Bolt holes loos or snug?

E-wan · 2 Jul 2018

Firstly apologies that this isn't purely woodwork.

I'm intending to reinforce some large half lap joints with M12 Bolts. I have found that if the diff I drill a 7/16 hole (11.125mm) this gives a very snug Fit for an M12 thread which cuts its own thread slightly through the wood on the test hole I have drilled.

Is it a bad idea to have something so tight fitting and should I consider a slightly wider hole to allow for a little movement of the wood? The joints are going to be made to connect a 9 foot 6" x 6 Beam between two posts.

Thanks

Ewan

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Phil Pascoe · 2 Jul 2018

I wouldn't think it mattered much - I'd do what suited the construction methods best - if it suits to have some leeway, bore the holes a little larger, if e.g. you're working on your own and might find it easier to have everything rigid as you go, keep it tight. It also depends upon how many bolts you have to line up at once, of course - you might be glad of the play.
Only opinion, of course.

MusicMan · 2 Jul 2018

Agreed it doesn't matter much; I'd personally prefer tight, as the movement of wood along the grain is very small, and the distance across the grain here will not be very great. If there is a big humidity change expected, do the bolts that are central and in line with the grain tight, and those off-axis a little looser.

Sideways · 2 Jul 2018

Also prefer snug.
If the aim is to reinforce the joint against movement, then I'd see a tight joint as better able to prevent this and to slow down the eventual enlargement of the hole. A sort of "racking leads to more racking" argument.

Jacob · 2 Jul 2018

Loose is better.
The only bits which count are the nut itself and the head of the bolt, plus washers. The size/shape of the hole between then doesn't matter at all and might as well be a loose fit to allow movement, ease of installation, adjustment, extraction etc.