Using J B Weld to repair alloy for stainless steel screws.

[shortjohnsilver]

Mast head plate is alloy and incorporates a plate that secures down fore aft.

Rig-rite schematic diagram NG - 1 Unfortunately I can’t seem to include the diagram here.

To access the forestay stem ball fitting, this plate had to be removed. Removal also needed enable access to the main, foresail and spinnaker sheaves, within the mast head.

However, stainless steel screws securing the plate down had seized entirely. After 22 years this is not surprising. The screws had to be drilled out. However, the chap that did this for me, has been a bit over zealous and over drilled the alloy holes that receive the stainless steel screws opening them up and not straight at all. It’s difficult to explain but the plate also secures a spinnaker bracket are blocks for the spinnaker up lift and the whole assembly is/was robust enough that I could also use the skinny up lift for a safety security line when up the mast. This bracket and the plate have to totally strong and secure.

So, some have advised bolting through, with larger bolts, however the way the alloy is moulded this is impossible as there is insufficient room o secure nuts. Hence this moulding had been machined or screws that don’t pass entirely though the alloy casing.

I’m thinking that I might be able to fill the holes now existing, with J B Weld a cold weld remedy, or other recommended product, and once totally cured and as hard as the alloy it’s in, tap in new correctly sized screw holes. The bumph I have read from J B Weld suggest that the product will be harder than the alloy it’s replacing and therefore suitable for a tap and dye process to re introduce the right thread.

Is this right and an approach suitable to put right the problem?

As an alloy moulded fitting, I’m not sure that heat welding would be possible, as to introduce the heat necessary to weld into the holes will fracture the alloy moulding completely or reduce its strength far too much that it would fail.
To be honest I wish I’d left the whole lot alone! But the rigger whose replacing the standing rigging wanted the stem ball out and removal of the plate was necessary.

 

[Poignard]

Is this what you mean?



NG1 Masthead Assembly

 

[Tranona]

Either drill and tap for machine screws or use something like this. accu.co.uk/962-self-tapping-inserts?page=1 I have just used one of these on a mast to repair a worn out M6 thread.

 

[PaulRainbow]

Either drill and tap for machine screws or use something like this. accu.co.uk/962-self-tapping-inserts?page=1 I have just used one of these on a mast to repair a worn out M6 thread.

Agree, or get a Helicoil kit.

If the holes are totally knackered and off centre, drill out and tap M8 or M10. Screw some short bolts in with some Locktite, let them set. Dot punch and drill/tap to the correct size.

 

[Tranona]

That insert is much easier. Drill a tapping hole (6mm for M4) and screw in the insert. However if it is those 2 locking screws at the back it looks like the casting might be thin and simple machine screw and nut might be a better solution. Depends also on how wide the slots in the top plate are.

Better to be able to see a photo of the actual bits.

 

[shortjohnsilver]

Poignard many thanks that’s it. And as you all can now see ( apologies my laboured description ) those screws at #2 were totally seized io the mast head body forward. They were drilled out with the result that they were over drilled width and depth into the alloy mast body and offline which isn’t helpful.
Thanks for the recommendations Tranona and Paul Rainbow that does seem to be the way to go.

 

[shortjohnsilver]

So, just to be clear, the recommendation is inserts helicoil kit, rather than using J B Weld or the like? Thanks again.

 

[thinwater]

... as hard as the alloy it’s in ...

... Is an odd claim, when the tensile strength of JB Weld is 5,200 PSI and most aluminum alloys are > 20,000 PSI.

Good stuff, though.

 

[Tranona]

Yes. I found that insert very easy to use and although individually expensive much cheaper than buying a helicoil kit and sourcing stainless helicoils. I bought a spare to experiment before the real thing but if you have enough meat left where the screws go in then just drill the 6mm pilot hole and screw the insert in.

 

[Poignard]

What is the thickness of the aluminium plate that needs repair?

 

[shortjohnsilver]

Brilliant. I’ve been stressing about this all Christmas & New Year.. Thanks all.

