When you are bolting your walls together for the final time how much torque do you use?
For information the outside beams are black walnut and the inside beams are white oak with 6 inch SIP’s between them the spacing is 12 inches on center and I’m using 1/2 x 12 inch stainless steel lag bolts hardened to 18/ 8 they are backed up with 1 inch stainless steel washers.. does it matter if you wax the bolts first or is that assumed?
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Replies
Tough to picture that scenario. What is different about these bolts than any other? When the washers just start to crush the wood, it is tight enough...when the heads break off the bolts, it is too tight. :-)
The OP does have a bit of a different situation, in that he's got a sandwich of two hardwoods with a SIP in-between. If this assembly is in an area of the SIP where there's no wood spacers then he'll be tightening against the foam, and it's likely to compress before the hardwood deforms noticeably.In this case one could contact the SIP mfgr and ask how much force should be applied (and then figure out what that means in torque on the bolts), or one could just go for "good and snug" -- tight enough that if it was pine you'd begin to see some compression. (In fact, if there's clearance and no visual issues involved it might make sense to put a piece of 3/4 pine or maybe 1/2" plywood on one side and tighten until that begins to deform.)
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
DanH,
Since the force of this torque is spread out over wide timbers the squeezing effect isn't localized as it would be without the timbers.. some of the timbers are 15 inches wide so while there is a localized force it's spread over the full 15 inches..
I had thought about making spacers for the foam but reconsidered once the logistics involved were realized.. I'm not sure I would have really gained anything..
All of these bolts are in blind holes so I can't see any wood compression
Dummy up a section, with the piece of pine in place, and measure the torque it takes to get to deformation. If you can find a scrap (window cutout, etc) of SIP that would be ideal for the dummy, so you can observe if there's any compression.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
DanH
That has merit, in fact i think I'll try it.. the trouble is that I'd need to repilcate whole panels since a short section could present a distorted picture. Oh and there isn't any pine involved, it's simply black walnut, SIP's and White oak..
I do know how strong SIP's are, in that I had panels that were well in excessof 7 feet cantalevered from a roof panel held in place with only the spray foam and a hand full of 6 penny nails My fat 250# butt and a friends 265 pounds could use all of our force and never get an once of deflection! We noticed that when both of us we out at the end lifting a very heavy timber up into place...
The actual walls are rated something like 200% stronger than a similar wallmade the conventional way.
Edited 5/19/2006 5:30 pm ET by frenchy
I know there isn't any pine involved. I was suggesting a piece, just under the nut and washer on the dummy, to let you judge when you have sufficient pressure.For that matter, do this:Get a piece of medium pine and a left-over chunk of one of your beams. (You want to have several inches of bolt in action to get a reliable test.) Drill through both, install a bolt, and torque until you see deformation in the pine (bury the washer about 1/3 or 1/2 it's thickness).Then, the first few assemblies you put together, closely watch to see if there's any distortion of the panel as you torque to the above setting. If not, use that setting, otherwise drop back a bit.You'll want to go around and retorque after a few weeks. Be sure to first loosen the nut a tad, then tighten, so you lube it up a bit.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Dan,Frenchy is using lag screws, so there aren't any nuts. I fully agree with your suggestion to use pine as a torque-determiner. Analog methods like this are proven to work.Bill
DanH
the exterior frame work I make up is equaled with the interior frame work. When I first started to do this I felt I could watch the beams deform and once they would move a little bit I'd know that I had tightened everything enough..
What I forgot was that beams move around.. panels that I carefully set as straight as humanly possible dried and bowed a bit, if two beams bowed together it could force a whole wall over an inch out of line.. The force on those beams must be tremendous.. Pulling a total of ten inches of timbers out of line thru a SIP must require fantastic force.. I know that just a six by six inch post can handle ten tons of crushing load add the strength of a SIP and the strength of the timber on the outside and I have no idea of the amount of force required to properly torque a lag bolt..
My point is that if a post is warping out of line the torque on that post might be off the charts while a post that remains straight could have a minimal amount of tension..
Thus the only way I think I can confirm that every lag bolt is properly tightened is to measure the torque.
jesss,
That's the trick, I'm putting these in blind holes where I can't see if any crushing is taking place.
My intention is to put plugs over the lags as per european specs regarding timberframe construction. I figure three benefits from the plugs,
1st in the event of fire the plugs will insulate the bolts and prevent failure due to extreme heating. (I learned my lesson prior to 9/11 , If those bolts had been properly insulated the building wouldn't have collasped)
Second the plugs will act as slight insulators and help prevent thermal conductivety
Third the plugs will look better than seeing bolt holes..
Use the same torque spec'd for mounting the counterweight on a Bucyrus 34B shovel (although counterweight bolts are usually SAE Grade 12).
But seriously, when bolting wood members together, the previous poster was correct....when the wood under the washer begins to compress, you're done.
Frenchy: How's that beautiful castle of yours going? Sure wish I had a source of wood as fantastic as yours near my place!
Unless I'm missing something, the 18/8 figure you gave just indicates that the lags are garden variety 304 stainless steel: 18% chromium, 8% nickel. It's not a hardness per se, nor does the hardness of the bolt matter much to your question- nor does it matter much what grade of stainless you have for this application. One suggestion, though- make sure you lube up the washers a bit to keep them from galling against the lag bolt heads as you draw them up.
As to how tight to make the joint, I agree with the others that seeing some compression of the wood under the washer is a good indication that you're there. Seems to me that you'd want it tight enough that seasonal dimensional changes in the big timbers won't loosen the joint, but not so tight that you're anywhere near stripping the thread the lag is cutting in the wood. What torque that effect is obtained at will depend on the size of the pilot hole you pre-drilled, how resinous and dry the wood is, and whether or not you've got any lubricant on the lag, the lag's surface finish etc. Torque alone wouldn't be a reliable method of telling whether the joint is tight or not.
