Sunday, September 27, 2020

Log Lifting Rigs for past cabins

In 2012 I salvaged oak, hand hewn, log floor joists, out of an old barn and decided to build my second cabin. To do the lifting I designed and built a pivoting yard arm lifting crane. All the parts were made from 6x6 timbers out of the barn. Getting the main beam up and onto the center pin (this allowed for 360 degree rotation) was a job but I managed using a gin pole lashed to the vertical. Also significant bracing to the cabin floor framing was required (this supported the main center support). This caused a lot of problems when trying to move around to do any work that required being on the inside. The two 2 x 8's in the front were in compression and the back 1/3 of the main beam was tied down with a ratchet come a long in tension (this kept the main beam level). I mounted the hay loft trolley and track to the bottom of the main beam (this allowed the log to be moved inward and outward for placement on the wall). A chain fall was attached to the trolly and used to lift up a log. 

Now one of the key parts of this system was the circular block that was made for turning the square 6x6 into a round form. The cross pin in the front supports arms had to ride here. It carried the load and allowed the main beam and support arms to rotate 360 degrees. Rotation was done when there was no load on.

A generous application of grease kept the system moving smoothly. I was pretty happy with the way this turned out and worked very well. Although a lot of extra work to construct but a good learning experience. When the cabin was done I disassembled the crane and stored the parts.

In 2015 I ran onto another set of logs and the idea to build another cabin this time with exposed log roof trusses got me thinking. I would need another crane and thought about using the old one but did like the idea of all the bracing inside the cabin area. So I decided to change things up a bit. I had scaffolding with a nice set of wheels. The ground around the cabin was flat and level for rolling. 

I would use two sections and attach the main beam to the scaffolding. Using the chain fall again to do the lifting. One problem was that as the load was lifted the leverage tipped everything forward. This problem was solved by adding cast iron counter weights to the back end of the scaffolding. I added a board to the bottom rung so I could slide the weights farther back away from the fulcrum point.  This system worked very well. It was simple to move around and position. It was used to lift all the wall logs and then to raise the log roof trusses.

Fast forward 8 years and a couple of cabins and here we are with the third generation of log lifting rigs. They all were designed to lift 300 + logs and allow just one person to build a log cabin. Although having a helper makes things go smoother. The Sky Hook so far has been the best. It was only blind luck that the two trees used to anchor the cable lined up with the center of the cabin. Here a helper holds the tag line and keeps the timber from spinning and I pull it toward the cabin wall.

The ridge beam will be lifted next and getting all the tenons to line up with their mortises will require some patience and maneuvering. Everything has been staged and planned out so this should go smoothly.

By hooking the ridge beam with a chain instead of the slings I shortened up the distance between the hoist and the beam. This allowed it to be lifted high enough to land on the support post tenons. Not having to deal with the weight of the beam made the work of lining up the mortises in the bottom of the beam pretty simple. All joints were then pegged together with 7/8" diameter Oak pegs.

Staging and lifting are key parts of the process of reassembling the cabin. The rafters for the back side of the roof were lifted and placed on temporary supports before the ridge and top three front wall logs placed.  The front rafters were brought up to the the front of the cabin and leaned up against the wall as shown in the picture. Because the Sky Hook wire runs down the center of the cabin movements left and right were not possible. The front rafters would be a two man lift job. One at the top to place it on the ridge and one at the bottom to lift. 
This was a tricky balance as you can see in the picture below. The back rafter was no problem, just lift up the top end and place it on the ridge beam. The front rafter was different. Because of the location of the center point of this rafter on the top plate the bottom end needed to be held up until the top half lap joint could be pegged together. Once that was done the rafter pair was secure over the ridge beam. The point where each rafter crossed the top wall plate log a 10" timber frame screw was drilled in to lock the rafter in place in it's notch on the wall. 
Here is another look at the roof rafter system. The rake end boards for the roof gables still need to be attached. Then 2x8 tongue pine boards will be put on across the rafters to form the cabin ceiling (the beams will remain exposed inside the finished cabin).  Two inch styrofoam will be placed on top of the 2x8 pine and then a steel roof added to finish off the roof.

The front beam was put into place using the Sky Hook and it was great to have the beam held up so I could take measurements and drop plumb lines for drilling the holes in the slab at the bottom of these support posts. The posts need to be adjustable in height as the cabin logs dry and shrink. Just like the clearance that is built into the window and door frames, the posts need to provide support and be able to be lowered (shortened). To accomplish this deep holes are drilled into the bottom of each post and 12" long 3/4" ready bolt with two nuts and washers installed. Holes for the bottom of the bolts were drilled into the cement and held the post at the bottom end. The top end was pinned tight. In the picture you can see the space at the bottom of each post, about 3 inches. As the cabin walls shrink the nuts will be adjusted to lower the posts so the roof rafters are not lifted up. Measurements will be taken and recorded on the posts today. Each post will be lowered the exact amount the walls shrink as the logs dry over the next 9 months.

At this phase it is good to take a break and ponder the work that has been done. For projects, for me, I believe there are two kinds of people, the thinkers and the doers. My philosophy is that if I think about something to much you kind of spoil it and probably won't do it. Best to just do it! Enjoy the process and solve any problems (learning opportunities) that come up along the way. And look what you get.

