Truss Joints

[Dibs-h]

I'm busy making the 2 Kingpost trusses (main workshop thread) and will be using pegs to peg the joints. I've got details on the min distance away from the mortise shoulders that the holes need to be bored.

I've come across mentions of using draw boring and tapered pegs - makes sense (later shrinkage etc.). Question is where does one get them from - or DIY? I don't have a lathe so was thinking that the taper isn't likely to be uniform - or does that not matter? I suppose lengths of 20mm dowel in a pillar drill and some lengths of coarse abrasive cloth should do the job.

Or is it overkill and constant diameter pegs do the job?

 

[Paul Chapman]

These might be helpful http://www.youtube.com/user/LieNielsen# ... AkWMHDKB-E

and http://www.youtube.com/user/LieNielsen# ... G1jNQzwvQ8

Cheers :wink:

Paul

 

[Dibs-h]

Paul

Thanks for the links - will have a watch when I have a little time. But sorry to appear dense - I've looked thru the list of videos and they all appear to relate to sharpening planes\saws, etc. Doesn't seem to be anything relating to draw-boring or making tapered pegs.

Cheers

Dibs

 

[Mikey R]

Pt 1:
http://www.youtube.com/watch?v=yAkWMHDKB-E

Pt 2:
http://www.youtube.com/watch?v=nG1jNQzwvQ8

I cant watch these at work, but IIRC they relate to drawboring in 3/4" stock.

I would guess the same concept would work with your massive joinery , except you wouldnt have the benefit of 20mm drawbore pins so maybe the lining up of the offset holes would need to be done by guesswork?

EDIT: Ok, so I did get to watch the last video at work - he just whittled the taper using a knife, and it doesnt seem like it needs to be exact either.

Dibs, Im planning on using drawboring on the short stretchers of my bench so Looking forward to how you get on!

 

[Paul Chapman]

Doesn't seem to be anything relating to draw-boring or making tapered pegs.

The two links I posted should open up the draw boring demos by Chris Schwarz. If not, scroll down the various topics on the right-hand side and you will find them.

The demos relate to frames. Not exactly what you are doing but the same principles would apply.

Cheers :wink:

Paul

 

[Dibs-h]

Thanks chaps - just watched those 2 videos. I've realised that the peg isn't tapered along it's full length - just a taper in the end to ease the driving. That won't be too hard to do - even by hand.

There's someone on Fleaby selling 6"x 1/2" pegs with the last 1" having a 3/16" taper for around 50p each. Might enquire about 20mm ones - which from what I've been reading is the sort of size I require, with the hole being offset in the tenon by around 5mm.

Failing that - see what the local timber supplies or Wickes have in - as I do recall seeing 1" dowel in 2.4m lengths before. I suppose as long as it's hardwood - I'm not too bothered.

Although I did think of using a contrasting timber for the pegs - but went nah!

 

[Chris_belgium]

I've recently used drawbore m&t joints for my driveway gate project, and made the pegs myself using a dowel plate, I found that the result was average and time consuming and very very boring , for future projects I will order them online. I couldn't find it right away but there is a company selling lengths of dowels, I'm sure someone else will post up the link.

I've also did some test m&t and found 2-3 mm to be the perfect offset, smaller doesn't pull the joint up tight, and more you destroy the peg when tapping it in. Even with the 3mm offset I had 2 (out of a total of 24) pegs wich broke when hammering them in.

https://www.ukworkshop.co.uk/forums/viewtopic.php?t=34019&highlight=

 

[Dibs-h]

I've recently used drawbore m&t joints for my driveway gate project, and made the pegs myself using a dowel plate, I found that the result was average and time consuming and very very boring , for future projects I will order them online. I couldn't find it right away but there is a company selling lengths of dowels, I'm sure someone else will post up the link.

I've also did some test m&t and found 2-3 mm to be the perfect offset, smaller doesn't pull the joint up tight, and more you destroy the peg when tapping it in. Even with the 3mm offset I had 2 (out of a total of 24) pegs wich broke when hammering them in.

https://www.ukworkshop.co.uk/forums/viewtopic.php?t=34019&highlight=

Thanks for that Chris. Earlier I came across the following,

http://www.greenbuildingforum.co.uk/new ... ionID=4487

which proved very informative. As for suppliers - I found the following.

http://www.greenwood-direct.co.uk/defau ... adindex.31
http://www.ecolots.co.uk/index.php/clas ... g-Oak-Pegs

or this guy who can make to order.

http://cgi.ebay.co.uk/20-OAK-OR-ASH-PEG ... 286.c0.m14

I personally don't see the point in buying ones that are 12" long to put in timber that is 4" thick. But having said that - the optimum length (I suspect) for me would be ones that are 6" long. Probably around 1 week away from needing to drill the holes and peg them, so still have time to decide who\what\etc.

