Clamping Octagonal Birdsmouth Spars

It's almost show time on the build of this big stick taking up the length of my boathouse. At 85' long, tapering 14" to 10", assembly will be a large group task, and the hot weather here in Thailand will limit severely the open time on my epoxy (even using "slow" hardener).
So, my clamping technique will be important. I'm looking at buying 85 bar clamps, but after the 2 masts and other spars are finished I'll have a lot of extra clamps (is there such a thing?)
I've made a pile of clamps already for keel lamination. Just two pieces of 2x4 with two pieces of threaded rod/nuts/washers pulling them together. Can't seem to work out how to modify these for this purpose, though.
Anybody seen any cool tricks to ease this sort of awkward clamp-up?

 

I have used a device called a Band-It. They typically are used for banding crates and equipment for shipping. Cheap and fast and good tension control. I make zillions of small 1/4" ply shims that I stick to the center of the staves with either double sided tape or a pin nailer. These take the load off of the corner and press down in the middle of the stave, giving nice sqeeze out. Works a treat and with a little practice before the actual event, you can move pretty fast.

 

You can wrap it with something stretchy such as bungee cord, strips of rubber innertube etc. Even small stretchy (nylon?) rope or heavy string. The more wraps, the tighter it clamps. It's like wrapping thread around your finger, before too long there is no circulation and it hurts, after awhile your finger will fall off. You have to use something like wax paper to keep it from sticking to the work. Sam

 

Hi guys -
Good ideas so far, problem is with the size of the staves. 3" wall thickness. These will be tapered out of 3"x8" stock, starting at about 5.5" wide (1 face) to 4" wide at the peak. So, the slight unavoidable bows in these long pieces will need some hefty pressure to straighten out and get a nice, intimate mating surface in the birdsmouth. I've thought about a spanish lanyard (a couple of wraps of line/rope with a stick in the end twist, twist, twisted) It'll be a hell of a lot cheaper than 85 clamps.

 

On a stick that size, you're biggest problem will be control. The staves will want to wander around, the mast will test your ability to make things straight and the pressures involved will be higher then the average build. With a long, heavy mast, you'll want for a solid bench to clamp against. This bench doesn't have to be fancy, but hold the pole straight, long enough for the goo to set. It could be as simple as shims on a concrete pad or saw horses carefully set up for level, but you will need to keep her straight or she'll cure crooked and be nearly impossible to fix after.

I find it handy to have a fence to work up against when building a stick. I've used hose clamps, inner tubes, bungee cords, slit PVC pipe sections and a few other devices to clamp up spars. All have pros and cons about their use. Most of these clamps allow you to insert a wedge or two under it, to provide some localized pressure to help with unruly staves.

On a mast that big, I'd want to make up some sectional molds, spaced at specific intervals along it's length. These could be keyed to the bench or setup area so they hold the stick straight too. If these were made in halves, setting up will be easier.

 

Clamps, bench and molds

PAR -
Aha! I was one step ahead of you!!. Yesssssss ;-)

I agree with you 100% about the control issue. These are big chunks of wood that have little brains of their own, it seems sometimes. So my 87' long spar bench is about 20' longer than my boathouse, but laser straight. Hope the picture here comes through with the post. I've also still got the 3 tons of lead in ingots laying around that I'll have at the ready in case the staves want to lift my horses.
Today I (gulp) ordered 90 pcs. of F-style bar clamps to be made at a local fabrication shop. They'll cost about $19 USD each and be of hardened steel on the bar. 18" length and 8" throat depth. Expensive in the short run, but cheaper than screwing up a mast.
The second picture attached to this post is of me making up the 24 sections of molds that will go in the staves. I made them of marine grade plywood so I have no problem leaving them in. I'll drill holes in them to allow any water that finds its way in to find its way down. The pyramid is in the picture still four sided, getting ready to be table sawed down to little octogons.
By the way, in the far background in the last shot, under the roof, is Tigger. Planking started yesterday. Woo Hoo!

 

I'm wondering how you can use those kind of clamps on that kind of mast? Don't you have to have a circular clamping action, like a hose clamp or strangling someone? Sam

 

For a big stick like that, I think I would have opted for the versatile strap wrench. It can provide light to heavy pressure and pretty much all around the diameter of the mast, it can easily be home made too. If purchased by the case, they would be likely cheaper then custom bar clamps, which only apply pressure at two, small contact points.

Fasten down the legs of your support horses. Do this once you're sure it's a dead level run from each end. It's very possible the stick will lift one or several of them if not nailed down.

I hope you used a good laser, as they can be off a fair amount across that distance, possibly over a centimeter. A taunt string will also have a substantial belly across 85'.

