Test Section Legs

Dear Fellow Basement Scientists,

Here we are, on to more construction. You may say, “What, I thought this was science not wood shop class!” Well, to conduct experimental science you have to build stuff. So, that is what we continue to do, building stuff to conduct our experimental science. Also remember, you have to build stuff right in order to get any good results.

As mentioned last time, it is time to build the legs for the test section. The length of my legs are based on the height difference in the staggered bench top, height of the test section, and diameter of my fan. You who are following along will need to determine the right lengths for you. Here is a sketch with my dimensions.

Very Technical Construction Drawing

I bought a 20” diameter fan, which I will discuss more later, and assumed an extra inch for mounting. I also then assumed the middle of the fan will line up with the middle of the test section. By this, the test section must be 7 inches above the upper bench top. The lower bench top is 7.5 inches below this. Add these together and the legs should be about 14.5 inches long. Lets give ourselves a little flexibility incase we need some unexpected extra space and make the legs 16 inches long.

Alright, how are we going to make these legs. I’ve got a 2×4 which seems like a great choice. Okay, we need to determine how we are going to make the joint between the legs and test section. We don’t want to just slap legs to the side of the test section because all the weight would be on the screws, which is never a good idea. We want the test section to actually rest on the legs so here is what I determined:



Joint From Below






Above, you can see the legs and the horizontal what I will call tie rods. The material of the tie rods is quarter inch thick strips ripped from a 1×6 I had laying around from an earlier project. Next is a picture from below and you can see the notch cut into the leg. The tie rod then the test section fit into the notch. As you can see in the next picture, the leg is attached to the tie rod and then the tie rod attached to the test section. The reason for the tie rod is because it allows the screws into the test section to be more spread out and for the legs to be connected together. I thought this would make the joints stronger and allow the test section stand with more stability.

The most important distances to get accurate are from the bottom of the notch to bottom of the legs, which is the height of the test section, and depth of the notch, which must contain the tie rod and overlap the test section. Also, make sure the legs are positioned on the tie rod accordingly so that good locations are left for the attachment screws into the test section. I made a little jig on the table saw so that the location of the notch was the same for each leg. I then used a hand saw to make the cut for the notch. Unfortunately, it turns out my bench top is not level so I have to put shims under the legs anyways.

To add extra stability, I connected the bases of opposing legs with an appropriate length of 2×4. For all screws, I pre-drill holes to not split the wood and then use screws with a suitable length.

Good work! Our test section now stands on its own 4 legs. This part was important because if it is unstable or weak we can’t attach the bell mouth or ultimately conduct good experiments.

Best Regards,

Ben Washington