Archives for Marc's Miscellanea

Epoxy to the rescue

stem epoxy repair

It’ s important to get the rolling bevel on the stems to match the angle of the planking. Otherwise the glue joint is weak and the planks pop off like what happened here. So instead of putting on another strip this evening I mixed up a cup of epoxy. I added cedar sanding dust to thicken the epoxy to the consistency of peanut butter. Then a popsicle stick lets me push the goop in and fill the gap.

In order to keep the planks held down tight (to the less than perfect mating surface of the stem), I screwed a couple of wooden blocks right into the stem. The screws are coated in paste wax and the blocks are wrapped in packing tape to ensure that they don’t become permanently bonded to the epoxy.

 

gap filling 3

The epoxy is dispensed by pumps which make sure the ratio is always correct. But that means you always get at least 1 pumps worth, which is about 20mL or so. Since this stuff is more expensive than Unicorn blood, I always make sure I have a way to use up the whole shot.

So the remainder of the cup went to filling gaps and irregularities in the hull. There will be more of this later on with the fairing and sanding process. What I did tonight was just get the worst offenders while I had epoxy filler made up.

 

gap filling 1

A little bit goes a long way.

 

The other thing I’ve been doing between glue strips is patching holes. Because the strips had some knots in them I need to do some proper wooden plugs as I went. On some of the worst strips they were cut out completely and the strips butt jointed together as in the above gap filling photo.

However, it is so much nicer to work with full length strips. Especially when the curves get complex. So wherever I could I’ve made up cedar plugs to fit the missing knot holes. Most of those are on the edges of strips, like this:

knot plug 2

But a few are small enough not to break the strip, but loose enough to fall out and leave a hole.

knot plug 1

This was a loose knot that had fallen out of its hole. It happened to be almost exactly 3/8″ and very close to perfectly round. So it took very little fiddling to get a section of 3/8″ dowel to make a snug plug.

Creative Clamping

turning the bilge

The past weeks I’ve been adding strips almost daily. While I was going up the sides of the canoe I could add three strips at a time. The curve was gentle and predominately in one dimension. The curve was also in the plane which the strips are thin, so they could easily conform.

Once I got up to the turn of the bilge, things got complicated. I knew I wouldn’t be able to do three strips at a time. I was hopeful I could do two though. I was proven wrong. Strips 7 – 10 went on as a triplet. I attempted to put 11 and 12 on together and it was a disaster. No matter how I arranged my wedges I couldn’t get them to lay tight together and conform to the forms at the same time.

With my glue setting up I had to just settle for fitting the forms or risk having to cut them off altogether. Which would be a ton of work and mean scrapping two unused strips to keep my bookmatched pattern.

 

gap in planks

So that leaves me with this ugly gap and a ridge between these two planks. It’ll get faired with the spokeshave later and the gap will have to be filled with glue and sanding dust. Because so much material will need to be taken off to get the fair curve the hull will be a bit thinner here unfortunately.

So all the strips after that have gone on one at a time. I’ve switched the orientation of the L brackets as well. Now I’m clamping on the long arm and trapping the strips under the short section. I’ve also abandoned the wedges most of the time. I can put enough pressure on the strips to get them into place, transfer the force onto the L block to hold the position and then tighten the clamp to keep it there.

The areas near the stems have required some very creative clamping solutions. In fact almost every strip needs a different setup as the angle is changing there so dramatically from one strip to the next. I’ve used wedges with sandpaper glued to them to provide a square surface for my F clamps. I’ve also used small blocks screwed right to the station mold as levers. And for the last few strips I’ve used a spring clamp with a caul supported on the far end by a block to increase clamping force and protect the hull.

 

spring clamp stem

That gap looks pretty bad but it’s not as bad as it looks. The camera angle is just looking right into it here. I have lots worse…

I’ve also used a whole roll of masking tape up to this point. It’s been pretty much my fall back clamping setup. I can’t recommend enough having lots of masking tape on hand for building a canoe. Even between the blocks on station molds I’ve used strips of masking tape to help keep the joints tight.

Planking Progresses

first three strips held up

In order to proceed with the planking I first had to do a few hours of jiggery. That is, making the fixtures and wedges needed to hold the planks tight to the molds and each other while gluing them up. I’ve elected to build my canoe without staples which means a lot more clamps and fixtures are necessary. I can certainly see the appeal of the stapler at this point as it would allow you to really fly through the planking. I think the quality of the finished product will be worth the hassle though.

tiny mitre box 1

tiny mitre box 2

beaded wedge

To make the small wedges that push the planks tight together I had to make a tiny mitre box that would just fit one strip. I had set aside a small bundle of strips at the beginning of the machining process and only put the bead profile on them for this. Cutting the long diagonal and leaving the bead on the long flat side gives you a wedge that can push against the strips without damaging the cove edge.

