how to cut top plate seats for NON step-lap angle rafters

[apratti]

Hi folks. Of the two barns I'm working on, one had rafters that used step-lap cuts into the plate. Now I'm working on seating the rafters to another barn that use a 90 deg. vertical into the seat of the plate. (and 37 deg. run-out). Rafters have been cut, but now I have to replace some of the plate and some of those seats. I'm worried about accurately making a 90 deg and 37 deg run-out on the plate - instead of those step-lap cuts I did on the first barn. And help would be great!
Thanks, Amalio Pratti

 

[Don P]

Judging from the responses, this is gonna take a picture  

[apratti]

I am so frustrated at trying to send you this pic. I give up. I'm not good at. this. Sorry

[apratti]

I did it. As you can see, it took some extra courage.
Mario P.

[Jim_Rogers]

Ok, so I guess I'm going to need more information. What do you mean by a 37° run out?
Can you make a drawing and take a picture of it so we can see what you need to cut?

Jim Rogers

[apratti]

Hi Jim. The "runout" is not the right term. I need to make two 37 degree cuts in a plate for the rafter to sit. I will try to add the pic but it is sideways and I can't fix it. My cut is going to be hard to make because it's not a step lap.
Thank you.
 

[Don P]

I'd be tempted to try making a jig to saw each side of the runout angle. A piece of ply shimmed level on the beam with a second piece of ply at the 37° angle on top of it. Then remove the remaining ramp of wood between those lines with a chisel. Map out the rest and sneak up on the fit. I might try to set the depth of the bottom of the 90, or close to it with a small drill bit if the top face allows holding a couple of squares to plumb the bit. A smaller test jig the shape of the rafter tail would make it easier to get close.

[apratti]

Yes! Thank you Don. I'm not crazy. this is a weird cut huh?
Mario P.

[Jim_Rogers]

I'm sorry but I'm still confused about where the 37° cut is being made.

Just to be clear, if you could use the correct terms it may help me to understand.

On the top of the plate is a cut to allow the rafter tail to go out beyond the edge of the plate, thus lapping over. This is called the lap of the rafter seat. Behind the lap is the step, as this cut usually looks like a stair step.
This gives the seat the name "Step Lap Rafter seat".

So the step and the lap have to be in the correct location and the correct angles based on the rafter roof slope.

Normally the step is 90° to the surface of the lap. The lap is the thickness of the overhanging tail, and the step is usually the same as the lap. For example a 1 1/2" lap and a 1 1/2" step. Or 2" x 2" depending on the size of the rafter.

I understand that you want one cut to be 90°. But is that cut 90° to the top surface of the plate?

If the back of the step is going to be at 37° then 37° from level?

Please draw the plate from an end view and draw the lines as you need them to be cut and we call all learn how to cut this joint.

Jim Rogers



 

 

[apratti]

Thanks again Jim. My term "run-out" is the rafter tail part of the seat cut. My cuts are not step lap. I completed step laps for the other barn.
I am sending another pic of it hopefully.... It's sideways - sorry.

[apratti]

I'm giving up. I saw the pic I posted. Now I don't. Thanks everybody for trying to help me. I think I need a break.

[Dave Shepard]

The pic is in your gallery.

[apratti]

Can anyone understand this? I sent pics in this threas. People have sent me directions and pics of different types of seat cuts. I was told I had too many pics in the gallery by the admin of this website. So I deleted them. Then I was also asked to show pics to some people that were hoping for more info.
I don't know what to do here folks. If nothing happens, I wish to thank you all for your interest in this thread. I believe there are pics to help explain this problem in this thread history. My basic problem is that I have to cut a NON- typical Step-Lap Seat on my plate.
You all all wonderfully kind folks willing to help. Thank you, Mario P.

[apratti]

BTW: Don P. picked-up on this weird cut and offered info. But no one has seen or known of the correct procedure for making this cut yet.
Mario P.

[apratti]

 

 

[apratti]

 

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I have a hard time understanding how to post a photo on this websight. The directions included six steps which I didn't understand. By the time I figure out this... my barn will have a new roof. Anyway...here is a pic (I hope - because I'm seeing it as I'm typing in this post) of my seat plate seat problem. Any help would be great.
Thank you! Mario P.

[Jim_Rogers]

How much is the lap distance? is the step depth the same? where is the 37° angle from level? or vertical? add to your drawing, and re-post.

This shape of seat is one thing, but the same shape in the rafter could create a point where the rafter could split.

How do you know it's 37°? do you know the pitch in inches? Is it a 9/12?

Jim Rogers

[apratti]

Yes Jim. I measured the pitch 9/12 ish with the old rafters sagging. Not perfect. But the 37 deg is exact to my rafter beam which I installed (there was no beam originally). And span has also been done. So 37 deg for the lap and the step which is abruptly interrupted vertically 90 deg to the plate. There are 16 of these cuts originally. I need to make 6 more where I replaced the plate. Is this as odd as I imagined - or have you seen this kinda seat before?
Anyway - I'm still waiting to cut the plate and I think I will just do step lap and cut my rafter. I just wanted it to be close to original specs.
Thank you, Mario P.

[Jim_Rogers]

What is the depth of the lap? what is the depth of the bottom of the vertical cut in the step?

I can give you step by step instructions of how to lay this out and cut it but we/I need to know these dimensions.

Jim Rogers

[apratti]

Thanks Jim.
Vertical depth is 2'' at the step. I will need to measure the lap depth but I would guess 2+3/8 or close. I agree about the splitting possibility of the rafters - but none of the old rafters show signs of stress at this joint. I do see the plate suffered from this cut, as splitting is evident at the vertical 90deg mark.
Thanks for your help!
Mario P.

[apratti]

Jim - The exact seat measurements:
Step is 2 -3/4" vertical 90 deg
Lap is 2 - 1/2"
Length of seat cut is 6-3/4"  across top of plate
MP

[Heartwood]

Plumb abutments were fairly common in historic structures; see the following from "Historic American Timber Joinery" by Jack Sobon, available from the Timber Framers Guild.
I think it would be easier to cut the plumb step first, cutting a block at 37 degrees to guide your chisel on the sloped side and using a bevel gauge set at 90 degrees (and has a mitered end to the blade to get into the angled space) to check from the top surface. Down-cut the sides with the chisel first then pare out the waste. Then crosscut the sides for the outer lap and pare away, using the block as a guide.


 

[apratti]

Wow thanks! I didn't even know what it was called. I appreciate the advice and agree. Well - it looks like I got a some work to do.
Mario P.

[Jim_Rogers]

Mario:
I drew the profile of the joint as if it was on the end of an 8x8 timber. And added all the dimensions for a 9/12 pitch roof.
Most of them agree with your measurement.

see attached pdf file for a print out copy.



 

Let me know if that helps.
as far as cutting goes you can follow Heartwood step by step if you wish.
Jim Rogers

[apratti]

Jim - Thank you for taking the time to prepare this! I'm sure it took a while.
And I'm very grateful for everyone's help on this too.
I've begun to cut. I'll tell you now, this is some work. Slow too.
The old seats look so effortless and mine look I'm angry at the wood.
The old way must have some tricks I'm missing. Any additional advice is gratefully appreciated.
I see what you mean about rafter split when I saw 2-1/8 parallel to lap..
Mario P.