The Mating Game, Post, Rim and Brace

 So if you are following the 6 posts, 12 rim joists and 12 braces have been rough cut and sized. Then the braces had the tenons cut. Now it is time to cut the mortises into the posts and rim pieces. If done correctly it will be a nice fit forming a hexagon rim with 6 posts held by 12 braces at 45 degrees. And this is what it will look like.

Here is the fit of the brace to the 3” by 6” rim joist.

And here is the fit to the 6” by 6” post.

So how do we do this ?

Let’s start with the mortise into a post. After determining the location for the tenon it has to be layed out. Now because this is a hexagon the holes need to be drilled at a 30 degree angle.

The 1 - 1/2” diameter bit was guided with this drill guide. Notice the marking rings on the drill shank. Yellow for 1”. White for 2 - 1/2” and Orange for 3” depths. Very important!

The blue lines show the depth of each hole in profile. This is used to control and assist in getting the correct 45 degree angle needed for the tenon. The chisels will do the work to remove the unwanted wood left after drilling.

The 3” deep holes need to be drilled at where the end of the brace meets the post or the rim joist. So in this picture the brace would be slanting down as it should be with the construction being up side down like I’m doing it.

You have a 50/50 chance of screwing this up if you’re left handed like me. And I did just that on my second set of braces. In this picture the post (not shown) is on the left. Meaning that the brace would be slanting up. Thankfully I caught my mistake at the last minute. But this will haunt me for the next 4 posts and brace sets.

If it can go wrong, it will, be prepared. The screw point came out of the drill.

Did I mention the 50 degree angle that needs to be cut for where the brace meets the post? You can see the compound angle that is formed as the brace folds in the wood a relief angle needs to be cut.

Compound angle between post and brace.

I had to build a “contraption” since I had no helper to hold the 6 by 6 after I removed the temporary 1 by 2 braces. 

The engine hoist secured the post end but allowed movement and adjustment after the temporary braces are removed.

Once the braces were fit to the posts and held in with a single screw it was time to get the exact location of where the brace mortise needed to be cut into the rim joist.

Now I know this could be looked at as cheating but I think of it as using your head. And it worked like a charm. In the normal way one would use a square and measure down and over. Or a real pro would just use the calculations from the brace layout. But you have to remember this is rough cut timber and not dimensioned planed lumber.

With the post plumbed.

The exact distance for the location of the mortis was marked into the rim joist for each brace.

After laying it out correctly and drill it out correctly then the 45 degree angle for the tenon was cut.

And this is what you get. One more post and brace pair to go tomorrow.

So what’s next? Disassembly and setting the roof rafters.

 

 

The Brace factory

This is going to be tricky for a left handed guy like myself. As explained in the earlier post I have to build the gazebo upside down. The braces marked left and right will be reversed in the final assembly. Keep in mind there is an inside and outside to each brace. 

Cutting the basic 45 degree angle was done on the miter saw.

The basic process is pretty straight forward. In most cases the rim joist and the post are at 90 degree angles to each other. That makes the cuts to the brace 45 degrees. Calculating the hypotenuse of the right triangle and laying out this length for where the tenon joins the frame. However I chose to make my structure a hexagon. This adds a 60 degree included angle (6 X 60 = 360) to the project. Laying out and cutting these compound angles will be a challenge.

Needless to say it is going to be a “process” and you have to be thinking a few steps ahead if you want it all to fit together. This is the part of the process that is lost on the casual observer and gives special meaning to the ol’ saying, “they don’t make things like they used to!”

After laying out the tenons the next step is to cut them and gage the thickness of each.

The tenon must be clean and smooth. An added problem is that all the cuts need to be marked before cutting and some of the lines will be cut off with the scrap this has to be planned for with “tick” marks.

Hand sawing the tenon end that goes into the rim joist is straight and simple

The finished results will look like this. 

The tenon end that joins into the post is a real animal.

