Glue for alloy mast?

[Greenheart]

I expect there are several (dozen) threads precisely answering this, but no single word in the search will seek them out.

Doubtless I ought to use rivets, but I don't want to weaken my mast by drilling holes, not even 3mm diameter.

I'm thinking I could scrub the alloy with acetone to get any crud off, then glue a few inches of 2-inch wide webbing around the curve of the mast, having stitched a loop of 2mm dyneema through the webbing...so the pull on the block I need up there, won't stress any single small point on the mast.

What adhesive do I need? Is there something better than acetone, to prepare the alloy surface?

Thanks.

 

[VicS]

Google will find instructions.


Id use pop rivets

 

[Norman_E]

Aluminium is a pretty difficult metal to glue anything to and I think your webbing will be pulled off fairly quickly whatever you use. Where is the block required? If its at the masthead can you attach it to the mast crane? All masts have holes in them, including big ones for halyard exits so a few 3mm rivets are not going to do any harm provided you are sensible about their location, i.e. not too close to other holes.

 

[vic008]

I'd use machine screws. Glue never takes to alloy too well.

 

[Greenheart]

Rivets are certainly tempting because I already have them, and know them.

But it can't be clever to put new holes in the mast, where it tapers above the hounds, specifically in order to increase the loads there.

The masthead does have a spare block, but the top 6ft of mast isn't stayed. I want a spinn block about 15 inches above the hounds, just before the mast starts to taper. I could be persuaded to drill small holes, but I'd rather give glue a chance first.

The webbing was just a wild idea to broaden the contact area of the glue. I could glue a plate to the front of the mast...

The loading wouldn't be very great in the winds when I'll hoist the kite - so I doubt it'd easily overpower the glue...

...it's even possible that I'd prefer the spinn halyard to let go, rather than have the kite capsize the boat.

 

[Norman_E]

If you glue something on to take the Spi halyard my money is on it pulling off first time it is used. If you are gluing metal to metal you might succeed by roughening both surfaces and using Araldite, but I really can't understand why you are so against using rivets, which is what everybody else does.

 

[Greenheart]

Pretty simple reasoning, I hope. Everybody may use rivets - I do myself - but not everybody drills new holes in a place where the mast isn't meant to have any.

 

[zoidberg]

I appreciate the 'simple reasoning', but you might consider using a Selden solution which is well-tried. This would involve fitting a single Selden Backing Plate (
http://www.seldenmast.com/en/products/masts/running_backstay_attachments.html ) intended for running backstays, and attach a Selden T-Eye Toggle ( http://www.seldenmast.com/en/products/rigging_hardware/terminals/t-eye_toggles.html to secure your spi block.

This would reinforce the mast wall where the holes would be required, not weaken it.

 

[Greenheart]

Thanks ZB, that does look clever; possibly overkill for my purposes.

It occurred to me that going down the smallest-possible-hole road, I could forget rivets and just drill a couple of 2mm holes, then run a steel wire strop through them.

Thanks anyway. :encouragement:

 

[William_H]

No I think the glueing idea is good. In the aviation industry aluminium is often glued to ali and also to repair patches of boron. They use epoxy. Indeed some helicopters and gyrocopters have aly to aly glue joints in the rotor blades. The secret is in the metal preparation. You need to have the oxide layer sanded off and get it perfectly clean. Free of oil and grit then apply epoxy ASAP. Once the epoxy layer is applied you can then lay on the webbing. However you might consider a stainless steel strap with a lug on it for the block or even aluminium strap or perhaps a kevlar strap. If using webbing or kevlar the epoxy will be exposed to sun light so will need to be painted. good luck olewill

 

[lw395]

Plastic luff tracks are often glued to masts.
Some flexible adhesive.

Epoxy can stick very well to aluminium.

 

[DownWest]

An ally light aircraft kit I was interested in was mostly glued with époxy. One of the techniques is wet sanding with unthickened époxy after carefull preparation to remove the oxide.

 

[Stemar]

I'm sure there's an engineer who knows, but everything I've learned about such things tells me that circular holes won't weaken the mast until they're far bigger than you'd want for a rivet. I'd use rivets rather than screws as the screws could put a "corner" in the hole which might act as a stress concentrator.

I don't know much about bonding metal to metal. I know it's done successfully in highly controlled conditions, but on a mast that was anodised and has been out in the elements for a few years, I'd be pretty leery. I'd also be concerned about gluing a stainless plate to aluminium because of the different thermal expansion.

 

[ghostlymoron]

I had a conducted tour of the Morgan car works last week and was shown the chassis construction for their top Aero model. It uses an alloy chassis which is glued together not welded. This technique is copied from the aero industry apparently. It's done under carefully controlled conditions though.

I'd use machine screws. Glue never takes to alloy too well.

