Best way to adjust dowel fit in oak?

[alanambrose]

Hi,

I have a design for some coat hooks I want to use in a few places around the house. This uses some rough green oak for the 'base' and 30mm bought-in machined dowels for the 'pegs'. I'm not much of a woodworker :) but I did a rough little prototype to check the design and figure out a fixture to drill the 30mm holes at a 30 degree angle on a drill press:

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(Please ignore the peg at 90 degrees - that was only done to check the dowel fit.) I was pleased to find that the 30mm Forstner bit I used gave a clean entry cut even being used at a 30 degree angle. The problem was that the '30mm' dowels are slightly bigger that the '30mm' Forstner bit I used. The discrepancy is about 0.3mm with the dowel being ~0.2mm too big and the holes ~0.1mm too small. I would be happy making the holes 0.5mm bigger than the dowels giving an easy fit and room for some glue.

The question is how? I don't have a lathe and anyway this would be tricky because of the 30 degree angle. Some kind of adjustable bit would work. Or I could buy a bunch of different bits to find one that cuts oversize - but I would need a bit that was happy with an entry angle of 30 degrees without tearing out the side of the hole. In one example I want to put about 30 'hooks' in a line so manual adjustment with a sander isn't looking a great way to go (and the dowels are quite hard anyway.) A trimming router and an oval template - I could cnc machine that in aluminium I guess? Any other ideas? (And yes, I know my mitre saw blade is blunt :) )

Ta, Alan

[Andrewg]

As you say , a Forstner bit is the ideal drill type to drill your angled holes - however they don't come in fractional sizes. However just as in metalwork, precise holes are reamed after drilling, so you want to open out your initial hole just a little. I would be tempted to get a cheap 30mm Blacksmiths bit that has a reduced shank so you can chuck it in a power drill. Then just use it to ream out the holes a bit by hand to get the fit you want.

You say the base is 'green' ie wet - as it dries this wood will shrink making your holes smaller. If your dowels are too snug a fit, then you might get splits, however get ot righ and you will get a tigher fit that will last better than any glue!

Hope that helps

[alanambrose]

Thanks and good point about the shrinkage of the green oak.

[Kitwn]

Sandpaper and elbow grease!:encouragement:

[the great waldo]

Hi
If the dowel wood is green you can try putting the dowels in an oven or micro wave ( you'll have to experiment a bit on how long and how hot, but it should get you out of trouble. If you have any kind of table disc or belt sander you could rig up a v block jig and roll the dowels against the sander.. One final method take a piece of your dowel, screw a woodscrew into the end of it (as central as possible) leaving15mm stickng out, cut the head off ,chuck it in a drill and run it against some coarse sandpaper making a very slight taper till it's small enough to fit your holes plus a bit extra for the thickness of your sandpaper , super glue some sandpaper on the dowel and enlarge your hole to taste .
Cheers
Andrew

[phill05]

If you have a lot of holes to do might be worth investing £5 in one of these Abrasive Sanding Flap Wheel Mop 30mm KLINGSPOR

The other way to do it is put a sawcut across the dowel and press fit it into the hole.

Phill

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[alanambrose]

Hey you guys are smart :)

I'll try to remember to report back after I try those methods.

Thanks, Alan

[alanambrose]

This is cute but not available atm:

https://www.amazon.co.uk/Forstner-Bit-Adjustable-30-42/dp/B01GRN28QW

[cropwell]

You can get an adjustable flat bit from Screwfix. https://www.screwfix.com/p/adjustable-flat-wood-bit-22-76-x-175mm/7261v?_requestid=832185

[Max Power]

You say the base is 'green' ie wet - as it dries this wood will shrink making your holes smaller. If your dowels are too snug a fit, then you might get splits, however get ot righ and you will get a tigher fit that will last better than any glue!

Hope that helps

The hole would get looser as it dries not tighter

[Andrewg]

The hole would get looser as it dries not tighter

Well that would be a blow to centuries of greenwood chair making!

See section on Shrink and Swell joints construction here (https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.agriculture.purdue.edu/fnr/faculty/Eckelman/documents/d200008a.pdf&ved=2ahUKEwij67K8nvPqAhUFoVwKHbZODKMQFjAAegQIAxAB&usg=AOvVaw3jBLzNAoDDwZlqEHc9qRO1) if you are confused.

[alanambrose]

Ah I'm late giving follow-up. I ordered an 11mm drill from RS recently and I was surprised to see they sent me a 7/16 Inch without asking. That didn't matter for the job it had to do though. Anyway that sent me thinking about imperial sizes slightly larger than 30mm. Hey presto, a 1 3/16" from 'The Toolpost' gave a good fit for most of the holes. The dowel must have been a little varying in size (it's been around for a bit) so I had to sand about 30% of the holes.

Thanks for all the great workarounds - v. useful skills for the armoury :)

A coupla snaps below of the completed items:

http://www.anagram.net/nuts/misc/IMG_4578.JPG

http://www.anagram.net/nuts/misc/IMG_4579.JPG