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Table of contents for this page. Using a Joggle stick. A tip from boat builders | Drawing a Circle and an Ellipse. | Threaded rods | Joiner Nuts | Slow concrete pour for columns | Termite problem in roof. |

Using a Joggle stick. A tip from boat builders

Joggle Stick - Simply made out of scrap material.

Here's a little tip that I have used a few times to help with tricky scribing jobs.  See my scribing page for more details.  I also talk about scribing in my coping saw page.

For centuries boat builders have been cutting and fitting curved surfaces together.  Say for example fitting a bulkhead to the inside curved surface of a boat hull.  For this job they developed what I know as a joggle stick, but I guess that there are many other regional names for similar techniques.

Joggle stick- Using the sick to plot important points of a shelf, onto a temporary plotting board.

Above is a sketch plan of an irregular recess in a wall.  Let's say that we want o fit a shelf into it.

1. First make up your joggle stick.  I've drawn a point on one end and that's really all that you need, but I show a couple of notches in it.  These help when you have your point offset to get in awkward spots, because sometimes you may turn the stick over, and you need to know which way up it should be.
2. Set up a temporary patten board, level and at the height that the shelf will be. This can be made out of scrap ply or Masonite. Anything that is clean and will show pencil marks clearly.
3. The pattern need to be held firmly in position.  Use clamps or temporary brace to keep it firm.
4. Place the tip of the stick at each point that you want to record, with the base of the stick on the pattern and trace around the outline of the stick onto the pattern with a sharp pencil.
5. Do this for each point of interest.  In the boat building scene, you would trace lots of points to give you the curve.

Joggle stick- Transferring the points onto the shelf to be cut.

1. Take the pattern and fix it firmly in position on the shelf material.  Clamps or even nails will do, the main thing is that once again it should not move during the marking out.
2. Place the joggle stick onto the penciled positions on the pattern, then pencil mark around the points on the shelf material to plot each point onto the shelf.
3. Join the points up with a straight edge.
4. Cut the shelf.
5. If you Have a series of points that describe a curve, then use a flexible batten to draw a smooth curve.

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Drawing a Circle and an ellipse

A pair of trammel heads from my trammel page

A Home made trammel

Required ellipse

Marking the focal points

Another tricky scribing job that comes up from time to time is cutting around pipes, which means drawing a circle if the pipe goes through the wall square off, and an ellipse if the pipe enters the wall at an angle.
For the most part circles are drawn so that we can cut around small plumbing pipes, and I try to find a paint can or drink container of near enough size to draw around.
Anything bigger is of no problem, I just use a trammel to scribe the circle.
I don't suppose a pair of trammel heads are available in most guy's toolboxes, but there is an easy way out.  A couple of nails or screws through a batten of timber can do the job just as easily for quick one off jobs.

When the pipe goes through say a wall at an angle then what we need to draw is an ellipse.  It is usually possible with a spirit level and a straight edge to get vertical and horizontal marks on the wall that define a rectangle around the pipe.

We draw that rectangle on the material to be cut, and then we mark two other lines that divide the rectangle into halve and quarters.

These are known as the vertical and horizontal axis lines, and the pass through the center line of the pipe at it's junction with the wall's surface.
The longest line is known as the major axis and the smaller one as the minor axis.

1. Take a batten stick and put two nails in it at half the major axis apart.
2. Place one nail on the top of the minor axis and scribe an arc that crosses the major axis twice.
3. The location where the arc crosses the major axis are known as the focal points.
4. Bang a nail or screw into each focal point.
5. Tie a piece of string to one nail, wrap it around the other, then stretch the string with a pencil, until the tip of the pencil touches the top of the minor axis.
6. Tie off the string firmly at that point.
7. Use the pencil that is constrained by the string to draw a perfect ellipse.

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Threaded rods

The illustration below I intend to use for the next in my Hurricane Construction series.   I have got a new intro page written, which shows a few shots of Cyclone Tracy (which wiped out Darwin in 1974) and I've shown a couple of sketches of how we used to build homes in those pre Tracy days.   The next page in the series will be about strengthening existing houses, to bring them up to cyclonic standards, and the shear wall detail is the type of thing that we did a lot of.