Moltenmetal,
These were sold to me as hardened And have the corresponding head marking and yes your 18/8 information gels with mine.
Since I have no way of seeing fibers crush in the blind hole these are going into I was hopeing somebody had done something similar and had a torque figure for me to use..
As for pilot holes I used the formulas I've always used regarding root size etc.. You should see the clever drill bits I had fabricated. One bit has the pilot hole, the shank hole and the counterbore hole on it.. three in one.. with 3500 holes to drill it saved me a great deal of time even if the bits did cost me over $95.00 each!
As for lube I found that Grizzly sells a inexpensive wax that is dramatically less friction than ordinary wax, soap or other lubes as tested by fine wood working.. As you can imagine I used a lot of those little tubes slicking up all the lag bolts. ;)
As for resious, oak and black walnut don't have a lot of resins, however they do have tannins which is the prime reason I used stauinless steel even when you won't be able to see the bolts once assembeled..
You should probably re-torque as things shrink. Give it a year or two, and go around again. Simpson has auto-adjusters for seismic hold downs, but that's for things that span a couple stories, not just a foot.
-- J.S.
John,
I let most of the timbers age for several years before I installed them, however due to lack of black walnut I wasn't able to get some of the really big timbers untill this spring. (and had to pay $1.00 a bd.ft. compared to the 17 cents I paid earlier) thus I need to deal with shrinkage and seasonal swelling etc..
If your bolts are stainless, galling (as if the metal likes sticking to itself) can be a huge problem. Don't use a wax like you would to lube a lag bolt. Go to an auto parts store and pick up some stuff called Never Seize or Anti Seize. It looks like silvery powder in goop. It is specially designed for metal lubrication, and it doesn't go away over time.
Don't worry about your bolts "slipping" loose because they are lubricated... it won't happen.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
XXpaulCPxx,
Long before galling would occur between the washer and the head of the bolt, the wood will strip out. The very most torque I can apply to a 1/2 inch lag bolt is under 50 foot pounds before I feel the movement of stripped threads.
I have plenty of antiseize from my racing days but since galling isn't a problem I don't use it.. I do use the wax lubricant that grizzly sells because Fine Wood working demonstrated that it was the most effective lubricant and actually helped prevent tearout.
The bolts will loosen and tighten according to moisture. Wood shrinks and swells depending on the amount of moisture in the air wood is hydrogyscopic (sp) and a ten inches of hardwood can easily move over a 1/2 inch add whatever swelling happens to the OSB in the SIP and you begin to see the magnatude of the issue..
I'm a little confused here about what you are taking about lubricating. I just reread your original post... I got in my mind you were talking about Carriage bolts, not Lag bolts - D'OH!
I put together a temporary seasonal outdoor structure using redwood and SS bolts. I never had a problem with galling on the washers and nuts, but I had a big problem with galling on the threads of the nuts and bolts. These were 1/4" and 5/16" bolts, BTW. This was before I knew about SS galling, so I spent alot of time chasing threads with a tap and die. I had nuts and bolts locking together using finger pressure that I needed a wrench to seperate again!
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
xxPaulCPxx,
I suspect what actually happened to your outdoor furniture was Redwood like white oak and black walnut has a lot of tannins in it.. that's what gives it it's decay resistance. However the tannins are acidic and corrode most metals. I do know that if you simply nail together oak outside in a few years the nails will rust away and the resulting areas be decayed from the acids produced. If however you use 304 stainless steel the nails will remain virtually indefinately.
Other stainless steels don't have that same resistance to corrosion yet can still be sold as stainless steel.. look for either 18/8 stainless or 304 stainless to avoid that trouble in the future..
I see what you are saying.
No, this structure is called a Sukkah, and only comes out during the Jewish holiday festival of Sukkot... it's basicly an old harvest festival. The structure is to be reminicent of the houses they lived in during the wandering in the desert. It has to be temporary, you have to have 75% coverage on the roof BUT still be able to see the stars, and the roof covering has to be natural material and can't touch non-natural materials.
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For the time it is not up, I built a couple of storage racks for them.
That galling happened when I was attaching the SS nuts to the SS bolts, like the picture above, and they would seize up before I was even able to get them finger tight to the wood.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Paul: as you've discovered, 304 SS bolts and nuts gall together unless lubricated. It takes surprisingly little tightening force to make it happen, and then you're cursing and reaching for the angle grinder or the hacksaw.
Two options: 1) antiseize paste or another similar lubricant that will stay in place long-term, or 2) choose another grade of stainless steel for the nut. 316 isn't different enough, but if you can find 303 nuts there will be a dramatically reduced tendency for the nuts and bolts to gall togehter.
I install a lot of steel brackets to 4x4 and larger with 3/8 by 4 inch galvanized lag bolts, parrafin lube (one swipe across threads) and install with 150 ft-# 12/ drive air impact, stop after 3 or 4 whackwhackwhacks and noticing the socket slow down - checked a couple of times and torque was about 40 ft-# in D. fir. for that procedure. I dont use any lead hole where the lag threads go, straight into solid wood.
Walnut may strip out first, but Oak should hold a 1/2 bolt. at 40 ft-# for sure, brobably do have to pilot drill oak.
3/8" bolts shear off the head before D. fir strips if the impact is left on till something gives.
Junkhound,
I've tried to run the lag bolts (screws?) into white oak with no success and if the black walnut has dried it seems almost as inpenitrible. even smaller 3/8ths won't drive themselves into white oak or black walnut with any degree of speed, it's faster to drill a pilot hole than to attempt to drive them in without one.