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Jimbo2004
10-31-2010, 06:20 PM
I have some Sitka spruce left over from another project and needed to make a radar pole mount to stand on the transom of my boat.

The plan was to make a 7' tall by 3" dia mast/pole.

two questions

1. I went to the online calculators and it appears that each stave should be 1 1/4" wide but I can't figure out how thick the wood should be?

2. Also planned on epoxy gluing up each stave then perhaps 6 oz glassing the outside for add'l strength, any thoughts on that?


.

Markmuk
10-31-2010, 07:15 PM
Hi Jimbo,

A suggestion before you try to epoxy your pole: Assemble and clamp (hose clamps work well) the staves "dry" without epoxy, then remove the clamp from one end, epoxy and reclamp, then work your way down the length until the entire mess is glued and to shape. Ensure that the clamps may be removed (polyethelene plastic works great at an adhesion insulator), and let the epoxy cure.......... Trying to align eight epoxy-slimed, 7 foot staves into a round shape can be much more than a challenge - I tried it once with disastrous results - doing it dry first, then applying the epoxy is a much kinder, gentler way to go. Good Luck!

wayne nicol
10-31-2010, 07:21 PM
check out the "grain orientation" for birdsmouth post on the plans/design section.
lots of good answers there.
g'luck

paladin
10-31-2010, 07:26 PM
I don't have my notebook here, but I would make it at leat 5/8ths and probably 3/4 inch is better. You are hanging some weight on it and don't want it to flex much. Google Duckworks archives birdsmout and you will get all the info. I have reduced all that info to 3 pages in my spar notes.

Jimbo2004
10-31-2010, 08:35 PM
Hi Jimbo,

A suggestion before you try to epoxy your pole: Assemble and clamp (hose clamps work well) the staves "dry" without epoxy, then remove the clamp from one end, epoxy and reclamp, then work your way down the length until the entire mess is glued and to shape. Ensure that the clamps may be removed (polyethelene plastic works great at an adhesion insulator), and let the epoxy cure.......... Trying to align eight epoxy-slimed, 7 foot staves into a round shape can be much more than a challenge - I tried it once with disastrous results - doing it dry first, then applying the epoxy is a much kinder, gentler way to go. Good Luck!

I was thinking about making a cradle to hold 4 staves epoxy them, then do the other 4, so then I would have two halves to to put together rather than managing 8.

Milo Christensen
10-31-2010, 08:54 PM
I was thinking about making a cradle to hold 4 staves epoxy them, then do the other 4, so then I would have two halves to to put together rather than managing 8.

I wouldn't do this. The alignment of the pieces is far too critical. You just need to get a second person involved and heavier than the thin disposable gloves for both. Slather up the insides then thicken the epoxy to peanut butter consistency and fill the bottom of the v of the "birdsmouth" about 1/3 full. Wait. As the expoxy starts to set up, assemble. Start with you and the assistant at both ends. Get it reasonably round and loosely zip tie your end while the assistant holds the other end also reasonably round. You then work out from the middle, the assistant still keeping things reasonably together at one end. As soon as you get the middle together, zip tie it. Move down a couple feet and align and zip tie, have the assistant switch to the other end, you move to the couple of feet the other side of middle, align and zip tie. The ends will be easy. Tighten all the zip ties really tight. Scrape off all the extra epoxy.

Any way, to answer question #1, stave thickness is half the width.
As far as question #2, I've never felt the need to cloth over a birdsmouth spar after I've put 2 coats of clear epoxy on the outside (keeping in mind all the epoxy also on the inside).

Jimbo2004
10-31-2010, 09:14 PM
ok, thanks

ByronB
11-01-2010, 05:08 AM
I have built a mast in two halves in the manner you have suggested and had no problem. Build some supporting cradles, slather on the epoxy on four of the staves and assemble all eight together. I used large hose clamps and non stretch tape wrapped tightly along the mast.
After the glue has dried, disassemble, epoxy the other four staves and reassemble the same as before but leaving out the epoxy on opposite sides so you have two halves. You can then add reinforcing inside the mast as required before glueing the two halves using the same method of clamping as before. I found that making some octagonal pieces to sit inside the mast while glueing the halves helped with alignment and assembly.http://lh4.ggpht.com/_Dr92OLmUrPw/SRAoN69kijI/AAAAAAAAAPM/gyo4g8MXJik/s720/103.%20Mast%20glue%20up.jpg

ByronB
11-01-2010, 05:15 AM
And another couple of photos of the process.http://lh4.ggpht.com/_Dr92OLmUrPw/SRAoNWZacPI/AAAAAAAAAPE/sNjNJ5FruRM/s720/104.%20Mast%20split%20for%20adding%20reinforcement .jpg

ByronB
11-01-2010, 05:18 AM
Oops, here's another.

http://lh5.ggpht.com/_Dr92OLmUrPw/SRAoOpgeD7I/AAAAAAAAAPc/XLvBrsbjkzA/s720/101.%20Mast%20dry%20fit%20up%20in%20supports.jpg

Jimbo2004
11-01-2010, 07:26 AM
Also any ideas how to attach a 1/4" 6"x6" aluminum plate to the top of this pole?
this is the base plate to attach the radar dome.

I was thinking about compression block at the top thru bolted to the plate.

Jimbo2004
11-01-2010, 07:29 AM
I have built a mast in two halves in the manner you have suggested and had no problem. Build some supporting cradles, slather on the epoxy on four of the staves and assemble all eight together. I used large hose clamps and non stretch tape wrapped tightly along the mast.

Thanks for the info & pics

any problem with the epoxy bonding to the hose clamps?

mcdenny
11-01-2010, 07:50 AM
Here's the "birdsmouth bible" link http://www.duckworksmagazine.com/04/s/articles/birdsmouth/index.cfm Scroll down to find the calculator, forget all the math at the beginning of the article.

The staves can be any thickness you like as long as you adjust the outer diameter to compensate for the wall thickness.

A seven foot pole is going to be much easier to snap into alignment than an 18 or 20 foot mast, don't worry about it.

"U" shaped cradles set up every couple of feet, like molds for a hull, makes it simple to get the staves aligned and straight. Slow epoxy at 70ish degrees will give you plenty of open time to get things set up. A hose clamp every foot clamps it all together. I never tried plastic wire ties but they ought to work as well if you can pull them tight enough. The clamps and "molds" need poly film between them and the epoxy.

You want plugs in the ends and wherever anything attaches to the pole.

You could screw the Al base to the top of the pole. Screw and glue with a generous fillet would be even better if it doesn't have to be removable.

I presume the radar wires run down the inside. Maybe you could bond in a small dia PVC pipe down the centerline to make a wiring chase that kept water out of the inside of the pole.

ByronB
11-01-2010, 07:54 AM
Thanks for the info & pics

any problem with the epoxy bonding to the hose clamps?

No problem. The squeeze out was not enough to cause trouble. If you use an assymetric birdsmouth the glue might stick to the clamps but a bit of heat will fix it.
Do a google search for "hollowma.exe". That's a program that does the calculations for stave thickness and width.