What is this symbol ?

[paul1956Participant @paul1956]

I’ve just come across this symbol on an engineering drawing, a circle with three bars inside, can someone please explain what the three bars signify.

 

[HOWARDTParticipant @howardt]

As a life long draughtsman, now retired and from the UK it is not one I have come across, I assume it is someone’s indication of a datum point, a point from which features are measured from.  It is quite usual to use a datum point, sometimes positioned at the intersection point of two lines. For me the indication used to be two short lines at 90deg with a bold dot at the intersection or a circle.

[JasonBModerator @jasonb]

Not one I have seen. What part of the world do the drawings originate from as that may be a clue to the system being used.

Can you post any other views of the part and say what it is, that may give a clue

[DiogenesParticipant @diogenes]

Yes need some more context / clues – intuitively it could perhaps be a demand for circularity (i.e. ‘ream’)..

[Michael GilliganParticipant @michaelgilligan61133]

I cropped your image to remove extraneous detail, and then asked Google Lens

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MichaelG.

[OldironParticipant @oldiron]

Michael G strikes again. Good find Michael.

[paul1956Participant @paul1956]

Not sure the AI is correct here. I tried the same and got similar results about welds, but that seems wrong given the dimensions and object (a model steam chest). My impression is that the 3/16th dimensions define the circular feature’s position, not it’s diameter.

The drawing is part of a set by Keith Bucklitch of Charles a 16mm scale steam loco on the steammodelloco.io group, (I assume UK based ?) and no particular drawing standard specified on the drawing.

Another part of the drawing has a similar circle, but with more segments and is defined with a thread size, but there’s nothing specified on the steam chest drawing.

 

[Michael GilliganParticipant @michaelgilligan61133]

Please don’t shoot the messenger 🙂

I only reported what I found.

MichaelG.

[paul1956]

On paul1956 Said:

 

The drawing is part of a set by Keith Bucklitch of Charles a 16mm scale steam loco on the steammodelloco.io group, (I assume UK based ?) and no particular drawing standard specified on the drawing.

this looks like the good place to ask

[paul1956Participant @paul1956]

this looks like the good place to ask

Indeed, but I’d wondered if this was some general convention for drawings I’m not aware of.
Maybe not and just a peculiarity of this drawing.

[Nigel Graham 2Participant @nigelgraham2]

I think unique to that designer.

The hexagon rather than triangle, the thead, context and likely material, does suggest a screwed-in rather than welded plug.

Or perhaps a weld symbol used to indicate a plug soldered in.

[noel shelleyParticipant @noelshelley55608]

Does it signify a blind hole ? Possibly with a thread at the top in the second case. Noel.

[Neil AParticipant @neila]

This is just my guess, I think the broken line is meant to be a circle. It would seem that the parameters chosen for the broken line in the CAD programme are producing straight line segments instead of a curve on small diameters.

Symbols for welding are completely different and are usually placed on an extended leader line.

It would be interesting to know which CAD programme was used to produce the drawing.

Neil

[JasonBModerator @jasonb]

Quite obvious when you see another view of the chest, it is a hole threaded 1/8 x 40 as per top left, ringed in red. Hence my asking for the remaining views.

[Michael GilliganParticipant @michaelgilligan61133]

So … if actually drawn correctly, those 3 short lines would be arcs concentric with the circle.

Mmmm ! … Just as Neil A surmised.

MichaelG.

[JasonB]

On JasonB Said:

Quite obvious when you see another view of the chest, it is a hole threaded 1/8 x 40 as per top left, ringed in red. Hence my asking for the remaining views.

Quite obvious if you look at a different plan sheet !

So the symbol is a threaded hole (with an unspecified thread on the plan I was looking at), but rendered differently to other threaded holes on the same sheet…… which are rendered the same as hidden parts…

Thanks for digging that out.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, this is a typical symbol for a plug or slot weld that you would see on a drawing, and shows the way it would be seen, as Neil A has pointed out.

Regards Nick.

[BazyleParticipant @bazyle]

I think it may be an artifact of the CAD program if by accident dotted or dashed lines got selected when the circle was drawn.

I have dropped Keith an email mentioning this thread.

