Tools, Jigs and Tricks

[Howard]

Measure with a micrometer........mark it with a yardstick........cut it with an axe?

 

One of the advantages of buying one of Graham's kit boats is that all the work of layout and cutout has been done for you. Precision cut parts from a CNC machine are hard to beat. Beyond that, quality material has already been sourced for you. A true win, win and especially so for those who don't have a lot of tools or background in woodworking, yet still want to build their boat.

 

On the other hand, not all designs are offered as kits, or if you chose to buy the plans alone and not a kit, you are left with the task of duplicating this yourself. The good news is you get a fairly detailed set of plans. But you still have to convert those 2D lines on paper to a 3D shape in plywood or dimension wood......and accurately to scale. Ideally, nearly the same exact replica you get from the CNC cut kit.

 

So in this vein, I thought it might be good to have a place to list some of the tools and tricks folks use to pull this off. I know there are a lot of gems imbedded in a lot of the builder threads, and hopefully, a lot of them will be repeated here. There are also boat building books, but they don't list nearly all the tricks people are using.

 

When you look at the plans, items like bulkheads, etc. are shown with various dimensions from a centerline and/or baseline.  Mark these out and you are left with intersecting points that when connected with lines, outline the overall shape of the piece. All that is left then is to cut it out (accurately). If plywood came pre-marked like graph paper, with square lines to scale, this would be easy. Unfortunately, plywood is a blank canvas, so you need to mark these out yourself. About the only thing you have going for you is that most sheets of plywood come to you cut with square edges.

 

My #1 tool to get this started is a drywall square. It took a couple tries, but I now have one that is actually square. It is remarkable how many "squares" are not. The test for this is to register your square on a square edge (such as the edge of your plywood) and draw a line. Flip the square horizontal or vertical (or to the opposite edge) and draw another line on top of or immediately next to the first line. If these do not run exactly on top of or perfectly parallel to each other, your square is off. Any line you draw using this will be off. Any piece you mark and cutout using this tool will be off (slanted). If you have two squares, register both to the baseline, then touch them together. If both are square, there should be no gap whatsoever and the measurement marks should line up perfectly as well. You would think an inch is an inch, but that is not always the case.

 

Once you have a centerline marked square, next step is to mark a baseline that is exactly perpendicular or 90 degrees to the centerline. I've given up trying to measure from the plywood edge and always establish a baseline just above it. (If the plans show a lateral waterline, that should be your baseline as almost all the dimensions in the plans are to the LWL). You can measure this up from the edge, but my preference is to register something I know to be square (like a long ruler) against my square base and mark my baseline off that. I always find that to be more accurate than trying to line up a straight edge to a pencil mark. So once you get that marked, you have a centerline and square baseline to measure from. I have adopted the practice of almost always testing this for "square", which leads me to tool #2: a set of trammel points (Stanley #4's).

 

To anyone with a background in geometry or drafting (most of what I have described are simply drafting techniques), you know the usefulness of a compass. The problem of most compasses is finding one large enough for this scale of work. A step up from a drafting compass is a beam compass, which tops out at around a foot or so. After that, trammel points allow you to make your own beam compass that can be as long as needed to get the job done. Again, I am using Stanley #4's, which also include a clip for a pencil. I use a mechanical pencil with a 7mm lead (fine enough detail for the job......large enough to to break all the time).

 

Back to the testing the baseline........the main critical next step is to set the tip of your trammel point exactly on the intersection of the centerline and baseline. (Since every measurement you make.....ultimately leading to the end product originates from this single reference point, this matters, so get it right). Once you do that, swing arcs of equal distance to the baseline, then from those points, back to the centerline. If your arcs intersect exactly on top of your centerline, your centerline and baseline are square and your problems are solved. The rest is relatively easy.

 

The key to the rest of this operation remains the trammel points. They are mounted on a wooden yardstick (is stiff and has accurate marks to 1/8"). In my mind, absolute accuracy to microns is less important than symmetry. Whenever I have two symmetrical points to mark, both equal distance from the centerline or baseline, when I mark one, I always mark the other. By swinging arcs with the same setting, a point established on one side will be in exactly the same place as it's corresponding point on the other side. Perfect symmetry is the goal.

 

Once your points are established, next job is to connect them with a straight line. For the longest time, I fought with trying to line up a straight edge, only to have one end or the other move, or in the process of actually marking the line, the straight edge would move on me. Finally, it dawned on me to set a tiny finish nail (1/2" to 3/4" braid) exactly in the center of my intersecting arcs. Those braids are not much wider than the width of a pencil line. Now all I had to do was register my straight edge against the nails, and hold it firmly against them as I marked a line from nail to nail. Now I had a perfectly measured, perfectly marked piece to cutout.

