Plug ends in Birdsmouth spars

[Carlsboats]

Anyone have ideas on how to fit solid plugs into
the ends of 3 1/2" to 4" diameter Birdsmouth spars? See no problem in plugging smaller diameter spars -- say 1 1/2 to 2 1/2" diameter for a boom or gaff. There, the open interior is small enough for ordinary wood bitts to bore out for a dowel. But a 4" mast has a pretty big open end, and making a snug,eight-sided shaped insert, six to eight inches long, is a neat piece of woodworking. A big dowel would be easy to make, but how to cut the hole for it? Do Forstner bitts come big enough for the job and, if so, do they require a special jig to keep them under control at the start of a bore? Make some sort of boring bar kept in line with a jig? Don't have any way to make my drill press run on the horizontal, and don't have a wood lathe. Ideas?

[NormMessinger]

I cut an eight sided plug and rolled it into the spar as it was assembled. Served to keep the staves from collasping in a heap as well. If you've already assembled the staves I'll defer to others.

[Bob Smalser]

When I didn't have Norm's foresight I used a large Forstner bit in the 14V DeWalt to make the mortise and turned the plug crossgrain on the lathe. A bandsaw and disk sander could also make the plug.

Like this one in another application:

http://pic3.picturetrail.com/VOL12/1104763/5424116/69403671.jpg

[kc8pql]

Norm, could you explain what you mean by "rolled the spar"?

[Bill Perkins]

Here's a plug design I drew up after seeing a similar square one . An octagonal plug is taken to the band saw where 4 deep V cutouts produce the 8 tines shown .If the interior of the spar tapers I guess you'd cut off most of the solid before sliding the plug in . Advanced features include : flexible tines to conform to a tapered interior ; smooth reduction of cross sectional area along the plugs length to avoid stress concentrations ; and somewhere in the center for the excess epoxy to go so it doesn't form a rigid lump on top , negating point number 2 .

I haven't had occasion to make a hollow spar , but did freehand a test plug that came out well. Some type of deep vee support bed while sawing would be worthwhile for long tines .

http://www.imagestation.com/picture/sraid72/p6090dd37b7cf0d46e40953a8e939a864/fb7eff98.jpg

[ 10-17-2004, 03:39 PM: Message edited by: Bill Perkins ]

[BillyBudd]

My approach to this, based on learning from all on this forum, having asked many questions about the process, was to a) set up the 8 sides in epoxy and clamps, b) slightly unclamp the octagon a small section at a time and slip waxpaper as bond-breaker across the octagon, c) reclamp, d) next day unclamp and split the mast in 2, coat insides with epoxy, make end plugs and other stiffeners to roughly fit, but with drain hole in middle, coat them, then goop them up with peanut-butter like epoxy and set them in 1/2 the mast, e) clean out any wax, f) re-epoxy remaining joints and clamped up. Sounds like a lot of bother but it was smooth sailing. Wires could have gone inside the mast; crumpled aluminum foil as radar reflector did. That was the 13.5' mizzen mast at 3" diameter. The main mast is next at 4" x 19.5' but frost may give me an out for the fall/winter. Hope not.

[htom]

You could, of course, make a birdsmouth plug. ;)

[bheys]

I used the method that htom recommends and found it quick and easy on my 3.5" dia. mast. The staves on the plugs were thicker than the indicated by the standard formula. On a much smaller spar for a boat hook I put it together without plugs - what a mistake.

[NormMessinger]

Originally posted by kc8pql:
Norm, could you explain what you mean by "rolled the spar"?The plug Bill illustrates is the proper shape. It spreads the load rather than making sharp transition from solid to hollow. Naturally I didn't do it that way.

By roll I mean, I have the eight staves laid edge to edge, all slathered with goop, flat on the work surface, the pre-fit plug laying on top the first two. These I fit together and to the plug. Roll slightly to fit the third stave to the second, roll a bit more for the fourth, etc. Gloved hands begin to get messy. Don't try to get the staves to snap together along the whole length until you've rolled in and banded the butt of the mast. Slip in the pre-fit plugs, if any, mid spar and top. A bit of a shake will cause everything into position at this point. Change to clean gloves and clamp.

[Tealsmith]

How about a big holesaw like plumbers use for drain sized pipes. That would make a round hole in the end. Then just turn the plug on a lathe or cut an approprite sized circle on a band saw.

[Figment]

I've nothing constructive to contribute to the problem at hand, but I gotta say.... Nice illustration Bill!

[DerekW]

The method illustrated by Bill [nice penmanship!] is the one I've used on several spars, including a mast of the diameter you ask about. Tines a foot or so long will bandsaw out without much trouble, unsupported. A double 'crowned' plug makes a good load spreader at partners &c. Making the blank for the octagon in the latter case from a lamination of two 'half thickness' pieces allows for an easy job of creating a centreline hole for passing cables. Drilling the same hole in the finshed plug is a bear.. DAMHIKT.

cheers
Derek

[kc8pql]

Originally posted by Tealsmith:
How about a big holesaw like plumbers use...Hole saws are guided by the pilot drill bit in the center. You can use them in a drill press without the pilot, but to try to use one freehand with nothing in the middle to hold the pilot will tear up the mast, your hand or both.

[ 10-12-2004, 06:15 PM: Message edited by: kc8pql ]

[Carlsboats]

Thanks to all. I like Perkins retrofitted insert.Spreads loads. Also looks like something to put mid mast, with fingers on both ends, to handle crushing load at spreaders. Maybe better to do it that way than to run a compression tube through the mast, which produces a hole for potential leaks/rot. Will give that a try.