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BIG mortise and tenon joints - joining oak sleepers

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jamesmerrix

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Hello,
I have had a search through some old posts, but dont seem to be able to find the answer i am looking for so hopefully you will be able to help.

I am planning to make a large (2.5m W x 1.2m H) fire surround from some oak sleepers; as i am looking for a solid, rustic look and having some knots, splits and twists will hopefully add to the character. What i am unsure of is the best way to join the mantel to the uprights. I will be using a 250x150 piece for the mantel and 200x100 pieces for the uprights. My thoughts so far are:
To use a traditional mortise and tenon - though how is best to accurately cut it?
To use a half lap style of joint - cutting a piece out of the back edge of the mantel
To butt them together and use a rebated metal 'strap' to hold them together

Below is an extremely basic sketch up image of what i am hoping to make;

If anybody out there has attempted something similar, or has any good ideas, i would really like to hear them!

many thanks
james
 

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Paul Chapman

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I wouldn't bother trying to fit them together. If the wall you are fitting it to is solid brick, then I would fit the two uprights using Rawlbolts http://www.rawlplug.co.uk/index.php?opt ... &Itemid=25 Fit the rawlbolts to the wall first, replacing the bolt with some threaded rod (M10 should be OK) then drill the uprights and slide them onto the rod and secure with washers and nuts. Fit the top piece the same way, resting it on the uprights. Make some plugs to block the holes.

I did something similar for a friend and it worked OK.

Cheers :wink:

Paul
 

matthewwh

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Hi James,

Reclaimed railway sleepers are not really suitable for fireplaces as they are soaked in tar to stop them rotting. At best you will find that when warmed by the fire they will ooze tar, make a mess and stink, at worst they are a fire risk.

A better bet might be structural beams recovered from an old building, a bit dearer I'll grant you, but better than discovering the above after you have gone to the effort of making it.
 

Jacob

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Have a look at stonehenge. Just short stubby tenons to locate the verticals loosely in rough mortices in the horizontals. Must be good - some of them are still in situ!
 

jamesmerrix

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Paul - I Like the idea of rawl-bolts - i am taking off the old suround tomorrow so i will see what sort of walli have to play with.
Matthew - Sorry i should have mentioned, i will be using new oak sleepers - so no tar, made that mistake when i edged the lawn...hot tar trodden into beige carpets are not a good mix!
Jacob - realise that i am after the 'rustic and chunky' look, perhaps thats a little too much - take you point though!

James
 

AndyT

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So, big chunky timber, probably not very dry, around a fire. Face exposed, back fitted to a wall. Assuming the fire will be used, you will get some parts drying out faster than others, so there definitely will be warping, twisting and splitting. That's ok; that's the look you are after. So which method of construction will look best after a year or so?

If you don't join the parts but fix them all to the wall, you will have a gap. If it ends up looking like the horizontal bit is floating above the verticals, I think that will look silly and spoil your work. If you fix them at the back, with a lap joint or the builder's metal strap, there is a chance that your joining method will be revealed. The best option is the mortice and tenon.

For stuff this big, the normal rule that the tenon is about one third the thickness still applies. I'd do them the full width of the verticals, or set them back with just a small shoulder of 10mm or so. Cut the tenons in the ordinary way by marking round and sawing. However, rather than finding a very wide mortice chisel, it would be more normal to drill out holes to remove most of the mortice and then clean up by chopping down the sides with an ordinary firmer chisel. You won't need to go very deep - I'd say about 30mm would be plenty. You could use a nice Forstner bit if you want to but a flatbit in an electric drill would be fine and much cheaper.
 

andersonec

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phil.p":3qphk63e said:
Gaps and shakes!............learn to like 'em mate!
Green oak indoors will give you a little more than a few gaps and shakes in a couple of weeks, specially if there's a few knots involved

Andy
 

jamesmerrix

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Thanks for all of your replies,
I appreciate what everyone says about movement, uneven drying and the resulting splits and shakes, however i am more than happy to see them appear and eveolve over time.
Andy - i think a shallow full width M+T will be the answer; i had not though of the movement revealing the fixing method.

The old fire surround is coming off today, so hopefully it will reveal a nice suface for fixing the new one to!
 

Eric The Viking

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T'other thing is using some sort of 'apron' to hide the top joint altogether - Thin Oak or ply or whatever fixed to the lintel wrapped around the verticals at the top - if they move, the gap is behind the apron and won't show. The apron itself is fixed (glued, etc) to the lintel and won't gap. It doesn't preclude you doing big M+T joints but it makes them less necessary, although it would interrupt the clean vertical line.

I've done a bit of restoration on marble fireplaces in the past - they usually have iron spikes into the wall at the top of the verticals to hold them upright, and the back edge of the shelf is plastered in, but there's usually nothing of the function of a mortice+tenon keying the uprights to the shelf. Gravity is quite sufficient. Traditionally, the whole lot was held together with plaster of Paris slip too, although modern manufacturers use coloured epoxy resin nowadays.

HTH, E.
 

woodbutcher

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hi.
why not just dowel the mantle to the legs with broom handle and rebate the back to take builders straps and screw these to the wall


woodbutcher (richard)
 
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