There"s so much more to it...

I like to tell the students. "Crossing a bridge in your future will be a bit easier after you have built one or two." Not sure that it sinks in right away but nothing beats doing it to bring the point into focus. Now we are getting into the cutting of Roof Rafter parts. One must become aware of the variations in width and thickness of rough sawn lumber. This will require careful selection and matching of the individual rafter pieces to produce good fitting joints and insure their strength. Once they are fitted and assembled they will need to be marked so when reassembled on the bridge in South Wayne there is no mix-up.

Puzzler - What Business Class Skills will come in handy during the building of a bridge? Why?

Tech Vocab -      =sum( cell+cell... )     Column     Cell    Row

Model re-assembled

The guys made good on their word. They took the model apart and did just what they said they would do.


Here is Alex in the school shop where they did the work. Now it will be on to cutting some Collar Ties , Buttons and more of the 2 x 3 clamps used in forming a 3" camber in the chords of the 32 foot South Wayne bridge #4.

Puzzler - How would you go about drawing a circle using a Framing Square?

Tech Vocab - Trunnel

Hanging from the Rafters...

OK! That is how I would describe the fit and function of the rafter assembly fixture. Looking at the pictures you get the idea that there are several pieces that must first fit together.  Then realize that  when assembled they must fit over the top truss chords and inside to the cleat and seat that will brace the roof to the truss.

Above -  Primary and Secondary Rafters meeting at the peak (Collar Tie not installed yet). The Secondary Rafters act as knee braces from the roof trusses to the bridge truss to control racking from side to side forces.

Above -  All the truss pieces assembled in the fixture. The large squares represent the top chords of the trusses that the notches in the horizontal Cross Brace must fit. At the lower ends of the inside, Secondary Rafters, you can see blocks that represent the cleat and cleat seat. Point where these will be fastened to control racking from side to side forces. Also,  there is a 1/2" Carriage boltsfastening the Cross Brace where it crosses over each rafter piece.

Above - And here you have it! The Collar Tie, at the top, keeps the butt joints of the Primary and Secondary Rafters lined up. In  this picture you can also see mortise slots in the horizontal Cross Brace. These are where the Lateral Braces will be installed to provide strength in the length wise direction of the bridge.

Above - The roof system is complex to say the least. See the Lateral Braces installed into mortises. Look close at the end of the piece right here and you can see the 90 degree shoulder that is cut to stop the piece in the mortise. Tricky! The roof rafters are 8 feet on center. So how long would each Lateral Brace be? By the way these are 1" x 6" boards.

Above - This is how the rafters will be installed and mated to the Lateral Braces. The Primary Rafters are removed and added later.

Puzzler - Why do the Primary Rafters need to be removed and installed later?

Tech Vocab - Lateral Brace - Racking - Mortise - Knee Brace

A full sized assembly fixture ...

Yes a "full sized" (this will be music to some that may feel there has been far too much scale model work up to this point) assembly fixture will be in order to position the rough sawn roof rafter pieces. I will say that IF I knew what I was doing I probably could go right to the real thing and "cut away", as they say! So if you know what you are doing, step up, bring your own wood and cut away. If you are like me follow along and keep tuned, slow but sure, and steady as she goes.

In the close-up above you can see some of the layout lines. The yellow square represents the top truss chord (top plate in house construction) The red line is the Centerline of the Secondary Rafter (this will act as a brace to the truss) it goes below the top chord. The black line shows the edge of this 2"x6" piece. At the end of I have drawn in the Wall Cleat and Seat that will be fastened to the truss web.

Here are the Secondary Rafters. Notice the cuts at both ends. Now getting to this point is no accident and not for the faint of heart.  Most are not going to appreciate the math, calculations and work with our "friend",  Mr. Framing Square required to get this done.

For now the pictures will have to do. The details will follow, so get some rest. You will need your calculator, pencil and paper. Or maybe you can just Google it?

Puzzler - Explain roof pitch and give an example.