Threaded rods and joiner nuts - A section through a shear wall hold down

The whole emphasis on structurally upgrading an existing house is improving the connections.   Nails replaced with bolts, rafters bolted to hold down rods passing through wall and into something solid.  In the drawing above I show a HD rod (5.) passing through a wall and into a new concrete footing.

• As you can imagine the number and variety of bolts needed to upgrade a house was enormous and expensive.
• Apart from standard sizes available at hardware stores we need heaps of odd bolt lengths in two main sizes, M12 and M16. (1/2" and 5/8")
• In the example above we have say an M12 bolt cast into concrete, connected to an extension rod which would be bolted to roof members above.

My old Makita metal cut off saw.

Enter the humble threaded rods. AKA "all thread"  These are lengths of rod which have a thread formed all the way, no smooth section as in normal bolts.  These are available in Zinc plated, galvanised or even in stainless steel.  (I recall seeing a very simple but effective set of shelves suspended from stain lees steel rods.)
They come in lengths of 1000 and 3000. (a bit over 3 feet and around 10 feet long).

If you have a project where you require a lot of different lengths of bolts, then threaded rods may be just the thing.  They will be cheaper and if you get extra rods, you will always be able to make up any odd bolts that you need, instead of making a separate trip to the store.
We would buy the rods by the pack, the nuts and bolts in large bags.  Very cost effective.

You can of course saw the rods to length by hand with a hack saw, but my tool of choice for this job is the metal cut off saw on the right.
There is a simple trick to using this that will save heaps of time and frustration.
If you just cut through the rod in the normal way, then a burr is created at the bottom of the cut.
This burr is a pain the the butt to get rid of so that the nuts are able to be put on easily.  We tried lightly grinding the bur off afterwards, grinding the end with a slight chamfer etc.  All of these ways work, but quite often you still need to grip the rod with a vise grip, and turn the nut with a spanner.

Cutting threaded rod on a steel cut off saw to create no burr.

The trick to cutting clean ends, first time, so that the nuts are easy to run onto the rod by hand only is shown in the sketch above.

1. Mount the rod in the saw's clamp, only just tight enough to to hold it in position, but loose enough to allow you to slowly rotate the rod as you are cutting.
2. This way, the last bit to get cut though is at the center of the rod, well away from the threads.

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Joiner Nuts

Normal good practice for bolted connections is for the nut to be completely on the bolt with a minimum of two and a half threads extra sticking clear of the end of the nut.
This generates the required strength out of the connection.

Joiner nuts are nuts that are about three to three and a half times as long as ordinary nuts, and they allow us to join two lengths of bolt together and still retain the full strength of the joint.

• You must make sure that the two bolts are joined at the center of the nut.
• Quite often with a rough end on one of the nuts, the thing jams when it is only a couple of thread in.
• My usual method in say a wall like in the above sketch is to hold the joiner nut alongside the end of the bolt in the right position, and then clamp a vise grip onto the bolt.  That is half the length of the nut down.
• Run the nut onto the bolt up to the vise grip, and it should now be half way on.
• Then run the next bolt on and tighten again with another vise grip.

Quite often before threaded rods and joiner nuts came on the scene, we had to get threads cut on the end of rebar steel.
Then when we had to join the bars we had to weld them.  Welding is fairly quick in itself, but when working in an existing house there is always a risk of fire, so with welding comes the need for maybe an extra guy to help the welder set up, and to keep an eye out for fire etc.
Using joiner nuts is so much easier.

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Slow concrete pour for columns

Here's a question that I have received from Matt S. who lives here in Australia.

A typical high set government house of the 1970's and 80's.

My reply to Matt, with a couple of extra points.

Above is a photo of a high set house that is common in Darwin where I live. We like the space under the house for parking, laundry etc. while the upstairs area (in theory) catches a little more breeze than the ground level houses.

The houses were sat on 225x225 (9"x9") concrete columns that we formed up with bolted steel forms.  We mixed the concrete in a standard petrol driven, 3cu feet, concrete mixer.
We had one guy on the mixer, one on the wheelbarrow and bucket, passing the mix up to the other guy on a bit of scaffold placing the concrete in the forms.

Regarding mixing and pouring by hand.
Should be no problem provided that you can keep up a steady rate of pour.

