Precision Modeling LIVE!

Architecture is a specification of a few millimeters, mechanics - 5 hundredths of a millimeter, Can you see the difference? Just because something can be done with a tool doesn’t mean it’s meant to be. Can you hammer screws? You can! There are people who paint amazing things with MS PAINT. They have talent, knowledge of colors, perspective, etc. But… they lose their lives… their time… I also know how to “cheat” these dimensions in Layout. but as i say it is not real dimension. Often burdened with an error resulting from the fact of interpolating curves to segments. But since you know “everything” and stick to your opinion, tell me how you will dimension the deflection arrow in LO from the example below??

Which dimension do you consider “precise”? The blue arc and the last dimension are theory. The polygon is curve interpolation by SU. As you can see, even for architecture this precision can fail. And when you have a lot of sides and a very small object, how sure are you which point has chosen SU/ LO to measure?

Create the arc with an even number of uniform-length segments. That way, a vertex will be placed at dead center of the arc, at the proper radial distance from the chord.


Precision modeling is not arc modeling. When you model, you often trim the geometry, you set the center of the circle at a certain distance from the edge, etc. The arc and chord are the result! Of course I can replace the result according to your concept but it’s not my concept of work. And they are still workarounds and a waste of time. And there are programs (imagine) where I don’t have to do it or think about it. Do you still think that a program that can cause such errors in dimensioning is suitable for precise drawings? Where one mistake can cost thousands of dollars? You will say: Sorry I didn’t notice? Will you check every dimension inserted by your employee because you are financially responsible? What if there are dozens of employees?

But I agree with you. SU is unbeatable. Boeing is also set to switch to this program. They will save millions.

Finally some precision modelling ^^
Hope we won’t hear “thats about right” this time haha :wink:
Looking forward to it!

Did I say anything remotely like that? No, I did not. I addressed a specific critique that you mentioned.

In my opinion (which you insultingly and wrongly assumed!), one of SketchUp’s greatest weaknesses is how it represents circles and circular arcs as line segments. There are ways to mitigate some of the resulting poor effects, but this aspect of SketchUp remains a sore point. It is not enough of a sore point to make me switch to another modeling application.


Let’s get this thing back on track… Here are the five images I was thinking of modeling… i guess I see a missing dimension or two as an opportunity to problem solve! We will see what happens… LIVE!



This should be an interesting challenge! Those studycadcam drawings have, in my experience, an (intentional?) combination of missing dimensions and dimensions placed in confusing ways that force you to do deductions and math to figure them out. Struggles to understand the drawings are a whole different issue than managing to draw them in SketchUp.


Wait… math?


I’m just gonna model a cabin or something…


I dare you to model the running gear of a tank.

And not some made-up thing, either. An actual, real, existing tank’s running gear. And get it all right.

Go on, ya know ya wanna!


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I think a little more than 2 dimensions are missing. But with such knowledge, program, mathematics - as you wrote - you can do it ;-). Seriously, I can hardly see professional modeling with such knowledge of technical drawing. You might as well model from Dave’s drawing which doesn’t contain any dimensions. As a blueprint

Thanks, Aaron, nice Live and useful!

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Good work as usual, @TheOnlyAaron. I finished up the wrench model while you were doing that last part. I hope you’ll model it next time. I want to see how you’d go about it.

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Well… Yes, Aaron, these drawings are for students. And they are used in engineering programs that can find tangency, parallelism or the same length of lines by themselves, I wanted to see more but… As I wrote before. For fan - yes, for work, precision work - not

It was a great livestream though I didn’t watch it live, next time it would be a good idea to do it using som plug-ins like bevel or round corner and solid inspector to fix everything faster. Also please Aaron set the shortcuts before your next livestream, it made me feel a bit anxious seeing you go to the menu to enable hide rest of the model, also enabling a shortcut to show hidden geometry would’ve been useful.

I would question whether the drawing #1159 is a “studycadcam drawing”. I believe it to be an engineering drawing from the 1920-1960 time frame. In that period a part such as #1159 would most likely be cast iron. The process would be for a draftsman to prepare an engineering drawing including the functional features and machining dimensions, then a Patternmaker would have made a wooden pattern and core prints to be used by the foundry. The foundry would cast the part, them the machinist would machine the part to the specifications of the engineering drawing.

“an (intentional?) combination of missing dimensions and dimensions placed in confusing ways that force you to do deductions and math to figure them out.” No those missing dimensions were not missing at all. Yes it was intentional.

The Patternmaker had great responsibility in the manufacturing process. The wooden foundry pattern had to include “draft” and “fillets” to enable the pattern to be withdrawn from the sand mold. Patterns also had to be made oversize to allow for shrinkage of the molten metal as it solidified. The Patternmaker knew what size the fillets needed to be and he added those. Fillets were sized to avoid cracks in the metal as it cooled. He also added bosses to the part as needed to setup the part for machining, thus he had to have some machining knowledge to pattern the part in a way that it could be accurately machined.

When the casting was completed, it went to the machinist. The machinist would work to the specifications included on the engineering drawing. Those “placed in confusing ways” items were of no interest to the machinist for their work thus were never a necessary part of the engineering drawing.

Drafting procedures back then were very specific about what should be included on a drawing. Dimensions were also placed in ways dictated by conventional practices.

Enjoyed the live stream. Thanks to those that make it happen.


It was another excellent live stream @TheOnlyAaron. Perfect!

It was mentioned in the announcement; ‘ONLY native tools’. By precisely only using Native Tools you show what is possible with SU to create technical drawings. Very welcome for the less experienced designers. Thanks!


You’re wrong. This is not a technical drawing from that period. /even the signature under it with copyright proves it!

Ale ten rysunek posiada wszystkie wymiary. Wszystkie do jego wykonania w … 10 min? Nawet na desce kreślarskiej z okresu lat 1920-1960. Niestety wiedza Arrona na temat rysunku technicznego a w szczegulności zasad wymiarowania nie podołała temu zadaniu. Swoim postem zachęciłeś mnie abym zajrzał jeszcze raz na you tube. I okazało się że to nie komedia. to dramat.

“I can’t find…”

Is it just me, or is this thread kinda turning into a Monty Python bit? :thinking:


The following clearly illustrates the precision of the SU. A circle of radius j1 unit. It would seem that the surface area will be 3.14, but not in SU… Only increasing the number of sides to 117 displays the correct result with 2 places of accuracy. Of course, the volume is even worse.

EDIT Aaronie’s post is absolutely on topic since we’re talking about precise modeling in SU. It shows the precision of the program.

But I see you’re covering your tracks with the old habit. Unfortunately, the video on Youtube remains.

Thank you for the interesting historical and technical perspective!

I don’t know where they may have lifted it from but the copyright notice at the bottom clearly states ownership by

I stand by the observation that there are missing dimensions. It is impossible to create a precise 3D model from those drawings without them. But, as you explained, the omissions were intentional based on the understanding that the pattern maker and machinist would fake them in based on shared understanding of foundry and machining practices and suitable approximations.