Tech Vocab - Blade Clips - Framing Square - Pitch - Run - Rise - Line Length - Birds Mouth - Plumb Cut - Seat Cut - Knee Brace - Sliding T-Bevel

"We'll have this together by Wednesday..."

Bruce and Alex wanted to know when I would be bringing the rest of the .60 scale bridge parts to South Wayne because they would have their truss re-assembled by Wednesday.  As they left my shop in Darlington and headed back to South Wayne with a truck load of truss parts I though that was a pretty bold statement. I had faith in them that they would succeed but by Wednesday?
Well, have a look. Here is the truss in the South Wayne Ag shop re-assembled as predicted by Bruce and Alex.

And guess what? This picture was taken on Tuesday! I went down to Black Hawk to see how they were doing. I dropped off the rest of the .60% model pieces and can't wait to see how they do. I'll stay away for a few days, don't want to get in their way or slow down these guys. Got to love it.

Puzzler - In what order will the next pieces of the .60 % scale model be re-assembled?

Tech Vocab - Floor Joists - Button and Rod - Deck Boards - Secondary Rafter assembly - Lateral Braces - Button and Rod - Wall Cleat Seat - Primary Rafter - Perlins

"Sticky Fun"...

Taking some time off from the "Serious Fun" of bridge building to have some sweet "Sticky Fun".  The first batch of syrup has been made. This is what 40 gallons of sap looks like after 15 hours of boiling. Imagine the smell of Maple sap boiling away. It has been a long winter. Go ahead, as the steam rises and swirls around your head, breath in and let your sense of smell enjoy this time of year. Ahhhh...

 A foaming boil like this is a sign that the process is close to complete and the syrup ready to be drawn off. Just like with the Three Bears, the hydrometer is the proof that the concentration of sugar is,  just right. This is critical.  Taste, color and thickness all depend on the 211 degree hot test for a 32 reading. Ah, "just right".

And here you have it, a gallon of the golden fluid, filtered through a linen dish towel. Bring on the Eggo's and lets eat!

I did manage to fit in a bit of work on the bridge while the sap was boiling too. Study the pictures of the 3/8 scale model of a roof rafter. (Note: the truss is on its side but the fit is very good.) Can you see the button and rod assembly?

If you study the two pictures above you can see an important difference. In the bottom picture the primary rafters have been removed and only the secondary rafter, collar ties and diagonal bracing remain. This is how the actual rafters will be installed. After they are secured to the top chords with a button and rod the primary rafters will then be added.

Puzzler - Can you explain why the rafters need to be installed this way?

Tech Vocab - Collar Tie - Primary Rafter - Secondary Rafter - Diagonal Brace - Wall Cleat - Wall Cleat Seat

esreveR gnireenignE

Taking things apart and in the process "thinking" about how and why, this or that was done is what Reverse Engineering is about. And lets face it "serious fun". Black Hawk high school students, Bruce and Alex spent the afternoon Sunday doing just that.

After going over a few of the finer points about the process and reminding them that this .6 scale model would need to be transported to Black Hawk high school and re-assembled, they said no problem! Got to love that spirit.  No doubt in my mind that they will succeed one way or another.

Step by step they move through the process - remove the roof - remove the floor - disassemble the truss. Now let the "serious fun" begin.

Really, how hard can it be...?

I mean after all Milton, in his book explains the process of re-assembling the truss parts like this.

   "To insure perfect alignment, drift pins made of sharpened trunnels are used and driven into holes which have been well lubricated with heavy cup grease.
   First, two members are lined up with short 7" pins (note: his 120 foot bridge used 3 - 1/2" by 14" chords 32 feet long!). Next, the first layer of lattice is pinned in place with a drift pin 3 - 1/2" longer than the first, and the second layer of lattice is secured with a still longer pin. This takes place in groups located near end joints.
   When the next chord member, which makes the fifth layer, is laid out, a longer and blunter pin is used which forces the first shorter pin out and replaces it through the five "layers". As the final chord members are laid out, the second short pin is replaced with a trunnel if alignment appears correct. From then on, trunnels are used in well greased holes to punch out and replace other drift pins.
   Before full length trunnels can be driven, a block supported by a jack must be placed near the driving area, to back up the timbers and prevent them from bouncing."

