hemisphere, cone or cylinder or a shallow depression. Without another view to clarify it is unknowable so maybe the omitted view(s) shows other details for this feature including dimensions. We should remember that the idea of the drawing is to pass on information in a clear and unambiguous way and as such anything that is unclear can have a text box with written details.

Martin C

[Neil AParticipant @neila]

My understanding of the positional tolerance box on the drawing is that the centre of the feature is to be contained within a CIRCLE of diameter 0.02 in relation to references A and B.

The boxed 5 and 10 dimensions are the exact co-ordinates of the feature from the reference sides.

As has been stated, we don’t know the details of the feature, that would have to be shown elsewhere.

It would be so easy to say this in words, but that’s not how it’s done in industry now, along with all the welding symbols that you see on modern drawings. Can be confusing if you don’t have the standards to hand to read.

Luckily, model making does not require such complications.

Neil

[HOWARDTParticipant @howardt]

Spent most of my working life as a mechanical engineers draughtsman.  Where I started we did work for RR and spent about a week learning to write in their preferred text style, all open figures suitable for microfilming, it stuck with me for most of my working days. In those days most drawings were drawn on plastic film sometimes with non erasable plastic leads.  Eventually started with AutoCad version 9, 1988, then moved 3D with AutoCad Mechanical Desktop in 1998 before Inventor in 2000. One thing I hated was 3D AutoCad, some people used it but could never see the joy. Spent my last ten years working as a contractor which is when the eye opener occurred.  Only worked for five companies during those years and only one had designers who had good grasp of CAD and component design, all the others relied on me to teach them. Can’t imagine going forward people going through the changes we went through over the last fifty years on the drawing board.  One of the books I picked up when it came out in 2005 was “The Geometrical Tolerancing Desk Reference” by Paul Green, for those still in work it explains all the symbols very well.

[HOWARDT]

On HOWARDT Said:

… Can’t imagine going forward people going through the changes we went through over the last fifty years on the drawing board.  …

Very true, it was brutal!   I saw it from both sides.

My dad was an Electrical Engineer who had served time in a big Drawing Office and made many friends. In his day there were Tracers, Draughtsmen, Senior Draughtsmen,  Checkers, Section Heads, and a librarian all working for the Drawing Office Manager.  The manager was an important big shot, an experienced fully qualified engineer, controlling a large team.

Computers dropped into this well-ordered world like an artillery salvo!  And the bombardment went on for years as technology developed, and although slower now, it’s still change upon change upon change.  My job was supplying the computers, so I too saw horrors.

Not everyone coped!  Two of dad’s Senior Draughtsmen friends had nervous breakdowns.  The reason, I think, was their minds were packed full of obsolete experience, and CAD was too much new learning for chaps coming up to retirement age.  Their status depended on experience, and, almost overnight, it, and they, lost value. Then, as old dogs struggle to learn new tricks, they were embarrassed by coming bottom of the class at training sessions.

Very difficult.   Oldsters with design experience couldn’t drive the computers whilst the youngsters who took quickly to CAD lacked real world experience.  Productivity dropped until the new technology bedded in.   The pain continued: computer efficiencies made many staff redundant, never good for morale…

Old-school drawing offices had to go because they were labour intensive, very costly, and didn’t support computer aided manufacture.  CAM is a related development in which manual machines are replaced by automatics.   That also caused massive redundancies.

Change is horrible. Something is wrong and fixing it hurts people.

🙁

Dave

 

[Alan JacksonParticipant @alanjackson47790]

I spent my working life as a draftsman and designer. When computers came along young engineering students were preferentially trained up for CAD systems. The older designers would give design layouts to CAD imputers and then the fun would begin. The Cad drawiongs were checked by designers and generally they had the problem of teaching the CAD jockeys how to design. The excuse given for impractical, stupid errors was that the computer can only do this.

A lot later on when older designers got trained up on CAD they found out that this was not true and the problem lay with the CAD back  up people who new very little about design and engineering. They were generally the caused of the problems. It took serious arguments with management to get the CAD back up to obey good practices a thing they really resented. They hated being taught by experienced designers. They considered themselves top dogs. A modern large design office proberbly has the same amount of personnel in the office, as in the earlier manual days. The split is about fifty fifty desingers and CAD backup.

Alan

[Speedy Builder5]

On Speedy Builder5 Said:

GT&D and Wikipedia

Just for clarification- Question.  The hole in this drawing has an allowable tolerance of 0.02 from either or both faces A,B.  But no tolerance of the hole itself or even diameter. Would that be my understanding and If so, how would you add diameter, hole tolerance etc to the drawing.

Back to question, this how we receive drawings from our customer

 

In this case, the hole tolerance is to a general value, noted in the drawing sheets Title Block, but could also be added in this position as required.

Hope that helps.

[Author]

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