Wood Joits - type of fit

Jun 28, 2008 3 Replies
A

Started cutting cross halvig joints and have some M & T joits to do soon. What type of fit is ideal?



eg slip fit - slips into place without pressure.



nice fit 1 - pushed together firmly by hand



interference fit 2 - requires pushing together with the tap with a mallet



interference fit 3 - requires pushing together with a few belts with a mallet



Incidentally I am using red hardwood for the verticals and mahogany for the horizontal members for an external door frame with side and toplights. It may be a bad mixture but I'm not going to change it now.



Thanks.



Arthur


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T

I'd go for Nice fit 1.

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N

Somewhere between the two is the usual fit for a mortice and tenon joint - push together with light resistance. You may need to assemble and dismantle the frame a few times, to get all the joints right, so you don't want anything more difficult to assemble, but too loose will weaken the joint. If you need extra strength, as you will for a door, make it a haunched through wedged mortice and tenon.

The first drawing here shows a through wedged joint - note the taper on the outside of the mortice. You tap the glue-covered wedges in as part of the final assembly, when you are also gluing the joints. The third drawing shows a haunched tenon. The haunch supports the joint to the edge of the wood and gives extra area for glue..

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Bignell

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D

Depends on the size of the timbers. Significant persuasion is ok if you're jointing oak beams. Generally you want to stop short of any danger of the joint bulging or splitting, and particularly for m&t joints that will be clamped, glued and back-wedged, a smooth sliding fit is fine.

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