 

In the end, if you want your finished piece to be an exact 3D replica of your 2D plans, an accurate cut to your line is the end game. There are various theories on this, depending on if it is a square cut or freehand piece, as is often the case with bulkheads, etc. If the cut is to a line that curves (one you marked out using a batten you sprung to various points), it is almost impossible to do a good job cutting to the line. Far best to cut a little outside the line, then use a hand plane to bring your edge to the line. Even with a curved line, if the sweep of the curve is gentle enough, I've had better luck using a circular saw than a jigsaw (limitation is if the curve of the line is gentle enough the saw blade won't bind in the cut......a shallow cut in thin plywood will make a pretty tight curve). But in either case, I have found I'm too shaky to cut to the line with any degree of accuracy, so don't even try.

 

On the other hand, if the cut is to a straight line, I have developed a way to make a straight cut exactly to my line. No planing necessary. What I do is leave those finish nails I used to mark the lines in place. On the "good" side of my piece, I register a straight edge that is cut to the exact same width of the base plate on my circular saw. This first straight edge is essentially a spacer. I then butt and clamp another straight edge to the spacer piece. The finish nails are pulled and the line cut with my circular saw. There have been times when that was cut so accurate that I was left with half nail hole on either end. The key here is to make sure the spacers and straight edge are on the piece you want to keep. That way, if you wander off, the damage is to the scrap side, not to your piece. Your straight edge prevents the blade from ever getting any closer to the piece than your cut line. To make your spacer, register the outside edge of the spacer stock to a straight edge, then make your cut with the edge of the saw base plate pushed against the same straight edge.

 

A big help for me in making these cuts has been to get the right kind of saw. I'm right handed, so to use a typical circular saw with blade on the right side would mean I have to have a long reach over the piece I'm cutting, or use the saw left handed (awkward), or let the base plate ride in air or on the scrap piece, leading to potential damage to the good piece I want to finish with. It has helped me a lot to get a circular saw with left handed blade. Remarkably, most worm drive saws have left handed blades (but narrow base plates). Most direct drive saws have right handed blades.

 

Lastly, if you have two pieces to cut that are to finish exactly the same (such as two halves for the sides or bottom), stack both halves and cut them out at the same time. That way, both will be mirror images of each other and exactly the same. I would not trust clamps to hold the pieces together, so in several places in the field of the piece, I would drive small finish nails into them to prevent any possible chance of one of them slipping.

 

BTW, in many instances, I have found small finish nails to be a better choice than drywall screws to act as clamps. They drive the pieces together (vs. pushing them apart as screws sometimes do) and they are easy to pull with almost no chance of them breaking in the process.

 

Anyway, these are only some suggestions to consider. If you have others, feel free to share them. That was my intention of starting this.

 

 

 

 

 

 

[tom151]

Howard, great idea to start such a thread for supporting new-comers to B&B and small boat building in general. Let's hope that this is made a "sticky" thread.

For plywood/epoxy building, the most valuable tool I ever had was a book. Many of us have forgotten how much of what we think we know came originally from "The Gougeon Brothers on Boat Construction"

For the novice or even semi-expert this book provides so much expertise in one place that is should be the "must read" before beginning any build.

The Gougeons have now made this goldmine available to all at no cost at http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

Download it so it can be available off-line, print out those especially relevant items for your personal "shop manual".

Cheers,

TomH

[Chick Ludwig]

Great idea for this thread. I've already gotten something from it. I downloaded the Gougeon book.

[PeterP]

Howard, I almost junked my metal drywall square a long time ago because it was way too out of whack for boat building. Pressed for time and money to go get a new one I drilled out the rivets and replaced them with shorty carriage bolts. ( after squaring the thing up) I've been very happy with the result. Peter P

[Howard]

Peter:

 

It really is remarkable how many "squares" are not. I think this is magnified when you start working with material as big as a sheet of plywood. I guess they figure marking and cutting drywall is a butchers game and "close" is close enough? Same with carpenter's squares. I had one once that I used for the longest time, thinking it was square when it was not. No wonder nothing ever squared up.

 

Remarkably, this also applies to table saws, radial arm saws, panel saws, etc. These have to be checked and possibly tuned so that the blade is running parallel to the fence and also 90 degrees square to the table top. A burnt edge on one side of the cut is a clue something is not right.