Translation - Lay down and pin together the first two chord layers (layers 1 and 2).  Place web layers 3 ans 4 on top and pin them together where they intersect each other (DO NOT pin them to layers 1 and 2 at this time).  Begin to pin one end of top a bottom chords to web lattice. Continue to move along down the web lattice pulling or pushing chords to line up holes and pin with 4 layer long drifts. Camber will now be in chords. Add layer 5 and pin with drifts. Add layer 6 and drive in trunnels. Use petroleum jelly as a lubricant for drifts.

Hint - Unless you plan to do some digging plan ahead by making sure that the false work is high enough to allow for the drifts to be driven out and removed.

So, how hard can it be?? After having read his book several times I think...  The old saying is true.
I hear it, I forget.
I see it, I remember.
I do it, I understand.

Eureka, Got'er !!!


Puzzler - At 2.35 pounds per board foot each 32' long truss will weigh in at around 2800 pounds. Using only manpower how will the re-assembled truss be raised to the vertical position?

Tech Vocab - Ginpole - Lifting Yoke - Cribbing - Block and Tackle

A super size Puzzler ? ...

Well I have gone and done it now. After days of building up layer after layer and clamping them in place the deed is done. I have reduced what was recognizable as a lattice truss (see previous post) to six layers of boards!  This could be risky as I tend to avoid jigsaw puzzles made of over 100 pieces. I must be out of my mind.

But I will try my best. If you study the pictures you can see some of the techniques I used to identify the pieces to help insure proper re-assembly. Each truss has three simple main parts, Top Chord, Bottom Chord and a Web. The Chords are located on both sides of the Web and can be further identified as Inside or Outside. Keep in mind there are six layers of wood that make up each truss and the layers are put down one complete layer at a time. Did I mention that each CHORD is made up of two layer of wood and it takes 2 and 3 lengths to go the span distance for each layer.

Talk about confusing?

In an attempt to simplify things (if at all possible) I used a deck of cards (a little something I picked up when I built my log cabin in 2004). Red suit Bottom Chord joints. Black suit Top Chord joints. Then I used metal number stamps on all layers 1 through 6. Layer one pieces got a "1" stamped on each end and each outer edge. Layer two a "2" stamped and so on... For the Web lattice, each piece was numbered with a Sharpie and its location numbered likewise on the outside edge of the Chord where it is located. That was easy, right?

Looking ahead, one of the things to keep in mind will be "materials handling" and "stock rotation". With the 3/8 model this is child's play. However when it comes to a 20' long 2 x 12 moving these will require a good breakfast, if you know what I mean.  Build in Darlington, Transport to South Wayne, apply finish, Transport to Bridge Site and re-assemble?

Puzzler - Will it work? Remember the truss assembly must start with layer #1.

Tech Vocab - Parallel wood clamp - Drift Pin - Chamfer

How much difference could 1/4" make?

Glad you asked. Take a look at this. 

To the right you can see the handy-dandy little hole locating gage that I made for trunnel hole layout on the lattice web intersections.

See anything "out of place" in the picture above? Time for a little puzzler. #1? What is the actual size of a  1 x 4 board from the lumber yard? If you said 3/4" by 3 - 1/2" you are correct. Keep going. For the full size South Wayne bridge the lattice will be made from rough sawn 2" x 10" material. #2? In 3/8 scale what should the size of wood for lattice pieces be?  If you got out your slide rule and converted 3/8 to .375 and then multiplied that by 10" and said 3 - 3/4" you are absolutely correct again!  The difference between the width of the 1x4's I purchased from the lumber yard for the 3/8 scale model and what I really needed? You guessed it 1/4".  I dismissed this "slight difference" as no big deal.

