Best Way to Make Semi-Headed Arched Frames

[Marek S]

Hi all,

A few questions have been playing on my mind of late regarding semi-headed arched frames. I thought I'd get your expert opinions to untangle them.

So here's the deal... I've made a couple of semi-headed (180 degree arched in the vertical) door frames and doors recently, essentially following the method set out in George Ellis's Modern Practical Joinery. I machined the head in 2-3 flat laminations, segmented and offset across the width. In one case I made up a square section (all laminations equal width) and machined the rebate after. In another case I used a diminished outside lamination to cut out the need for rebating (again, as per Ellis).

In all cases I machined the curved segments to size using a small, banana-shaped MDF template before gluing them together, meaning that each laminated segment had to be perfectly aligned with the next in order to create a perfectly square section. I then finished off the head with a compass plane and sandpaper. The doors and frames turned out nicely.

However, since then my colleague has made another arched frame using a different method. He laminated the segments as straight lengths and glued them up into a kind of trapeze before machining the curve, which he did in one go, using a full-size curved MDF template. This has the advantage of reducing the curve work to a single process but it strikes me as being more wasteful in that it uses more MDF, and eliminates the possibility of getting two short segments out of the same width of timber (imagine the two segments drawn on the timber, one above the other, basically spooning!).

So, question 1: which is better/quicker/more reliable? How do you make your semi-headed frames?

I note that New Yorkshire Workshop do a kind of hybrid of the two methods, cutting the curved segments close to the finished width, assembling the segments then doing a final pass on the spindle moulder using a full size template. Not sure I want to go down that route as it seems like making two templates = twice the work. NYW also tenon-join the segments rather than laminating. Is there an advantage between one method and the other?

Question 2: I'll shortly be making a bunch of natural-finish arched window frames and therefore can't have any screw holes/plugs showing on the faces. Can I rely on double-sided tape to hold down the template for spindle ring-fencing? The answer to this question has a bearing on Q1, since the template screw holes can be hidden on the inside of the lamination using my technique, whereas my colleague's technique requires him to screw the template through the face of the finished arch section (he has ended up with a few visible screw holes -- not great).

Question 3: Ellis recommends screwing the laminations together through the face. But if the laminations cannot be screwed together (because of the unpainted finish), will the glue be strong enough on its own? We usually use cascamite for edge jointing and exterior lamination.

Anyway, sorry for writing an essay. If anyone has any insights into this, I'd be very appreciative!

 

[Trevanion]

I like to glue it up in segments in two or three overlapping layers as a single oddly shaped piece made up of square sections of timber, then bandsaw the majority of the excess off and then attach a full-sized template to machine it on the spindle moulder to final size. I would imagine it's a huge amount quicker than individually shaping pieces, Yes, you may get the extra segment out of a piece of timber that way but you've wasted a huge chunk of your valuable time to save £1 worth of timber.

Here's a pro tip, run some masking tape over your timber section and your template pressed down hard, then glue them together with superglue like mitre bond. Holds super secure and it's easy enough to pry off without leaving a complete mess of the workpiece or the template.

Whilst it is an excellent resource for traditional work, you do have to bear in mind that Ellis' book is over a hundred years old at this point and things have moved on a smidge. The glue they had back then wasn't particularly great so they needed to put extra fasteners through the face which you see quite often in old work such as chapels.

 

[deema]

I make them the same virtually the same as above, apart from I screw in the waste section the pieces together when gluing up. I also cut trapezoidal sections (easy 45 degree cuts) to minimise waste especially if it’s out of something expensive. I always on anything other than gates make them out of three ply so the face sides match with the only cut / join is at top dead centre.
I make two full size templates, one for the inside and another for the outside. The stuff gets clamped down using toggle clamps mounted on Buttresses and then it’s through the spindle. I use 12mm MDF for the templates / mounting boards and screw in a couple of handles on the side away from the cutters.
Do not make a single template, attach with double sided that will allow you to spindle cut both sides and expect to be able to count to 10 all your working life.

Budget a sheet of MDF into the cost.

 

[thetyreman]

you could do it the way mr chicadee does it in this video, using butterfly keys to hold the pieces in place,

https://www.youtube.com/watch?v=WN9DA8qGT88&t=2s

ignore the first half of the video.

 

[Trevanion]

you could do it the way mr chicadee does it in this video, using butterfly keys to hold the pieces in place,

Where I used to work we had a Hoffman dovetail key machine that we used in a similar way for joining the segments but with plastic keys, it was a luxury for keeping things aligned and together more than anything :lol:

 

[Marek S]

Thank you all for the excellent advice. It sounds like there's a consensus re: assembling 'in the square' then machining the curve in one go.

Re: this part:

I would imagine it's a huge amount quicker than individually shaping pieces, Yes, you may get the extra segment out of a piece of timber that way but you've wasted a huge chunk of your valuable time to save £1 worth of timber.

I also imagine it is quicker, but perhaps not much quicker, since the 'one go' method requires you to work out how the square segments overlap (presumably on the set out), and as you'll know from experience these then have to be laminated in such a way that the curve can be cut out without any gaps (obviously quite easy, but still something to work out). Also factor in the time taken to machine out the full-size template (presumably using a router set up on a radial arm) and it doesn't seem like there'd be all that much in it -- maybe half an hour or so?

About wasting the timber -- it's more the principle than the money saved. And the ecological aspect, too.

As I think about this in light of everyone's comments, I wonder whether there isn't an even better method here, in which we dispense with the template altogether. If I'm going to spend time setting up the router on the radial arm, why not machine the curve directly using a long 1/2" flute or flush bit? I can imagine assembling the segments, leaving approx. 2mm extra over the final width on the inside and outside, then finishing off with a router set up on a radial arm with the centre pin raised to the same height as the frame thickness. If the radial arm establishes the inside and outside circumferences, why bother making a template? It should also be possible to rebate the arch using the same set up, simply by changing the router depth.

Has anyone heard of / tried this technique?

Thanks again for all the help!

 

[Marek S]

PS: This is great tip!

Here's a pro tip, run some masking tape over your timber section and your template pressed down hard, then glue them together with superglue like mitre bond. Holds super secure and it's easy enough to pry off without leaving a complete mess of the workpiece or the template.

 

[Trevanion]

That's actually a pretty clever idea, I've never used a radial arm saw that could take a router bit though so I would never have thought of that.

 

[Marek S]

That's actually a pretty clever idea, I've never used a radial arm saw that could take a router bit though so I would never have thought of that.

Was thinking of something more along the lines of a shop-made arm, using a couple of threaded steel bars passed through the router bed, a bit like this: https://www.youtube.com/watch?v=l0gM-TqxYbE&t=21s

Sorry if 'radial arm' was confusing - my bad!

 

[Trevanion]

Ah! I'd call that a router trammel!

 

[Marek S]

Gotcha!

 

[Max Power]

I make curved templates regularly and used to use a router in that way. I now use the same method on the bandsaw. Its quicker, cleaner and cheaper so better all round. I then use the spindle as above to complete the job