I don't understand the need for internal molds on a birdsmouth pole. Swallow tails yes, but not an internal mold. I often use a half mold (sectional) of the stick, placed at even intervals along it's length while installing hard points. They only serve to keep the partly assembled mast from rolling around and supported during machining operations.

The real beauty of this method is the stick sort of assembles itself when you have things lined up correctly. Once this is done in a dry run, mark the staves and butter them up with the adhesive of choice. I use clear plastic sheeting on the two joints dividing the stick length wise, but glue everything else. This produces a set of mirror image mast halves, which can be opened, so the hard points and other details can be installed, like wiring chases or internal halyards. After this work is done the two halves can be glued up, alignment is pre set from the first go 'round, but hit your marks anyway. Then machine and sand 'till you like it.

 

Here's another way...

 

Cinch straps, clever Sam. Is that a Buehler design in the background? A Spanish windless would work too and be quite cheap, just bits of line and a stick.

 

Stole my thunder!

This is what I was going to suggest, but your picture is worth more than my thousand words would have been.

 

Occasionally I'm clever, but this is somebody elses clever solution from another forum and I'm only clever enough to cut and paste. Scott mentioned the Spanish windlass in post #4.

Yes , I believe it is a Buehler design. It came from a Yahoo group, BackyardBoatbuilding2 and another, BackyardBoatbuilding3, which is just more photos from the first group. The boat's name is Alaya, and the handywork and craftsmanship is amazing. The attached photo is the Sampson post with a cast bronze top the guy made for it. Sam

I just found this in another forum about the boat....

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=52998

 

I've often seen work boats polished off like class A yachts, which has always bothered me, a bit like teak trim on a harbor tug.

 

Clamping Plan

Here's the plan, to the best of my ability to predict how difficult this will be, even given a good plan.
The length of this spar (85') dictates the time it will take to apply the adhesive. In this case, West System's 105 with some 406 filler, just in case my joints aren't as tight as I want to believe they are. As mentioned, I'll use a slow hardener, which might buy me 20 minutes on the high side to wrangle the staves into position and get clamped. To position all 8 staves, accurately and this "quickly" would be a gamble at best, more likely impossible. So I like the idea of breaking the glue-up into sections, as shown in the (hopefully) attached drawings. This reduces the amount of clamping I need to get done in a short time, and it also lets me address any peculiar twists or bows in a particular stave on its own, rather than dealing with 7 other pieces of wood simultaneously.
Thanks to all for the clamping ideas. I'd still like to hear from anyone who has assembled a spar near to this size using birdsmouth assembly.
PAR, re. your question of the internal webs, I'll use these simply as a guide to ensure an accurate 45 degree asembly on the glue ups of the pairs and then the pairs of pairs. Like I said, I have good joints, according to me, but a gage doesn't hurt.

 

West system 209 hardener in room temperature conditions (23 - 24 C) will have a working time of 50 minutes. This is much better then 205's 15 minutes or so. 206 will provide about a half hour. I'd use the 209, but be sure to have enough temperature to get a full cure. Below 20 C, it will not cure completely.

Experiment with thickeners before you mix the epoxy. 406 is fine, but you may find that you'll want some other stuff in there too, like 303. You want a strong, gap filling adhesive, but not one that will be a lot harder to sand then the surrounding wood. I very rarely use just one filler type in a mixture of thickened epoxy.

I'm about to begin a 37' spar and related pieces (boom, reaching pole, etc.) for another forum member. I've not built one much bigger, but don't imagine it would be much different, other then scale. A 40' mast is unwieldy and an 85' one is too. Lets face it, not many calls come in for masts the size of yours.

One of the things that makes birdsmouth spars easy to build is the self alignment aspect of the birdsmouth (notched staves) It's important (I think) to have all clamping pressure around the mast at the same point, spaced along it's length. This permits the notches to self align and key into each other. This is why most of us use sections of hose, straps, tape, rubber bands (small spars) and other devices to secure the assembly. We glue the whole mast up as a single unit, in one shot. Some of us (myself included) glue the whole mast up at once, but don't glue two opposing joints (so it can be halved and opened).

It may be wise for you to build a meter long (or longer) sample mast section. This will show you how simply the method works, when assembled as a whole unit. After the glue cures, it can be opened up and the inside treated to the other features often found inside a mast. This may include halyard sheaves, wiring chases or hard points.

Building the mast, stave by stave (gluing two at a time) seems like it's going to offer many more opportunities to get out of alignment. When assembled as a whole, with some sort of banding device, the staves will self align.