Reciprocal rafter assembly

 

In my mind this is what the 12 five inch diameter 8 foot long fence posts will look like in a few days.

In case you’re wondering, like I did, this is the machine used by the people I got the untreated fence posts from looks like. Pretty wicked and very noisy when in operation.

With my fresh load of 12 tamerack fence posts loaded I could begin the process. 

I am not going to go into all the details for designing and calculating a reciprocal roof rafter. Spend a few hours on google and you can see how it is done. But I will say that if the idea of designing and laying out a truss for a hip rafter scares you then a reciprocal roof will be more difficult.

With the rim joists layed out and leveled the first rafter is put in place. The Charlie stick is in place and holding the rafter at the correct pitch angle for the roof. All this is based on the calculations using the diameter of the posts and the “Rummy” (look it up) distance used. 

All the posts were layed out. The lower end of the first rafter was tied to the rim with twine. Now the lay up could begin.
 

Posts would be added and tied to the rim. The last post, number 12, would be slid under the first post, number 1. This would require that the number 1 post be jacked up to allow this. Tricky…

Needless to say it did not go well on the first couple of tries. 

But after a few adjustments and fine tuning on the pitch and Charlie stick success was had. Doing all this with the posts 8 feet in the air at the top of the gazebo would be a real killer if you know what I mean!

The next day it was time to begin the steps to anchor the rafters in place. First the posts were secured to the rim joist with 10” GRK screws.

Now with the bottom ends secure I could drill the holes for the bolts that would lock in place the top ends of each rafter. This would require several steps for each hole and need to be repeated 12 times.

Each hole would need to be located so that it went through the center of both the top and bottom post it sits on. This was no small task and required several visual observations from different angles to make sure it was good. The drill guide used for the framing holes was a big help.

Several different drill bits and parts were used in the process as you can see. I “built” a work table to keep all these tools handy but still had to make many, many trips up and down the ladder and out of the frame squeezing between rafters to do it. 

Here is the small stud bolt that I put in the bottom of each post to help locate, and hold the correct position on the mating post below it during assembly. This stud bolt needed to be removed before I drilled or it would kill my 3/4” auger bit. 

Here are the steps I needed to do for each hole -

1 - Jack up post with handyman jack.

2 - Remove stud bolt.

3 - Lower post and remove jack

4 - Position drill guide and secure to post with GRK screws.

5 - Drill 3/4” hole through top and bottom post.

6 - Change to 2”diameter counter bore bit. 

7 - Counter bored 3/4” hole to match length of 3/4”dia.  12” long ready bolt. 

8 - Change to 15/16” dia. Bit.

9 - Enlarge 3/4”dia hole to 15/16” diameter.

10 - Install 3/4” bolt washers and nuts.

11 - Change back to 3/4” dia. Bit

- Repeat process.

I just had to remember to perform step #3 twelve times!

Well so much for that. #$@%!^&@ I remembered step #3  10 times and then sure enough drilled right into the stud bolt I forgot to remove. My mother would say it was enough to make a preacher swear.

 

And after all that here it is all bolted up. With all the posts and rafter numbered. Re-assembly when the ground thaws this spring should go well. Until then I’ll be working on making the pegs to put the frame together on the shaving horse.

 

  

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.