Box section or angle?

[Drayke]

1 minute ago, blackrose said:

 

Penny washers? You think 20mm washers will pull through 5mm steel plate?

No was just thinking about the bolt heads as aluminium is a soft ish metal.

[blackrose]

6 minutes ago, F DRAYKE said:

No was just thinking about the bolt heads as aluminium is a soft ish metal.

 

Ok. I'll use washers but not big penny washers

[cuthound]

22 hours ago, blackrose said:

Which would be stronger if bolted to a steel bulkhead to be used as supports (in the orientation shown below) for steps?

 

For the box section support, the bolts would only go through one vertical wall up against the bulkhead, not through the whole thing.

 

I'm thinking the angle is stronger simply because of the wall thickness. Or does the box section shape give it a lot of extra strength?

 

 

Why not use Unistrut and get the best of both worlds?

 

https://www.unistrut.co.uk/index.php?M1=Support Systems&M2=Single and Double Channel

 

Edited January 30, 2021 by cuthound
To remove a duplicate post

[blackrose]

23 hours ago, cuthound said:

 

Why not use Unistrut and get the best of both worlds?

 

https://www.unistrut.co.uk/index.php?M1=Support Systems&M2=Single and Double Channel

 

 

Because I've cut the sections of aluminum box section and angle that I already had and don't want to spend more money

[jacko264]

Hi all in my job I repair accident damage buses and coaches so do a lot using aluminium sections 

If the bolts are only going through 3mm aluminium  there is a good chance the bolt will pull though  if using the box I my self would put a piece of hard wood in the box and bolt right though the box and wood

as far as I can see it would be easier to use the angle and repair washers on  the bolts 

Graham

[blackrose]

On one of the aluminium brackets for my steps it was impossible to get the 25mm OD washer onto the bolt inside the boat because of the gap between the wooden paneling and the steel so in the end I just put the nuts on without a washer. I haven't put washers on the outside - they're flange headed bolts.

 

 

I don't think a 8mm dia/13mm AF A2 stainless nut is ever going to pull through 5mm steel plate but is the lack of washers to spread the load really going to be an issue? When you think about rivnuts which someone suggested earlier, they only put a relatively small dia flange on the inside, certainly smaller than a 13mm AF nut.

 

Edited February 15, 2021 by blackrose

[jacko264]

You will be fine with just a nut on the bolt  a lock nut is better then just a nut 

Graham 

[blackrose]

1 hour ago, jacko264 said:

You will be fine with just a nut on the bolt  a lock nut is better then just a nut 

Graham 

 

Thanks. They're nylock nuts so hopefully it will be ok.

 

Out of interest does a washer actually take load off the threads of a nut or bolt? I can't see it would make any difference.

Edited February 15, 2021 by blackrose

[DHutch]

The washer doesn't take the (tensile) load off the shank and threaded interface of the bolt, it distributes it more evenly over the surface of the clamped material, in this case the steel plate of the boat. You will fail the aluminium well before you pull the bolt through it, let along the 5mm steel plate. I expect the bolt would fail in tension before than happened, even if you used A2-80 grade high-tensile bolts. However, its likely not in pure tension, and its not going to be the bolts or steel plate the fail anyway!

 

On the other hand, I am glad to see you appear to have bedded the ali angle and bolts down on some pu sealant, else the most likely failure would be unsightly dissimilar metal corrosion! I too would have used the ali not the box, but with the short a section, it all depending how near to root/heal of the angle you apply the load as to how it will fair.

 

Daniel

[blackrose]

Thanks. The end of the long piece of aluminum angle that's going onto those brackets will be a few mm away from the bulkhead, so fairly close to the heel of the bracket.

[jacko264]

Putting sealer is ok to put a barrier between the aluminium and the steel where I work we put plastic  like a carrier bag type plastic  as a barrier 

Graham  

[blackrose]

4 hours ago, jacko264 said:

Putting sealer is ok to put a barrier between the aluminium and the steel where I work we put plastic  like a carrier bag type plastic  as a barrier 

Graham  

 

In my case the steel is painted, but if anyone is really concerned about dissimilar metals in contact then a bit of paint, sealant, or a plastic bag isn't really going to help if the two metals are electrically connected by the bolts holding them together! ? Think about it. A bit of paint behind an anode welded or bolted to a hull doesn't stop the anode working does it.

 

The point which I have mentioned already, is that dissimilar metals corrosion is primarily a concern on submerged metals in the presence of an electrolyte, i.e. below, not above the waterline.

 

Most of us have dissimilar metals all over the topsides of our steel boats: aluminum windows, brass mushroom vents, stainless skin fittings, etc. Do we worry about dissimilar metals corrosion in those examples?

Edited February 17, 2021 by blackrose