Mast splicing?

3ft sounds good. I'd also use 5200 rather than epoxy

Is this for Gismo or your Tornado?

Richard Woods

 

Gizmo, I'm re-purposing the Tornado's mast (sails also maybe)

 

If epoxy I'd ponder the g-flex. In truth I've seen old mast splices with no goo at all. If sensibly stayed and placed in the right space a spice should be as good as a continuous length.

Does the long term galvanic corrosion between the SS rivets and aluminum help prevent them loosening up?

 

The 3M 5200 is not a silicone but a polyurethane and a ferocious adhesive. the defect is being too elastic for this purpose.
Aluminum masts can be perfectly glued with epoxy. There are several formulations of epoxies for gluing alu. Special etchers are necessary (sulfochromic acid). Various masts made by Marechal for the F40 were glued with no problem, the aluminum rivets were just for positioning.
It's not advisable to use a cuprous metal like monel on alu even with insulation and inox is not the best, but acceptable. Unless using special PCV insulators, no hope of insulating the SS from the alu with some goo.But it's acceptable on the mast of a small boat, not staying at sea. Wash the mast after every sailing in salt water.
As already being told, the fit must be perfect, and NEVER make the holes in line as alu is very sensitive to crack propagation. The holes must be perfectly round and adjusted that means you buy the rivets, measure them (there are surprises...) in mm unless you can get aviation Cherry type 1900 rivets at 80 bucks the pack. You buy a 1/8 drill bit (with 135° point would be nice) for the pilot hole and the drill bit of the size of the rivet plus 1/10 of mm. Imperial measures are not the best for tight riveting. Measure several 3/16 drill bits and you'll be surprised by the dispersion of the measures.
So you buy a metric drill bit simply because you'll find them 1/10 of mm by 1/10 of mm. for example if your rivet is 4.80mm (3/16) you take a drill of 4.90mm. That will give a rivet in perfect contact and that's 80% of the final strength.

Another trick is, after riveting with alu rivets , to push out the small steel ball often remaining of the shank and close the hole with a bit of aluminum (from a TIG 4043 metal rod of appropriate size) and some epoxy glue.That makes it almost as strong as an aluminum screw. But it's simpler to buy structural pop rivets like those for truck body work...the (rare) watertight rivets for riveted tanks are almost as good.

 

No idea...

Specialized rivets sounds expensive and annoying to try to find...

 

I don't think those rivets are necessary on your rig/boat.

It depends on where the splice is, of course, but I assume it is not in the high load area, nor where the bend is high

Richard Woods

 

The splice is near the top of the mast about 1.5-2 feet above the top spreader wire attach points 7 inches above where the reacher halyard goes into the mast.

 

Ordinary alu rivets use steel shanks, and the steel remaining (the small ball) is an annoying problem in see water. You have to push them and to seal the hole.

The Interlock have a serie of all aluminum 5056 (ie no steel shank) structural rivets. The 5056There is no hole and it's almost watertight. The 3/16 has a strength of 600 pounds (about 280 kg) in shear so you use far less than ordinary rivets

Price in USA:
http://www.rivetsonline.com/aapie-67-all-alum-interlock-.062-437-grip.html
$27.25 the 100.

Uses drill #8, no need to measure....

Animation to see how they work
http://www.avdel-global.com/en/products/breakstem-fasteners/interlockr.html.

Sometimes for this kind of job "special rivets" are better and simplify the task. I have used them extensively and none has broken or gotten loose.

"ALLOY 5056 RIVETS.—These rivets are used primarily for joining magnesium alloy structures because of their corrosion-resistant qualities. They are supplied in the H32 temper (strain-hardened and then stabilized). These rivets are identified by a raised cross on the head. The 5056-H32 rivet may be stored indefinitely with no change in its driving characteristics."

 

it's not the best place as the mast bends heavily in the upper part and controls the shape and power of the sail...and you have an halyard hole very close.
The main problem will be bend of this portion of mast: it will be uneven because the stiff section of the reparation. And the stresses will be reported to the immediate lower section where there is a hole...

The best place is just under the top attach, as locally the bend is minimal and the mast working mainly in compression..

 

Rivets look cool, I'll probably use them for later projects, but seeing as I need the mast functioning before April the >8week delivery time makes them unfeasible for this.

As for the pattern for the rivets I thought I'd use this is what I was thinking.

This pattern, at the splice seam, on both sides. Would this work or do I need to have rivets at the seam AND at the bottom of the insert?

IE:

 

I've no choice on where the splice is, that is where the mast is cut...

 

Hard...but try it it may work. It seems you have not the choice. A little prayer may help. Use SS rivets 3/16. Do not worry with glues. Just seal it with some 5200.
you need to have rivets at the seam AND at the bottom of the insert, no play allowed.

For spacing of the rivets, a good explanation, that gives the minimal requirements of spacing:
http://navyaviation.tpub.com/14018/css/14018_547.htm

Interlock all alu are more common than you think. Look for a provider in Canada, they do repair planes and trucks in this country. Try to find a company making truck bodywork, they may help you.

 

So will the diamond pattern in the two pictures I posted work?

 

Yes but maybe a bit more rivets. Read the paper, and try to figure out the total stresses.
Try http://www.quebecbolts.com/eng/home.htm

 

I'm getting the feeling I should just have the guys at ProTech do this for me... The bill might be easier to stomach than the head ache I'm getting over this right now...