Simple Drawing

Lines should be tangent to arc at left.

Dimensions don't match the original drawing.

 

Yeah, there seems to be some discrepancy in the original dimensions, as though it was first done in inches, then converted to metric, so that you cannot perfectly hold all of the dimensions, e.g.,

All of the dimensions from the original drawing can be honored out to as many decimal places as desired.

All of the dimensions from the original drawing can be honored out to as many decimal places as desired.

May be, as the original is quite blurry and a dimension has even been written in by hand for whatever reason.

It seems to me this is another "one of those". The 64mm dim could be very misleading unless the center point is very clearly shown offset. But even then, the 64 is not a necessary dimension. Better to just leave it off.

Edited May 20, 2014 by neophoible
added "is"

The instructor would have been better off selecting pertinent drafting assignments had he/she used French's book "Engineering Drawing" copyright 1947!

 

It's pretty amazing the number of these types of assignments that come through with errors and/or omissions in them. Apparently no one checks the diagrams for accuracy, prior to publishing; everyone is keyed in on the text.

The 64mm dim could be very misleading unless the center point is very clearly shown offset. But even then, the 64 is not a necessary dimension. Better to just leave it off.

 

You are assuming that the center of the arc is coincident.

Dimensions on a drawing (unless shown as reference) take precedence over all else.

 

In typical classroom type problems these are the tricks that separate the "A" students from the "B" students.

Instructors look for this attention to detail and throw in tricky stuff like this.

 

There is nothing wrong in this part/assignment.

 

See Post #7 where I clearly show the dimensions as given in the original drawing.

You are assuming that the center of the arc is coincident.

Dimensions on a drawing (unless shown as reference) take precedence over all else.

Or maybe you are assuming I'm assuming? The 64mm is a dimension, but to what? Maybe I know, if I'm the one originating it. Experience tells me that such a drawing is too easily misinterpreted. The student should be taught to make it clear. It seems to me, this is a case where that is not the case. However, it is a good problem for demonstrating what happens when you don't make it clear. (Hmm. I wonder if anyone can understand that?)

In typical classroom type problems these are the tricks that separate the "A" students from the "B" students.

Instructors look for this attention to detail and throw in tricky stuff like this.

 

There is nothing wrong in this part/assignment.

 

See Post #7 where I clearly show the dimensions as given in the original drawing.

I think the drawing in post #2 is more appropos to the discussion, and it isn't tricky, it's misleading or incorrect. The 64mm is not an exact dimension when holding all the others exact. Post #7 is where the solution comes in. If the student is told that the center is not along the line, that the 64mm is not exact, then you have a more bona fide problem. Or you could just drop the 64mm dimension altogether.

I think the drawing in post #2 is more apropos to the discussion, and it isn't tricky, it's misleading or incorrect. The 64mm is not an exact dimension when holding all the others exact. Post #7 is where the solution comes in.

 

Post 2 and 7 are the exact same file.

You are wrong, the drawing is correct. It is an exact dimension holding all others dimensions exactly as given. I am done with this one.

 

BTW, it isn't tricky or misleading for the "A" students.

Post 2 and 7 are the exact same file.

You are wrong, the drawing is correct. It is an exact dimension holding all others dimensions exactly as given. I am done with this one.

I never suggested they aren't from the same file. But it is too obvious that they do not show the same information, that is, #2 does not even come close to indicating the offset center for the R32 dimension that #7 does. What is not clear is where or how the 64mm dimension applies. This was not answered. As far as I can tell, my 63.9700, while not exact, is correct to 4 decimals and, as far as I can tell, nothing has been posted thus far to demonstrate differently. If someone would like to show a more correct solution, that might prove useful for other students looking for help. I don't mind being wrong, especially if demonstrating such helps someone else.

 

I sense there may be a fundamental difference in what the goal should be here, and that may very well be up to the individual teacher and class situation. As usual, I'm looking at it from my own real world perspective where those receiving drawings need clear information so that they can efficiently and correctly create the part. Students definitely need to be very aware of this, but, from what I can tell, this problem does not directly demonstrate it. However, in a classroom, where students are trying to solve problems, perhaps even including those involving illustrations by sloppy designers, tricks may very well be the way to go.

As a tricky problem, maybe it's OK. But now that I see what the solution likely is, we'd probably fire someone who designed like this on the job. While the problem is solvable, I seriously doubt the original intent was other than straightforward. Again, this is another "one of those".

 

For students looking at this, the center point location is approximate to 4 decimals. If your teacher really wants such a solution, you will have to solve it graphically in CAD.

I would like to offer a few comments, that may be at variance with some previous.

 

For this exercise, units do not matter. Geometry is the same shape whether it is in millimetres or inches. This is a drawing exercise.

 

Finally, I see that someone has eventually twigged that the centre of the 32 arc is not on the centreline.

 

What is given are two fixed points, with an arc passing through them. The usual way of ensuring this geometry is to strike an arc from each point, and where they intersect is the centre of the required arc. There is no need to know further dimensions, whether to zero places or eight places of decimals. That is just unnecessary confusion for a geometry exercise.

Would the units matter if the OP were going to print the drawing on an A4 size sheet of paper?

I thought that it was merely a drawing exercise, where the shape is important.

 

Do students always get their work printed? I would have thought printing to fit a sheet of paper could suffice.

 

If it is a lesson in real life, then realising, from the units, that millimetres are the most likely units is a valuable lesson, but not one touched on by the OP.

I suppose it depends on the instructor. When I took an AutoCAD class the instructor wanted both a print out and a copy of the actual DWG file.

Perhaps the OP is already working in a millimetric environment, and had no need to check the default units.

 

It is not necessary to start with a metric template to make a metric layout. It is just a case of choosing the plotting units, and checking VIEWSIZE.

"It is just a case of....."

You are assuming the OP knows about plotting units and how to check the view size.

"It is just a case of....."

You are assuming the OP knows about plotting units and how to check the view size.

 

 

If the student is drawing geometry in drawing units then the shape will be perfect.

Guys I just gave the drawing to my teacher, and he accepted it.Thanks a lot for your help.