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Author Topic: Tension pegs without draw boring  (Read 1324 times)

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Offline glen_h

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Tension pegs without draw boring
« on: October 23, 2018, 03:54:49 PM »
Hi,

I'm getting to the final assembly of my timber frame gazebo and about to drill the pegs.  I'm wondering how to set the right tension.  In books I've read they say to "draw bore" the pegs so they pull the joint tight by offsetting the hole in the tenon (eg by 1/16").  When I check the fitting of the frame I use ratchet straps to tension it up and it gets nice and tight.  When I release the straps there is about 1/8" gap between the post and purlin.  I'm wondering if it is acceptable to tension the frame up with ratchet straps and then drill the peg holes straight through (including the tenons) without "draw boring".  This seems like it would be much easier to do and end up with a better fit with less room for error.

Here's some pictures for reference.  

The first one shows the assembled non-bent side.  



 


The second one is the top left corner of the first zoomed in.  The purlin is coming out of the picture on the right.  Under the bottom of the purlin (its far left) there is a 1/8" gap between it and the bearing surface on the post when the tension is released.  The purlin is about 8' long, the braces are 41" long, and the timbers are 8x8".  


         

Thanks for taking your time to look at this.

Glen

Offline D L Bahler

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Re: Tension pegs without draw boring
« Reply #1 on: October 23, 2018, 04:08:22 PM »
Yes. This is acceptable, and avoids the potential problem that drawboring may cause, which is blowout of the tenon. 

I don't know how many American framers do this, but Europeans use the technique a lot

Offline Jim_Rogers

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Re: Tension pegs without draw boring
« Reply #2 on: October 23, 2018, 04:22:48 PM »
My process is to bore the mortise peg hole first, dead on the mark where it should be. Then insert the tenon and pull it up tight where you have it. Put the bit down the mortise peg hole and create a mark on the tenon, know as a dimple. Remove the tenon and offset the peg hole in the tenon from the marked dimple by the 1/16". and re-assemble.

This process puts some "spring" tension on the peg to hold the joint tight.

Many frames are done your way but there is no spring tension in your pegs.

I have seen some tenons with blow out when the pegs were not tapered or the draw bore was too much.

Good luck
Jim Rogers
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Offline canopy

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Re: Tension pegs without draw boring
« Reply #3 on: October 24, 2018, 09:32:53 PM »
Good technique eliminates blowout. Drill the peg hole before making mortises, finish drilling mortise/tenon peg holes from the other side. And as Jim says scribe the draw bore and taper the pegs. Old timers knew how deep to drive pegs by the note the peg makes when it gets driven true.

Offline Brad_bb

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Re: Tension pegs without draw boring
« Reply #4 on: October 25, 2018, 12:26:43 AM »
Canopy, I think they are talking about shearing the tenon shear area, whereas you are talking about blowing out the backside from drilling.  Two different things. 

Draw boring can be done correctly, and "line to line" pegs can be done correctly.  

For draw boring on the second to last frame I worked on, the holes were offset by 1/8".  Other than that, same as what Jim describes.  The thing you want to be careful of, is how hard you drive the peg in.  It's hard to describe, but you want to go where it makes contact and a good "thunk", but you don't want to drive it past that.  Too hard and you risk shearing the tenon shear area.  Remember, you can always drive it more later if it's loose.  We haven't seen any loose ones in that second to last frame.  Our pegs were pretty dry too so they aren't shrinking much.  Starting with riven octagonal blanks, I kept them soaking in a tub of water(they were totally green when riven), then made the taper on a shaving horse with a draw knife.  I tapered about 3/4 the length of the peg down to about 1/2".  Once tapered, I left them on the shop floor to dry for a couple months or more.  Consistency is less important with draw boring because you will drive the peg in up to where you get the "thunk", unlike line to line pegs which must fit better as they need to be driven further making more contact with the hole walls.

Line to line works just as well.  You can drill through all after you pull it all together with come alongs. The critical part is sizing of the pegs versus your hole.  Use a good 1" boring bit and double check the measurement.  Then you want to size your pegs accordingly. On the last frame I worked on we did a line to line fit.  My pegs were riven octagonal blanks.  White oak pegs going into white oak or other hardwood timbers. While green, I tapered the ends, and then left them spread out on an unused area of the shop floor to dry for 2 months.   I then drove them through a sizing die.  The die was a steel plate with a 1" hole drilled in.  The sharp edges of the hole do the shearing. I used a 3 LB. sledge to drive them through.  I had to drive them through twice.  They compressed some on the first drive, and were too tight for the holes.  You would really have to hit them hard to drive them all the way.  Driving them through the die a second time removed enough material to get the fit right.  Again it comes down to a "feel" when driving them into the timbers.  You want a snug fit, yet not so much resistance that you have to really hit too hard.  These method yielded round pegs.  Some may use octagonal pegs, which in softwood would compress the softer timbers wood.  In hardwood, if the fit was too tight, resizing would not be all that easy.  Driving through a round die will give consistency to the sizing.  If the peg is still too tight after driving twice, you may need to drill a new hole in the plate with a slightly smaller bit.  Less than 1" you'd have to special order one (like if you needed 31/32nds).