Had you been working with me you could have pointed out the folly in this before, I learned it the hard way. You can see that the top hole is way too close (actually 3/8" in 3/8 scale) to the edge of the material. Arnold A. Graton advised me to keep 2" ( that's 3/4" in 3/8 scale) of material beyond the outside diameter of the trunnel and the edge of the piece.  The bottom hole is the way it should look.

 

Ah, there it is. Looks much better with a little more "meat" between the hole and the edge of the wood piece. Don't you agree? Much more strength.

 With the help of my trusty drill guide (used 1" PVC pipe and a couple of mounting blocks) I got down to the serious business of drilling over 120 - 5/8" diameter holes straight and true.

And here you have it. One Town Lattice truss, cambered, layed out, drilled and marked?

Puzzler - Since this truss must now be un-clamped and removed from the false work for transport and installation of the trunnels how would you mark the pieces??  Keep in mind they must be reassembled exactly as they were drilled or the trunnel holes will not line up properly. Flip, flop or flip and flop (there is a difference) one piece and BIG trouble.

Tech Vocab -  Flip -  Flop  -   Flip and Flop - Lead Screw - Back-up Block

What's this all about?

Over the past few weeks we have been going through the design and development steps in building a 32 foot Town Lattice Truss covered bridge for the Village of South Wayne, WI. For my "proof of concept" in the process I am building a 3/8 scale model of this bridge truss design. 

There is much to see and learn. Can you figure out what is going on in this picture?  How and why?

Why the dial calipers?

During an interview with Art Hackett, from In Wiscsonsin of Wisconsin Public TV. One of my former Darlington students was asked what the hardest part about bridge building was? He said it this way, "Thinking. It is all about the thinking. That is something we don't like to do very much in shop classes. Mr. Anderson tries to get us to do a lot of thinking." 

Puzzler - See picture above

Tech Vocab -  Dial calipers - Annual Rings - T x W x L - Checking

A funny thing happened on the way to the bridge ...

Spring has sprung! Saps running. So I had to put my taps out today and get the cooker ready before I could go to Black Hawk High School and check on the progress students Bruce and Alex are making.

What do you see ???

The Sap Sak pictured below is a great piece of engineering. Study the design and you will see how it works. If installed properly the Sak cannot come out of the holder.

Bruce and Alex are setting up a Clamp and Button factory in the Black Hawk High School shop. Earlier I talked about the need for over 100 parallel clamps for assembling the bridge trusses. Plus 28 Buttons will be needed to secure floor joists and roof rafters in place.

They will get plenty of practice setting "stops" and "making fixtures" to locate parts for hole drilling.
Will have to introduce them to some GO  NOGO  gages so they can keep up the quality and meet tolerances of + or  -    1/16".  Even though this is rough sawn material we don't want to get sloppy.

Puzzler - How many gallons of sap to make one gallon of Maple syrup?

Tech Vocab - Spile  -  GO    NOGO   -  Radial Arm Saw

Meet the Holz Master...

The difference between the two drill bits is plane to see if you know what you are looking for.

To most observers a hole is a hole. Not so in the bridge building business. The difference in quality of performance for each drill bit is glaring. The high quality of results by using the proper drill on the right is that the hole finish is smooth and circular. The surface of a proper hole will be so smooth as to almost shine.

The single lipped $30 Irwin from the local hardware store and it's hole is on the left.  The $45 two lipped 18" long Holz Master from Timber Tools does the job right. This is a big deal in the process.

Considering that the load placed on the bridge truss will be transferred though the many, many trunnels (114 per truss) in the chord and lattice web intersections. Imagine the poor performance if the holes are not round. Worse yet the surface not smooth. Over time any small fiber pieces between the trunnel and hole will be compressed and the Camber will be lost or worse the truss will sag.

Puzzler - How will we ensure the holes are drilled perpendicular to the chord surfaces?

Tech Vocab -  Bushing,   Drill Guide,  PVC pipe,  Forstner Bit

"Button" pops up...

