Do These Prints Make Sense?

[Bill Gruby]

That's called NAG for short or Noggin Aided Drafting. Use it all the time. Most pros do.

"Billy G"

 

[vtcnc]

It appears to me that you have not actually located the holes. I can infer where the centers are but it's best to be explicit. Have you studied geometric dimensioning and tolerencing?

Location of the holes may depend on the mating part, and not relate to the center axis of this part, i.e. if this isnt a rotating part, locating from the center may be irrelevant. Check how this fits up, and if applicable, call out the measurements you want to represent your design intent. For example, it may be more important that the c'bore to c'bore distance is more important than the relative distance of each c'bore from the imaginary center of a non rotating part...assuming it doesn't rotate.

Sent from my Nexus 7 using Tapatalk

 

[wrmiller]

"I often work it all out in my head and then start cutting metal. That doesn't always end well."

Similar style for a lot of things, but I will still put pencil to paper when I need to be more accurate.

 

[RJSakowski]

In section BB, you have over-defined the horizontal measurements. You should not have the overall dimension and the three dimensions adding up to that overall (1.250 and .250+.920+.080). as a machinist would not know which dimensions match your design intent. I would guess that the .920 dimension would be the one to leave off the print but that may be a critical dimension for you. From your block tolerance of +/- .003", if all the dimensions stacked unfavorably, the .920 dimension could be as small as .9111 or as large as .929.

That said, I often over-dimension on drawings for my own use because 1. it is convenient for me when I am in the shop not having to do the math to check a measurement and 2. because I know what the design intent is and which dimensions are critical. I have used parentheses around a dimension to indicate for reference only for drawings sent out to a job shop.

Another way to dimension horizontal and vertical positions is to establish a reference point and dimension using horizontal and vertical ordinates. The advantage of this is twofold. 1. There is no tolerance stack up as there would be when chain dimensioning. I use it when I have an array of features because a +/- .003" tolerance means that the feature is located within that tolerance at the nominal position. and 2. When actually machining, I will pick a reference point on my workpiece and all my machining positions are measured from that point.

For the hole positions, I would dimension each hole position from the center. Another way would be to draw a bolt circle and dimension the diameter. It wouldn't hurt to extend your center lines and add center lines for each of the holes. This will reinforce the location of the hole centers on the horizontal and vertical axes.

I usually do not put surface finish on a drawing unless it is critical. I have found that every machinist has a different idea of what a good part looks like and no two machinists will make the part the same. To that extent there is a component of artistry involved in machining. When sending work out, you quickly learn which machinsts do good work and which do not. Putting a surface finish on a drawing technically requires the machinist to verify the finish which adds extra cost. We did however, have some information in our title block

I generally don't use GD&T but it does come in handy when specifying things like perpendicularity, cylindricity, parallelness, etc. that would be hard to describe otherwise.

The important thing is to define your part in an unambiguous way. If you are machining the part yourself, it becomes very obvious if you have underdefined or overdefined. If you doing this in a work environment, you probably have a set of drafting standards to guide you.

Bob

 

[Dan_S]

I tend to put some chicken scratch on a piece of graph paper and start cutting metal.

I do this as well, but only for projects I know I'm going to get done right away. A lot of my projects get spread out across several days or weeks, due to work, & family obligations etc. If I don't make some kind of print I forget stuff. That usually leads to me getting irritated, because instead of making something when i do have free time, I'm sitting in the office, analyzing the cad file or re-designing the thing from scratch.

The chamfer is more easily dimensioned and produced (on a manual lathe for instance) as an angle with a dimension in one plane, for example .031" X 45° from the theoretical sharp corner in either the Z or X axes.

Good point, I have a tendency to just break out the calculator, and do the trig. If I dimensioned them the way you mentioned, I could just look at the print, I'll try and remember to do this going forward.

Not bad at all,first CAD drawings I have looked at that I did not have to spend my entire morning coffee time reading them to see what was there. Kudos.

Thanks Bill

That said, I often over-dimension on drawings for my own use because 1. it is convenient for me when I am in the shop not having to do the math to check a measurement and 2. because I know what the design intent is and which dimensions are critical. I have used parentheses around a dimension to indicate for reference only for drawings sent out to a job shop.

I just learned about the parentheses last night from the videos Bob posted. I definitely over dimension a lot of stuff, just because I don't want to do the math, and so I know what tools to get out.



attached are some updated files, now i just need to see about dragging my butt out to the shop to finish making these parts. It's 40 degrees in the shop, and even if i run the heater for a while I doubt it will get above 50.

 

[Andre]

I made the mistake of showing a draft to someone who's in college to become a mechanical engineer. Bad idea!

 

[RJSakowski]

attached are some updated files, now i just need to see about dragging my butt out to the shop to finish making these parts. It's 40 degrees in the shop, and even if i run the heater for a while I doubt it will get above 50.

Looking at your updated drawings, I would dimension to the centers of the two remaining holes and I would use vertical ordinate dimensioning to locate the center of the radius of each groove. Is drawn, the bottom groove cold be as much as .010" away from your design dimension based on your box tolerance.

 

[RJSakowski]

I made the mistake of showing a draft to someone who's in college to become a mechanical engineer. Bad idea!

When I first started drawin "professionally", I used to run the drawings past our well seasoned draftsman. He was almost always able to pick up on some missed point. I guess that is why they have the "checked by" and "approved by" boxes in the title block.

 

[Dan_S]

Looking at your updated drawings, I would dimension to the centers of the two remaining holes and I would use vertical ordinate dimensioning to locate the center of the radius of each groove. Is drawn, the bottom groove cold be as much as .010" away from your design dimension based on your box tolerance.

How do these look?

I'm bound a little bit by the features fusion 360 currently has, through from what i have read they are adding more drawing features in the future.

 

[TOOLMASTER]

I always run it through my head so many times by the time i make it. i can do it blind folded.