And requires you to keep the angles in mind and how they intersect. This was something I learned during the model building I did in the early stages of the process.

The piece removed looks like the one on the left. The one on the right is the piece from the normal 90 degree tenon going into the rim joist. 

Another twist to the cut is the relief angle that has to be cut where the tenon meets the vertical post to allow for the 30 degree angle as the brace folds inward. Again another thing that only the builder has to contend with and appreciates.

One final look at the surface planes of the end that will mate up with the 6 by 6 vertical post.

And here’s what it is all about. If only you could go to the local lumber yard and buy a finished brace like you can for a stair stringer.

Next “The mating game” cutting the mortise.
 

 

40 for 40 project begins

 

The small model in the right corner is the finished gazebo with the reciprocating rafter system made out of 5” by 8’ round fence posts. The first step was to layout the hexagon and level up the construction site. With that done I could place the 3” by 6”  six foot long rim joists on the concrete blocks. This formed the 12’ diameter hexagon. The tricky part about this is that I plan to build the structure UPSIDE DOWN! This will allow for stability and bracing of the 6 main posts during construction.

The plan is to cut the parts and make some assembly in my shed. The Amish sawmill guys did a nice job of cutting the 6 logs into the necessary sizes. Now the next step is to layout and cut the tops of the 8’ tall 6” by 6” posts. Here is the layout and a finished post. 

Most of the cutting can be done with the 7” skill saw. With a maximum 2 and 1/2” depth. The final cuts needed to be hand sawn.

One down and 5 more to go.

Keeping the untreated pine timber posts up from the ground will be accomplished by a 1/2” rebar system that will be attached on the bottom end of each post. This requires a 1 and 1/2” diameter hole 10” deep to be drilled.

To keep the hole straight I used a drill guide made out of some scrap PVC pipe.

Using the two sawhorses I made with my new Alaskan sawmill I built a jig that would hold the 6” by 6” at the right height to allow the rim joists to be held and drilled for the 3/4” diameter wooden pegs that will be used. 

Another jig was used to guide the drilling of the 3/4” holes. 1/2” diameter threaded rod will be used to assemble the parts for trial assembly.

OK here is the first post and rim joist set up. Lost in the picture is the tricky part of this process. The rim joists need to be set up and drilled in pairs. So the next post had one new rim piece and one drilled placed in the setup. Keep in mind that each assembled piece was unique and needed to be orientated to match holes with the original post it was set up with. Very confusing. 

Anyway it worked. Each post had a number and each side of the joint and had an “A” on one and “B” on the other side. Then the ends of each rim joist was marked with the matching post number and A or B side on it’s end.

Next will be setting up the “BRACE” factory. Stay tuned… 

 

NEW low cost 4 fan KidWind wind tunnel

 

This NEW wind tunnel design has the same 48” by 48” opening and it powered by 4 ValuTek 3-Speed Floor Fans 20” from FarmTek for $303.80 plus tax and shipping. The 4 mil vinyl can be purchased (4’ wide 25’ role for $30) at Ace hardware and is held to the 1’ PVC pipe by 1” black hook and loop. The front and back frames stay together with the 3 Way PVC 1” elbow corner Side Outlet Tee fittings from Amazon for $21.  Just the four pipes connecting the front and back frames are removed for storage against the main fan holding section. The storage footprint for this tunnel is 12” X 48” X 48”. It takes less than 5 minutes to set up or take down. 

And here is the wind tunnel loaded for transport or storage storage in your classroom. 

This is a project that can be made in a day and requires only common tools and machines to cut the pieces.

Lets begin…

The first step is to cut the 4’ X 8’ sheet of 1/2” 3 ply plywood in half. This is best done by using a straight edge to guide the saw and get a straight and accurate cut. Use of proper PPE will be important thought out this project. 

This next step might seem a bit odd but you will come to see that saving and taping the four boxes that the fans were shipped in will be a good idea. Be sure to go all the way around the four boxes and make this a strong stable work surface.

