What size drill bit for octagonal Oak dowels.

[JohnMi]

Hi,

I am doing a Green Oak Timber Frame for the first time. I have octagonal oak dowels.

I have drilled holes in the oak where it will be joined with the dowels with a 22mm drill bit.

I am not sure what the size of the dowels need to be as they are octagonal. I am making the "m" measurement there to be around 21mm which makes the "longest diagonal (l)" measurement to be 22.7 to fit in a hole drilled with a 22mm drill bit. Is this the correct way to do it? any thoughts?

 

[niall Y]

I believe you're overthinking it Width of dowel - face to face - will be a tad over hole diameter. They need to be tapered as well so they will fit a way into the hole., before you start to hammer them home. It is best to use riven stock to ensure the grain is straight so that they are strong and do not break. And give yourself a long enough length to play with. I have used sawn stock on occasion and managed OK ,though it's a bit of a bummer if they do break.

 

[HOJ]

Why octagonal, maybe square or round, they are going to need a fair hammering to get them in.
Anyway I reckon your drawing should show 20.8mm across the flats so they will be gappy in a 22mm hole, how you are proposing to make the dowels?

You've been here before, we never did get an update on the success of your last "Project"

 

[JohnMi]

well the last project is this very same project. It started one way and transitioned into this now. I removed the concrete posts and will be putting in a green oak frame in. The dowels are octagonal because i bought them from a timber framing guy in wales and he claimed octagonal ones are easier to hammer in. I bought them last year and they have been sitting in my shed since. They were sold as 25mm but I need to make them smaller as my tenons are not that big. I have not done this before so I do not know if I try to hammer in a 22.7mm in "l" diameter octagonal pin inside a 22mm hole would that split the wood. or if I make them smaller across the flats would that have sufficient grip after for a really snug fit once the dowels are in.

 

[HOJ]

I would bang them through a dowel plate and make them O and taper the ends as @niall Y said.

 

[johnnyb]

don't make them to tight through a dowel plate twice at least then a bit more.

 

[Adam W.]

Traditionally, they are both tapered and octagonal.

 

[Daniel2]

Exactly. Octagonal +/- and lightly tapered.
Don't overthink it.

 

[HOJ]

I was being dense, I presumed they were machined octagonal pegs missed the fact that they would be cleft and drawn, never used these as I make my own in the round
with a dowel cutter or plate:

 

[JohnMi]

the ends are tapered. I do not have a dowel plate. I have a table saw that i am using to cut them into shape

 

[Daniel2]

the ends are tapered. I do not have a dowel plate. I have a table saw that i am using to cut

They really need to be tapered over their length. That is what pulls
the tenon into the mortice as they are knocked in.

 

[slimshady]

Only the first part needs to be Tapered, to find the Off-set hole. The rest should be tight-ish in order to keep the tenon pulled in.
Not too tight or danger of splitting the beam. Kris Harbour has a bit of a Youtube episode about pegs that he had to adjust because the pegs he bought were not correct. .
Alex.

 

[Daniel2]

Only the first part needs to be Tapered, to find the Off-set hole. The rest should be tight-ish in order to keep the tenon pulled in.
Not too tight or danger of splitting the beam. Kris Harbour has a bit of a Youtube episode about pegs that he had to adjust because the pegs he bought were not correct. .
Alex.

Have you done this in reality, or are you just spouting theory ?

 

[slimshady]

Yes , I'm not a timber framer by profession but I have built a workshop and currently cutting joints for a garden room/office thing. 6x6, 6x8,6x10 oak timbers.
My first couple of pegs were too tapered and didn't pull in enough. Replaced with others and fine since.
If I'm going through 6inch beam then my pegs are about 9 to 10 inches long and tapered for the first 2 inches-ish.
Please don't take my word , search out the Kris Harbour vid.
Alex.

 

[JohnMi]

so to update you. I ended up dong them to 22mm octagonal shape. And tested. That did not go well. A few of them went in 3/4 of the way and got stuck. The rest I reduced further with the belt sander. I got the belt sander secured upside down and running and just rolled the dowels on the belt several time until they were almost round and this did the trick. I treat them with osmo base coat just before hammering them in and that provides some lubrication I believe and things started happening. Here are some pictures of it starting to come together. I made a ton of mistakes including making two of the beams 10cm shorter than they should have been but I managed to recover and correct for all the mistakes so far.

 

[JohnMi]

I will post some pictures once it is all done if I live long enough to see the end of it.

 

[JohnMi]

This is the end result

 

[JohnMi]

A view of the frame

 

[Daniel2]

What you have done looks really good, except that you have round
dowels. Traditionally they are octagonal.

 

[okeydokey]

Nice work