Wedged through mortices.

[Mailman14]

Hi folks,

I'm new in this section, so please forgive me if it's been asked before?

Is there a mathematical formula for positionig the kerf for a wedge, when cutting mortice & tenons? I'm currently planning a shelf / display unit, and drawing it in Sketchup, I'm not sure where to put the cut-out. I've not seen it mentioned in books, but looking at photo's of work done, it seems intuitive, or is that just "it looks good, 'cos a professional's done it"?

I was working on a 1:4:1 spacing - is that too much?
Overall length of mortice is 1 1/2", equal sided 'v' cut-out (should it slope to the 'outside'?), width & length (thickness of planks) 1/2", if that helps - not made any sawdust yet - so all help gratefully received before I ruin it...

I'll see if I can post a pic from sketchup on here in a bit.
Help! Thanks,

'Bvt

 

[Mailman14]

Just for clarification - top view, the cut is longer than the thickness of the plank (wedge extends into the visible part of the shelf), lower view is in line with edge of shelf. L/H 'V' cuts, R/H angled to outside edge.

Any suggestions?

 

[MikeG.]

Tradtionally, methinks, they are through tenons.

I reckon you are being unnecessarily fussy about this detail. To be honest, it doesn't really matter. The location and the shape of the cut is going to be down to aesthetic choice and your judgement of the grain and strength of the wood. The only thing about wedging tenons that really takes any thinking about is driving the wedges in together such that they end up the same width when cut off and cleaned up.

If in doubt about the spacing or proportion of anything, always fall back on the good old Golden Section.......it seldom lets you down.

Mike

 

[OPJ]

That looks about right to me. Don't make your saw cuts any longer than ¾ the length of your tenon, otherwise, I reckon you'll risk splitting the wood... :? If you are concerned about that, you could even drill a small hole (larger diameter than width of the saw kerf) at the end, which would prevent the slot from elongating.

 

[Night Train]

I also tell my students to make sure the wedges are the same with as the tenon so there are no gaps. They should also be proper wedges, cut sloping on both sides and not just one side. If they are cut with the slope on one side only they can break the short grain and leave the wedge with a flat.

Also make sure the wedges put pressure against the end grain of the mortise and not the long grain as it can split the mortise.

 

[Mailman14]

Mike - I'm a picky so-and-so, so, positive criticism taken in good stead! Your mention of "golden section" also is helpful.

OPJ - I had wondered which way to go - shorter or longer than the tenon, thanks! Already know about the hole stopping the split (but always willing to listen to advice).

Night Train - thanks for advice on the shape of the wedges - this is what i was hoping for! Have grain oriented in the correct direction, but thanks again for the advice - would be a waste of wood otherwise (and I wouldn't be happy!)

I'll carry on when I've finished my pinboard off, have saws, hammers and screwdrivers up now!

"slowly, slowly, catchee monkey.."