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Author Topic: Cutting a step lap rafter seat at recent workshop in Nebraska  (Read 352 times)

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Offline Jim_Rogers

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Cutting a step lap rafter seat at recent workshop in Nebraska
« on: October 24, 2017, 10:57:22 am »
During the recent workshop at VictorH’s Nebraska site we had to cut many step lap rafter seats in the two plates.
Here is an example of the joint:

 

 

Here you can see that the 45° slope that is the “lap” where the rafter tail laps over the plate. And the back section is know as the step as it appears like a stair step. Normally these two things are the same depth. In other words the lap is 2” and the step is 2”.
In the above picture the combination square is set at 2” of depth. When you hold the combination in this position you can check the slope of the step as well as the depth.

The way I was taught to cut this joint is to cut the slope first. We do that by cutting the sides of the lap with a saw. Normally a hand saw. But VictorH created a jig for his skill saw to ride on at a 45° angle.
As shown here:

 

 
 
This worked great and VictorH was able to cut all of the set lap sections except the very end one as there was no place to rest the jig.
The crew cut the laps and then it was time to cut the steps. Gordon, one of the members of the crew said he used a router to cut a relief in the plate so what when he chiseled out the step the wood could release and it worked for him.
We thought we’d try it. VictorH when to the hardware store to see if he could buy a “v” shaped router bit. They didn’t have any.
And VictorH’s router was not a “plunge” router. Gordon suggested that we bore a hole in the plate and then use the fixed router to cut the relief.
So we set up a power drill to drill a hole for the router bit to set into:

 

 

Next we set up the router with a standard straight router bit and cut a line down the middle of the step:
 
 

 

We had many of these to do.
Kevin and his son developed an offset jig with a framing square to rest the base of the router against so that it would cut a straight line:

 

 
 
In the above picture the yellow framing square is the jig, held in place with two blue clamps
This worked great and we were able to cut all the step lap rafter seats in the two plates.
Here is one of them during wall fit up:

 

 

I often tell the story about when we did this joint in another frame many years ago. My friend Peter from Boston was here with the group and he asked if we should cut the lap first or the step first. I suggested to him that he could try it each way and see which way worked best for him. He did and he cut the lap first on the first one. And then cut the step first on the second one. He soon found out that cutting the step first was much harder to gauge as to whether or not if it was cut to the right shape. We learned that cutting the lap first is the way to do this joint.

I just wanted to share with you one way we found to cut the rafter seats in the plates.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline Dave Shepard

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Re: Cutting a step lap rafter seat at recent workshop in Nebraska
« Reply #1 on: October 24, 2017, 01:18:01 pm »
One of my favorite joints, if there are no big knots.  ;D

How long did it take per joint? I just did the plates for my 12x16 frame. 4" wide 2"/2" step laps took 73 minutes and 75 minutes per plate with 9 laps each.
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Offline Jim_Rogers

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Re: Cutting a step lap rafter seat at recent workshop in Nebraska
« Reply #2 on: October 24, 2017, 01:43:50 pm »
We didn't time them so I don't know. They were done over several days. We did 11 on each plate.

At one time we may have had three of the crew working on one plate. Usually at least two working on it as it was 20' long.

Jim Rogers

edit PS: One of the plates was hackberry, I don't recall what the other one was.
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Offline VictorH

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Re: Cutting a step lap rafter seat at recent workshop in Nebraska
« Reply #3 on: October 25, 2017, 12:29:44 am »
Nice write up Jim!  Both plates were Hackberry.  They worked easier than I thought they would,  they were green having been felled about 10 weeks and sawed 4 weeks before the workshop.  I would not want to work with hackberry after it has dried much.  A friend and I screwed some dry 1" up on his shed and the torque style deck screws were snapping off before we were even through them.  We had to pre-drill them.  Dave, I cut 7 and finished up an 8th in about 2&1/2 hours.  That was just the chisel work. The jig certainly made that first lap a lot easier.  I was using the jig in a way that I was pushing the saw uphill, next time I'm going to set the plate on ponies and run the saw downhill.  That should help with some of the fatigue I felt while cutting all 11 at once.  I only had one small knot to deal with.  I was pleased with my time on them as I had never cut one before and that 7th went faster and looked better than the first.
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