Tuesday, June 26, 2007

gin pole / block and tackle

i've done my typically obessive bit of research on lifting timber frames and have spoken to a few folks with experience and i'm voting for raising our frame ourselves without a crane. here's why: first, it's less expensive; second, less fossil fuel involved; third, it will go slower making me more comfortable; fourth, if we discover mistakes in the frame, we don't have to pay the crane to sit around while we figure out what's wrong (at about $120/hr); fifth, it will be really cool to know we did this ourselves; sixth, the technology to raise it ourselves is very very simple and also cool; seventh, we'll have all the hardware we need to raise other projects without power equipment at no additional expense.

the simple equipment is known as a gin pole. to make one you find a nice straight tree somewhat taller than the highest thing you need to lift and preferably with a crook near the top to which you can attach a block and tackle. the tree is held slightly off vertical by three or four guy lines that are secured to other trees or staked to the ground. the block and tackle is this very cool piece of gear that creates mechanical advantage so that one person can lift what would otherwise take two, four six or more, depending on the number of pulleys. you may have seen them on sail boats or on some cranes.

the picture shows the loads developed in a four pulley block and tackle. the load is held up by, in this case, four lines that share the work so that each line carries only 1/4 of the weight from the bottom block to top top block, which is secured to something capable of supporting the entire load. in our case, we'll be using three-pulley blocks so the line will carry just 1/6 the total load.

because the frame is in contact with the ground as it is tipped up, half the load is taken by the ground, half by the block and tackle. therefore, if we lift a 2000 pound section, the block and tackle's load is 1000 pounds. because the block and tackle load is taken to ground by the gin pole, all that's required to lift is 1/6 of 1/2 of the weight of the timbers. for a 2000 pound section that amounts to 167 pounds. an informal test with a bathroom scale shows that i can pull comfortably 130 pounds so with two of me the lift would be easy. add into the mix a few people helping to lift the frame directly (each reducing the load by perhaps 80 pounds), the job gets easier yet. as the frame tips up, less pulling force is required because more of the load transfers through the timbers to the ground and ultimately no effort on the rope is required when the timbers are standing. because the load through the rope is so much less than the full load, a relatively small and inexpensive rope can be used, which is good because the rope has to be six times longer!

almost finished with joined frame

FCD Timber Frame 6/26/07

photo: stuart auld

timber framing in underwear
it was hot (photo: jim jackson)

well, we're almost finished with the "underframe"--that part of the frame that supports and braces itself--essentially everything but the roof. the picture shows the completed pieces (completed pieces in light tan). it deceives just a bit--there are about four more hours of work to get to where the picture shows. after that, we cut the rafters and then we'll be ready to raise. i expect rafter cutting to proceed quickly because there isn't much to do to them--probably just a few days with four people. they will be fastened to the structure with metal, a breach of timber frame etiquette to some, but in our case, with a shed roof with substantial uplift loads from wind, we decided to be safer than sorry. i'm thinking we might be able to cut the rafters, and then have a second crew lift them up onto the roof.

we have yet to carve the porch timbers. we plan to use whole logs for the posts and we have plenty of them around already cut from our clearing. the porch beam will have to be milled as well as the rafters.

next weekend through the following weekend is our long summer gathering at the camp and i'm hoping that enough people will help out that we'll get the underframe erected by july 8th.

also on the horizon: the dining room slab. for this we have to submit more plans to the state, which is my job. this will be another concrete on grade insulated slab that will form the floor for our indoor dining/gathering space. we won't be putting a structure on top of it for a while but so that concrete trucks can get into the site we'd like to get it prepped and poured before the porch structure goes up.

Tuesday, June 12, 2007

lots done, lots more to do

stuart bores

we completed the tie braces last weekend, bringing to completion all the carving for the bottom of the frame (columns, braces and tie beams). we're now moving on to the top plates, of which there are seven. here stuart bores a mortise that will receive one of the end posts on the west side of the frame.

with the frame raising nearing, we need to start peg production. to facilitate that i'm making a peg jig up here in white river junction this week. it allows you to hold down a stick of wood using your foot and shape it into an octagonal peg with a draw knife.

once the top plates are complete we'll move on to cutting rafters, of which there are 24, if i recall correctly. these are pretty simple: just a couple notches so the rafters seat on the top plates and some end dressing. i'm afraid we're going to cheat with these: the rafters will be fastened to the top plates with lag bolts. the potential wind uplift made this necessary. you won't see it. don't tell anyone. shhh!

Wednesday, June 06, 2007




above is our newly minted checklist of framing timbers shot with my crappy cell phone camera. it's a moody shot of analytic information. how about that? and also, our new frame-o-meter, which shows graphically how much of the frame is completed, waiting to be carved and, in bright green, timbers that have yet to be milled. we anticipate milling the remainder of our timber on site because it reduces the amount of energy involved in the wood production substantially (no transport of timbers to and from mill, no kiln drying). an aside: i recently looked into the embodied energy of kiln dried versus air dried lumber. kiln dried uses 10 times more energy.

we accomplished a great deal last week with several faeries staying up on the land during the week and then staying over the weekend. i was there three days to try to keep ahead of everyone's improving carving skill.

with a couple more days of carving and planing (planing seems to be the ire of many--i have to figure out how to explain how to do it better, because when you do it right it's a joy and the plane almost literally sings) we will have the lower part of the timber frame structure complete, we could stand it up! but, i think we'll wait until we have the top timbers cut so that we don't have to lift them up onto the posts. traditionally, entire bents are lifted at once, but i'm thinking we might want to lift bent sections (three or four per bent) so that we don't need a crane.