Cheers

Dibs

 

[MikeG.]

I wouldn't make too big a deal of the pegs. They were seldom properly round, and seldom perfectly parallel along the long axis. I make them with the bandsaw initially to cut square sections, then use a deep-set box plane to roughly take off the edges until they are sort-of octagonal. You will need a bench hook for this.

A final clean up with a finer set box plane, and a quick flick around the ends to give a bit of a taper, then whack them in. Make them a couple of inches overlength, drive them too far and cut off the taper, but don't cut either side off flush. You could perfectly well make them with a draw-knife, or a spokeshave.........but, I repeat, they don't need to be very round, and you don't need to play with too much. Aim for a peg-a-minute.

Don't forget that whilst the framing is of green (unseasoned) timber, the pegs must be of dry seasoned stuff. American White Oak is fine for use as pegs with English oak framing. This is what you kept all those offcuts for all these years!!


Mike

 

[mickthetree]

Sorry to nick the thread, but watching the vids, the bit I dont understand is the use of the pin before the peg is whacked in.

Surely the pin just enlarges the hole, rendering the offset useless?

I'm obviously wrong as its been used for centuries and still works, but I would just assume that the action of driving the peg in would pull the joint up without needing to enlarge it first with the pin?!?!?!

Can someone enlighten me?

 

[Paul Chapman]

Can someone enlighten me?

This description from the Lie Nielsen site explains the theory

Drawboring is a great way to make a strong mechanical joint. A wooden pin is hammered through slightly offset holes in the two pieces, and pulls the joint together. You use Drawbore Pins to pull the joint together first (with some force and a twisting motion). This eases the edges of the hole making driving the wood pin easier. You can also disassemble the joint if you want to work on the fit some more before permanent assembly.

Cheers :wink:

Paul

 

[MikeG.]

A pin is no more than a removable peg, and I have never really seen the point. The only danger with draw-bore pegging is that you gamble a bit too much on the offset of the two holes, and either the peg jams and refuses to budge (or snaps) or the tenon breaks along the grain from the peg-hole. It doesn't take any time at all to work out the correct off-set just from trial and error......on 150x150 stuff I would reckon on about 3 to 4 mm, I suppose.

Incidentally, the drills to use for this job are either a brace & bit (if you fancy a bit of a sweaty work-out) or a spade bit.......not a Forstner or an orthodox wood-drill. This is because the first two have a nice point in the middle, which marks the position of the hole on the tenon (ie drill the hole in the post first, and into the mortice. Offer up the tenon, spin the drill in the hole just to mark the tenon, withdraw the tenon and drill 3 or 4 mm closer to the shoulder than the point you just marked).

The skill and guesswork is to drill all the way through the post from the one side, so that the two holes line up......and here again, with either a spade bit or a brace&bit, you drill just until the tip breaks through on the far side, then go to the other side and drill in from there (to keep the hole edges nice and clean). I saw my pegs off roughly 10mm proud.

Mike

 

[Dibs-h]

I wouldn't make too big a deal of the pegs. They were seldom properly round, and seldom perfectly parallel along the long axis. I make them with the bandsaw initially to cut square sections, then use a deep-set box plane to roughly take off the edges until they are sort-of octagonal. You will need a bench hook for this.

A final clean up with a finer set box plane, and a quick flick around the ends to give a bit of a taper, then whack them in. Make them a couple of inches overlength, drive them too far and cut off the taper, but don't cut either side off flush. You could perfectly well make them with a draw-knife, or a spokeshave.........but, I repeat, they don't need to be very round, and you don't need to play with too much. Aim for a peg-a-minute.

Don't forget that whilst the framing is of green (unseasoned) timber, the pegs must be of dry seasoned stuff. American White Oak is fine for use as pegs with English oak framing. This is what you kept all those offcuts for all these years!!


Mike

Cheers Mike.

It wasn't a case of getting hung up - just never done one before and it's always good to be aware of the fuller picture. :shock:

Wickes sell a hardwood dowel - 18mmm x 2.4m, which I suspect would be upto the job. Perhaps I'm just being a lazy so and so - but may well have an experiment.

Dibs

 

[MikeG.]

Just be sure that it is strong enough, Dibs. You will be amazed by how much strain the peg is under......and by how much it bends. Oak can cope, but some hardwoods are quite weak in comparison.

Mike

 

[Dibs-h]

Just be sure that it is strong enough, Dibs. You will be amazed by how much strain the peg is under......and by how much it bends. Oak can cope, but some hardwoods are quite weak in comparison.