I also put a 90ยบ cut in the box to quickly cut out broken or unacceptable sections of the planking and make flush butt joints. I tried to keep the tight knots in for visual effect but some of my boards had loose knots that make for weak sections or areas that would need filler.

 

wedge setup

This is how the wedges work. The L shaped bracket gets clamped to the station mold with a small gap between the long arm of the L and the strips. Three strips at a time fit under the bracket. After the glue has been applied to the cove of all the strips, the wedge with the bead gets pushed in under the short arm of the L and clamps the strips down tight to each other. Then a flat wedge gets driven in the gap between the long arm of the L and strips to keep them tight to the mold.

Be sure to put packing tape or wax on the flat wedges so they don’t get glued to the strips by the squeeze out.

I wipe all the squeeze out off with a wet rag once all my wedges are in place.

 

first three strips glued up

Where two shorter sections of strips are joined I put two small blocks (covered in tape) and a clamp across the joint to keep it in line.

 

masking tape setup

The trick is getting all the strips under the L brackets but still having room to apply the glue. At first I used the flat wedges to try and keep them up. It worked sort of but it was difficult to drop just one strip at a time when I wanted to. Masking tape worked much better because I could peel it back and move each strip down in turn.

It’s also great for adding some extra pressure between molds.

seventh strip glue up

One of the better decisions I’ve made on this build is to spend the money for better glue. I’m using Titebond III for gluing the strips together. The longer open time is a huge bonus. I don’t know how you’d do three strips at a time using yellow PVA carpenters glue unless you had a helper.

I’ve found that I can prefill two syringes with glue and that’s just enough for three strips. I keep a bucket of water in the sink so that when the first syringe runs empty half way through the second plank I can just suck up the water and leave the syringe in the bucket. Then I can adjust wedges and get the strips cleaned up without worrying about the syringes getting ruined by dry glue.

The First Strips

shaping stem rolling bevel

To put the strips on the inner stems need to be profiled with a rolling bevel. The sides are very acutely angled at the top of the stem and change to being almost flat where the stem turns into the bottom of the boat. It’s best to tune this bevel as the strips go on to make it fit as best as possible. It’s much easier however to work with the stem off the mold so I roughed it in on the top half of the stem on the bench. I made sure to leave some material for adjusting in place. It turns out I left quite a lot once I got to the first strips.

Which also made me realize that if I had used 3/4″ material for the stem molds I’d need to remove some of the mold material for the strips to fit the bevel. So if I do use MDF for another boat, it’ll be 1/2″ I guess.

I really love working with the spokeshave so this part is quite fun. The epoxy in the laminated stems is pretty tough on the blade though. I had to sharpen twice to do the rough shaping on two pieces about 1m long and 2cm square.

 

tapered stem

Here’s a view of the bevel starting at the top of the stem. It got a lot sharper than this once I started checking with the strips.

 

clamping strips to stem

This is the first two strips clamped to be glued to the stem. You can see how sharp it got below the clamped area. The wedges are just there to provide a parallel surface for the clamp to act on. They aren’t glued on at all. In fact they are some of the wedges I’ll be using to keep the strips against the molds later on.

 

first strip clamped

Here’s the first strip held in place with wooden brackets and clamps made from ABS pipe with a slot cut in it. I don’t have near enough C clamps to do all the strip clamping jigs I need so the clamps made of pipe are an economical alternative. They don’t hold very tight compared to any screw type clamp but for getting things aligned they are sufficient. I put a brad nail in the strip on the centre 5 molds where the strip will be covered by the gunwhale later on to keep that strip anchored once I got it dialed in. All the other strips take their shape from this one so you need to get the fair line established here.

 

levelling second strip

Once one side is tacked in place the other side is held in by clamps and using a level you can make sure they are parallel to each other. That’s important so the strips will proceed up each side at the same rate.

The area below this first strip will get filled in with shorter strips to make the shear line rise up to the stems.

Next I’m going to need to make a big pile of L shaped brackets to attach to the molds to clamp the strips with wedges.

Installing the Molds

stem mold installed

Now that my strongback is setup I got to install all the station molds. This was a pretty exciting and rewarding day, since you get to see the shape of your canoe in 3D for the first time. It took all day to get things set up since there is a lot of checking, clamping, adjusting, checking, and then screwing. Trying to get this many parts aligned to a centre line, plumb and square is fiddly business.