During the "proof of design" some problems with the Button have popped up. Take a look at the picture of the first one made. What design recommendations you would make to improve it?

You may want to look at the 3 view Orthographic blueprint for the button in the earlier Feb 17th blog  post - Things You Should Have Learned In School...  

In the picture below you can see the Sliding Compound Miter Saw being used to cut the 45 degree angle on the ends of the button. I will be taking the raw material and new blueprint to the students tomorrow for them to begin work making the Buttons. 

Puzzler - What steps would you do to cut out the buttons? What machines and tools would you suggest be used in the process?

Tech Vocab - Plan of Procedure,  Stop,  Dado Blade 

Serious fun ...?

Serious fun. Can there be such a thing? I always told my students that Woods Technology classes were about having "serious fun". No surprise the majority heard and locked onto the last word in my statement! The saying goes, "Everyone like to learn but, nobody likes to be taught."

Keeping that in mind, I dare to try this.

The following list contains the Tech Vocab words that have been used or covered in the Bridge building process to date. In "school" this would result more often than not in a test (punishment in my day, now they call them assessments) of some sort. Take a look at the list. Imagine you were on a game show or over coffee, struck up a "bridge building" conversation.  How would it go?

Technical Words Used in a Bridge Building Context...
26-29 words - 90% - Advanced -- Ahead of Time - In Front - Very Progressive
28-23 words - 80% - Proficient -- Highly Competent - Skilled
22-20 words - 70% - Basic -- Fundamental - Essential
19-17 words - 60% - Minimal -- Smallest Amount - Least possible
Less than 17 words - You cross the bridge first.

Air Dried
Alphabet of Lines
Annual Rings

Board Feet
Button
Camber
Cant
Chamfer
Chord
Doyle Scale
False Work
Fixture
International Scale
Isometric Projection
Jig
Kerf to a Line
Kiln Dried
Lathe
Lattice
Orthographic Projection
Parallel Clamp
Peg
Scribner Scale
Sticker
Tree Nails
Trunnels
View Projection
Wane
Web

The best part of building things I find is the instant feedback. Although responses will vary here is what I would say in a "Bridge Building" conversation applying the Tech Vocab covered to date...

When logs are sawed the resulting Cants may have some Wane (bark on the edge) on them because the sawyer is trying to get wider boards out of the log thereby increasing the efficiency of yield. The Board Footage for the sawn boards can be calculated (T" x W" x L' / 12) longhand or there are several "yard sticks" (Doyle Scale, International Scale, Scribner Scale) that have scales on them that give you the Board Footage results directly. Wane will not be a problem for some things like False Work the bridge is layed out on or Stickers used to separate layers when stacking the boards for drying. The rough sawn boards contain a lot of moisture (green state). The Chords and Web pieces that make up the Lattice truss must be Kiln Dried down to 17% moisture content so that when they dry out naturally and shrink the wood around the Trunnels (Pegs) does not crack. The rest of the bridge parts can dry out naturally (Air Dried) and will shrink harmlessly over time.

Good blueprint drawings are critical in making any project. Isometric Projection sketches will help to visualize the finished part. More detailed three view Orthographic Projection drawings using the Alphabet of Lines and following the rules for view projection come into play when parts are to be layed out. Like a Button to hold floor joists tight to the Truss Chords for example. A 3 inch rise or Camber will be built into the Chords of each Lattice Truss. In the assembly of the Chord it is important to observe and orientate the Annual Rings of each piece used correctly. Another detail will be the process of sawing the Kerf To A Line at each joint in the Chords to insure a tight fit up. Many, many Parallel Clamps will be used to hold the Chord/Truss assemblies in place until the Trunnel holes are drilled.

It would be advised to build Jigs and Fixtures so that the Trunnels (Pegs) can be made consistently to size. Turning a slight Chamfer on the ends of the Trunnels using a Lathe will make driving them into the holes easier.

Puzzler - What's next? Hint, It will be pretty sweet...
Tech Vocab - Each month I will continue to add to the list.