 

Also, it is possible to use plywood sheets themselves to mark lines square. Assuming all four corners and thus edges are square (can be checked by measuring the diagonal corners), as long as the sides of both are registered flush to a straight edge (can be a larger thickness sheet of plywood, straight board, etc.), the shorter edge should be perpendicular and square to the long side, so a centerline can be marked off it. Move the sheet up equal distance on both ends, the edges should be parallel and a square baseline can be marked off that. I have evolved away from trying to measure, then mark, anything, preferring to simply register one straight edge against another whenever possible. Same if I need multiple pieces of dimension wood cut to the same length. I get it close to the right length, then clamp a stop on one end. Simply push any additional pieces against the stop and all of them will be cut to the same length.

 

As for really long lines, in regular construction, chalk lines are used to mark straight edges. These are not nearly accurate enough for this work. Lines and strings are used to create long straight edges for truing up.......such as a reference for plumb bobs...... but not for marking and cutting.

[Ken_Potts]

 

As for really long lines, in regular construction, chalk lines are used to mark straight edges. These are not nearly accurate enough for this work.

They're accurate enough when I use them :)I think it's good that the inaccuracy of squares is being pointed out. I always try not to trust a measuring tool more than I have to. If I use one tool to measure the space a part will fit into, I try to use the same tool to mark the actual part (it's not just squares that vary, tape measures and other tools have individual personalities too).I find when building a boat I start out with a very (very) careful layout for the first cuts and as the project progresses the cuts are more and more made as necessary to fit. It's like there's a gradual transition a cabinet maker's mentality to a sculptor's. Both are fun.

[Paul356]

I've used a chalkline to mark long planks for ripping out stringers.  It works fine, if you're careful, get the line tight, make a clean, vertical snap of the line.  I also know I'll be cleaning up the pieces in the table saw later, so slight variations are not a problem.  I would not want to rely on a chalkline for cutting the side of a panel that had to be perfectly straight. It's an exercise in matching tools and degree of accuracy to the job at hand. Efficiency is one goal.

[bruegf]

While its common practice to check for squareness by measuring both diagonals, its not a guarantee unless you know at least one corner is 90 degrees. A trapezoid shape will measure equal diagnonals and still not be square.

 

While these are not cheap, they are well worth the money. http://www.woodpeck.com/ott2616square.html

 

Fred

[Designer]

Do not forget the old 3,4,5 rule. For those who do not remember it, if the base of a triangle is 3 and the height is 4 then the hypotenuse must be 5 if it is square. I often use it to check for square on larger work, just multiply out the mumbers so that it just fits to your job and you will know for sure if it is square.

[Hirilonde]

While its common practice to check for squareness by measuring both diagonals, its not a guarantee unless you know at least one corner is 90 degrees. A trapezoid shape will measure equal diagnonals and still not be square.

While technically that statement may sound true,  it really isn't.  If the diagonals of a trapezoid are equal then it is square to the centerline connecting the 2 parallel sides.  Your sentence should read: "A trapezoid will measure equal diagonals and still not be a square."  The only time a trapezoid has equal diagonals  is when it is symmetrical.  So when you are trying to square up a hull, even measuring the diagonals of a trapezoid is useful.  An example would be measuring the diagonals of a trapezoid made by connecting the transom to any thwart by straight lines at the ends of each.  If the transom and thwart are parallel  (hence you have a trapezoid) and the diagonals are equal, then the hull is square to the center line, at least in that section of the boat.

[PAR]

Cover your tools with plastic tape or inside plastic bags when doing an epoxy run. This way when you grab your cordless drill to drive a screw into an noncompliant piece, it's not going to get covered in fresh goo. Ditto a scissors, utility knife or your favorite coffee cup.

[bruegf]

 

While technically that statement may sound true,  it really isn't.  If the diagonals of a trapezoid are equal then it is square to the centerline connecting the 2 parallel sides.  Your sentence should read: "A trapezoid will measure equal diagonals and still not be a square."  The only time a trapezoid has equal diagonals  is when it is symmetrical.  So when you are trying to square up a hull, even measuring the diagonals of a trapezoid is useful.  An example would be measuring the diagonals of a trapezoid made by connecting the transom to any thwart by straight lines at the ends of each.  If the transom and thwart are parallel  (hence you have a trapezoid) and the diagonals are equal, then the hull is square to the center line, at least in that section of the boat.

 

 

Howard was talking about checking a sheet of plywood for squareness (sorry, should have quoted that part of Howard's post), in which case you can have equal diagonal measurements but not have 4 90 degree corners when the sheet has the shape of a symmetrical trapezoid.  My point was that if want to know if something is truly square (90 degree corners) you need a good square to check it. or follow the 3,4,5 rule - diagonal measurements can be misleading.

