Can someone explain to me the construction line?

matt_wegrzyn

Hi,

Just getting started with OnShape and cannot understand the need for the construction line? What is the construction line used for? The tutorials fail to explain this.

Would also like to know the need for the Coincident tool as well.

Any help is greatly appreciated!

viru

@matt_wegrzyn, Kindly find the below detail.
Construction Line:- Construction geometry are sketch entities used in creating other geometry but not used in creating features. It is used for to draw new construction geometry or convert existing geometry into construction geometry.
Shortcut key used from keyboard: q (to toggle Construction state on and off)

You can take two approaches to drawing construction geometry:

• Draw the sketch entities first, select the sketch entities to toggle, then select the Construction tool:

  

• Select the Construction tool, then a sketch tool and draw the sketch entities in Construction mode:

  

Tips

• Select the Construction tool and then a sketch tool to create construction geometry.
• Select sketch entities and then the Construction tool to toggle construction mode on and off.

Coincident

Shortcut: i

Makes two or more entities coincident, including a sketch entity and a plane.

Constraints can be toggled on while you make selections. Toggle Coincident on and each pair of entities you select are constrained to each other. Click Coincident again to toggle off, or select another tool to toggle off automatically.

Kindly refer below video link for all dimension Constrains,

https://cad.onshape.com/help/#dimensions_constraints_video.htm

ethan

I use construction lines mostly for mirroring in sketches. Also for placing holes at certain angles from the normal, add a construction line to the center of the hole and dimension the angle between the normal and the construction line.

Coincident I would say I use 10-20 times per sketch, very important. You can think of a coincident constraint as attaching two things. For example if you are sketching in context to another part that has already been built and you know that one side of your part is connected to a face of another part, you can easily add a coincident constraint between the sketch and the face of the part that already exists. 

billy2

I use construction lines to convey design intent. Think of the next guy who's working on your model. He has to figure out what you are doing and I find graphical representations work well.

As ethan says, mirroring is a good reason, axial symmetrical parts with diametral dimensioning, construction circles...

Any thing that'll help you remember why you did something. To me sketches should tell a story.

I had one friend that used an equation to represent a design intent sin(30), and I convinced him to draw a construct line and dimension it with 30˚. It's far easier to see a construction line with a dimension and understand it's meaning vs. looking through some equations trying to understand what's going on.

He wanted to show the world how smart he was and begged him not to do that. 

Keep it simple and tell me what you are doing. Well built models tell a story, the design intent.

shashank_aarya

Construction line is useful typically in the complex sketches containing combination of multiple profiles. Suppose I have created the fully constrained sketch profile with combination of circle, rectangle, lines, arcs etc. But while creating I observed that some of the entities are not required to be a part of feature. Suppose I delete such entities it is highly possible that the sketch may lose some of the constrains. So, once again I should make it fully constrain by applying dimensions or geometric constrains. To avoid this situation instead of deleting something I will convert that to construction line. Whenever it is required I will once again turn it back to solid line.
Additionally I will use construction line as a reference for mirroring the sketch entities. However this operation is possible by solid line also. But to have some differentiation for reference it should be in different pattern other than solid line.
Coincident constrain is used for attaching the separate entities together as explained above.