Building mast with bird's mouth bit?

[Ocean Spray]

Can someone direct me to the thread with the photo essay illustrating a mast being built with a bird's mouth bit?

[WX]

Try this mate.
http://www.duckworksmagazine.com/06/howto/birdsmouth/index.htm

[StevenBauer]

I've built a few spars with the birdsmouth technique but it always seemed easier to use the tablesaw, not a router. Just my take.


Steven

[andrewe]

The glue question is often raised. The guys who built Cambria´s 157ft. mast used urea formaldehyde after advise from the techies.(I talked to them about it) Then Duckworks say not to use epoxy. And implies that U F is not good. Resorcinol requires high clamping pressures. Can you achieve these with hose clamps? I used epoxy and a router jig for my little spars, but my next boat is a bit bigger.
I will probably go for epoxy again---Any thoughts?
Andrew

[Bob Smalser]

Then Duckworks say not to use epoxy. And implies that U F is not good. Resorcinol requires high clamping pressures. Can you achieve these with hose clamps? I used epoxy and a router jig for my little spars, but my next boat is a bit bigger.
I will probably go for epoxy again---Any thoughts?
Andrew

No glue unprotected by uv-resistant coatings survives much UV light. Not just epoxy.

UF resin glues used since before WWII have probably produced more successful masts than all other glues combined. They produce a stiff joint and clean glueline, easy to varnish. But most UF glues don't fill gaps well and even the best birdsmouth joints have gaps to fill. The same applies to resorcinol....it doesn't fill gaps well.....and both UF and resorcinol like more clamping pressure than you can generally achieve using hose clamps.

That leaves epoxy as probably the best choice for birdsmouth joints. Keep it painted. That said, in a large mast where I wanted the stiffness, strength and proven reliability of either UF resin or resorcinol, I'd consider a box-section mast I could get high clamping pressure on.

http://www.duckworksmagazine.com/06/howto/birdsmouth/index.htm

http://www.duckworksmagazine.com/06/howto/birdsmouth/image021-s.jpg

Note: Contrary to the terms he is using, the author in Duckworks is using a Resorcinol Formaldehyde glue formulated to cure at room temperature. Phenol-modified resorcinol glues require significant heat and pressure and their use is generally limited to plywood factories. The amount of clamping pressure provided by only packing tape is questionable.....think he's getting the 150 psi throughout all those gluing surfaces required to draw the glue film thickness down to the .002"-.007" required for resorcinol? I don't. Not by a long shot. A 70-ton M1 Abrams Tank produces around 16 psi of ground pressure. Sixteen. This builder appears to be using techniques significantly more questionable than using epoxy in a mast. Even Aerodux 500, the most user-friendly resorcinol-formaldehyde with fillers that help fill gaps requires clamping pressures of 100 - 145 psi.

http://cpadhesives.com/media/CP-0900TDLC.pdf
http://www.svsp.co.uk/Shop%20Website/HSE%20Sheets/Aerodux%20500.pdf

[kc8pql]

Well said Bob.

[David G]

Well said Bob.

Ditto.

[andrewe]

Thanks Bob, as always concise and to the point-A

[Banjo]

Good one Bob,
I agree with all you said. Epoxy would be fine if protected with a light colored paint from UV.

To be fair on the author in Duckworks, here is a copy of his comments on questions about not using epoxy:


roy mc bride 15 Jul 06 00:47

Hello, Its really nice to read all the readers comments!The one repeating question is of course the reference to not using epoxies? My reason for saying this is based on some trade insider informations,this was handed down to me by a Master Craftsman,Karl Stremple,of what was then called 'Stremple Marine' here in Cape Town.He now resides and works in/on? Lake Constance in europe Karl found out that a very well known English, South Coast,yacht restorer had used epoxy on a set of masts on one of their rstorations.We are talking about a large boat,80ft or so.Those masts failed and had to be replaced,they used Recorcinol Glue the second time.This makes sense,the best marine plys have Recorcenol (phenolic) glues,as far as I know plys do not use epoxies? So it may be my personal view and even unfounded but based on what I know and that Recorcenols are Boil Proof and Moisture proof,I will stay with my comments,Rember,epoxies arenot UV proof and are said to fail around 180 c? Yes thats hot but is why one should never paint an epoxy build boat Black or any dark colour. Regards Roy

[kc8pql]

All glues have limitations and will fail if used improperly. The problems come when hearsay information like the ducksworks post above is taken at face value without doing any research about when, how and why to use each type. Is this guy going to amend his post when his mast fails because he didn't take the time to find out about the lack of gap filling ability or the necessary clamping pressure resorcinol requires? Probably not. The misinformation will just continue to be passed along as fact.

[kc8pql]

bump

[werner]

Why must a epoxy glued mast be painted ?
I understand that UV brakes down epoxy (coatings) but if I just varnish the mast the UV rays won't hardly reach the visible glue line let alone penetrate deeper ?

[Banjo]

Heat Werner, your varnished mast will get 3 times hotter than a white painted one. Epoxy softens when hot.

How big is your mast?
Is it stayed?
Will it be exposed to lots of sun and hight temps?

[werner]

Banjo,
it is a stayed mast 13,5m long 112mm to 46mm double stayed,
I think this could be marginal but these are the original dimensions I found,
could be problematic with the use of epoxy , and I don't want to worry about the temperature all the time.

[Banjo]

I would paint it, otherwise you will be cursing later every time you need to sand and refinish varnish on that mast.

[kc8pql]

Why must a epoxy glued mast be painted ?

It doesn't varnish will work just fine.

[kc8pql]

Epoxy softens when hot.
Yes, but it will never get hot enough to be a problem. There's no evidence that wood/epoxy structures come apart because of normal heat, even in the tropics. If it was a real problem we'd all be seeing wood/epoxy boats coming apart all over the place. It just doesn't happen.

[kc8pql]

Banjo,
it is a stayed mast 13,5m long 112mm to 46mm double stayed,
I think this could be marginal but these are the original dimensions I found,
could be problematic with the use of epoxy , and I don't want to worry about the temperature all the time.

My birdsmouth mast is 15.3m (50'). Epoxy is the only practical glue for a mast that size given the open time you need to assemble, the gap filling you need for the inevitable gaps and the clamping force you can reasonably expect to exert. You'll still need a lot of help when you glue it up. I had 12 people. A few more wouldn't have hurt. I pulled my mast this fall after two years out in the weather. It looks like new.

The best reason for varnish rather than paint is that any developing problems with rot can be seen easily and fixed.

[werner]

that makes one helper pro meter, are these the same guys who promised to help me with the boat ?

[kc8pql]

...are these the same guys who promised to help me with the boat ?

Probably not. They'll be anyone you can find. Most won't know anything about boatbuilding, or building anything for that matter. What you need are hands to spread glue. My mast has 400' of glue line. The slow hardener I used with the epoxy gave us about 50 minuets to spread the glue before assembly and clamping. Most of the people who helped were just interested friends. With two people mixing and 10 spreading we had the mast together and clamped in less than an hour. The brunch afterward lasted well into the evening however.