Almost half the time was spent getting the two ends established. The stem molds need to be set up square to the #6 station mold and then the #7 station molds are actually two halves that go on either side of the stem mold. Because I used 1/2″ birch plywood for all my molds it has some flexibilty to it. The stem molds ended up having a bit of curve to them which was troublesome to get out.

I went with the birch ply because I really dislike working with MDF, but I think if I do another canoe I’d do all the molds with 3/4″ MDF. The extra rigidity and stability would make setting up the molds go a lot quicker. I’d also want to have a good band saw for making them…

 

alignment groove

When I cut the dados in the riser blocks, I dropped the blade down to just about 5mm after the last pass. Then without adjusting the fence position I ran the blocks through on end from each side so that I’d have a reference mark down the block to exactly where the walls of the dado were. Since the edge of each station mold is supposed to be on the twelve inch intervals perpendicular to the centre line, this cut mark lets me line up each block with the mold in the right place.

 

alignment centreline

I also marked the centre of each riser block and carried the line all the way around. This allowed me to get the riser blocks aligned with the centre line on the strongback and the centre line of the molds aligned as well. I wasn’t sure how it would work out when I made up the blocks, but after doing it I have to say that it was very easy and straightforward. Having the blocks flat and square is essential though.

centreline string

With the two ends set up finally, I clamped a string above the strongback to establish an upper centre line. The blocks clamped to the stem molds which the string is attached to are cut away by half the width of the plywood (0.230″ for this particular plywood). I used some neon green braided backing line from my fly rod for the reference string. I highly recommend it for anyone looking to do the same thing. It’s very visible and holds tension very well (as you’d expect it to do).

 

complete mold

With all the molds installed I’ve got a skeleton of a canoe !

One snafu I did discover with the riser blocks was that the ones I had put in at the front of the stem molds stuck out too far and would interfere with the strips right at the top of the stem. Luckily I figured this out before I established the top string centre line and had put any of the station molds in. I had to remove the stem molds from their blocks (but not take the #6 and #7s off) and cut the front blocks down as you can see above. I also put the screws holding the riser block in from underneath the strongback on those ones and took out the ones that would be underneath the mold in the bottom of the dado.

Now once I have some of the strips on from the shear line down to the curve of the bilge which will stabilize the stems I can take those end blocks out by removing the screws from the bottom and sliding them out the ends. Adding the last few short strips to make up the shear line below the initial strip should be free from impediment then.

Strongback Assembly

joining strongback

Now that the Strongback halves have done their duty as support for machining the strips it’s time to assemble them into their proper form. In the photo above I’ve got the halves laying on their sides with the middle section clamped in place. You can see there’s a 1/4″ drill bit taped to the corners with a string clamped tight over them to give a straight reference line along the length of the whole box beam. Then by using a 1/4″ steel rod and making sure it just fits between the string line and the edge of the strongback I got the whole thing aligned straight before driving screws into the middle section.

 

strongback standing

Next the legs get attached and the whole thing is stood up where it’ll be located on the floor for the rest of the build. I used a level and a pile of shims to get the whole assembly as level as possible in both directions. It took quite a bit of back and forth as each shim changes the measurements all over. In the next photo you can see the levelling feet between the two long strips of plywood that make the bottom of the legs. Once everything was as level as I could get it the feet get pushed down against the floor and screwed through to lock the position. Then I am free to take out all the shims and the strongback stays as I want it.

 

strongback top

To put the top on I cut spacer blocks the width of the overhang and clamped them flush with the tops. When cutting up the plywood I made sure that each of the pieces that were to become the tops of the strongback kept one factory edge. The spacer blocks are clamped to those factory edges and then all my measurements I make for putting these tops on are referenced from that side. Once I get the centre line put on that becomes the reference line for everything else.

 

riser blocks

The strongback is sixteen feet long, being made of two sheets of plywood. Because the canoe I’m making is 15’9″ the stems don’t hang over the ends of the strongback so I need to raise all my molds up two inches to allow me room to work right down to the tops of the stems. I decided the best way to do that was to make riser blocks out of 2×4 with a 2″ dado in them that is exactly the width of my plywood molds. These are real 2″x4″ blocks, not ‘nominal’ size 2x4s like you’d buy at a lumber yard. I’ve jointed two sides and then ripped them on the table saw (in both directions) and crosscut them on the sled to make sure they’re all six-square. I cut the dado with a 1/8″ blade and flipped the blocks side for side with each pass to ensure that it is perfectly centred in each block. The plywood fits the dado with a snug friction fit which will let me make adjustments easily until I drive the screws in to lock the molds.

These riser blocks are not something that Canoecraft mentions other than a passing note that if your canoe is less than sixteen feet you’ll need to bring it up to work the stems. It’s left to the reader to implement that. We’ll see if this solution works out.

