I am new to mold making, and I am trying to figure out what is meant by Negative vs. Positive draft angles.
I understand that the part needs to be drafted to more easily pop out of the mold. I found this explanation from Solidworks:
2010 SOLIDWORKS Help - Draft Analysis Overview
From this site, I understand that defining a part's face as having a positive or negative draft is based upon the reference angle, but I really don't understand what this reference angle is in "reference" to. My guess is the pull direction somehow, but don't understand why the upper cope of the mold wouldn't just be pulled straight up at a 0 deg reference angle (if this is what that means).
I created a part file to create an example and attached it here. I just picked the front plane as the reference split plane, and the pull direction is normal to this. I am just using the default green, yellow, red color-coding for Draft Evaluation.
In the part, the angles are all 15 degrees, and the flat sides have no draft. If someone could please explain to be the actual meaning behind the relationship between the positive and negative part angles and the reference angle, I'd appreciate it.
I think I am partially confused because other sites have images such as these:
Thank you!!
The "Reference angle" is nothing more than a value that YOU set.
Let's say, for instance, that I am tasked with designing a mold for this part...
And when I go over the finish requirement for this part, I learn that they are wanting to have a specific "leather" texture on all the "show" (visible by the end user / customer) surfaces. I quickly check and find that the minimum draft required for that specific texture is 6 degrees. So I launch the Draft Analysis tool, select the proper reference plane, and enter 6 degrees for the reference angle. Now, any area of the part that has less than 6 degrees draft, Solidworks will color yellow.
As we can clearly see...the part, as currently designed, has areas that do not have enough draft for the desired texture.
(One thing that is important to note regarding the "Reference Angle" in relation to the "Reference Plane"...Zero degrees is perpendicular to the Reference Plane, NOT parallel.)
So now I can quickly go back to the customer and show them that their part does not have enough draft for the texture they had originally desired. At this point, they could choose to change the part model to allow for the desired texture, or they could change the texture specification to accommodate the existing part design.
The "Reference Angle" can be any value you desire/require.