Fabrication Begins

After creating the computer model and ordering our parts and steel, we were ready to start building this thing. Since we were still waiting on parts, we could only start work on some of the stock we already had in our shop. So, we started by cutting the 2" rod that would be the sleeve as shown in the picture below. The Acme threaded nuts will be welded on to the ends, and there will be a sprocket welded on the outside. This whole assembly will be what pushes the Acme threaded rod and the crush block.

Click to enlarge

The first thing we did was to cut the 2" diameter rod into three 6" sections. While we only need about 3" for the final part, cutting it long will allow us some extra to put into the lathe chuck. This lets us do all of our lathe work for the piece at one time, instead of having to stop and flip the part around to work on the other side. This also further insures that everything will be concentric, where if we take the part out of the chuck to do the other side, there is no guarantee that the part will line up exactly as it was. We did the cuts on our "drop saw", which is a band saw that cuts by falling onto the part. We control the fall rate with a dial. Since steel takes awhile to cut, we will spend quite a bit of time in front of this machine before we finish this project.

Our "drop saw", a band saw connected to a hydraulic piston

After cutting, we put the rod into the lathe. The first thing we needed to do was drill the clearance hole so the Acme threaded rod won't touch the sides of the rod, and only make contact at the Acme nuts. Since we will be using 3/4" threaded rod, we went with a 7/8" clearance hole. It's a little bigger than we need, but better safe than sorry.

One of three lathes in our shop

Before we drill the hole however, we need to "face" the cut surfaces. Machining has a lot to do with accurate measurements and that means precision is very important. The drop saw doesn't leave a flat or a smooth surface, which means we won't be able to measure off of it until we face it on the lathe. The bar with the triangle shaped end is the tool we use to face the part. We move that tool across the face of the part from the outside towards the middle. Since the tool doesn't move left or right, it makes the surface of the part flat and smooth, which allows us to measure off of it later. 

A facing operation on the lathe

After this, we can drill the holes through the center. In order to do this we start with a center drill, and then move up in drill bit sizes 1/8" at a time. By stepping up in sizes, we reduce the chances of the drill bit wandering off center. It also reduces the amount of metal taken away by the larger drill bits, which keeps the heat down and increases tool life. 

Faced and drilled part

It doesn't look like much, but for all three parts it took us almost 3 hours, which highlights the scariest part of this project. We really can't estimate the time it will take to fabricate any of these parts. This is due to lack of experience (for example, a professional machinist would have a much better idea of the time involved), as well as the fact that we have to work around other project teams in the workshop. Either way I never would have guessed how long these parts have taken so far, and there is still a lot to do. All we can do is be in the shop as often as possible and work steadily so we don't get bit later on.