Roof lantern, best king post to rafter joint

[Gaz]

Hi everybody, I am new to this forum, also I am by no means an experienced joiner so please forgive me if I sometimes come across a bit confused :-k I am halfway through building an orangery which will have a 2m x 3m roof lantern, I am constructing this myself from hardwood, it will have a king post/finial at both points each will support a ridge beam, 2 hips and 3 rafters, my guess is I would machine the finials with six sides, square to the rear with 3 faces to support the hips and gable rafter, my problem is how to achieve the strongest joint, I always had it in mind mortise and tenon joints would be used, thinking again would this weaken the finial too much? The last thing I want is a weak roof to come crashing down, your advice would be very much appreciated,

Thanks in advance

Gary

 

[kostello]

Hi gary

no need for any joint........if you look at any cut roof the tops of the rafters have a plumb cut and just lay on the ridge.

as long as the rafters are held in place at the bottom then a screw is enough to hold them in place at the top..

 

[Gaz]

Hi kostello,

Thanks for the reply, sorry I don't think I explained myself properly, the orangery roof will be visible from underneath and will all come together at the finials, check the orangery roof construction in this link http://www.massonjoinery.co.uk/products/conservatories/ there is a pic of the finials from underneath on that page, I was wondering if all the rafters would be tenoned or wether this would weaken the finials too much.

Thanks Gaz

 

[Dee J]

Depends on the characteristics of the wood you're using. if it's something with a twisty knotted grain (like elm) then you could easily use mortices - think of a traditional wheel hub for example. Mortices in such a short stub of straight grained timber may well be problematic. Given that the join will be in continuous compression then wooden or metal dowels would probably be sufficient.

Dee

 

[Gaz]

Hi dee j, sounds logical to me, I will be using sapele, I did think about using festool dominoes top and bottom, like you say the joint will be in constant compression so am I right in thinking that large mortice and tenons will be a bit overkill

Gaz

 

[Richard T]

Hi Gary

I it t'were me, I'd use very shallow M&Ts just to keep everything seated.

 

[Dibs-h]

Hi kostello,

Thanks for the reply, sorry I don't think I explained myself properly, the orangery roof will be visible from underneath and will all come together at the finials, check the orangery roof construction in this link http://www.massonjoinery.co.uk/products/conservatories/ there is a pic of the finials from underneath on that page, I was wondering if all the rafters would be tenoned or wether this would weaken the finials too much.

Thanks Gaz

Gaz

Looking at the picture of the finial and the other one,

I'd say the ridge is sat fully in the finial - the common rafters and hip rafters, these would birdsmouthed at the bottom and the top doesn't really need anything - as there are equal and opposite forces acting there. You could use a small M\T for locational purposes, but I think I'd rather just screw and plug them.

Look closely at ends of the rafters (all) in the above picture and you can see the pairs of screw\bolt holes.

HIH

Dibs

 

[Gaz]

Hi Dibs, you are right about the ridge I didn't notice that, thank you so much, I think I know where I'm going with this now, I am not sure if I can find large enough timber for the finials without burning my legs off so may have to laminate them, looks like the guys have done this in the picture,

Thanks for all your help guys, gonna start on making a saw table, then I'll be tackling it, I will post pictures of how it turns out fingers x'd

Cheers

Gaz

 

[Dibs-h]

Hi Dibs, you are right about the ridge I didn't notice that, thank you so much, I think I know where I'm going with this now, I am not sure if I can find large enough timber for the finials without burning my legs off so may have to laminate them, looks like the guys have done this in the picture,

Thanks for all your help guys, gonna start on making a saw table, then I'll be tackling it, I will post pictures of how it turns out fingers x'd

Cheers

Gaz

Gaz

Go with laminated - I'd do it out of 2" thick pieces. Remember to alternate the growth rings!

You could also cheat and miss out the middle lamination for part of it's length - allowing you to drop the ridge right in! :wink:

HIH

Dibs

 

[Gaz]

Great advice dibs, I think I will go with that, next lesson to learn, laminating :-/ , cheers

Gaz