The torso of our ill fated friend is built off of a single shaft of 1" X 1" X 1/8" wall tube steel like we used for the leg assembly and is 39 7/8" long. We will be attaching our air cylinder to the bottom of this "spine", 1/2" from the end and then measuring up from there 2 3/4", or 3 1/4" from the end to attach our return spring. I will be using an angle grinder to make a notch for the spring end to pass through the first side of the spine and to a pin I will be locating toward the very back of the tube. If you look closely at the photo (click to enlarge) you will see the spring slot and also the pin hole already drilled in the side. Below that you will see where I have marked the place on the side where I will be drilling a 1/2" hole through to insert my air cylinder connecting pin. I have drilled a hole just above this section on the face of the tube which represents where I will stop cutting to make room for the ram's plunger rod. You will also need to slot out the back of this area as well to allow room for the nuts and rod end. Here is a picture of what it will look like once drilled and attached to the ram. You can see that once again we have made a connecting pin from the 1/2" solid steel rod and attached it to the tube with hitch pins. Heavy wire would do the same job as the hitch pins. Next you will measure up from the bottom of the spine again but this time to 9 3/4" up and that is where you will drill a 1/2" hole through the tube from side to side. This is the hinge point the entire torso will pivot from, so be sure this hole is drilled precisely square to the spine. If not, your dummy will be throwing himself forward and off to the left or sitting in the chair crooked or a combination of both. It will be held perfectly centered to the chair with steel 1/2" flat washers and set collars as shown here.

   A significant thing to mention here is the connection of the air cylinder to the connecting pin. In the photo on our right you will see a close up from another project I did not long ago. Usually you will have to put a nut on both sides of the pin, unlike this photo where we only have space for the outside nut which has been tightened and then carefully drilled all the way through both the nut and the rod and a heavy wire has been inserted then bent over on each end. This keeps the nut from ever coming loose during use. You can also use safety wire to achieve the same thing as the heavy one I used here. One way or the other I do not recommend just using Locktite alone, since it would eventually still come loose due to the constant concussion while in use.

   For the rib cage assembly we will be using a combination of 3/4" x 3/4" x 1/8" angle iron and 3/4" x 3/4" x 1/8" aluminum angle. To start we will cut out 18" of the iron and notch one of the surfaces back 3/4" as show in the left photo. Then using a crescent wrench, bend the lip up on a 90 degree to close in the end. Do this to both ends and then attach the iron to the front of the spine 11 3/8" from the top. This is the dimension to the top of the angle iron. Use a 1/4" bolt with a lock nut. Now  measure away from the center bolt 5 5 /8" and drill a hole through the back of angle on both sides as shown in the top section of the rib cage (shown here on our left). You can see this is where you will be attaching your angle aluminum  which is a total size of 9" high and of course 12" wide. On the right side of the cage you will be attaching two 5 7/8" pieces as a mounting platform for your variable speed drill to rest on. The drill I used for this build was a 3/8" Chicago Electric unit from Harbor Freight Tools, item no #41844-1VGA . It had the features I needed such as a locked-on button as well as a dial on the trigger that allow for a preset speed to be chosen when locked on. Plus if you wait for a sale you can pick these up for a mere $12 apiece! I did a lot of research before taking on this project and know quite well to expect the bearing of the drill to wear out from the out of balance cam we will be running, so not only did I design the drill to be very quickly removed and replaced, but I purchased two drills at the same time to ensure that I would have a spare when the time comes. This mount was meticulously shaved and shaped around this exact drill and to expect to just drop in another brand drill later would be wishful thinking. Once you have fitted your angle to hold the drill suspended so the chuck doesn't rub against the spine (see the short vertical section in the center of the spine), reinforce the ribcage with another horizontal brace to the left side like is shown. Here we see the attachment which is much more solid than it looks. Two pipe clamps and this is fast to replace and easy as well. In the chuck you will notice our cam assembly. I call it an assembly because my original idea of simply bending over the end of a 3/8" steel rod wasn't heavy enough to really throw the chest around so I added a U bolt that is called a Clip that is normally used to attach cables. This added weight did the trick, so now it is only a matter of setting the trigger to the on position and turning the speed dial until the right speed is achieved for the most effective shake.

   Since I didn't relish the thought of this flying saber tooth claw eating the chest out of my thrashing thug I decided to use 1/16" aluminum sheeting to cover it up. I simply rounded the sheets with my hands and then bent a tab on each end that would allow me to bolt it securely to the rib cage, making sure I was fully clearing the cycle of the cam. Since the drill simply slips into this aluminum sleeve, it will present no challenges when and if the drill will need to be replaced.