Now we all know that the layers of plywood have the grain running at right angles to each other. This gives the plywood its strength in both directions, To maximize this take the half sheet you just cut and turn it 90 degrees like shown in the picture. Doing this will also make sure that there is a factory cut edge on all four sides.

Clamp the two halves together and even up the edges. Then use some screws to temporarily hold the halves together. Keep the screws close to the edges. Now use a straight edge to draw lines from each of the corners. 

Now might be a good time to look over and study the plan drawing for this project. The centers of the fan holes are measured out on the diagonal lines you have just drawn. The location and size of these four holes is the most critical part of this project because the clearances are less than 1/4”.

Just as a double check of my measurements of 1’ - 5 1/2” on the diagonal I also used a framing square to measure up and over from the edges of the plywood and verify the center locations of the four fan holes. I hope you have also noticed that I have now placed the two pieces of plywood on top of the four shipping boxes that the fans came in.

You are going to use a large dividers or make one out of a stick with a screw in one end and a hole for a pencil EXACTLY 10  - 3/4” away from the screw for the RADIUS of the fan holes to be cut. Drawing the circles for the holes is a must. They must be just right and the diameter MUST be 21 - 1/2” ! Ok you are going to have a choice here as to how you cut out the holes. A jigsaw will work but I prefer a Roto zip with a radius guide. Either way you will be cutting through the two pieces of plywood and the cardboard top of the shipping boxes below (not the table). 

OK one down and three to go! See how the boxes help out?

Now you are going to want to check your work and now is the time to do it. If the hole is to big and the fan drops through you are going to change that for the next three. Making the hole smaller will require some added material. On the other hand if the hole is to small you will have to make it bigger and that take some hand work you will not want to repeat on the next three.

Did I mention that when you get the fans you won’t have to assemble the stand frame and will have to remove the hardware that the stand frame bolts to so that only the rim of the fan wire grills is left. This rim stops the fan from going through the holes you are cutting in the plywood.

Four holes cut and looking good sitting on top of the cardboard box working surface.

The fans have two sides. The air flows in one side and out the other. You will want to get it right because in a wind tunnel the air is drawn into the tunnel and then hits the turbine blades that are being tested. This is different than when you use a single 20” box fan in your classroom. You have a fifty fifty chance of getting this right. Don’t blow it. For these fans the air comes in on the motor side. Now if you haven’t figured it out yet the fans are going to be “sandwiched” between the two pieces of plywood you cut. In the picture the fans are laying on the first player of plywood. The 1/4” thick pieces you see are spacers that equal the thickness of the rim of the fans grill.

There are also some little tabs along the edge of the grill and some wood will need to be removed so the 1/4” thick spacer fits flat to the plywood. I used a 1” forstner bit to drill this semi-circle of wood out.

The fans are pretty heavy and the two layers of plywood do a good job holding them. But just for a little extra I put a small cross of the 1/4” material in the center of the fans. All this spacer material should be tacked in place with short nails or screws so they don’t move when the top piece of plywood is added.

So now the top layer has been added and the fans are locked in place. Now all you have to do is fasten them together, right?

Not so fast. You need to add a rim of 1 by 2  (actual size is 3/4” by 1 - 1/2”)  to both sides of the “sandwich”. This will give it strength and thickness for longer screws. 

Now the the box ides was pretty good, right? Well then you are going to like this for the 1 X 2 pieces. If you look ate the plans carefully you can see how each of the 8 pieces are the same length.

This save some extra measuring. But the lapping at the corners is reversed from one side to the other. This gives the joint more strength. Trust me on this.

You are going to use 2 - 1/2” GRK screws to put the “sandwich” together. You will clamp the 5 layers that make up the “sandwich” together and then drill pilot holes for the screws. Yes I know that the screws are self drilling but again trust me when I tell you drilling pilot holes will make for a better job. Also you will drill the pilot hole ALL THE WAY THROUGH the 3” of material. This will leave a small hole on the other side so when you screw that side you can go in between the screws of the first side.

