how to bend some oak - advice pls

sarabande

sarabande

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I need a new pad under the mast tabernacle. I have a piece of oak 18" x 7" x 1". And a problem.

View attachment 31493

The wood needs shaping to conform with the curvature of the deck beneath the tabernacle. The depth of the bend in the middle of the long edge of the oak is just under 1 inch.

If I rig up a steam generator (old water trough and a gas jet) and suspend the wood in the steam box, is it

1 likely I can bend such a short plank

2 how do I do it


Or is it back to marine ply ? (The oak is home grown, home sawn, home dried, and - with considerable trepidation and sweat - home sawn, so I have a bit of personal attachment to it. :) )

TIA
 
Doubt you will get that section to hold a bend of that radius. Sounds like a laminating job and a waste of good oak to use that piece.
 
You could try cutting a series of bench-saw cuts across the width ( or use one of your famous routers ), the depth of each cut corresponding to 3/4" leaving 1/4" uncut thickness. I imagine spacing the cuts about 3/4" apart with a 'kerf' width of ~1/8" or less, should work. That should bend, in steam, much more readily than the full-depth 1" dry oak. The series of kerf-cuts can be filled with thickened epoxy and the steam-bent workpiece placed in position - with a sheet of polythene top and bottom to prevent premature adhesion - with some heavy weights on top ( them wot holds the front of tractors down are ideal ) to hold the shape while the epoxy gunk goes off.

Next? :cool:
 
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Hi Sarabande
Hopefully this is a bit of encouragement to keep going.
Sorry for the quality as it is a photo of a blownup postcard hanging on a pub wall.
I think there is a 50/50 chance that she is the one you have built by Lesley Hanna.
photo taken early 70's I think or may even be very late 60's, at the time I was living just out of shot to the left.

GetAttachment.jpg
 
I am so grateful, Salty ! I've not seen that pic before, and yes I still have the Hanna transfer on one of the deck beams, and the colours of the hull remain the same..

When I bought the boat with a bequest from my father, I was told that she was built for the Captain of one of the Irish Sea ferries.

What's the name of the pub please ?

Amazing forum. I was sent a full set of the original blueprints by a forumite several years ago.
 
I would suggest that it will be near impossible to bend the oak into a curve. Best idea would be to laminate cross pieces of oak sideways and at the front and rear of the base. Use a router and sander to carve the desired curve into the under side of the oak and thicker area made by the added pieces of wood.
You could carve a little out of the middle of the big block and add near an inch of thickness front and back. This will give a flat top which I don't imagine will be a problem.
For the same component in my little boat I built up the block with GRP. Lay cling wrap on the deck if you want it to be removable. Build the block up with chopped strand mat or woven rovings to the thickness desired. Then cut the edges to size and neatness when GRP is hard. But I don't imagine you like that idea. GRP Yech!!! good luck olewill
 
I can't visualise the set up on your boat. I have a wooden block under the steel mast step on my boat but although the underside is machined to fit the curvature of the coachroof, the upper side has to be flat to support the flat base of the mast step. If you were able to bend your pad (which would be far from easy) wouldn't you end up with your mast step sitting on a curved surface? Or is it meant to be like that?

If I had to make a new pad for my boat I would do as NigelMercier says and use a router. All you need is two long steel rods through the router base running on a couple of plywood templates cut to the same curve as the coachroof.
 
parsifal said:
...use a router. All you need is two long steel rods through the router base running on a couple of plywood templates cut to the same curve as the coachroof.
Click to expand...

Interesting, never thought of using a router for this type of job. What sort of blade would you use? Presumably you would be taking out strips, would they be 'with' the curve or 'across' the curve? Sorry for thread drift.
 
sarabande said:
I need a new pad under the mast tabernacle. I have a piece of oak 18" x 7" x 1". And a problem.

View attachment 31493

The wood needs shaping to conform with the curvature of the deck beneath the tabernacle. The depth of the bend in the middle of the long edge of the oak is just under 1 inch.

If I rig up a steam generator (old water trough and a gas jet) and suspend the wood in the steam box, is it

1 likely I can bend such a short plank

2 how do I do it


Or is it back to marine ply ? (The oak is home grown, home sawn, home dried, and - with considerable trepidation and sweat - home sawn, so I have a bit of personal attachment to it. :) )

TIA
Click to expand...

