Arm Segment Fabrication

Arm Segment Fabrication

Date: 3.25, 3.28, 3.29
Goal: Fabricate sections of the arm and test the new gas spring.
Time: 6 hours
Students: Taren and Grant
Instructors: Mr. Pitz and Mr. Johnston

This segment of the project was much anticipated as the results of the test would direct us as to what we would have to fabricate in the future.  After some extensive testing (see past blog posts) we ordered a couple of gas springs (30 and 40 pound tension) to test on the arm to see if they could replace a traditional spring. We wanted to go with the adjustable gas springs, but they were cost prohibitive. Also, if we let too much gas out, we would have to send the spring back to be recharged. We did feel however the adjustable gas spring would be the best choice for the application.

A trip was made to PT Welding and Driveshaft in La Crescent to see if Pete had any 1 1/2" aluminum tube stock. He had a some shorts he gave us for free that worked out well for our horizontal arms. Thanks Pete!

The first thing we did was make the aluminum sides by cutting and then using the vertical mill to remove the metal where the spring would be placed. You can see a video of the action below.

Tube stock placed in milling machine

Milling out opening for shock and support arm.

Next the horizontal arms were cut and drilled to accept a 1/4" bolt to make a pivot point in the corners. We attempted to use plastic washers wherever metal met metal. The aluminum still needs to be filed and polished up. Research was done on the shear strength of a 1/4 in zinc plated bolt. We felt the rating was close to what we needed, but are considering replacing the bolts with a new graded bolt.

We will now need to make one more of these except with a 40 pound spring because it will connect to the one you see below and need to support more of the mass and load.

Horizontal arms drilled and bolted in place with gas spring attached.

Bolt head and plastic washer. 

Mr. Pitz started working on a design for the grinder mount. Part of this was previously completed but we were still looking at different ways to mount it to the arm and allow for flexibility of movement. We picked up some flange bearings (5/8") that we thought might make the rotation easier and smoother, then turned down some aluminum blocks on the lathe to accept the bearing. This will allow the grinder to rotate up and down while in the mount.

End blocks with bearings inserted to help grinder rotate smoothly.

We now have the mount to the point where the grinder will move up and down and rotate around its center longitudinal  axis. The next part will be to secure the grinder mount to the arm so it can also rotate right and left perpendicular to the body.