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Author Topic: verify soffit tenon location and size  (Read 341 times)

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Offline windfall

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verify soffit tenon location and size
« on: August 18, 2017, 06:31:14 pm »
Need to make sure from what I have read...that I am fully understanding the location of a soffit tenon and a few other related questions...The joists are 6x8x12ft in between tie beams which are 9x12 x24ft  One end of the joists will be drop in, and the other end will be soffit tenons.  The drop ins will be a full 6" inch wide seat by 1 1/2" deep, down from top side of beam 6".  Does this end sound alright?  The other end with the soffit tenon would be a 2inch thick by full width tenon 4 inch long.  This tenon, if I understand this part correctly, will be centered on the 6 inch mark, mid way down the tie beam, so that half of the tenon is above the neutral plane axis and half below?  Correct? From what I have been reading this is the best location to locate this type of tenon?
Both bottom  ends of the joist will be tapered to the 8 inch depth of joist.  Anything here sound a bit off?  Should I increase soffit tenon thickness to 2.5 inches?  I'm using this method as I lack help and am trying for ease of installation but also retention of meat in the tie beam....Thankyou again for any help!!

Offline Jim_Rogers

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Re: verify soffit tenon location and size
« Reply #1 on: August 18, 2017, 06:47:52 pm »
Are the timbers rough sawn?

If so you may need to "size" them to a constant size to match the pocket you are dropping into.
If the drop in end is 6 1/16" or larger it will not drop into a 6" wide pocket.

Square rule joinery usually says: "size each joint 1/2" under the timber size".
So your drop in pocket and end should be the same width and depth.

Jim Rogers
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Offline windfall

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Re: verify soffit tenon location and size
« Reply #2 on: August 18, 2017, 11:34:32 pm »
Hi Jim...yes they are rough sawn.
Does my soffit tenon location make sense?
Thanks steve

Offline Jim_Rogers

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Re: verify soffit tenon location and size
« Reply #3 on: August 19, 2017, 11:26:08 am »
Hi Jim...yes they are rough sawn.
Does my soffit tenon location make sense?
Thanks steve
I think so, but it's hard to tell without a drawing of it.

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

Offline windfall

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Re: verify soffit tenon location and size
« Reply #4 on: August 19, 2017, 12:38:52 pm »
I understand...I found a few more bits of info from past postings on the soffit depths, locations etc...the 4" soffit tenon length seems to be the magic number with the size material I'm using.  Staying just above the neutral axis with the soffit mortice  I understand...what type of angle would you use on top side of the mortice for the joist to slip into? thanks

Offline Jim_Rogers

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Re: verify soffit tenon location and size
« Reply #5 on: August 20, 2017, 11:33:57 am »
One way to determine what slope you'll need is to set up on four saw horses the two beams that the joists will connect to. Place them the correct distance apart and at the same elevation. Basically set up a test fit.
Next try and slide in the tenon until the other end will drop into its pocket. Trim the tenon/housing/mortise as needed to make it go together.

That's the best idea I can come up with in order to fit these timbers together.

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

Offline windfall

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Re: verify soffit tenon location and size
« Reply #6 on: August 20, 2017, 12:43:19 pm »
Jim, thanks again for the ideas, test fit day is coming soon...a bit anxious!