set back mortises
#16022
06/25/08 11:07 PM
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mo
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Hi all, I have seen this practice in a few shops now and was wondering how many are designing and cutting like this. Basically instead of mortising from the face of the intersecting timber the mortise is then inset X from the face so that four shoulders are created. I guess shops do this reduce visible sloppy mortises but I think it only adds to the problem ("just cut the tenon back some more" or lay-out doesnt need to be perfect). The braces are cut the same way (setback mortises for lack of a better term) only adding to design time for stick drawings, layout time, cutting time, and alleviating the consequences for bad mortising and cutting. Only on pieces with out housings in mill rule. Does anyone think that this adds up to too much wasted time (a lot more tooling, I'd would say twice as much on the stick below)? *not to scale
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Re: set back mortises
[Re: mo]
#16024
06/26/08 12:23 AM
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mo
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No, three times as much 1. Layout a. shoulder to shoulder b. tenon lengths c. tenon placement (top and bottom) * d. lay-out "setback" 2. Cutting a. end of tenon cut (big saw) b. layout tenon (endgrain) * c. layout setback (endgrain) * d. Drop cut setback ((this would be tricky on one side, unless you want to flip the timber, Argh! not anymore than I have to),kerfing too much time)). e. Drop cut tenon cheeks * f. cut little shoulders g. cut real shoulders Basically disregarding lay-out you would have to make 8 extra saw passes (two ends). one being very trick if you do not want to kerf. One more saw depth set. This is just the quick stick (not the brace)
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Re: set back mortises
[Re: mo]
#16026
06/26/08 01:07 AM
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Joined: Nov 2003
Posts: 1,124
Mark Davidson
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I use this if the tenon/mortise are taking away too much wood, as in the rafter tenon below
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Re: set back mortises
[Re: mo]
#16027
06/26/08 01:12 AM
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Joined: Dec 2007
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TIMBEAL
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I don't see it taking three times as long, but quite surely more cutting. I am looking for short cuts, ways to lessen the time. Surely not on braces and or to hide a mortice after a few years of drying.
I do a similar cut to the tenon on a english tying post, the one going into the bottom of the tie beam. The post is flared or fan tailed and is 13"x9" at the top. The plate uses up 6" and the tie tenon is 6" leaving 1" on the shoulder as you have shown. I do this because in the past I have been left with a 11-1/4" post top and had to make adjustments I didn't like. So now I saw them a bit deeper and have plenty of wood for my tenons. Also this is the case when the post has a live edge on the inner face, plenty of wood then. Tim
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Re: set back mortises
[Re: TIMBEAL]
#16028
06/26/08 01:17 AM
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TIMBEAL
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And as Mark shows also, even more so if the rafter is pushed out to the slope. If it is my choice I cut them like Marks drawings. You can see the tenon on the post I referenced. Tim
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Re: set back mortises
[Re: TIMBEAL]
#16035
06/26/08 03:20 AM
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Posts: 687
Gabel
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We do it often in high-spec jobs where shrinkage will create a peeking mortise.
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Re: set back mortises
[Re: Gabel]
#16036
06/26/08 03:25 AM
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Posts: 687
Gabel
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It is called boxing the tenon.
(I miss the edit)
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Re: set back mortises
[Re: Gabel]
#16044
06/26/08 01:08 PM
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Joined: Apr 2002
Posts: 895
daiku
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We do this on post top tenons when square ruling. If the post is 1/4" wider than called for, we trim the tenon back 1/4" to the correct measurement. Secondarily, it hides the mortise when the post shrinks (as Gabel mentioned). We don't do it on girts, which are usually housed - we'll cut back the entire end, not just the tenon, and use a gradual reduction, not a square cut. CB.
-- Clark Bremer Minneapolis Proud Member of the TFG
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Re: set back mortises
[Re: daiku]
#16047
06/26/08 09:24 PM
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Joined: Mar 2002
Posts: 965
Ken Hume
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Hi,
Another reason for cutting back on the edge of a tenon is to remove sap wood and hence to frame a joint using only heart wood.
Regards
Ken Hume
Looking back to see the way ahead !
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Re: set back mortises
[Re: Ken Hume]
#16051
06/27/08 01:07 AM
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Joined: Nov 2003
Posts: 1,124
Mark Davidson
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I don't see why it takes much longer to do this. You have to cut the tenon full size, then sizing it down afterwards is pretty quick. This is a good job for the handsaw.
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