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#15753 - 06/04/08 02:37 PM Brace Joints?
8ballmoose Offline
Member

Registered: 11/20/07
Posts: 4
Loc: Bancroft, Ontario, Canada
I am starting a heavy timber pergola type structure and have a few questions as a rookie?
My posts are 7.5" square going into a sill plate 7.5" x 11.5" with brace sizes being 5" x 8" to accomadate a slight arch.

First question 2 braces will be coming out from a single post (one each side). I am worried about making a weak section in the post caused by back to back mortise? Should I offset the mortise and tenon joints and or shorten up the depth of mortise.I was planning on using 3"min. depth.

Second question regarding pegging, I was planning on using standard 1" hardwood dowels and bevelling the ends however I am open to suggestions? The timber is my own Hemlock and I am planning on using a slight (3/32")offset on the hole for tighening?

Regards
Lloyd (Bancroft, Ont.)

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#15758 - 06/04/08 03:45 PM Re: Brace Joints? [Re: 8ballmoose]
mo Offline
Member

Registered: 11/04/06
Posts: 850
Loc: Charleston, SC
Welcome 8ball. Are you talking about bracing from top plate to post? I have to admit those are some big braces. Are you going to put an arc on the underside of the brace and how much from the edge will the center point of the arc be laid out. I did a quick draft at 2.5" and it looked alright.

Since you are dealing with compression joinery it gives you more flexibility than say a tie-beam to post joint. The brace joinery is in compression as long as there is a mirror equal in the same plane somewhere. In my opinion since there is no tension on the joint I would use a 1 1/2" wide tenon so more of the post wood is left. I do not know if you are centering these braces and mortises. However even if you go say 2" from a reference face, then a 1 1/2" mortise you still have 4" of wood on the other side. I would think centering the mortises on the post would be best. If you are square ruling just say 3" from reference face. I would think that offsetting the tenons is unecessary and might be worse for post strength (anyone?). I would put the mortises in the same place on each side. Under normal brace dimensions (3X5) I would also just make the mortise a thru mortise for both tenons and be done with it.

The 5x8 (assuming no nosing on the brace and it is 12/12) will require you to cut 11 5/8" of mortise in the vertical plane of the post. I still think this would be alright as long as the tenon is 1 1/2". I could be terribly wrong on this particular instance though.

Also with a 3" tenon a 3/4" diameter peg would be better according to some rules I saw somewhere along the way (3/4" dia for tenons less than or equal to 4" in length).

It would help to see the frame as a whole.

mo

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#15774 - 06/05/08 10:03 PM Re: Brace Joints? [Re: mo]
Gabel Offline

Member

Registered: 11/18/03
Posts: 687
Loc: Georgia
Welcome!

A quick note on pegs and drawboring -- if you are going to drawbore , you need to use a tapered peg. I would deifinitely not use a standard store-bought dowel. You can get pegs from a few places -- one is Northcott Turning (www.pegs.us). They make a variety of peg shapes, including one for draw boring.

We split and shave ours from new straight grained oak and reclaimed dense old growth heart pine. They are slightly tapered octagons with a point on the last couple of inches. They are made to work with a 1/8 or so drawbore. I would also recommend 3/4" pegs for a 3" tenon


keep the mortises opposite each other and lined up on each face -- that way you have more continuous grain. On the braces opposite each other, cut the mortise through, but make sure the tenons won't touch -- leave 1/2" between them. Are you housing the braces? If no housing that will leave 3 1/2" for the tenon. That is still a pretty short tenon and I would go with a 3/4" peg in it.

GH


_________________________
Gabel

www.holderbros.com

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#15823 - 06/09/08 07:06 PM Re: Brace Joints? [Re: mo]
8ballmoose Offline
Member

Registered: 11/20/07
Posts: 4
Loc: Bancroft, Ontario, Canada
Thanks mo
Yes bracing is from top plate to post.
I have not determined how much arc but I will try your 2.5".
I have also decided to go with a 4" width on the braces, thanks for the peg suggestion.
I have forstner bits for cutting the mortise however I am limited to 3-3.5" depth. Any ideas other than chisel for more depth or through cuts?
I appreciate the feedback.

Lloyd

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#15824 - 06/09/08 07:16 PM Re: Brace Joints? [Re: Gabel]
8ballmoose Offline
Member

Registered: 11/20/07
Posts: 4
Loc: Bancroft, Ontario, Canada
Thanks for the welcome GH

I checked out the Northcott site and have decided not to drawbore (mostly because of my rookie status). I did like their tapered pegs with the head on the end.
I have also decided to reduce the brace width to 4". Any suggestions for cutting mortise deeper than my 3" frostner bits allow? (I realize I can chisel) or through cuts?

Thanks for helping me in he pre-planning state.

Lloyd.

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#15831 - 06/09/08 10:42 PM Re: Brace Joints? [Re: mo]
Waccabuc Offline
Member

Registered: 10/16/07
Posts: 112
Loc: Waccabuc, NY (NYC Metro area)
Hey welcome Moose,
Mo and Gabel have given you good advice and mortises, tenons and pegs.
Here's more: Put aside your forstner bit. Buy some good auger bits, new or used min. 8" long, sharpen them if necessary. You can drill mortises into your hemlock with a 1 3/8" or 1 1/2" bit using a hand brace, or an elec drill. Score the outlines of the mortises w a knife and a steel straightedge 'cause hemlock can splinter coarsely. Also buy a 3/4" auger bit for pegging.
Buy some pegs from Northcott rather than making your own, with the time you you just saved practice some drawbore drilling in a few mock-up joints in waste wood but of same size you'll do in your frame. Draw your joints on paper, take your time on layout and double check. Then go ahead mark, score, drill, chisel and check. Do a few, you'll learn and get better w each. By the time you do your first one for real in your pergola frame it'll be much better than what you did 1/2 day earlier at the start of practice.
As Mo says "It would help to see the frame as a whole." Good to get it on paper and show it to someone qualified who can review w you and constructively advise. TF is a big wheel to re-invent! Be prepared to pay for this valuable information. Changes and corrections on paper are much faster and less expensive than in 8"x8" hemlock. An Architect we did some jobs for said many, many times, "A job well planned is a job half done." Us, being the hands-on guys didn't want to argue fractions w him, the point was well made and well taken.
Work safely and have fun too.
Steve
_________________________
Shine on!

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#15917 - 06/17/08 08:03 AM Re: Brace Joints? [Re: Waccabuc]
8ballmoose Offline
Member

Registered: 11/20/07
Posts: 4
Loc: Bancroft, Ontario, Canada
Hey Steve
Thanks for the advise, I am keeping an eye open for auger bits and will lay out my plans better. i just finished cutting the remainder of my logs and have set aside some 1" boards for templates. I will also take your suggestion of ordering the pegs, Thanks again.

Lloyd.

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