Iroko expansion?

[dgadee]

I am making an extension replacement for the boarding ladder. I have two 1" stainless vertical tube rails which I have had bent to shape. The steps are to be iroko (30mm thick) with the rails going through these (and then the steps bolted to the stainless rails).

My query is what fit should I have between the steps and the rails? I don't know whether iroko swells when wet or whether an 'engineering fit' is ok. My options (ie my drills to hand) are 1" hole and fitted with a knock from a hammer, 26mm hole or 1 1/8" hole (which I think is too loose).

Any idea from boat builders out there?

 

[Catalina36]

I'm no boat builder but I've worked a lot with wood including iroko. Any wood swells when wet, the only question is how much. If it has no room to do so it's likely to split. A 1" hole gives no slack at all. 26mm gives you 0.6mm overall slack, ie 0.3mm all round which might do it or might not.

Have you got an offcut you could drill and soak then measure the slack?

 

[Plum]

I am making an extension replacement for the boarding ladder. I have two 1" stainless vertical tube rails which I have had bent to shape. The steps are to be iroko (30mm thick) with the rails going through these (and then the steps bolted to the stainless rails).

My query is what fit should I have between the steps and the rails? I don't know whether iroko swells when wet or whether an 'engineering fit' is ok. My options (ie my drills to hand) are 1" hole and fitted with a knock from a hammer, 26mm hole or 1 1/8" hole (which I think is too loose).

Any idea from boat builders out there?

Iroko is one of the most stable woods and any movement will be across the again, not along it, so even if it did split the bolts will ensure failsafe. I would try a test hole with the 26mm drill to see what size hole it ACTUALY makes as I would have aimed for 1mm larger diameter. If you do try wetting the wood to see what happens, with iroko you may have to soak it for months. Anyway, would the hole get larger or smaller with increased moistue content???

www.solocoastalsailing.co.uk

 

[dgadee]

Anyway, would the hole get larger or smaller with increased moistue content???

Ah, you are making it even more complex! I thought the hole would get smaller but now you have me wondering. It's a ladder so will be in the rain and sun more than dipped in saltwater.

 

[Laminar Flow]

I would split the steps lengthwise and clamp them around the rails using bolts through the front and rear edges. This resolves all the inherent problems of the wood splitting, either from torsion as one puts weight on the front of the step or from expansion due to moisture.

For wider steps use threaded rod and you may insert plugs to conceal the holes.

 

[dgadee]

I would split the steps lengthwise and clamp them around the rails using bolts through the front and rear edges. This resolves all the inherent problems of the wood splitting, either from torsion as one puts weight on the front of the step or from expansion due to moisture.

For wider steps use threaded rod and you may insert plugs to conceal the holes.

The steps are about 75mm wide, so your plan would work. What I have been thinking about is dirilling the holes 1 1/8" and using mastic to fill the space between the step hole and stainless tube. Will give it a day or so to let ideas percolate.

 

[Laminar Flow]

I would drill the holes at 1" or slightly less.
That way the step will be firmly clamped to and around the rail with no need for fillers or anything.
Additionally, you actually may not need to drill through the rails either, thus weakening the SS tubing. The clamping action would hold the step in place without further ado.

 

[Babylon]

Alternatively bore through the Iroko steps very slightly bigger (say 27mm) than the 25.4mm stainless, then secure with collars (nylon or s/s, with bolts or even rivets) above and below each step?

Whatever method you use, I'd avoid adding mastic - better to let the wood breath evenly, and easier to keep clean.

 

[Hacker]

I think that you should make the holes a reasonably tight fit. If the iroko does expand it will take the line of least resistance and expand away from the tubes.

 

[dgadee]

I was too cheap to buy a 27mm drill bit so used the 1 1/8" and filled the gap with CT1 which was just about to go off. I decided not to split the iroko since I thought it would be stronger in one piece. With the larger hole it was bit more difficult to get the holes in the stainless rails correct, but it's not too bad. If I was doing it again I would buy a 27mm drill bit.

 

[Graham_Wright]

I was too cheap to buy a 27mm drill bit so used the 1 1/8" and filled the gap with CT1 which was just about to go off. I decided not to split the iroko since I thought it would be stronger in one piece. With the larger hole it was bit more difficult to get the holes in the stainless rails correct, but it's not too bad. If I was doing it again I would buy a 27mm drill bit.

View attachment 94194

How do you deploy that (without tempting concussion) if you have taken an involuntary dip?

I ask because I have the same problem.

 

[dgadee]

How do you deploy that (without tempting concussion) if you have taken an involuntary dip?

I ask because I have the same problem.

I didn't think about that! Which is a surprise because I always over think things.

In practice there is some buoyancy in the steps, so it slows the process . I'd imagine if you've fallen overboard and this is let down for you, you would need to be out of the way.

 

[AntarcticPilot]

I didn't think about that! Which is a surprise because I always over think things.

In practice there is some buoyancy in the steps, so it slows the process . I'd imagine if you've fallen overboard and this is let down for you, you would need to be out of the way.

But what if there's no-one to let it down? How can you get it down from the water?

 

[vyv_cox]

Interestingly, my experience is that iroko does expand, or possibly contract, but not in water. About 20 years ago I had the table top shown in the photo made in Iroko. After about 10 years it became very difficult to fully open. Investigation showed that the edges, with grain normal to the axis of the boat, had lengthened relative to the main panels, parallel to the boat axis. The ends of the edges were interfering with the fixed top, preventing opening. I sanded perhaps a couple of millimetres off the end of each edge, which solved the problem. Since then I have done the same again on at least one, possibly two occasions.

 

[dgadee]

But what if there's no-one to let it down? How can you get it down from the water?

A short piece of rope will bring it down on my head. A longer piece of rope will give me the chance to avoid it.

 

[Catalina36]

A short piece of rope will bring it down on my head. A longer piece of rope will give me the chance to avoid it.

Or alternatively, which seems more likely, the other bits had shrunk relative to the edges.

 

[Catalina36]

A short piece of rope will bring it down on my head. A longer piece of rope will give me the chance to avoid it.

A piece of bungee of suitable length might slow its descent.

 

[vyv_cox]

Or alternatively, which seems more likely, the other bits had shrunk relative to the edges.

Yes, as I said, although odd that they have shrunk outwards and not inwards. The edges still line up with the outsides of the planks.

 

[dgadee]

A piece of bungee of suitable length might slow its descent.

Or pull it back up out of the way.

 

[Laminar Flow]

Interestingly, my experience is that iroko does expand, or possibly contract, but not in water. About 20 years ago I had the table top shown in the photo made in Iroko. After about 10 years it became very difficult to fully open. Investigation showed that the edges, with grain normal to the axis of the boat, had lengthened relative to the main panels, parallel to the boat axis. The ends of the edges were interfering with the fixed top, preventing opening. I sanded perhaps a couple of millimetres off the end of each edge, which solved the problem. Since then I have done the same again on at least one, possibly two occasions.

Indeed, Iroko is not as stable as teak and will "work' a fair bit by comparison. It is arguably a prettier wood, very rot resistant and available in large dimensions. I milled down quite a lot one time for a boat project, the slabs were 20' long, well over 3.5' wide and 3" thick.