Baz

[JasonBModerator @jasonb]

Even if you don’t have the same drawing that I found a bit of looking at other drawings, parts, images and video will often reveal what something on a drawing might be.

If there are general arrangements or the plumbing is shown then it should be possible to work out that steam has to get into the chest somehow. So there may be a pipe with a matching 1/8″ thread or at the very least a pipe shown going to the side of the chest in the GA.

Or the way I found it once the engine and part was revealed was a quick google for the engine and I could see from a couple of videos that steam entered the side of the chest, a bit more looking at videos found that image of the drawing in the background and the guy drilling and tapping the hole ( though at a larger 3/16″ x 40.)

[BazyleParticipant @bazyle]

I have received this reply from Keith:

“The drawing was made using TurboCAD. From vague memory, I think it was probably V4, which at the time was being given away as a cover CD on computer magazines in the UK. (Notably in W H Smith’s reading room.🙂)

The hole in question was for the steam inlet to the steam chest. I think the markings concerned were to represent a thread, and from memory, as the part became smaller in dimension, so sometimes the markings on the drawing were modified/simplified/reduced (no idea why), and that is what I think we are seeing here. There is another possibility. When I released the drawings into the public domain, they were converted to .pdf format and that could be the result. The model loco was designed (as a 16mm:foot scale) model) in 1994 and I no longer use that particular CAD program. Charles the prototype is of course much older and can be seen ‘stuffed and mounted’, in the museum at Penryn Castle near Bangor in North Wales. Sister locos are Linda and Blanche which now operate on the Ffestiniog Railway from Portmadoc to Blaenau Ffestiniog.”

Hands up all of us who used one of those free CD versions of Turbocad. 🙂

[Nigel Graham 2Participant @nigelgraham2]

That does seem the answer: a CAD artefact.

I have TurboCAD Deluxe 19 and 24, and have just experimented using the latter.

These make it easy to scale the dashes to give presentable hidden-line circles of small diameter, but they are very coarse if left to the default “Pen” scale.

So perhaps the dash-scale settings options in that free CD version were so limited they could only give that rather peculiar result on small circles.

Even in more modern versions of the “Deluxe” editions of TurboCAD, a default circle is a polygon of perhaps 36 sides, especially obtrusive when used as the foundation for extruding a cylinder. You can edit it to finer facets.

 

Most likely the free V4 edition on magazines was a sort of taster / introductory edition, very heavily reduced from the far more powerful, and costly, professional-user editions. That was when CAD was primarily very much an industrial tool at industrial prices; with serious enginering-drawing versions inaccessible to most amateur users.

IMSI, TurboCAD’s manufacturer, seems to have twigged the potential market long before others did, and TurboCAD 19 Deluxe was the first proper engineering CAD available at sensible price to model-engineers. It was even advertised in Model Engineer, and came as the programme CD plus a pdf introductory manual on another CD.

Despite the name, “Deluxe” is the basic form of each TurboCAD version, not desperately expensive; although very well equipped and allowing both orthographic and 3D-model modes by choice. However I think its biggest drawback, having used both makes, is that its 3D mode lacks the neat Assemble-From-A-Parts-Library character that is one of Alibre Atom’s strengths.

 

So very likely the peculiar “symbols” were indeed all TurboCAD V4 could manage when the user asked it to generate small hidden-detail circles.

[duncan webster 1Participant @duncanwebster1]

I’m fairly sure that in BS 308 (that dates me) tapped holes were just represented by 2 concentric circles. Unfortunately I’ve mislaid my copy. Paul1956 drawing is a bit odd, it dimensions the outer circle as 1/8 then calls up 5/32 thread. I’d just have had a leader drill 1/8, tap 5/32……

[duncan webster 1]

On duncan webster 1 Said:

I’m fairly sure that in BS 308 (that dates me) tapped holes were just represented by 2 concentric circles.

That makes sense. It’s not good the software misrepresented it.

[Michael GilliganParticipant @michaelgilligan61133]

My “find of the day”

https://littlewordsfromme.wordpress.com/wp-content/uploads/2008/11/e0750651202.pdf

MichaelG.

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See page118

[Graham MeekParticipant @grahammeek88282]

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,

[Author]

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