I assume that the oak goes on top of the deck beneath the tabernacle. I would be inclined to rough out the centre part of the oak so that I could get the edges withing a mm or so of the deck. Then I would paint the deck beneath the wood with release fuid, and make up an epoxy mixture with a high density filler in it and use this between the wood and the deck so that the surface when the epoxy had cured matched the deck exactly. Have a look at the West Epoxy website.

I have in the past bent green oak but only in one plane whereas your deck will likely curve in both directions.
 
No need to bend...

Hi Sarabande,
You don't really want to bend that Oak ...because of the short grain, or included bark, or whatever that fault is in the timber on the edge furthest from the viewer, I'm afraid it wouldn't bend evenly no matter how much effort you expended ...it would always look a bit like a potato crisp.

You'll need to shape the underside of the Oak as near to the curve of your deck as you can be bothered - using a circular saw, wood chisel, and belt sander; and then give the underside a good bed of thickened epoxy resin when you put it in situ ...providing you're sure you want it to stay there for many years to come. (The epoxy can be thickened with the 'wood flour' from the belt sander's dust collection bag.) That way you'll offer a flat bearing upper-surface to the heel of your mast which is what your mast loves best ...assuming that the heel of the mast is intended to sit directly on your Oak. Don't worry that the Oak will be thin at the point of load bearing - providing there is a generous bed of epoxy resin the mast load will be transferred to the deck, deck beam, mast post, keelson, and finally, keel.

Good luck
Justin
http://amzn.to/xc4qn3
 
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We're getting there.
Put a 24grit grizzly flexible sanding disc in yer 4 or 4.5in angle grinder and simply wizz off what you need from the centre
You mark the curve by placing the unshaped block in situ level and run a pencil around the edges on a scrap of wood.
If you need more depth add another partial or full width piece of oak acc to what you want the mast step or tabernacle to sit on.
A light touch, a grizzly disc, a pencil mark, you'll have it done in 40 mins max and it will be stable.
 
just got back from a NFU meeting about sheep and cattle health. Who says we have an easy life :)

Yes, thank you all for the multitude of suggestions.

The base of the tabernacle is 6mm flat steel, so it will need a flat surface on which to stand. It is the underside of the wopoden 'plate' which needs to have a concave shape (the deck is a simple single curve, not a compound one BTW).


I'll look at the suggestions in details in daylight when it all will make sense, no doubt. :)
 
OK, so not bending oak 'plank', but cutting away waste to deck profile....


mastbase.jpg



Diagram 1. shows the **12 x 7 x 1" plank in profile. Drawn on is the form of the deck curve, scribed on both front and rear edges ( block and tape workpiece, marker pen taped to piece of lath or plastic ruler of suitable thickness )

Diagram 2. shows the plank with saw cuts at suitable intervals and 'almost' to depth.

Diagram 3. shows the plank with much of the waste cut away and some still to remove. There are many ways to do this - power plane to half-depth, then sharp wood chisel/mallet, then course scraping disc in power drill..... or repeated passes over bench saw at different depths of cut, different angles as 'scraper' using simple jig ..... or router using 'ski jig' at different depths of cut....

The finished surface need not be to 'salon' standards. 'As sawn' will provide good adhesion with decent weatherproof mastic.

Oops - it is 18" long - but the principle remains..... and the use of a router on batten/rods 'skis' is the simplest solution. You will need very sharp cutter(s) on oak.
 
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the purpose of the pad under the tabernacle is to spread the load of the mast but you also need to avoid point loads and thats what you risk by attempting to get the profile of the underside of the wood to match the top surface of the deck by carving away at the wood. You need a filler inbetween to ensure they match well and epoxy with a hard filler will do that job well. Wouldnt advise sawdust - its a proper engineering job and you need proper materials rather than thrift.
 
There's a lot of weight resting on that pad (spars, sails, rigging, mast climbers!) plus the rig tension, so you want it to be distributed evenly over the mating surface.

Whatever technique you choose, it's important that the hollow you cut accurately matches the coachroof curvature. If you can't make an accurate fit you can always bed it on thickened epoxy as someone suggested above (the technique for bedding hardware onto curved surfaces is well described in the WEST manuals)
 
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