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[derekwarner]

 ....question for Neil......

Kerf Cuts in timber Hull top Railing Support

Have you used Kerf cut timber hull top rail supports?...[adding strength without necessarily any or minimal distortion?]

I have asked Mr Google, however the information is rather limited 

From the depiction I see in Violin manufacture, we could us Kerf cut timber supports in either direction of bends, convex or concave 

Do you have any wise words or tips on this subject?

[The image below is just an extreme example  of Kerf cutting.......not really what I had considered]

Derek

[tigertiger]

I have seen it used in some cabinet making, although I haven't done any bent work yet.
However, the kerf cut method is noted for NOT being strong. It works well with plywoods and in your example above pine. However, it may be a different matter with many hardwoods as they are brittle. When I have seen kerf cutting used for bending wood, it was used in conjunction with a former to hold the shape of the curve as you glue it to something else.
Personally, I would not use it with the cut edge on the outside of the curve. The risk would be getting all of the bending stress along a single line (cut groove), and snapping.



There is additional information in this link http://www.rockler.com/how-to/bending-wood-part-i/
Doing a search on 'bending timber' might throw up a few more results for you.

[tigertiger]

Addendum.
I am not sure what you mean by top rail supports. If I was going to use this for a cap rail, I would still use a thin layer of ply flat on top, and then trim the ply to fit after the glue has dried. You would need something flat to glue the cut piece too, to hold the shape of the curve. I would still use a former.
If I wanted a very strong bent piece, and did not want to glue it to a flat piece, I might use this method, then flood the kerf cuts with epoxy resin, bend around a former, and then sand back the surplus resin when everything was dry. However the epoxied piece would still be visible, unless painted.

[derekwarner]

Yes TT.....

The Top Rail supports the Cap Rail......the former is a construction piece, whereas the latter name is a more definitive and commonly used term

I would not consider offering upwards a Kerf cut wooden board as a top piece

Lets see what Neil thinks.....after all he was a teacher of Chippies

Derek

[Neil]

not to such a high degree in teaching and projects with kids, as to  form a right angled bend,nor in model boat building but as a teacher I did once as was helping a lad construct a telephone seat for his grade 11 exam whilst in Canberra and he got excellent results from the oak he was using, using a pad saw across the width  to round the external frame, and then we set a jig to hold each section at right angles.the outer frame was akin to a modern IKEA  chair, but without steaming the timber and laminating.


however I use it all the time when laying out the inner longitudinal stretchers at deck height to take the cross beams. I put my cuts to the inside usually so that the 2 part epoxy bends both into the cuts and the grp hull, with excellent results..........never had a beam break off.


if you have a look at any of my lifeboat builds you'll see it used constantly.

[Neil]

having now looked at the link you gave.....we actually came very close to the bottom right picture of the u shaped structure but almost a 360 square, with the centre section of the bottom missing forming an open bottom with the 4 base shorter sections forming the feet of the table. then two smaller lower frames were made in the same manner for the seat. it was quite a complex but radical design that the boy drew up and then constructed...........but it worked well and both he, I and the moderators liked his work.

[RAAArtyGunner]

A far stronger and simple method is to use plywood or thin timber layers cut roughly to shape and built up to thickness required.

Missyd's current build shows this in simple format. The principle is the same just add extra layers/thickness to reach required size.

Alternatively join sections of timber together if a large "block" is not available to accommodate the shape.

Kerf cutting is used where it can't be seen and strength is not required.

[derekwarner]

So Neil says................"if you have a look at any of my lifeboat builds you'll see it used constantly"

OK...please confirm a Link or two  ........

Derek

[Neil]

So Neil says................"if you have a look at any of my lifeboat builds you'll see it used constantly"

OK...please confirm a Link or two  ........

Derek

http://www.modelboatmayhem.co.uk/forum/index.php/topic,51021.100.html    reply 104


http://www.modelboatmayhem.co.uk/forum/index.php/topic,51021.100.html    reply 110..overall view


http://www.modelboatmayhem.co.uk/forum/index.php/topic,39214.100.html     reply 100.....another boat.

[derekwarner]

Ahah.....thankyou for the links & thankyou all for alternate considerations

It appears that bending with Kerf serrations is a useful method to compliment solid steaming........however laminating pre-bent timber also has certain  advantages

Derek   

[grendel]

I have steamed all  of the curves in my model (up to 12mm square) using my homemade steamer (wallpaper steamer and 1 1/2" drainage pipe)
though the tight curve around the prow was a combination of lamination and steaming to get the wood for the top rail around the curve (it was steamed as 4 laminations, then glued).

[grendel]

like this

[Neil]

Ahah.....thankyou for the links & thankyou all for alternate considerations

It appears that bending with Kerf serrations is a useful method to compliment solid steaming........however laminating pre-bent timber also has certain  advantages

Derek   

if you are talking about ply as your prelaminated timber...........make sure that it is outdoor or marine type ply that has been laminated with water resistant or waterproof glue, otherwise you'll end up with a sticky mess and debonded ply.

[david48]

Not to put a morbid thread into this ,but, the kerf shaping is used to form the shoulder bend in coffins made  from  elm or other wood . I have not used man made sheet material . I can not remember how many I have cut with a hand saw . Just another use for bending wood .
David

[derekwarner]

Far from being morbid David......I cannot think of any form of woodworking that is not pleasing to the eye or mind.....[and we all know that good old English Elm is a pretty tough specie with a Janka Rupture Test value of 12, 080 PSI  ]

I think most would agree than only materials made by Mother Nature should be considered for this purpose....next they will be using Cardboard 

And as for Neil espousing that a particular grade of Plywood should only be used for laminating & bending......well would that not be going against the grain?

So I have a selection of small HSS blades for a trial....with the smallest being 16 diameter x 0.3 plate + set ² = 0.6 Kerf 

Derek

[RAAArtyGunner]

Far from being morbid David......I cannot think of any form of woodworking that is not pleasing to the eye or mind.....[and we all know that good old English Elm is a pretty tough specie with a Janka Rupture Test value of 12, 080 PSI  ]

I think most would agree than only materials made by Mother Nature should be considered for this purpose....next they will be using Cardboard Already the case, MDF is essentially thick cardboard.

And as for Neil espousing that a particular grade of Plywood should only be used for laminating & bending......well would that not be going against the grain?

So I have a selection of small HSS blades for a trial....with the smallest being 16 diameter x 0.3 plate + set ² = 0.6 Kerf 

Derek

[derekwarner]

Keeping with the nautical theme. Body Bags as stored for use on our Australian warships in years gone by were specifically made from a flaxen canvas material [sourced from Mother Nature]

As all things progress  these same items are now sewn from Polypropylene synthetic material

Ashes to ashes and dust to dust seems a little more appropriate than being placed in a cardboard box or a plastic bag   

[nemesis]

I have used this system for years, Coffin cuts is the term I was taught, nemesis

[RAAArtyGunner]

Keeping with the nautical theme. Body Bags as stored for use on our Australian warships in years gone by were specifically made from a flaxen canvas material [sourced from Mother Nature]

As all things progress  these same items are now sewn from Polypropylene synthetic material

Ashes to ashes and dust to dust seems a little more appropriate than being placed in a cardboard box or a plastic bag   

  So we don't open any big floating plastic bags 

[Neil]

THIS Kerfing technique.............seems to be topic of the moment as I have seen it on 3 different sites in the past few days...........what is this sudden interest, as I have used it mainly on model construction for years, without a thought to its process........


just wondering why an upsurge in interest.