Note:As canopy indicated, you should stop when the tip of your auger bit just pierces the backside.  Remove your bit and use that tiny hole to start your bit on the opposite side ensuring you get a nice clean hole with no blowout.
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Offline Don P

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Re: Tension pegs without draw boring
« Reply #5 on: October 25, 2018, 05:47:53 PM »
You can also sit the timber on another or clamp a board under the hole area as backup for the drill rather than turning things over. I'm not a real fan of stressing connections.
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Offline Hilltop366

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Re: Tension pegs without draw boring
« Reply #6 on: October 25, 2018, 06:20:22 PM »
Or pull the joint apart and just flip the beam over to finish drilling from the other side (more convenient if it is not the final assembly).

I used a mechanics air chisel with a flat disc welded to one of the chisels to drive pegs through a plate. The plate had a short 1" piece of pipe welded over the hole that allowed me to hammer the pipe at the top to make uneven finished peg after driving through the plate. I took the corners off with a draw knife first.

I have also seen a hydraulic wood splitter geared up to press pegs through a plate.

Brad if you want that 1 inch hole a bit smaller you can peen or centre punch around just outside the edge of the hole and it well push a bit of steel towards the hole. 


Offline Brad_bb

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Re: Tension pegs without draw boring
« Reply #7 on: October 25, 2018, 10:18:32 PM »
When I was pounding pegs in that video, I pounded like 500 pegs in 4 days (due to a miscommunication they weren't done ahead of time).  I tried rigging up an big hammer drill, but it wouldn't work.  So I ended up doing it all like you see in the vid.  I got a workout that week!  

You're right about clamping a board on the bottom side to prevent blowout.  

Keep in mind that I think the OP was talking about blowing out the shear area of the tennon while driving a draw bore peg.  Hope he read this thread.
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!

Offline Telluride74

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Re: Tension pegs without draw boring
« Reply #8 on: November 04, 2018, 10:52:58 PM »
I made a jig with 4" square tube 14" long with a plate welded on the end. burned a hole then welded a 1" dia.X1" stub of pipe over that hole. I clamped it to my log splitter and pushed my riven 1" blanks thru.  It worked flawlessly, took very little time to make and treenails were popping out lickity- split !

Offline glen_h

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Re: Tension pegs without draw boring
« Reply #9 on: November 05, 2018, 11:31:48 PM »
Hi,

Thanks for all the tips.  I ended up using ratchet straps to get the joints snug and then marked dimples and moved the hole 1/8" (or so) in towards the shoulder of the tenons.  In one of my books is says you can go  up to 3/16" offset if you have 6 inches of tenon/relish so I kind of changed the offset distance depending on the amount of relish.

By "blowout" I meant not enough relish on the tenon and it breaking -- sorry if it is the wrong word.  I used Wood Owl bits with the snail end and they work like magic and naturally stop when the snail is poking out the back side so I can finish it from the other end and get no tear out.  I'm working on saw horses so I can drill from the underside.

I am worried about making the pins right.  I bought dry white oak from the wood store and it is dry.  I first tried making a pencil sharpener jig out of some wood and a chisel blade and that worked ok but got worse over time and I abandoned that method after getting frustrated.  I don't feel I have good enough tools to make a hole in a metal plate to pound them through.  I decided to use a table saw instead and cut octagons with the height about 1/64" under my peg diameter but the corners of the octagon are about 1/16 or 1/32 larger so I tapered the corners on the entry side.  I'm a bit worried about how hard to hammer.  For using dry white oak one book I read said to dip dry wood pins in unseed oil (what is that?) just before driving them in to prevent splitting the pegs and to oversize by 1/64th.  I'll be doing some tests and hope to pin it together this week and raise it on Saturday.  I really hope it all goes well.

Thanks for all the great advice!

Glen

Offline Don P

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Re: Tension pegs without draw boring
« Reply #10 on: November 06, 2018, 07:21:07 AM »
Musta been a typo... linseed oil. I use paste wax.
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Offline Brad_bb

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Re: Tension pegs without draw boring
« Reply #11 on: November 10, 2018, 12:17:22 AM »
glen_h,
You said you are draw boring (offsetting your tenon hole from your mortise hole.  Therefore you need like a 12" long peg that is tapered about 3/4 of it's length.  To do this you need to start with green pegs, keep them in water, and draw knife the taper.  I would not attempt to taper DRY oak pegs.  It just doesn't work well.  Also, you CANNOT rehydrate dry white oak peg blanks.  They will not reabsorb water enough.  If you are making Octagonal pegs and trying to drive them through an offset hole, that will not work.  If you are doing line to line pegs(no offset), you can take your octagonal pegs and drive then through the die.  All you need a  piece of 3/8" thick steel and a 1" drill bit.  I'd start with a smaller hole and work up to the 1".  then screw the steel down to some timber cutoffs with a space for the peg to fall through.  Then you can set the cutoffs/die on saw horses to hammer them.

Feel free to PM me if you want a source for green blanks or a drawing to build a shaving horse (that I got from Jim Rogers). Or ask Jim. He's also been a good source for draw knives.  I recommend a solid one, not a folding handle one.  Even on line to line pegs that get driven through a die, I get green blanks and tape 2-2.5" of the tip down to 1/2" as a lead in for the peg and it looks good.  After tapering the tip, let them dry a couple months, then drive them through the die.
Anything someone can design, I can sure figure out how to fix!
If I say it\\\\\\\'s going to take so long, multiply that by at least 3!


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