Timber Framers Guild Forums General General Forum Questions mortise and tenon in round timbers

are there folks out there using round timber?
how are you laying out a basic mortise and tenon with shoulders for load bearing?
i normally use a snapline technique for square stock
i was imagining today that most of the cutlines in round work could be created with snaplines....

ok
here is what i have so far
level and plum lines on the end of the log
a line paralel to the plumb line to create the mortise and tenon cuts
two lines paralel to the level line for the shoulder and pegs
then these lines are snapped from end to end

the challenge is squaring around the log from line to line but i can see it will be possible to create a M&T with shoulder this way.....

i would appreciate some feedback on this if you are working in the round
-M.

yes
squaring the shoulders is the hard part
may as well throw away the square...
what i'm doing is cutting the surface of the tenon, staying well back from the shoulder, then using the surface of the tenon itself to square the shoulder....
-M.

Mark:
In order to make any suggestions on your layout work it would be helpful to know what you are trying to do. Are you working round to round, square horizontal member into a round post or round horizontal member into a square post.

thanks, i'm certainly doing a bit of hair pulling
i'm working round to round
cutting a 2X8 inch mortise and tenon
the timbers are around 11 inches in diameter
i'm laying out for the mortise shoulder to bear wieght, as in a principal connection

I hope some of what follows will be helpful.

From your description, I am assuming that you are working with relatively straight logs and that the members will be at 90 deg. to each other. The joint you are trying to layout and cut sounds like a fully housed M&T with the bottom of the housing being the bearing part of the joint. The starting point is to layout plumb and level lines through the log center at each end of the log and snap the lines on the surface of the log. These will serve as your reference for all layout work. Parallel plumb lines on the ends will mark the tenon or mortise width and you can chalk them on the face as you did for the log center lines.

To layout the tenon shoulder, start by marking the shoulder point on one of the reference centerlines. From here........flexible straight edges are a must. I use japanese framing squares for this because they are flexible. Lay a square along the centerline reference with the tail side aligned with your shoulder mark. Tack this square in place with small flathead brads each side of the square. On an adjacent reference centerline, tack another square in place with the tail side touching the shoulder side of the previous square. You now have a reference square..........bend the squares down towards the
log and mark several points on the log along the face of the squares. Do this same procedure around the entire log so that when finished you have marked points around the entire log that will form the line of your tenon shoulder. Connect the dots around the log and you have a shoulder line that is perpendicular to the log center line. To do this I use salvaged pieces of metal banding. The kind that comes off of lumber bundles works quite well since it is long and straight. Wrap it around the log, connecting the dots, and mark your shoulder line. Depending on the accuracy of the tenon faces you can, as you are doing, use the tenon as a reference for checking square on the shoulder.

Using this layout method you can also layout the mortise on the other side of the joint. Layout and cut the mortise first and then mark and cut the housing for bearing. To mark the housing around the mortise you will be scribing the profile of the log on the tenon side to the log on the mortise side. Trial assemble the joint and hold the tenon shoulder back an inch or so from the face of the mortise log. Make sure the logs are square to each other by checking centerlines on the faces. On the bottom of the tenon log.......mark the depth of bearing you want along the centerline using the tenon shoulder as reference. Using a double pencil/pen scriber, set the width of the pencils from face of
mortise log to the bearing depth point. Proceed to scribe the profile of the tenon log onto the mortise log all around. Score the line just marked on the mortise log and remove the housing material to the depth of bearing. I've learned that good scribing is an art that requires much practice.

I hope this brief description helps. If nothing else it will give you a starting point to work from. Methods and techniques vary from person to person so ask around for pointers. Good Luck!

Thanks for this info!!
i do lack a flexible square(trying to build one out of plastic)
How about 2 more questions?
how do you deal with pegging the joint?
how do you deal with "finishing" the timber (erasing the chaulk lines,etc.)
I'm working with a different conception of the join this tlme around-i will be running the tenon sides back into the round log to create a flat area 2 inches wide joining the top and bottom of the tenon. The round log surface is radiused into these flats with an adze.
The mortise is cut and the shoulder area is flattened out.
Then the joint is fitted and the profile of the mortise shoulder is scribed onto the tenon shoulders. This line is scored and again radiused back to the round log surface with the adze.
It would be good to post a photo once the joint is finished....
thanks again
-Mark in Ontario.

the flexible squares have arrived but we had no luck bending them around to the four quadrant lines on the round timbers....
the best results we have is laying a pair of squares on two lines and letting them cross each other above the timber, so one square is touching on the inside face and the other square is touching on the outside face(the short blades of the squares make an X)
i do like using small nails driven into the lines as a register for the squares
this gives four spots on the four snaplines and the flexible squares work great for filling in the lines between the snaplines.....
I would say again that the round work is frustrating but beautiful stuff
-Mark in ontario