 

Fred

 

Fred

[Charlie Jones]

For cutting long pieces, you can use a piece of ply wider than the saw base, attach a narrower one to that on one side, use THAT as the guide and ride the saw along, cutting off excess.. This leaves a piece exactly as wide as your saw base (to the inside of the blade) that you can then clamp (or nail) to any long piece and just cut. You'll get a clean straight cut every time, as long as you use THAT same saw.

 

I have a guide like that, made professionally, with an aluminum piece attached with adjustable knobs. On is 4 feet, the other 8.

 

And for long cuts on whole sheets of ply, I just toss the ply out onto the grass, set the blade draw to JUST cut through and cut away. On many sheets of ply, you can crawl around on the wood while cutting- makes it easy to see the lines.

[PAR]

Most sheets of plywood are square. It would be an odd cut, where something shifted during the cut, if it wasn't. The 3,4,5 rule works, so they're easy enough to check. I have a sliding sled for my table saw, that was made from a corner off a piece of plywood. At the time I made I didn't check it for square, assuming it was, though I have since and it still is.

[Howard]

For cutting long pieces, you can use a piece of ply wider than the saw base, attach a narrower one to that on one side, use THAT as the guide and ride the saw along, cutting off excess.. This leaves a piece exactly as wide as your saw base (to the inside of the blade) that you can then clamp (or nail) to any long piece and just cut. You'll get a clean straight cut every time, as long as you use THAT same saw.

 

I have a guide like that, made professionally, with an aluminum piece attached with adjustable knobs. On is 4 feet, the other 8.

 

And for long cuts on whole sheets of ply, I just toss the ply out onto the grass, set the blade draw to JUST cut through and cut away. On many sheets of ply, you can crawl around on the wood while cutting- makes it easy to see the lines.

 

If I am envisioning this right, the plywood cutting jig Charlie describes is essentially the same thing I use, but combines the spacer and straight edge into one tidy contraption? Essentially, the saw rides on top of the jig, but you still register or aline the edge of the base the saw rides on to the cut line? If so, I'd be curious to know where the clamps go. One of the bigger problems I've encountered trying to clamp straight edges onto pieces is working around the clamps. On the ones with aluminum and clamps with knobs, photos would help. Pictures, 1000 words and all that.

 

I also have some of the clamp-on straight edge guides (Emerson and Bora). The shorter ones seem to work OK. I was surprised to find the longer 8 foot one actually flexed in the middle during a cut, leaving a curved cut. Not only did my good piece have a curved edge, but so did the residual scrap. Once you get a curve in it, it is difficult to get it out.

 

I also use a rip fence on my circular saw that I use to make long rips in lumber. But it has the same hazard. Once you get a curve in your stock, it will follow it faithfully.

Most sheets of plywood are square. It would be an odd cut, where something shifted during the cut, if it wasn't. The 3,4,5 rule works, so they're easy enough to check. I have a sliding sled for my table saw, that was made from a corner off a piece of plywood. At the time I made I didn't check it for square, assuming it was, though I have since and it still is.

 

Paul:

 

Do you have a photo of you sled?

[PAR]

Not my saw, but pretty much the same thing:

 

[Howard]

Although I have never used one (or even seen one for that matter), I understand there is a similar type jig to use on a table saw to make the 12:1 cut to scarf dimension lumber. As I recall, that is about a 4.5 to 5 degree angle. For some setups, that does not leave much room for the clamps to stay clear of the blade towards the end of the cut. The advantage of using a table saw for this is makes a square , vertical cut.

 

Of course for larger sizes, like a 1 x 6, a table saw doesn't have enough blade to cut all the way through. I presume a person could also rig a similar jig to fit some band saws? Or start the cut with a table saw, or even circular saw, and finish it with a hand saw........then plane it flat and square? (Gap filling properties of thickened epoxy being the saving grace).

[Hirilonde]

When ever you are cutting sheet goods, with Charlie's guide or not, always lay out the measurements for the cut at least 3 times (in 3 places along the line), not just 2.  It is a common error to measure out a distance different than intended , often 1 inch more or less while getting the fraction correct.  Now when you lay out the straight edge, snap the chalk line or place your guide you should find the line hits all 3 measurements.  If it does not then you probably made that common error at one of the marks.  Now you know this and can correct it before cutting the sheet.

[PAR]

You mean you've measured twice, cut three times and still came up short?

[Charlie Jones]

Here's some pics of my table saw scarfing jig. It runs in a miter gauge slot.