 

[Norman_E]

I had a conducted tour of the Morgan car works last week and was shown the chassis construction for their top Aero model. It uses an alloy chassis which is glued together not welded. This technique is copied from the aero industry apparently. It's done under carefully controlled conditions though.

Controlled conditions are the key. The old (1960s?) Bluebird speed record car had a chassis made of "Ciba Aeroweb" if I remember the name correctly. That was an aluminium alloy honeycomb glued together with Araldite.

 

[prv]

new holes in a place where the mast isn't meant to have any.

Surely it's the same aluminium extrusion all the way along. If one part of it can take rivets for the shrouds, and another part can take rivets for the gooseneck, why shouldn't a third place take a couple of rivets for a block?

I think you're worrying over nothing, complicating your job unnecessarily, and likely to end up draped in wet nylon when your glue comes unstuck

Pete

 

[Greenheart]

Pete, my Osprey's mast is straight, thick tubing up to a point about 18" above the spinnaker halyard block; beyond that, it tapers considerably and after close inspection today, I wouldn't wish to increase the loading up there, regardless of how I made the attachment.

I'm grateful, and very encouraged by the descriptions here of demanding alloy applications relying on adhesive, and I'm sure that it can work. And on the basis of knowing more after this weekend than I did before, I'll happily give it a try in future...

...however, I did indeed chicken-out...I went for the rivets, rather than immerse myself in glue and doubt.

The remainder of this post will bore the tackle off anybody who looked in here for the glue-versus-rivets question.

Same old project - make an RS400 asymmetric fit the Osprey. Last week I hoisted the sail to the Osp's standard spinn height...

...and it's a tad saggy and baggy. I made that white bowsprit ten feet long, so I could stretch the luff to make it less so...

...but the sail's foot is too short for the tack to go so far ahead of the bow...so, back to the old idea of making the sail taller...

...and rather than make the hoist-point height-adjustable (as I did previously, to experiment with different sails), I decided just to affix a block as far above the standard position as I could, without straying into the tapered section of mast. That's what I did today...the spinn block is now 16" higher than this morning. Which may or may not be enough, but it'll be better than last week.

My rivet work isn't very lovely, but it wasn't too painful either. 4.8mm monel rivets are a challenge for my tongs-style riveter, but the 3mm tiddlers I used today, went in without much difficulty.

My hope is that by raising the head, I'll get the sail-shape closer to the way it looked, rigged on the height-adjustable hoist-point in the pic below. That idea wasn't bad, but it was flawed because it was attached partly at the masthead, and a lot of the load would have been applied up there.

Even if the sail sets well, there remains lots to do before it's usable afloat. I've given up on the bow-mounted hoop as a fabric-chute-mouth - it creates so much friction. The convenience of the kite emerging forward of the forestay, is too hard to retrofit to a boat where the forestay is inches from the bow...I don't know how it works on those tiny catamaran kite-chutes...

...instead I'm thinking I'll set the kite up to hoist and drop on starboard tack only, through a recessed tube under the foredeck...my non-racing purposes will (I hope) always allow for an extra gybe in order to drop the kite without dragging it round the forestay.

 

[lw395]

I can understand not wanting to drill holes in the tension-side areas of the mast where it bends.
The front of the mast is under tension when the sheet or kicker applies leech tension, bending the mast.

One thing you could consider is making a sleeve that goes 170 degrees around the mast (leaving the luff groove free) and attaching the block to that.
Just buy (or find) a short length of ali tube, attach a fitting to that and either glue or rivet it on, with the rivets towards the back of the mast.
Rivets in the back, compression side of the mast don't weaken it nearly so badly.
Or you could use two 'p' clips riveted to the mast around 5 and 7 o'clock, where 12o'c lock is the front if you understand my rambling? and attach a block to a short strop slung between them?
But ifyou add rivets in the aft side of the mast, keep it in compression by keeping a little leach tension in the main. basically, never let the sheet go completely in a breeze.

I would consider gluing on an external ali sleeve, with a fitting bolted to it using countersunk machine screws from the inside. The sleeve could be say 5" long with the aft sector cut out to clear the luff groove?
If you epoxy something to the mast, you can always remove it with a little heat.

 

[lw395]

PS, that's not actually an RS400 kite as it's made by Ullman's?
Looks sweet enough though.

 

[Greenheart]

Thanks for the thoughts LW, the sleeve is a fine idea, just a little late now. After riveting my mini-fairleads on, in place of the P-clips you describe, I rigged a scruffy but effective short strop between them, and it secures the halyard block. I believe it'll work fine.

Well spotted, it is an Ullmans sail...I was looking for a 2nd hand RS400 kite, and found this one, pristine and unused, for just £100 on the Ullmans website. I suspect it had been ordered by, and made specially for, an RS400 owner who found out too late that it wouldn't be race-legal...so he refused payment.

Its ineligibility for RS racing doesn't trouble me, of course. And I've seen used RS400 kites offered for twice that much.