Dowel hole tolerances question

[Kenneth Moar]

My best option for drilling some dowel holes in hard maple is my brace and auger bit, but the bit is .635 inch and the dowels are only .620 inches. I drilled a test hole and the dowel is a wee bit loose. The dowel purpose is to pin a mortise and tenon joint for additional strength. Just wondering if using Titebond III will fill a .015 gap and provide strength. Thanks

[Edward Weber]

Do another test and glue the dowel.
If you're using PVA glue, the dowlle will most likely swell up a bit and tighten up in the hole

[Jimmy Harris]

Agreed. If you need to, thin out the glue and let it sit for moment to absorb into the wood. It should swell the dowel.

Also, the dowel won't be adding any strength anyway. A dowel serves no structural purpose in a mortise and tenon joint in today's world, what with our modern glues. It's purely decorative. It's an element that harkens back to an era where glues were less reliable. And even back then, if you made a good and tight M&T joint, it's probably still holding today, even with the old, inferior, glue.

[Brian Holcombe]

Would not use dowels .015 undersize. They should be a snug fit.

[mike stenson]

Would not use dowels .015 undersize. They should be a snug fit.

Agreed. I'd drill a hole in a metal plate with your drill bit and make my own dowels.

[Richard Coers]

I'd have another bit ground down for a better fit to the dowel, or use a spokeshave to make new tapered pins. How many mortises are you draw boring? Timber framers have always made their own pins, they don't have to be perfectly round when you drive the pins into the hole

[Thomas McCurnin]

I'm going to go a different direction here. I think most of the strength in an edge joint comes with the glue, not the dowels, which while adding some strength, are used mainly for alignment. If the dowels are undersized, I wouldn't worry about it.

[Rob Luter]

So buy a 5/8" brad point bit and use that instead of an auger. The ones I use are crazy accurate.

[Mel Fulks]

I don’t think the dowels swell much . I’ve got a piece of scrap steel about an inch thick with slightly undersize holes. All the old timers
I worked with had them . Holes had flared EZ to start holes. Dowels are driven through and become skinny, then swell up tight.
Ive seen some commercial plates ,but they are thin and don’t work as well as the thick steel. We would add a bit of water to the
glue, dowels go in easy , no splits in the project. I’ve seen lots of school oak chairs loose and falling apart, from normal kid abuse.
No doubt they would have been fine with better gluing.

[Jim Becker]

I agree with Brian...use a dowel that's the correct size for your application. For pinning jointery, they should be very snug. The glue certainly helps hold them in, but the strength of the connection comes from the snug fit of the dowel holding the M&T together. In fact, there are many applications where the dowels are not even glued by some makers, especially if draw-bore technique is used.

[Edward Weber]

I would suggest double checking the measurements on the bit and dowels.
I'm guessing we're supposed to be using 5/8" (.625") as the main measurement.
Dowels are rarely uniform, so the OP's size of .620 is most likely at one or two measured areas.
Try another dowel, it may be thicker. Also, the .635 is a "fat" 5/8", check the bit.
Most 5/8" dowels will easily swell the .015 needed, once water based glue (PVA) is applied.
The OP is pinning a joint, not draw-boring, there is a difference. There is little to no pressure in pinning, the dowel is only there for insurance in most cases.
JMHO

[Kenneth Moar]

I went ahead and drilled for the dowels with the brace and bit, eight holes in total. I let the glue absorb for 5 minutes or so, all but one seemed to be pretty snug. I'm not going to worry about the strength as Jimmy pointed out, it's probably providing little strength. I could have bought a 5/8 brad point from Lee Valley, they are about $40 CDN, just didn't want to spend the money or be delayed. The dowels are Wenge so the appearance is a great accent to the hard maple. Thanks for the responses.