Monday, March 16, 2009

Cradle Design and Operation in Detail

Several people had asked for a more detailed description of the log cradle's construction and how it works. So I've published some more photos focusing on the cradle itself. Here they are:

The cradle consists primarily of a stationary stand, comprised of two supports, each of which consists of two 6 x 6 pressure treated pine posts, cut to four foot lengths, and fastened together with lag screws. There is also a four foot long 4 x 6 post that acts as a brace and ties the two supports together, giving them stability. Each support also has a chock fastened to it, about 4" inward from the brace. The chocks are cut from a 4 x 6 post, and are beveled at a 45 degree angle. The photo above shows the stationary stand, with the maple log rolled back a bit to give an unobstructed view.

The photo above shows the stand, from the other side.

The other two supports are shown above. These are the movable supports. Each is also comprised of two 6 x 6 x 4' posts and a chock, all fastened together with lag screws, just like the supports in the stationary stand. Note that the two chocks in the photo above come from opposite sides of the same cut of a 4 x 6 post. My 4-1/4" circular saw, beveled at 45 degrees, can't cut the post all the way through, so I cut one side, and then repeated the cut on the other side. Only I just didn't get the second kerf to quite meet the first one. Hence, the little ridge in the middle of the slanted face of each chock. (Turns out that that little ridge enhances the mechanical keying of the face of the chock when pressed against the log surface -- it's an unintentional optimization!)

The above photo shows the other side of the stand, with the two movable supports positioned along side the stationary supports and slightly under the log. I use the pickaroon at the far side of the photo to pick one end of a support up from the ground, so I can get a grip on it without having to bend my back.

In the photo above, I am using a log peavey to roll the log back toward the other end of the stationary stand, until it more or less comes in contact with the chocks on that side.

A couple of sharp taps from a sledge (a sixteen-pounder in the photo above) forces the movable support under the log until its chock makes contact with the log surface.

The photo above shows the view from the over side. The movable support is the same height as the fixed support, and just clears the underside of the brace.

Above, both movable supports have been tapped into place, with their wedges securely locking the log. If you need to re-position the log for some reason (e.g., you need to cut on another face), the easiest thing to do is tap one (or both) of the movable supports from the other side to release the log a little, use the peavey to rotate the log, and then tap the movable supports back in place to securely lock the log again. Note that the movable supports do not require a brace like the stationary ones do. In fact, you wouldn't want one, because the movable supports need to be free to move independently of one another (they have a way of "finding their place" when they are driven up against the log).

Finally, the photo above shows the stationary stand and the two movable supports, with the log completely locked in place, from the other side of the cradle.


Cassie said...

Okay, I just went back a ways in your blog & can not find what it is you're doing with the logs you're using this cradle for. Are you hand peeling them? If so, what for?

John Poole said...

Hi Cassie,

I am using them to build a very heavy woodworking bench. The log that I am hewing right now will become a slab for the bench top.

Here is a post I did a while back when I started constructing the cradle. There is a link in that posting to an article describing the style of bench I am attempting to build (Roubo).

All the logs are already peeled; I did that back in the late summer, so they've been drying over the course of the winter time.

- John

John Poole said...

Hi again Cassie,

Actually, there was yet one more layer of indirection in my last comment. Here is a link directly to the article. Sorry!