Mike

How would one check? What I had in mind is seeing if one can snap a piece that is say a short length - one end held in each hand. Not exactly scientific - but...

 

[Paul Chapman]

Just be sure that it is strong enough, Dibs. You will be amazed by how much strain the peg is under......and by how much it bends. Oak can cope, but some hardwoods are quite weak in comparison.

How would one check? What I had in mind is seeing if one can snap a piece that is say a short length - one end held in each hand. Not exactly scientific - but...

Maybe that's why it's better to use the metal draw bore pin first, to draw the joint together and thereby not put so much strain on the peg?

Cheers :wink:

Paul

 

[EddieJ]

Dibs,

I tend to use 26mm dowel/trunnels for my frames, but I'm lucky enough to have a friend who has a trunnel making machine. As Mike has said, we also use oak that has been air dried for about three years, then store the dowel in a heated environment.

I'm in the process of having my own dowel making machine made, which should have cutters ranging from 12mm- 26mm. Sadly, its still a way off, otherwise I would have sent you some up.


In respect of shape, everyone seems to have their opinions, ranging from round, tapered to even square. The gate maker where I rent my workshops, is always ranting onto me about how he doesn't understand why I don't use square!

The joint shown below, is a very time honoured method, and in this case, you can clearly see that the pegging has been carried out using tapered pegs.

I haven't banged them too tightly in this shot, but you can get the idea.

 

[Dibs-h]

Just be sure that it is strong enough, Dibs. You will be amazed by how much strain the peg is under......and by how much it bends. Oak can cope, but some hardwoods are quite weak in comparison.

How would one check? What I had in mind is seeing if one can snap a piece that is say a short length - one end held in each hand. Not exactly scientific - but...

Maybe that's why it's better to use the metal draw bore pin first, to draw the joint together and thereby not put so much strain on the peg?

Cheers :wink:

Paul

I was going to ask where does one get one from - Ray Illes has them, but they only go up to 3/8" and 18mm is 3/4" approx. So slightly stuck there.

Eddie - the pegs you show have a full taper - I'm inclined to use cylindrical ones, which just have a taper in the last 1" or so. Just easier to do for me.

 

[Dibs-h]

Just found a local firm that will make me 2 tapered steels pins that will work (hopefully) for an 18mm diameter peg and hole - £20 for 2 pins 8" long - 1" tapering down to 1/2" - worth an experiment.

 

[Simon]

Dibs your tenons look short, in addition to minimum distance from shoulders you need to ensure that there is enough oak beyond the oak peg to withstand "withdrawal forces". The amount of oak beyond the peg in the tenon (referred to as the relish....not quite sure why) is the limiting factor of joints in tension. Additionally if you draw bore you can blow out the relish if it is too short. For that reason a usual rule of thumb would be a couple of inches of relish beyond the peg.

The basic theory is that joints are under tension when the joint elements are trying to pull themselves apart. So in the case of a brace under side load (like wind) the M&T joints will be under tension and compression (depending upon the direction of wind load). Simply this means that one M&T is being compressed (so no real problem), at the same time the opposite M&T is trying to pull itself apart. At this point much of the load is being taken by the pieces of the tenon behind the oak peg, so if this piece of tenon is too short it can break along the grain.

The easiest way to imagine this is a roof truss with a basic "A" shape, if you place this "A" frame upright on a piece of glass and press down on the tip of the A. The frame will be held together by the cross / horizontal tie (which is holding the two legs of the A from splaying out across the glass). As the top of the "A" is loaded the tenons on the ends of the tie are both being extracted from the mortices, so you are relying on the peg to hold the joint together and by design the timber behind the peg on the tenon.

Loading can be caused by wind or static load (heavy snow for example). Excessive shrinkage and poorly executed joint carpentry could load a joint and draw boring too.

A rough guide to pegging given by Steve Chappell
"When the tenon is in tension, the pegs should be 4 times the peg diameter from the loaded edge"

some examples

http://3.bp.blogspot.com/_CJU0xtZNtR0/Sf5N7Ye9YWI/AAAAAAAACCI/L0jFJNWQGPw/s1600-h/IMG_1947.JPG

http://3.bp.blogspot.com/_CJU0xtZNtR0/Sf5M7IJGkLI/AAAAAAAACCA/j9SvfPGkqzo/s1600-h/IMG_1948.JPG

Jack Sobon's guide may be of use and it is free!
http://www.ncptt.nps.gov/historic-american-timber-joinery-a-graphic-guide-jack-sobon-2004-08/

Steve Chappell's book is here ... it is a very practical guide
http://www.amazon.co.uk/Timber-Fram...=sr_1_2?ie=UTF8&s=books&qid=1253947334&sr=8-2

hth Simon