Lag screws

[Romany 162]

I have new 7/16th lag screws and assume the hole into which they are going should be smaller. The big question is how much smaller?

Going into glass sheathed kauri. Is 3/8ths too tight?

[LBD 128]

Not to tight on the face of it but possibly too loose... there are so many other vairables to consider...

Below or above water line.

Thread profile on the lag screw and root diameter of the thread.

Inboard or outboard

How much load... how long are the threads into the timber?

What is the potential for water ingress leak into the threads and timber... and the consequence?

I personally am a fan of using threaded studs epoxied into the timber with nuts on the outside. this method then seals the timber as well as retains the stud with a good degree of strength into the timber. 

[Romany 162]

Thanks for reply. 

Lag screws to secure cutlass bearing housing and resist it spinning with the shaft. My understanding is that there isnt much load and logic says it gets less as time marches on.

45mm embedding into deadwood I think.

I intend to apply some 4500 sealant/adhesive onto the screws as they begin to reach max penetration and also on the mating face of housing as it screws onto shaft tube as well as thread sealant for tube to housing.

I did think about setting threaded rods into the hole but it feels like reinventing the wheel. The old screws lasted 48 years so its not a performance thing..

 

[LBD 128]

1 hour ago, Romany said:

Thanks for reply. 

Lag screws to secure cutlass bearing housing and resist it spinning with the shaft. My understanding is that there isnt much load and logic says it gets less as time marches on.

45mm embedding into deadwood I think.

I intend to apply some 4500 sealant/adhesive onto the screws as they begin to reach max penetration and also on the mating face of housing as it screws onto shaft tube as well as thread sealant for tube to housing.

I did think about setting threaded rods into the hole but it feels like reinventing the wheel. The old screws lasted 48 years so its not a performance thing..

 

If the stern tube is threaded to the  cutlass then the threaded rods/studs would not work.

9mm drill... drilled a fraction less depth (say 3 to 5mm less) than the lag screws will go in... do not over tighten just a nip up... if the stern tube is threaded to the cutlass than it is this thread that applies the clampung force and the lag screws are only to stop it unscrewing.

I would be more inclined to use Sikaflex 291... a mastic instead of epoxy... put a smear on the threads to lubricate as they screw in and then seals the threads that can then be removed in the future. Do not put 291 in the hole as it may hydraulic up in the hole if it cannot squeez out past the thread.

 

[Romany 162]

Thanks that all makes sense.