The next phase will be to finish the roof and install the electric service entrance. 

Sunday, September 20, 2020

Cabin #6 Re-Assembly Begins

The dis-assembled cabin is at the other end of my 6 acre woods. Logs for one round are loaded onto the trailer and brought to the re-assembly site. Just as luck would have it the Sky Hook line runs right through the center of the cabin. Logs are rigged here with a sling or set of log hooks and lifted off the trailer.

With the sling positioned so that the log balances the lift is made

The lifted log is then pulled into the cabin. To keep the lift as low as possible I left the header of the door frame off.  Back and front logs are the longest and heaviest. The lift makes light work of placing them right into position on the wall. Because there is no left or right movement of the hoist side wall logs require a support plank to be placed parallel to the long cabin wall as a temporary support. The hoist is removed. The logs are then inched along with one end on the wall and one end on the temporary support until they reach the side wall where they finally sit. 

The half dovetail notch area on each corner is covered with a 2" thick pad of fiberglass insulation. This seals the joint. Later the excess that sticks out will be cut flush to the surface of the log and become invisible.

Window frames were set in place using the hoist.

Then they were braced level and plumb. A little side note here. When I went to the local lumber yard to get the four 10 foot 2x4's the guy said, "Gees lumber prices have really gone up." I took it as just shop talk. Then I saw the bill $41.78 !!! Imagine building a house.

I adjusted the height of the anchor by about 4 feet to be able to clear the door header. Looks like the force on the tree anchor is pretty high. Lucky this is the last of the 7 inch thick heavy logs. From here on up the logs are hewed 6 inches thick. This will reduce their weight to less than 200 pounds max.

It's not all work. Took a break and enjoyed a nice fire "in the cabin" with some friends. 

So this is it. Three days work and first level is back together and tied together with full length logs in round 8. For an extra measure I drove in screws in the top corners to make sure they did not move or shift as I begin work on the loft level walls.

Friday, September 18, 2020

Rigging the Sky Hook

These pictures are going to be in the reverse order I wanted them to be in but the Blogspot people have changed the program as to getting pictures up loaded and this will have to do until I learn how to move them around.

The true test a 300 pounder is lifted off the trailer and heading to a landing on the back wall of Cabin #6.Coming off the trailer and ready to make the move to the cabin

Not wanting to find out the hard way if my calculations and the system was worth of the task I decided to test it out with one of the smaller logs first. Chicken that I am.

If you have ever tried to stretch out a line you know that pulling it starts to get pretty tuff as the line starts to straighten out. Especially with a 50 pound hoist on the line. A 5/16 inch cable with a 1900 pound capacity was used. Two ton come-a-longs were used to pull it. As they only had a 10 foot cable one was used to start the pull and a second one was used to finish the pull. 

To allow the 1300 pound hoist be able to move along the cable from the trailer to the cabin wall I installed a set of 1 1/2" cast iron pulleys in the hangers. It was tight but with a washer spacer below the brackets the cable cleared the top of the housing. I also had to extend the wiring to the remote control switch as the hoist would over 12 feet. This was tricky as it needs four wires to make the circuit for up and down control.

Here is the drawing of the layout for the Sky Hook

Here are the details on the calculations and the web site I used to determine the forces at play.

In closing all I can say is that this experience allowed me to learn a lot about rigging rope for a system like this and opened my eyes to the engineering that goes into lifting loads with cranes and such. There is plenty of information on the web about this if you want to learn. Finally,  this experience answers the question I asked every day in some the the more difficult classes I had in high school and college, "When am I ever going to use this."

Sunday, September 6, 2020

Before and After - Cabin #6

 Nice weather. Today would be a big day.

BEFORE - 9 am Sept. 5, 2020
So how do we get from here to...

AFTER - 2 pm Sept. 5, 2020

The process begins with the marking of the logs. As each half-dovetail joint is unique they must be put back together exactly with their mate. To accomplish this there are many ways but I prefer using a deck of playing cards.

The deck is sorted into the four different suits. One suit is assigned to each corner of the cabin. Each card in a suit is cut in half and stapled to it's mate for each round of logs. Round one here is the Ace of Spades. Round two is the 2 of Spades and so on up the wall of logs on each corner a different suit. Pretty simple as long as the cards don't get scraped off in the process of moving them to the site.

With roof framing removed and stored to the side out of the way it was time to begin taking down the walls round by round. Each log stored on "sleepers" parallel to it's wall to keep them off the ground.

A Bobcat and boom rigged with a set of log tongs attached made the job of lifting and removing the logs pretty simple. What was not simple (and not shown) was the drilling of 1 -1/2" diameter holes down through the logs as they were removed to provide a pathway for the electric wiring to be run. This needed to be done as the drill bit was only 18" long. So one log at a time was drilled until the bottom log was reached. This was done in several places to conform to the wiring schematic I had earlier talked about in planning the placement of outlets and switches in the finished cabin.

So 5 hours later the deed is done. A "cabin kit" ready to be loaded one round at a time and transported to the site on the other side of the woods and assembled on the slab. Easy peazy, right? Stay tuned future cabin builders.