What is this symbol ?

[Neil AParticipant @neila]

I can’t find my old copy of BS308, but from memory it showed tapped holes as two concentric circles with a short break in the line of the outer circle. This was easy to accomplish when drawing with a compass, but when using CAD it was always depicted as just two unbroken concentric circles as it was easier to do it this way.

The information on the detail of the hole, tapped or plain, was on the end of a leader line. Where multiple holes were involved it was usual to put a letter indicator beside each hole, ie. A, B etc , and then add a note to the drawing, without a leader line, stating “X number of holes marked A, B etc , and then the details of the holes”. This was the standard way in our office, whether it was the same on drawings from other companies I can’t remember now.

The sole purpose of a drawing is to give all the necessary information to produce the part in an unambiguous manner. We don’t always get it right first time, I couldn’t tell you how many times I have had to go back and make a correction. But I have to say that going from manual draughting to CAD certainly reduced the number of times this happened. Moving from 2D CAD to 3D CAD was also another big step, this made the interference of adjacent components much less likely. Another gain for moving to 3D CAD, it is a steep learning curve but the rewards on complex assemblies is worth the effort.

Neil

[Graham Meek]

On Graham Meek Said:

I had thought the original view was the interpretation of one drawing package over another.

In the good old days of Technical drawing at school with Mr Gilbert F Fern DFM. We were taught that a tapped thread was represented by two concentric circles. The top RH Quadrant, (1-3 o’clock), was removed for a RH thread and the top LH Quadrant for LH threads.

Threads on shafts were treated slightly differently in that the Pitch line of the thread was “drawn in”, as a Centre-line and this had the Quadrants removed to show the direction of the thread. I have seen later in my career that the Root diameter was treated in a similar fashion. This seemed slightly odd to me as it signifies a tapped hole.

Lots of Manufacturers like Boeing, McDonnel Douglas and British Aerospace had their own interpretations, but broadly they were based on the same theme.

Sadly the old style drawings are a thing of the past and we have lost another art form.

Regards

Gray,

Hi Neil,

You are absolutely right as regards the BS 308 representation.

Checking DIN 6401-1 (1993), this also gives your interpretation.

Regards

Gray,

[BazyleParticipant @bazyle]

Once Jason had provided the full drawing it was perfectly obvious what the details were, and Keith kindly provided his best recollection of the item drawn many years ago.

I do wish professional engineers would decline from nit-picking details on model drawings. These are amateur designs with amateur’s drawings for amateurs to make in amateurs’ workshops. Not Defence equipment to be mass produced

[Martin ConnellyParticipant @martinconnelly55370]

Out of curiosity I looked in my copy of Practical Engineering Drawing (Vol 1) 1945 reprint, part of the Technical College Series. It says that there should be two concentric circles with one a part circle (ie with a section missing) and a right hand thread will be assumed.If you want a left hand thread you should specify it with LH. Also for a threaded hole the part circle should be the outer one not the inner one.

Martin C

[Engine BuilderParticipant @enginebuilder]

Paul, I have built this model. One thing I did was make the cylinder slghtly longer than drawn.

If you check the stroke and piston length it is the same as the cylinder length meaning the piston will touch the

covers.

My model has inside Walshearts valve gear and RC .

[Martin Connelly]

On Martin Connelly Said:

[…] Also for a threaded hole the part circle should be the outer one not the inner one.

 

Perfectly logical when you think about it

… the larger circle illustrates mostly hidden detail.

MichaelG.

.

P.S. 

My congratulations to ‘Keith’ for getting a mostly useable drawing out of an early freebie version of TurboCad.

[Neil AParticipant @neila]

Hi Bazyle

I hope that you did not consider my remarks as “nit-picking”, it was not my intention. If I have upset anyone then I am sorry. If anyone did not like what I said, then please ignore my post, I don’t mind.

If anyone is interested, I have used TurboCad V15 and I found that sometimes it produced a result which was not quite what I wanted. I also found it difficult at times to find the parameter in the programme to give the result I was after. Sometimes I gave up searching and left it as it was rather than waste more time searching. CAD can be frustrating at times.

The OP was puzzled by a symbol he was not familiar with, I think that question was answered, a quirk of the CAD programme.

Neil

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