• Matt is right in thinking that a slow rate of pour helps to reduce the pressure on the formwork.
• On a few occasions when pouring the corefill in high hollow block walls, I have had the boys fill the bottom half and move along, leaving the top half for half an hour or so.
• This gives lower section time to settle and start to stiffen up.
• The guys on the pump and the hose don't like it, for them it is easier and quicker to fill the wall in one hit, as they go along, but of course they are not the ones that have to sort things out when a blow out occurs.
• At the same time though, the pace should not be so slow that a so called "cold joint" occurs.
• A cold joint is where the first lot of concrete has taken on it's initial set and the next layer can't be vibrated into it.
• Cold joints should be avoided at all costs, they result in at the least, ugly cracks and at the worst structural defects.

As a three man team we could do say 21 of the house columns in a morning, (Matt is talking about doing slightly less than four) at a time.
You will need a hand though to keep up a reasonable speed.
We used to vibrate the concrete by belting the steel forms with a hammer and tamping the inside with a lump of timber. A small electric vibrator (Hire) would be excellent for this though.

• I would say treat the formply with some sort of form oil.
• Clean the forms really well after each use.
• What happens is that when dropping the concrete in by bucket, some of the mix sticks to the sides of the form and on a slow pour it could start to go off.
• When the forms are stripped, this stuff that has partly dried on the form can be a bit flaky.
• It is not really a structural defect, more cosmetic, it looks bad to see flaky bits on the surface.
• If the forms are in good condition and clean then it is less of a problem.
• Naturally, always finish the column before stopping for a rest, otherwise the spillage on the side will really set and the flakiness will be worse.

Regarding the join between separate day's pours.

• Strictly speaking, on an engineer inspected job, joints in walls, walls to footing, or the bottom /top of columns, should be scabbled to remove the laitance.
• Laitance is the sometimes greenish, watery, sandy scum that rises to the top with the action of vibration on a plastic concrete mix.  It is always there but with a well engineered mix it is rarely a problem.
• Normally, with residential jobs, providing that good quality concrete is used, then nobody bothers scabbling between pours.
• Sometimes in really obvious cases, like heavy rainfall while pouring or, in the case of mixing it on site, you used a too wet mix, then laitance will be obvious and scabbling will be necessary.
• The Laitence should be chipped away and removed, to expose solid sharp clean concrete.
• This gives a good surface for the next layer of concrete to bond to.
• The scabbling is done on small jobs with usually a hammer drill with a chipping chisel.
• Larger jobs mostly use air scabblers etc.

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Termite Problem in a roof.

Here's a note from John A. who live in Laguna Beach Ca. Hi John,
It seems that you are lucky that you got them when you did, just a few rafter ends is not too bad.

• I'd try my best to do the whole of the work from the outside.
• Set up a scaffold at a comfortable height and remove whatever cladding or eaves lining necessary to get clear access.
• If you have got rid of the termites, (poisoned the source, removed the entry point etc) then there is no real reason to saw off the damaged timber, apart from cosmetic reasons of course.
• Take advice from your local pest exterminator on this point of course, I'm only thinking out loud here.
• If the eaves are open, then you have to trim them off, but if they are closed in (lined) then you can leave the old damaged ends as they are, it will save a lot of work.
• I've had good success cutting off rafters like this with my recipro saw. (that's what I bought it for). You may be able to get a power saw to cut a bit out then finish them off with a sharp hand saw.
• Sister each damaged rafter with a new piece of equivalent timber, cut up to and fixed to carry the fascia.
• I like to use bolts for jobs like this, say two 3/8th bolts per join, with washers each end.
• Try to make them at least one foot apart, better still two feet if you can. So you may be using say 2ft to 3ft long timbers.
• It really depends if you can get tools where you want them, working from the outside.

"Best of luck with it John and watch out for those little bastards in future.   I've had the same trouble myself on a job, a lady had leaned bamboo poles against the house, (to provide a shade structure for a kids plays area) thereby bridging the termite protection.  If we hadn't come along to build a veranda the whole house could have suffered."

We have termites up here of course and anyone who has been around the building industry here long enough will have stories to tell.
We were working at a high school an few years back and I was asked to lend a couple of guys to a pest exterminator.
We had to remove from a ceiling in an old part of the complex a huge termite nest.   There would have been say three or four wheelbarrow loads of material to move, say 10 cubic feet.
I have always been told that termites live underground and return to their nests every day, and so if we can break up there tracks and stop them doing this, then they will die.
Not this lot obviously, another urban myth busted?

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All for now
Cheers.

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