Wednesday, 21 November 2012

Timber Framing 7 - More Scantlings

After the full fitting of the entire bent there are a few things that still need to be done.  

While the come alongs are still in place and keeping alignment perfect we go around to all the joints and drill the pegging holes.  The knee braces all receive three holes 3/4", and the rest of the joints receive one or two 1" holes.  

Knee brace with 3/4" holes drilled for pegging.

Hammer Post and Rafter joint with 1" holes. 

Additionally, the edges of the timbers receive chamfers, the through tenons all get an end treatment, the ends of the hammer posts get a pendant carved onto them, and in our case, the principal posts needed to be shortened to match one which was cut too short by mistake. 

Jamie routing a chamfer profile onto a hammer girt.

The curves on the knee braces are drawn out using a quarter point technique.  Quarter point allows for scribing a perfect arc without the need for a large trammel so it works great in this situation where the knee brace arc has a large radius.  A chainsaw is used to rough out the curve to about a quarter inch from the scribed line.  Then, a curved base planner makes short work of shaving down to the line. 

Roughing out the curve with a chainsaw.

When all the odds and ends have been taken care and the timbers are ready to go the end grain is coated with end seal to help preserve it.  This is particularly important when working with green wood as it will help slow the seasoning process and thus reduce checking and other deformation.  Once threated with end seal the components are stacked up and will wait for pickup.  

Ends are sealed and the timbers are ready to go. 

Monday, 19 November 2012

Timber Framing 6 - More Test Fitting

So there is actually quite a bit of test fitting to be done before the whole structure can come together.  A joint which contains a knee brace has 4 fittings to be done.  The connection below is of a principal post and a connecting girt and their knee brace.  

These three joints require four fittings. 

- The knee brace with the principal post. 
- The knee brace with the connecting girt.   
- The connecting girt to the principal post.  
- Lastly, the knee brace with the principal post with the connecting girt.  

While this may sound a bit tedious, it is necessary so that small problems can be located at each individual connection and there is less of a chance for a large unknown error to show up later.

Of course there are a total of 54 joints in the structure, and with all the testing it takes days of to peice the project together. 

My joint from above, drilled and ready for pegging upon assembly.  

A tight fitting joint with a 3-4-5 closing under 1/32"

We work together to bring the components together.  The pieces are large and it takes a couple people maneuver them.  That being said I did get quite a bit of personal satisfaction when this joint came together.  I built the components (principal post, connecting girt, and knee brace) that are joined together here, so when it came together with ease on the first attempt I was pretty happy.

Jamie dancing upon a tight fitting joint. 

Richard persuading a joint to come together. 
Test fitting a set of rafters with their purlins. 

We cleared out the sawhorses and components under construction to make room for the assembly of the first bent.  We are building a set of sub-assemblies which will be joined together.  The anchor beam with two knee braces and the hammer posts are one assembly and the principal post with hammer girt and knee brace on each side are additional sub assemblies.  These three sub assemblies are then connected and the rafters are joined on to complete the bent.

Most of the components from bent 1 laid out for fitting. 
The three sub-assemblies are brought together into one assembly.  The rafters are then joined onto the assembly, which pulls any slight misalignment into place.  The use of center lines creates a series of way points at each of the joints.  These way points can be measured and referenced against each other to ensure triangulation and that the frame is true. 

Bent #1 completely assembled. 

Pretty Satisfying to see it come together.

Thursday, 15 November 2012

Timber Framing 5 - Centerline Layout

In the first timber framing post I mentioned that we are using center-line layout techniques.  This is somewhat different from how I have traditionally done woodworking because for furniture most of the time I use face layout.  As it has been so new to me I thought all my other woodworking buddies would be interested in how to use this technique.  I have tried to take some picture of the process but gave up and decided to make three short videos that capture the process.  One of the good things about this technique is that it does not require stock with is true.  It will work on timbers which are true, those that are askew, and logs too. 

Before any layout can begin the timber must be leveled and well supported.  In this situation level refers to leveling one face of the timber, generally the one with the most joinery, the rest need not be true.   

Step 1.  An approximate center point from which to start working.  
Step 2.  Use the center point and a level to trace a horizontal center line. 
Step 3.  Find the mid point of this line as a reference point to trace a vertical center line.  
Step 4.  From these vertical and horizontal center lines work outwards to create a full square grid. 
Step 5.  Repeat on the other end of the timber.  

In the video I am working on an 8 x 8 timber so the offset lines from center are 3 3/4 inches.  This gives us theoretical timber of 7 1/2 x 7 1/2.  It is this theoretical timber which we will cut our joinery to.  The extra outside the theoretical will remain attached but will  be worked around. 