Edge Profiling

router at night

With the strips all cut to the same width I spent this weekend putting the bead and cove edges on them. By adjusting the outfeed setup a bit I was able to put the router table I’d made right on the box beam from the strongback. The router just fit down into one of the partitions in the box. And since the both the router table and strongback top are 3/4″ material it made it level with the top of the table saw. Which gave me a great infeed surface to work from and made it so I didn’t have to move the table saw again.

The first step was to clear the middle of the shop floor and layout the strips as I wanted them to go onto the canoe.

 

strip layout

 

 

By splitting the bundles of strips up as they came from boards and mixing them up in pairs I’m hoping to achieve a bookmatched look to the finished boat. It also makes sure that there aren’t large patches of uniform colour or too many knots in the same place.

 

router table setup

 

I made a few more featherboards to help with the routing setup. I ended up moving them closer together than in this picture, but they did work out just fine. You can also see the split face boards I added to the router fence I made earlier. This lets me close the gap around the bit and shim the outfeed side out for the cove cut to support it.

Re-ripping Strips

me ripping strips

So the less than stellar rip fence on the table saw doesn’t hold its setting apparently. I found after checking some of my strips that throughout the day the fence had slipped away from the blade and some bundles of strips were thicker than others. So I had to re-rip several bundles of strips to get them all the same thickness. The measurement I was going for was 0.220″ and some of the strips got as thick as 0.260″. Forty thousands of an inch doesn’t sound like much but if the strips aren’t all exactly the same then the bead and cove on the edges won’t be centred on all the strips. Which would make the fairing of the canoe a horrendous job later on.

 

re-ripping setup

The good news is that 0.040″ is easily dealt with by the featherboard so once I got the table saw set up (with a clamp on the fence this time) I didn’t have to change it for each strip. So re-ripping the strips only took a third as much time as the first go round.

The moral of the story is check your strips every so often to make sure the fence hasn’t moved. It would have saved much more time to catch the problem early and clamp the fence then. Or maybe the moral of the story is to use a table saw with a good reliable rip fence… ?

 

 

Ripping Strips

pile of strips

Many hours on the table saw and several garbage cans full of sawdust later, all the boards are now strips. This was a pretty tedious part of the process and I imagine that doing the edge profiling is going to be similar.

The good thing is that I have more than enough strips. Without knowing how much would be lost to waste and blade kerf I was just crossing my fingers that the boards I had would be enough. I used a think kerf ripping blade (0.070″ thick) to minimize the waste and that helped.

 

ripping setup

Part of what made the whole process take so long was resetting the featherboard for every cut. Because the boards are all slightly different widths and I could only put one or two boards on the infeed support at one time, the featherboard setting changes every time. I’m using the dark coloured featherboard in the mitre track just to support the back edge of the long featherboard which is actually supporting the work. The mitre track featherboard doesn’t work with the fence that close to the blade as the fingers are too long.

 

outfeed setup

I’m using the sections of the strongback for infeed and outfeed tables to support the boards as I’m ripping them. I’ll set the router table up in a similar fashion so once the strips are fully machined I can put the strongback together.

 

Steam Bending Stems

stem on mold

The stems are the structural members that tie the ends of the canoe together. There is an inside stem which all the strips that make up the hull are joined to at each end. Then once the strips are fastened down, an outside stem caps them all off so you don’t see the end grain. This outside stem is what takes the abuse to keep those fragile strips from taking any.

Because the stem profile at the ends of the canoe has such a sharp curve over a short distance, the stems need some help to bend without breaking. The first help is that they are made out of three thinner strips which will be laminated together with epoxy, as opposed to one solid piece of wood. The second is that those strips get steamed, which softens the lignin in the wood and lets it compress and stretch more more than it normally would.

 

steaming apparatus

The apparatus you see there is my steaming setup. It’s our kettle on a portable one burner grill, with a large piece of pipe and some rags. Pretty sketchy huh ?

After 20 minutes in the steam tube the bundles of strips came out decidedly more noodley. The effect only lasts as long as they are hot though, so you really have less than a minute to make them bend to the shape you want. I had the stem molds clamped in place, and all my clamps pre-set standing by. You need a lot of clamps for building canoes.

 

bunch of clamps

Each time I did this I had a helper to put the clamps on while I bent the hot strips around the mold. I’m not sure how you’d do it by yourself.

After a full twenty four hours of drying the clamps come off and the strips have held their shape mostly. They still have some spring back but you can easily push them into place with your fingers. They got tied with some string to hold their shape and I’ll wait a few days before epoxying them together to make sure all the moisture is out of them.