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Preferred Mortise & Tenon

Started by SwingOak, July 23, 2008, 10:25:09 AM

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SwingOak

As I'm reading about timber framing in a few of the books I've bought, as might be expected I'm coming across a few contradictory methods and recommendations. So  I thought I would ask for the opinions of some of you experts.

Which is the better mortise & tenon joint for cross beam to post connection, shouldered or fully housed? Which takes less time to cut, and/or is easier to get perfect? Is one stronger than the other?

Is it better to drill peg holes after the joint is assembled, or drill the holes so that the joint tightens when the peg is driven home (draw-pinning)? If draw-pinning is preferred, how much offset in the holes?

One writer favors a pegged lap joint for sill beam corners, while another says a blind mortise & tenon is better as it protects the joint from weathering. Is one really better than the other?

I'm sure I'll have more questions as I learn more, but that's the way it works - right?  :P  :)
Thanks!

Jim_Rogers

Quote from: Lurcherman on July 23, 2008, 10:25:09 AM
Which is the better mortise & tenon joint for cross beam to post connection, shouldered or fully housed?
I'm not totally sure what you mean by shouldered, without a picture of what you think this means, or if you can point us to a book/page/drawing of what you mean. But a fully housed joint is what is usually done in square rule timber framing. As the joint has to follow a "general frame rule" to be undersized by a standard amount less then the actual timber dimensions.

QuoteWhich takes less time to cut, and/or is easier to get perfect?
Well, again not sure about shoulder joint, but if you mean one that is cut at an angle so that only the bottom of the joint has a housing then this may take less time, as you're not cutting into the post for the top of the housing. But then again you're making two angle cuts one for the shoulder housing in the post and one for the shoulders on the cross beam. It maybe harder to get these two angles to line up.

QuoteIs one stronger than the other?
Possibly, it really depends on a lot of factors. Each joint has to be looked at as part of the entire bent and then the entire frame. How this joint is effected by other joints near it has to be looked at as well.

QuoteIs it better to drill peg holes after the joint is assembled, or drill the holes so that the joint tightens when the peg is driven home (draw-pinning)?
Well, we call it draw boring. And there are several opinions on this. Some say it has no value, but we have always done this and we can see it pull joints together when we assemble them. And with the peg being somewhat bent after it has been installed it can add a spring like effect to the joint. When it drys a little the peg could help keep the joint tight.

QuoteIf draw-pinning is preferred, how much offset in the holes?
Depends on the types off wood being used. Less offset for hardwoods then softwoods.

QuoteOne writer favors a pegged lap joint for sill beam corners, while another says a blind mortise & tenon is better as it protects the joint from weathering. Is one really better than the other?
I would think that you would agree to have a joint properly protected from "weathering" would be the best joint to use.

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

Brad_bb

I think you are thinking correctly Jim, I think he means where a beam sits an a small sholder on the bottom but the sides are not housed vs.  a fully housed beam in a post.  It would be more typical to find the first in a mill rule frame (where you assume your timbers are square to start with), whereas the fully housed joint would be more likely found when using square rule layout technique like Jim said.  In square rule layout, you assume your timbers are not square and must compensate.  You do this by establishing a particular set of layout rules(which is too long to explain here and now, but there have been past posts about square rule).

Which takes longer?  hard to say.  Depends on the framer perhaps.  There seem to be more steps in fully housed, but then again if doing the angled shoulder, getting the angle right might make up that difference too. 

Yes, here we typically call it draw boring.  The holes are bored through the mortise sides, then the tenon is inserted and marked with the tip of the bit.  Pull the tenon out and use an awl to make an offset mark and then drill the tenon with the offset mark.  The holes should be bored offset by the amount of your marked offset with the awl.  I've heard as much as 1/8 inch for pine.  Go less for hardwood.  I haven't done much of it myself yet.  I've heard that it's more critical to draw bore joints that are in tension, while compression joints don't need it.  As Jim said though, it may make a difference if working green wood for when it dries and shrinks.  Housing joints would also help hide gaps that would open up and be visible in a shrinking mill ruled frame.
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

SwingOak

Sorry guys, I tried to link to some pictures in you-know-where but FF won't let me. I'm having some trouble putting them in my gallery here. Hopefully I'll figure it out soon...  :-[

moonhill

Scribe rule frames didn't have shoulders, for the most part.   They were pegged in the way Brad mentioned, but square rule peg layout isn't tested and marked, they are just laid out with the square and bored.  Tim
This is a test, please stand by...

SwingOak

OK I think I've got it. Here is what I mean by fully housed joint, per Sobon's book:



And this is what I mean by Shouldered M & T, as per Benson's book:


moonhill

I think the Benson pix is a haunch or more likely a diminished housing.  I like them for the way the grain of the wood works, it's slick work.   Tim
This is a test, please stand by...

Jim_Rogers

Quote from: moonhill on July 23, 2008, 08:40:39 PM
but square rule peg layout isn't tested and marked, they are just laid out with the square and bored.  Tim

Tim, I agreed and did this for many years. Although when I went to Guild raisings I saw this process of boring the mortise peg hole first, test the tenon in the mortise, poke the tenon with the bit, remove, move offset, and then bore the tenon hole as the standard procedure. Upon doing this myself (the method you have mentioned), here with my students we would often have tenon holes in the wrong place and have to plug and re-bore. Not completely understanding why this would happen, but it did, we moved to this "Guild" method.
This helps to insure that the tenon fits the mortise as well as places the tenon peg hole in the correct location for draw boring.

So, what we do now is cut all the joints in all the timbers. Then just before the raising we do a full frame fit up. This is testing each joint's tenon to each joint's mortise, one on one, in one bent or wall assembly. Then once each bent's joints have been tested one on one, we put the entire bent together, check for square and true dimensions. When all adjustments have been made, if necessary, we then poke the bit into the tenons and remove and offset the holes, and bore the tenons. By doing this, in this method, we have insured that each joint will fit together, and that the entire assembly will fit together. And this make everything go together very easily and quickly on raising day.

When we put things together like this frame:



which is a 12' x 16' garden shed, it can be done in three hours.



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

Mad Professor

Any reason NOT to have a joint housed AND shouldered?  If the beam is weight bearing seems like the right thing to do if the housing is not sufficient (deep enough) to take the weight off the tenon.  It also takes less wood out of the post than a deep housing.

If I can figure out how to post a picture I'll post a picture of a housed and shouldered joint laid out with scribe rule. 



SwingOak

Quote from: moonhill on July 23, 2008, 10:20:59 PM
I think the Benson pix is a haunch or more likely a diminished housing.  I like them for the way the grain of the wood works, it's slick work.   Tim

Sobon calls it a "diminished haunch".

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