IF you did all the steps correctly you have a four fan “sandwich” like this. Congratulations!

Again on the plans PVC cutting list it calls for 2 - 30” support legs. Screw them into the back side 1 X 2  rim pieces (drill some pilot holes for these screws) and you will have a nice stand for the fans while you finish the work and when you set up you wind tunnel in the future..

CABLE MANAGEMENT - A big deal when you are moving a tunnel like this around and setting it up. Lets see how we do it…

First we are going to go 2” in on the diagonal lines we drew. The location for each 1 - 1/4” hole is shown on the plan drawing.

Use a 1 - 1/4” hole saw to cut the hole to run each fans plug through.

Whoa that is a big hole and will leak a lot of air. We need to seal the hole around the plug wire.

Remember those 8 big circles of plywood you cut out earlier. Well here is a small use for one of them. Use a 2 - 1/2” hole saw and cut four discs out. Then saw a 1/4” slot from the edge to the center hole in each of the disc’s. This is for the wire to slide into.

And here is how it works. Put a small screw in to hold the disc in place and you have the holes covered.

You are looking into the tunnel and this is what you will see when you put a turbine in to the tunnel for testing. The 3 speed control switches and fan motors are all here and ready to go. Now if you only had the testing tunnel part made. So let’s get on it.

From the PVC cutting list on the plans you have cut the eight 45” long pieces that will form the front and back frames of the tunnel. 3 way Tees will be attached the the end of 4 of them. Lay the assembly on a flat surface to make sure the Tee’s line up. 

Then you can add the other two pieces. Be sure to hammer everything together with a rubber hammer to make sure the pipe’s are all the way into the Tee’s. Then put a 3/4” lath screw into each pipe and Tee. These frames are never taken apart.

Now the four shorter 43 - 1/2” pipes can be add to set the distance from front to back of the tunnel. This distance needs to be less than the 48” so the 48” vinyl can be wrapped around the pipe and attach to the black hook and loop material. One full length piece of hook and loop material is needed on each of the bottom sides of the tunnel.

This is the part where you secure a piece of 20ga annealed stove pipe to the PVC frame in four places so that the tunnel can be attached to the fans. The 5/32 X 7/8” fender washers are held inside of the frame with screws and the wire is twisted around the screw.

Two #10  - 1” sheet metal screws are put into the back frame pieces for the wire from the tunnel to be fastened to. Use a figure 8 motion to secure the wire and it will hold better and be easier to remove when taking the tunnel down for storage.

Here you can see how the rubber hammer is used to to make sure the joints are together. You can also see the strip of hook and loop that will be on the bottom edge of each side of the tunnel.

A word about attaching the 4mil vinyl. The hook and loop material has an adhesive backing. I had pretty good success if I put a the hook and loop material together. Then I adhered the loop side to the PVC frame where I wanted it. Then I started in the top center of the vinyl and pulled off the tape so I could stick the vinyl to that piece. Then I worked from the center out doing the same thing. Removing the tape from the hook and loop stuck to the PVC and then sticking the vinyl to it.

Another ting to do is to place a tape marking the TOP FRONT cross piece frame and another marking the TOP BACK cross piece of the frame. Remember these frames a never taken apart. Only the shorter pipes connecting them together come out. Taking the pipes apart is best done using the rubber hammer.

As a little bonus I cut two of the scrap plywood discs and made some plates that can be set on the top of the tunnel. The back one holds the power strip the the fans plug into and had a switch that can be easily reaches to start and stop the fans. The front piece is where you can set the Lab Quest data collection equipment.

So there you have it. A KidWind wind tunnel that will get you wind speeds of 4 m/s or less for less and $500. If you have questions or comments post them on the blog and I will try to help you out.

Dick Anderson

Wisconsin KidWind Advisor