Clamping Octagonal Birdsmouth Spars

One of the great pleasures of this forum is that I can wake in the morning and be thinking about someone else's project!

A couple of thoughts:

If using epoxy the challenge is to get the spar components arranged together, glue applied and clamped up within the thin film time of the slow cure products.

The length of this spar makes this all a tall order and I see why you wish to preglue sections beforehand.


I asked myself how to approach this problem if the spar section were of infinite length and the glueup process could not be done on the total spar.
If this were the case I would design the assembly process in a progressive manner starting at the end and laminating as I proceed down the length.

I would start by gluing up your scarf's. I would then arrange all the bits on the horses in 'dies' made of 1/2" ply as follows:



Maybe dies set every eight feet?

To laminate I would start at the butt end and butter up the birds mouths for say 10'. Draw the facets together and start to band. Once the facets are drawn together at the butt it is just a question of proceeding down the run by buttering up and banding. The 'dies' will be cut off with a saws-all as soon as they interfere. After running say twenty feet the banded up section can have the bands tightened up as the spar takes level on the horses.

This approach buys you several things. The most important is getting all the bits held in a nearly assembled form BEFORE the clue is applied. This is 90% of the battle in large laminating jobs. Next you can pace the clamping well within your thin film time as you proceed down the length of the spar. Also a 'dry' run is easy to practice by just sliding the dies along as you band the spar. If satisfied all is well pull the bands and slide the dies back in place as you go to set up for the glueup.

Needless to say thinking about this problem is simpler than fighting the battles I have on my plate

*Just reread your post. 3"x8" wow! Maybe no way this would work with the weight of this spar. Also sounds out of bonds for epoxy on such large bits??

 

I agree, epoxy isn't the best choice for this spar, though a environmental window could be selected, for laminating up this spar full length, within an hour, which would be his window, for workable extra slow goo at room temperatures. He could further increase this time with lower ambient temperatures, then raise them to effect a cure. The other glues possible for this spar may require considerably more clamping pressure and fine fitting joints, but still within the ability of an amateur builder who uses care. I would use three stages of assembly; the first is scarf the staves full length, second to glue the mast together, but skipping two of the joints (opposing) and last to glue those two remaining mast halves after interior assembly is completed. This likely would require more then one laminator to apply goo to the staves, during the second and last stages.

 

Yes- Use gallons of epoxy but not for woodwork. Have lots of luck with lowly Titebond

I had a contract this fall trying to fix a rig which had sprung joints in the spar. 80 foot hull, had a main of about the same dimensions as Scotts and had lost about 1/3 of its glue lines. In this case it was a modern build of traditional rig. Epoxied. The main was on hoops which kept the spar free of any finish. This no doubt contributed to the problem as the weather got the rig, had no maintenance, etc...

 

Bntii -
Your post has reminded me that I'll face this same problem (weather vs. epoxy = weather wins). My main and fore will have hoops so the bare wood of the spar will be exposed, and being 75' or so in the air will be a challenge to stay motivated about re-oiling, etc.
Off the stated topic of this thread, how about finishes for an...er, unfinished wooden mast with hoops? Suggestions? My ideas tend toward oils like teak oil or lignum vitae, but I'm uneducated in this (and admittedly many other) areas.
Thanks
Scott

 

As far as using metal bands or hose clamps with epoxy.. Epoxy will drips onto bands, bonding it to the work...
Hummmmm, Epoxy bond well to metal.. How do you get the bands to come off?... Darn, I hate grinding.....

 

I don't know about the finish Scott but there are experts here who do.

PAR?

Boyle- nice boats on your site

The straping used is fabric

nylon/poly etc.

cheaper the better- 3/4" ratching type in short lengths- cut off when the deed is done

 

Hey, thank you... Your're welcome to my site anytime.... And using a nylon tie-down strap is an great idea... I didn't think of that...

 

It's easy to protect most things from epoxy. My two favorites are clear plastic packaging tape and clear plastic poly sold in rolls for painting drop cloths.

As far as finish on a hooped, bright stick, I too would tend toward oil and have my own secret recipe for some. If you intend to inspect and touch up at least once a year, then a hard coating like polyurethane may be a choice for you. Oils will require you climb the poles a few times a year at least, to keep doing it's job of preventing UV from breaking down the fibers in the wood.

Having owned a schooner with hoops, I'll never use the beasts again, preferring beads, gaskets or lacing much more, as they stack neatly, are a lot easier on the mast and it's finish, jam less often and don't make the racket that hoops can. Even if I owned a replica, I'd toss the hoops, though they do make climbing handy and are salty as sin.

 

Hey Scott, I don't have a clue as to your weather/working conditions....if your weather is warm consider "cooling" your glue down a little bit, that will give you a little extra time for clamping. The thicker glue will also be slower to absorb into the wood, you don't want it too cold. You might also think about a "pastry bag" kind of arrangement to put your glue into, just squeeze it out like a pastry chef decorating a cake??? I saw a guy make a funnel kind of thing from a newspaper..folded it into triangle, taped on one side, opened up from the middle...glue dropped in, top folded over, use scissors to cut whatever size "spout" you need for your application. Good luck
mobjack68

 

The pastry bag trick works pretty well, but is only good for small batches of epoxy, or batches that will go on the work within a few minutes. Epoxy confined to a small place, like a pastry bag, will heat up very rapidly, so it has to get out of the bag quick or you'll be trying to squeeze hot cookie dough through the little hole on the end.