The second phase of center line layout prep is to connect the grids from end to end using a string line.  The three lines on each of the four faces of the timber are connected to draw out the full length 7.5x7.5 theoretical timber we will be working on.  Once done, accuracy can be easily checked by ensuring the measurements between the lines remain the same for their entire length.  Also, in the case of a bowed timber the locations of the lines can be adjusted to allow for changes in joinery. 

The third component of timber layout prep is a squaring line.  This is done at each location where joinery will be done.  A point is selected which will be a reference point for the joint we will make.  A carpenter's square is referenced true against one of the reference lines drawn in the previous step.  Then a line is drawn perpendicular to the reference lines through the point and off both edges of the timber.  The timber is rolled and the line is continued around from side to side to side returning to the side it started from.  The key is to always reference the lines and not the edge of the timber.  When the line returns to its starting point it should meet itself exactly. 

I am now ready to start drawing out the joint, in this case a shouldered tenon.  The joint is drawn completely from the reference lines looking only at the theoretical 7.5x7.5 timber.  Any extra wood that is outside those lines will be removed along the way. 

Sunday, 11 November 2012

Timber Framing 4 - Some Test Fitting

As we have started to complete some of the components we are starting to test fit the joints.  So here's an overview of the work.  We are building two bents and associated connecting girts and kneebraces.  To provide a point of reference for the following photos of joint testing there is a diagram of one of the bents we are building. 

Plan for one Bent.

The scale and tight fitting nature of the joinery requires using large mallets called beetles and come-alongs to close the joints.  

Testing the left principal post with rafter. 

Testing the anchor beam and the two hammer posts.

Bringing together the Anchor Beam with the Left Hammer Post and their Knee Brace. 

Final Product.

Thursday, 8 November 2012

Timber Framing 3 - Some Miscellaneous Scantlings

So in the last post I showed how to quickly rough out a mortise using a chain mortiser and also a more common way to rough out and prepare a tenon.  However, the tenon I was working on last time was relatively short (about 9 inches long).  When we scale up the tenon we scale up the tools.    ;)

So the basic idea here is to use a circular saw to create kerfs that will guide a chainsaw on the long cheek cuts of the tenon.  These tenons are about 20" long so the extra setup time required is not really a problem when compared with how much wood can be wasted away relatively quickly. 

Circular Saw midway through a kerf cut.

In the following video the shoulders of the tenon are cut with a 10" Makita circular saw and then the guided chainsaw is used to make the long cheek cuts.  (The glitch in the second cut is a 10 minute gap looking for the breaker we tripped.)

Of course the chainsaw only speeds up the roughing out.  The reality is that I still spend a long time creating a garbage can full of shavings cleaning up tenon cheeks afterwards. 

All cleaned up and ready to test fit. 

All of the joints in the building we're making will be pegged, drilling freehand through a 10" post leaves a pretty good chance that I'd be off by quite a bit by the time I got the other side.  To help make sure that the holes are perpendicular we're using a guide jig which the drill bit is aligned with until it's trajectory is well established.   

Hole Drilling Alignment Jig.

As we're been working through our wood pile we have discovered that we were short on timber for one of our hammer posts.  We require a 6x10 at least 10 feet long.  This was a good excuse to fire up the wood mizer band saw mill.  

Sunday, 4 November 2012

Timber Framing 2 - Mortise and Tenon

The mortise and tenon is the king of joints in timber framing.  It has a myriad of variations to be used in the wide range of joinery situations that come up in a timber frame.  Whether it is augmented by simple pegging, draw boring, or wedges it is used everywhere.  So find below some of the making involved in some mortise and tenon joinery. 

Fist off, the tenon.  
Prior to the video starting a circular saw was used to kerf almost down to the tenon cheeks.  The bulk is cleaned off with a chisel and then pared down with a slick.  Then back to the chisel to define the base of the cheek (end of video) and then to a jack plane to finish off.  The video is sped up 3x, it is a lot funnier to watch that way.  

Hand tools are still the go to for final cleanup and precision. 

Flip the board and repeat. 

The mortise video only shows the roughing out by using a chain mortising machine.  It's a pretty cool machine, essentially a small chainsaw guided on rails.  This mortise is 2 inches wide, 8 inches tall and 5 inches deep.  Six and a half minutes is a pretty quick rough out.  It is followed by paring with a chisel to clean up the side walls, bottom and corners.  This video is also sped up 3x. 

This particular mortise is on a rafter which will receive principal post and hammer post tenons.  These will join at an angle and thus require a sloped shoulder to get full width joint support.  The slope was primarily cut with a pair of guided circular saws and finished off with a hand saw.