Clamping an arch

[rafezetter]

This is the connection between the two sides at top of the arch, the other connections are similar. If the double tenon, if that is the right term, is not big enough I could still cut something longer.

If I am understanding it right, a glue block is made a of a soft wood and glued onto the arch so as to provide a clamp point, and then when it is removed the soft wood should rip apart leaving the oak intact. I have some thinking to do there.

Right idea but wrong bit - the simplest way would be to make a block that's glues to the side of the door rail at the point the top (or bottom) face of the clamp meets that point.

If you read my last paragraph in my above post and do what I suggest, that will give you an idea of what you are needing.

Apart from the issue of making a glue block that will sit "nicely" on the arch, which would involve making it match the curvature of the arch (more work), I can't envision any way that this would help your situation because the geometry is all wrong.

Soft wood or hard for the block is irrelevant as there'll be no "ripping" of anything :shock: - if you use wood glue as many people do, you'll PLANE it off down to the level of the door rail, a little sanding and it's done - if you have a hot glue gun then you can either soften it with a heat gun (can get a bit messy) or make it cold and brittle with one of those air cannisters used upside down so it sprays the propellent in the can which will come out very cold.

I've seen Norm Abrams use the paper trick and put copy paper in the glue joint to reduce it's effectiveness - essentially apply glue on both faces to be glued, and slip a bit of paper onto the glue on one of the faces, then apply the item you are gluing. I've seen it's a firm enough bond to do what's needed but then he's able to break apart that glue joint with his hands, leaving some easy cleanup.

 

[rafezetter]

I don't want to be a naysayer but I don't think that connection is going to be strong enough to hold against seasonal changes and wood movement. It's a very small tenon with minimal long-grain glue faces, the whole joint is going to be practically relying on an end-grain glue joint which with the instability of oak and the changing seasons the joint will just "pop" and get worse, and worse.

Ahh have to agree with Trevanion - even though I'm by no means an expert I beleive it's pretty much a cardinal rule with this sort of thing (splines etc) that the grain of the loose tenon be perpendicular to the joint.

What you have now is sympathetic grain running parallel with the joint - which makes it a lot weaker and if the loose tenon seasonally expands inside the joint, which it will do parallel to the grain, the joint will have no option but to "pop" as Trevanion says.

Pegging /drawboring / dowelling won't fix this and will actually guarentee a bad result.

The block needs to be re-made - and this is pretty imperative you do it - and done so with the grain running the opposite way. However if you made it square, just turn it 90deg Actually on reflection if it's not square, gluing a thin shim of wood to the side to make up the difference is just as good.

 

[rafezetter]

Here's Mr. Vondriska doing the woodblock clamping trick: https://www.youtube.com/watch?v=AFUrpRTI6q0 It's not so much the softness of the block as the weakness of the (hot melt in this case, but sometimes people use PVA with a sheet of paper in between) temporary glue joint.

(I said that )

 

[dzj]

What you have now is sympathetic grain running parallel with the joint - which makes it a lot weaker and if the loose tenon seasonally expands inside the joint, which it will do parallel to the grain, the joint will have no option but to "pop" as Trevanion says.

Pegging /drawboring / dowelling won't fix this and will actually guarentee a bad result.

The block needs to be re-made - and this is pretty imperative you do it - and done so with the grain running the opposite way. However if you made it square, just turn it 90deg Actually on reflection if it's not square, gluing a thin shim of wood to the side to make up the difference is just as good.

+1 regarding the grain direction, but even if he turned it 90 deg, it'll still be short.

If I understand correctly, the door would be boarded on the outside. In such cases a halflap joint, glued and secured with screws (hidden under the boarding) would be enough for a door this size.

 

[Woody2Shoes]

Here's Mr. Vondriska doing the woodblock clamping trick: https://www.youtube.com/watch?v=AFUrpRTI6q0 It's not so much the softness of the block as the weakness of the (hot melt in this case, but sometimes people use PVA with a sheet of paper in between) temporary glue joint.

(I said that )

(... yebbutt after I did (and I found a good video of it) :lol: :wink: ...)

 

[Wurm]

Can anyone recommend a method for cutting a mortice right through the arch? My router has an 'edge band' attachment which might allow me to run a straight cutting bit perpendicular to the face of the arch, but there must surely be a standard method.

 

[AndyT]

Can anyone recommend a method for cutting a mortice right through the arch? My router has an 'edge band' attachment which might allow me to run a straight cutting bit perpendicular to the face of the arch, but there must surely be a standard method.

Sorry this is another "you can't get there from here" answer, but for most curved work the standard method is to cut the joints first, on square timber, then cut the curves.
Seeing as how that's not very helpful for you, you could try adding a shaped piece onto the curve so it's square again, cutting the joint, then removing the extra bit. Somewhat like the temporary blocks to angle the sash cramps.

 

[owen]

Can anyone recommend a method for cutting a mortice right through the arch? My router has an 'edge band' attachment which might allow me to run a straight cutting bit perpendicular to the face of the arch, but there must surely be a standard method.

Hand saw and chisel? From above? By edge band attachment I think you mean a fence?

 

[Wurm]

Can anyone recommend a workstand designed to clamp a piece of wood such as this in a vertical orientation? I have figured out (I think) how to cut the mortice so I just need to hold it in place while I work on the end.

I could clamp it to the banister but I would rather keep the dust out of the upstairs hall.

 

[AndyT]

A proper (ie old) B&D Workmate could work, if there is enough space.

Or possibly a big piece of wood on each side (such as a joist offcut or scaffold plank) clamped onto the work, arranged to butt up against the opposite wall.

These are just guesses and might work in your space, or not!

 

[Wurm]

This is for the top of the door so the two sides of the arch are joined by a 3/4" piece connecting two mortices. The pictured mortice measures 1 5/8" X 3/4", is that likely to be deep enough? I can run a longer bit through them if necessary.

I am making progress with some of the books recommended on here, and have also signed up to do a woodworking course, but the size of joint to use is clearly an experience thing.