 

[shortjohnsilver]

Poignard, as per the diagram, you so kindly provided, the two screws #2 are set into the two lugs that are on the end and each corner and stepped down a fraction. It’s those lugs that have had the screws drilled out. Badly! It’s those lugs I’d like to repair, so as to be sufficiently strong enough to take fresh screws.
Having understood the recommendations above, I’ll further drill out - squarely - so as to accept a suitable helicoil inserts then screw to those and hopefully making the job secure and strong.
Once the plate is back in position and recessed down properly, the spinnaker bracket (crane) is bolted over the plate at the back and screwed through the bracket at the front and into the mast head body lugs.

 

[Poignard]

So the 'lugs' are part of a casting and the two 4mm screws just keep the cover plate in place. No great load on them?

The problem with using inserts is that they must be located so that they are concentric with the original tapped holes.

If those holes, having been mauled, are no longer concentric and go off at an angle, you will have to correct that when drilling for the threaded inserts.

That might be tricky if you are trying to do it with the mast on trestles in a boatyard. If you can take the whole thing off and work on it on a bench it would be easier.

If it was my boat, I would use JB Weld or something similar.

 

[Tranona]

It is only critical in one direction - fore and aft, not laterally as the plate is slotted. Should not be difficult to make a jig to guide the 6mm pilot drill centrally to the slot fore and aft. If slightly out, just enlarge the slots. The screws are really just for locating the top .

 

[shortjohnsilver]

Yes, you’re right Poignard the screws go into the lugs and retain the plate in position and as far as I can see not a great load on them. That’s why I was considering using JB Weld then tap & dye ready for replacement screws.
There’s also the spinnaker crane bracket. This bolts on at the rear and the front utilises the screws at #2 through the crane into the lugs, this securthe crane and also the plate.
Today I’m going to assesss whether there is sufficient meat remaining of the lugs to use the helicoil approach and if so proceed that way.

 

[Norman_E]

There is a completely different method that you can use if the fitting is in your workshop. Use Lumiweld rods or similar to fill the holes, then re-drill and tap. It is not actually welding, as the temperature is lower than the melting point of aluminium, but the rods form a lower melting point alloy with the parent metal. The end result is strong, and can be drilled and tapped. I have used it sucessfully to repair cast aluminium parts and to rebuild a broken motorcycle brake pedal with a piece of plate "welded" to a cast part.
Although I have only used Lumiweld, here is a video of a similar product filling holes in aluminium. The basis principle is the same, you have to scratch through the oxide surface on the parent metal to get the molten "solder" to mix with it. First use a stainless brush to clean the part, then a pointed stainless steel rod to initiate the "weld". This video just shows the alloy rod used to initiate the weld, but a pointed stainless rod will eliminate any tendency for the solder to sit on the oxide layer that forms almost instantly on most aluminium alloys.

 

[garymalmgren]

You can fix the threads ( helicoils, other inserts or tap to a larger diameter).
After that you have the choice of bolts/ setscrews down from the top or instering lenghts of stainless allthread and locking the plate down with nuts.

 

[Restoration man]

Could you use some rivnuts ?? You would have to drill out slightly over size but nothing much, You don’t even need the special tool to set them ,just a bolt of the correct size a washer and a nut , there very cheap and incredibly strong for what they are , google rivnuts if don’t know what I’m on about

 

[shortjohnsilver]

Thanks all. The lugs fortunately were more substantial than I had recalled and I was able to re drill the holes and realign them sufficiently, that I could introduce M6 30mm stainless steel bolts, inverted, up through the mast head body lugs, through the two holes in the mast head plate and also through the spinnaker bracket crane, then lock down with washers and nyloc nuts. It’s now very substantial.
Many thanks again.

 

[shortjohnsilver]

In addition to aforementioned and having now secured the mast plate body securely back into position, I’m looking at tidying up things.

To secure the plate, I had to bolt up through the alloy mast head body and this is now very strong and secure. But this required drilling through the pre existing lugs to allow the bolts to insert up through the lugs.

This process however impacted the alloy metal of the mast head body somewhat cosmetically. Now I’d like to coat over the mast head plate with a ‘hammerite’ type of paint to protect those areas of unprotected metal surface. I’m assuming that the mast head body alloy has some sort of anodising treatment to it and to leave bare metal exposed may not be ideal. I figured that coating with a suitable paint barrier would protect it and a hammerite paint would be fine?
Your opinions observations would be appreciated. And I’d rather get this done whilst the mast is still down. ?
Thanks.