VAV Box family creation

[JKRevit]

VAV dimensions.JPG

I'm trying to create a VAV box family, with several family types. Each family type will have different family parameters, including different dimensions (see attached). I'm trying to follow the guidance of the 2010 MEP Family Guide as I build this family. I start in the Generic Model template, which has two reference planes; (Center Front/Back and Center Left/Right) I create reference planes to constrain the geometry of the extrusions. Generally speaking, this family is two rectangular extrusions, and one cylindrical extrusion. I create dimensions for the length and width of each reference plane of the rectangular extrusions. I use the Label command to create family instance parameters for each of the dimensions. I create a cylindrical extrusion to represent the air inlet for the box, and create a radius dimension with a family instance parameter to control the air inlet size for each family type. At this point, when I flex the family, the cylindrical extrusion is not staying centered on the face of the rectangular extrusion. How do I associate the cylinder to the rectangular extrusion? Do I use a reference plane, or a work plane? As I change the dimension parameters of each family type, the extrusions do not stay centered in relation to the cylinder. I would like the center of the family to run through the center of the cylinder; (dimension D in the attached sketch) I would like extrusions to change size equally in relation to the family's center reference plane; i.e.; if the center reference plane divides an extrusion, when the dimension parameter of an extrusion is changed, the extrusion will stay centered on that center reference plane. I feel like I don't understand something about the Is Reference relationship between extrusions and reference planes. Any advice would be welcome. At this point, I'm simply trying to create a family that will represent geometry accurately. MEP connectors will come later.

[Steve_Stafford]

Have a look at the stock Revit families VAV Unit - Parallel Fan Powered.rfa & VAV Unit - Single Duct.rfa. They are both provided by Autodesk but are very different in how they are assembled.

The Parallel Fan Powered family is much neater when you first examine it. The constraining dimensions and parameters (I call muscle) are part of the sketches for the various solid forms (I call Skin). There are not many reference planes (I call Bones). It sits straddling the hosting Level, called Ref. Level. This means that the elevation offset that is assigned in the project is equivalent to the "center" of the unit, like what you wrote was one of your goals.

The Single Duct VAV is much messier, Reference Planes everywhere and the habit of labeling and naming them is applied inconsistently. It also incorrectly creates a link between connectors which will not permit it to work with duct sizing, has to be unlinked first.

Both families have examples of what you want to accomplish however and you can examine the techniques used. The metaphors I mentioned earlier, Bones, Muscle and Skin, are the underlying idea behind organizing the family. Create the bones (reference planes), then add muscle (dimensions and parameters) and finally add the skin which should be constrained to the bones. As soon as bones and muscle exist they should be tested, flexed to make sure the move correctly when you change dimensions. The same is true as you add skin, each time you introduce another...flex it.

Looking at your sketch you should use reference planes to define the basic form for each solid you need, as well as change parametrically. Check out the stock families to see how the EQ constraint will keep things equally spaced relative to a centerline. One you've created the reference planes in plan and elevations, you can add the muscle...probably equivalent to the dimensions in the sketch. When you create forms remember they depend on workplanes and any of the your reference planes can be one, remember to provide a name (it's a parameter listed in the properties palette when you select a reference plane) because it makes it easier to assign a reference plane as a work plane for a solid.

Post a copy of the file as you progress if you need more input.

[neightyeight]

I've attached a screenshot of my VAV Box family. For your cylindrical extrusion, you'll want to turn on the center point of the circle in sketch mode when editing the extrusion. Then you can lock it to the 2 reference planes using the align tool when viewing it head on. That will keep it centered to the origin of the family. For your box extrusions you'll need to use an EQ constraint along with the Width parameter (you can see that in my picture). This will keep the geometry centered on the origin also.

The Is Reference option for reference planes will affect whether there are grip edits visible when the family is inserted into a project. In most cases (other than the 3 origin reference planes) I have that option set to "Not a Reference" so that no grips appear. A good example where grips would be useful is a baseboard radiator. In that case I often want to stretch it to odd lengths to fit between walls rather than trying to manually edit a length parameter.

Hope it helps!

VAV Box Family.PNG

[JKRevit]

VAV alignment.JPG

I'm still having trouble controlling the cylindrical extrusion in the family. I'm able to activate the extrusion edit, but how do I lock the extrusion to reference planes as you suggest? I've set up two reference planes, (please see attached), that I want to control the size, (radius), of the extrusion. I've set up a parameter for the extrusion's radius. If I change this parameter, the reference planes will move correctly in alignment with the extrusion radius parameter. But, the extrusion itself does not change. Could you please provide more description of what I need to do to lock the cylindrical extrusion to the reference planes?

Thanks!

[neightyeight]

Using an extrusion in this case the reference plane you created to control the radius will have no affect. The extrusion is made using a circle. So you have to constrain the radius of the circle to the Inlet Radius parameter. To do that in your family you should go to the front elevation view. Click on the extrusion and go into edit mode. Select the circle that is the basis of the extrusion. You will see a temporary radius dimension appear, which you can click the little mark next to the radius value to make it a permanent dimension (You could also simply use the radius dimension tool, choose the circle, and place the dimension). Now click on the dimension. In the properties palette choose the label dropdown and link it to the Inlet Radius parameter in your family. Now the extrusion will change size when the parameter does.

[TROYDYALL]

Im having the same problem with a plenum box. The cylindrical extrusion does not stay central but moves in the diagonal.
Did you solve this problem?