 

Great idea Mobjack on the paper applicators. I'll have 10 gluers and 10 spreaders working on each glue up, and I'll have 7 glue ups to do so that's a lot of pastry bags (which I've used before).
Now, against (groan) PAR's recommendation, I'm going ahead with gluing this up in pairs. I have an ultra straight and level, 90' long set of spar-horses (after previous warnings about laser levels I rechecked with a 110' long piece of 1" clear urethane tubing water level and all faces were +- 1 mm or perfect. I just can't see getting all pieces hefted and placed and glued and clamped all within 20 or so minutes (or, using Mobjacks idea of refrigerating the goo first then maybe I'll have 45 minutes or so). My 90 clamps are almost finished (18" sliding "F" bar clamps) so I'll be equipped on that end, now it's just a matter of getting 18 non-English speaking Thais and 2 non-Thais working off the same page come glue up time. More on that drama another time.
Bntii, after rereading your post about the dies I think I understand. In considering a complete (or 1/2) glue-up as has already been opined on, am I to understand that (in your picture) the non-crosshatched areas are cutouts in the plywood, through which the staves would be placed to pre-position them before glue-up? And, if so, I think this would still work on my tapered spar (I'm tapering the stave width, not just planing off the excess material on the outer face to affect the taper). I'd just start at the mast head and slide the dies toward the larger diameter end after goo is applied and band clamps are ready to apply. Does this sound like what you were on about?

Also, what about this epoxy for big pieces you (Bntii) mentioned and with which PAR agreed? Is there a size cutoff on something like this? I would really have thought this was a good application for West (or whatever) epoxy. Can you elaborate on your concern/comment re. spar size (e.g. big) and the suitability of epoxy to glue? I'll further inquire with West System on this issue.

 

Hello Scott,
On epoxy- The advisability of using epoxy to bond wood is not a function of the total project size so much as the size of the component cross section.
A large piece of wood is tough to bond to another due to the dynamic nature of the material. Any glue is challenged with large pieces of wood. Epoxy is just less well suited than some other glues in this regard.
To illustrate consider the cold molded hull: small cross section of wood well served by bonding (encapsulating/waterproofing/etc) with epoxy. I try not to rely on bonding with epoxies when the cross section of the component exceeds ~1/2". I don't even build tillers with epoxy when the laminates are just 3/8" as the varnish is so often allowed to go and the seam will split with epoxy. I am conservative in this regard I know. I think that many start by using epoxy for everything. One learns where to use but more importantly where to avoid.
I would not glue up this spar till you have some very direct and certain advice on the glue to use. A 3" x 8" cross section in the weather is a tough nut to crack for the glue (to my mind). At the very minimum fillers should be used with the epoxy. You will have some very real concerns about joint starvation if you do not use care. Just shooting from the hip if I were bound and determined to glue up these sections with epoxy I might concider putting some light mat in the joints.

On the "dies"

Think pasta maker or an extrusion process. The dies I describe are simply plywood discs which have cut outs to hold the spar sections in proximity to each other. Sort of like holding the staves of a barrel before banding.
Tapers or what not do not matter to this approach. The key is simply to hold all the spar sides in alignment. I wouldn't slide the disks along during glue up, just cut them off.

Made from 1/2" ply in a few hours- you need maybe eight? Four sheets of rough ply ~$40.00 USD.

I didn't want to draw it out but could.......

 

Laminations of an inch (250 mm) or less is the accepted recommendation of the manufactures (West System and others). Above this size, the adhesive competes with the internal stresses within the lumber and checks or other unseen internal defects, can mar an otherwise perfect job (strength of joint wise). Call the West System folks, they love challenges and will answer an email promptly.

 

Glue Up Begun

Sorry for the repeat picture posts (there's another thread with some of the same pictures). But I thought these were appropriate here, as well.
I've opted for West after talking to them about this. Using an internal fillet as shown below is a big step in keeping the joints together. They also recommeded mechanical fasteners strategically and very carefully placed along the length of the joint. I'm on the fence about that one. Ideas?
My procedure is a bit of a hybrid of many suggestions from you folks.
The first step was to glue up about 6 scarfed stave sections to 88' or so, plane them down, taper the entire stave from end-to-end from about 7 1/2" to 4 3/4" with a circular saw, then cut the birdsmouth with a circular saw and custom bed/fence for this purpose. I then cleaned up the birdsmouth with a rabbetting plane to ensure 90 degrees (critical). THAT was a huge job.
Once the parent stave was finished, we made it ultra straight and flat (it's actually like an enormous rubber band). All of our future stave sections have their scarf faces already cut, which we are now just laying in, gluing and clampng one at a time. The beauty is that we can place 1 stave section at a time (about 4.5 meters long each), which is an easily manageable job. This also lets us select (and trim if necessary) each stave section to make sure no 2 adjacent stave scarfs are within about meter and a half or so of one another.
Once we place 6 or 7 of these and are full length, we lay out the taper of the newly glued stave and cut it. Then we come back and cut the birdsmouth on the same edge we just tapered. By the way, if anyone has a recommendation on how to cut the taper and birdsmouth at the same time that would be soooooper. Save about 88' of circular-sawing.
I'll probably do this 4 times then start over, opting for the clamshell approach to final assembly with 4 staves glued up being set down on the opposite semi-spar, laying in the swallowtails easily this way as well. I've made a couple of 135 degree plywood gages to double check the interior angle of the stave section as it's glued inc and can easily clamp it either direction if the angle's a bit off.

 

I am wondering if you could pre assemble the whole spar dry, open one joint, apply epoxy and clamp. Repeat 7 more times? Might work