Finishing mast head of hollow mast

[Jim Wellman]

After building a hollow mast, using a bird's mouth method, how do you finish the masthead portion? Is it left hollow right to the top and then fitted with an end piece?

Also, should the last 12 to 18 inches at the top be solid? Various hardware will be mounted in this area so that's a consideration.

[TomRobb]

Yes, I'd plug the tip. And it'd be easier to fit the plug as the mast is fabricated than afterward. It could be tapered on the outside as the mast is tapered inside. and I'd make it long enough for all the fittings plus some for a longish conical inside taper of the plug to avoid a stress riser, but that may be overkill.

[Andrew]

Tom, In the spirit of splitting hairs on a gnats behind, I think a conical taper would actually be more of a stress raiser than a 90 deg. A concave on the bottom of the plug would be better, but, as you say, overkill.

[This message has been edited by Andrew (edited 11-13-2001).]

[Andrew]

Err... was that a positive or negative conical taper?

[David Tabor (sailordave)]

Well, I made a short section of Birds Mouth spar (12") long so as to have a round section roller. I took a 1.25" Forstner bit and drilled into the ends about 2" and plugged each end w/ dowel epoxied into place. It helped that the side to side measurement was just over 1" so I didn't have to remove much wood. If I was doing a mast top I would have a pc of rod welded to the bit and run it down about 18".

[Thad]

You could always install a truck, covering endgrain and allowing for a flag halyard

[TomRobb]

Andrew, negative, a conical hole to make a gradual transition from hollow to solid. Probably overkill on a small mast with plenty of safety factor. And a truck would be cool too http://media5.hypernet.com/~dick/ubb/biggrin.gif

[Don Maurer]

How would you go about cutting a long conical inside taper in a plug?

[TomRobb]

I'd fabricate it in six vertical pieces to match the six sides of the mast. It wouldn't really be conical, more of a six sided negetive space pyramid. Then glue it together, after that fabricate the mast around it.
Or find a long tapered drill bit http://media5.hypernet.com/~dick/ubb/biggrin.gif

This really is nuts, isn't it? Just make a hexagonal plug, slather it w/ thickened googe and glue it in. Only you will know what's there.

[This message has been edited by TomRobb (edited 11-14-2001).]

[capt jake]

Sounds like this may be a job for a wood lathe (if you have one or one you can borrow). From what you all have described, I could turn one out fairly quickly on it. It would be easy to adjust the 'plug' to accommidate the interior size of the spar, as well as cutting the conicle taper.

[Syd MacDonald]

Capt J- I did it your way, wrapped it up inside the mast after attaching a string and lots of thicnened epoxy. when the mast was clamped I pulled the plug up snug with the string.

[NormMessinger]

I found the eight sided plug at the top and bottom of the mast made it a lot easier to snap the staves together when it came time to glue up the assembly.

--Norm

[Charlie J]

I've fabricated four spar sections so far using the birds mouth method. I've been toying with how to include solid sections also and have come up with this- tell me what you think.

When you do the initial glue up, run packing tape ( or something to prevent adhesion) on two mouths, on opposite sides of the spar. Apply glue (I used epoxy) to the other six mouths and glue. Apply the clamps and tighten just as if all the joints were glued. After the glue cures you can pop the spar apart at the packing tape. Then you'd have two halves in which you could fit solid sections where ever needed. Then when you glued it together ( the final two mouths)with them inside, the remaining joints would HAVE to fit since everything else would be epoxied.

For the ones I'm doing at the moment, I'm fitting octagonal plugs to slide inside, well buttered with an epoxy/filler coating.

[Charlie J]

Originally posted by c e jones:
I've fabricated four spar sections so far using the birds mouth method. I've been toying with how to include solid sections also and have come up with this- tell me what you think.

When you do the initial glue up, run packing tape ( or something to prevent adhesion) on two mouths, on opposite sides of the spar. Apply glue (I used epoxy) to the other six mouths and glue. Apply the clamps and tighten just as if all the joints were glued. After the glue cures you can pop the spar apart at the packing tape. Then you'd have two halves in which you could fit solid sections where ever needed. Then when you glued it together ( the final two mouths)with them inside, the remaining joints would HAVE to fit since everything else would be epoxied.

For the ones I'm doing at the moment, I'm fitting octagonal plugs to slide inside, well buttered with an epoxy/filler coating.

Brought this back up as I'd really like some feedback on the question

[Jim Wellman]

Seems as though there should be at least a couple of tried and true methods from way back, or were the old boats built with solid masts?

The eight sided plug sounds like a good solution for the "two halves" method. The only thing I wonder about is could there be a problem with a bending or twisting tendency because all joints aren't glued initially. Even though they are clamped, could this make a difference?

Seems that putting the plug(s) in place when the initial glue-up is done would be the best.

[garland reese]

If memory serves correctly, the WB article on birdsmouth spars suggested that the ends be plugged by drilling the inside round with a proper sized bit, using a block centered on the end of the spar as a bit guide. This would work nicely for the ends of small non-taperd, or very slightly tapered spars.
Other methods discussed would seem to be appropriate for tapered sections or for sections along the length that might need some re-enforcement for mounting hardware n stuff. Might be easiest here to make a hexagonal plug as Mr. Messinger suggests.
Keep us up on what you find to work best. I'm wanting to build us a small birdsmouth spar to use as our flagpole at the home.
garland

[Charlie J]

The ones I've done so far seem really stiff for the weight- of course, time will tell. I will say this - I did a 5 foot bowsprit in three hours flat, from walking to the radial saw to cut the planks in half to final sanding, including drawknifing the edges sticking out and planing round. I doubt a solid spar could have been done all that much quicker. I did use a molding head with a planer blade set at 45 degrees to cut the mouths.