More AR-180 Upper News

Chuck at has been working on AR-180 uppers and has reverse engineered the trunion and has put up a very interesting article.

AR-180B Trunnion Design

I on the other hand, lacking any semblance of expertise in CAD took a differing approach when I reverse engineered my AR-180B upper.

Good friend of the site, Carl, sent me some square tubing that he has successfully used in his home builds. I decided to duplicate my upper using this material. It is much thicker wall than the original and I will have to shave this down at least on the bottom surface to get it to work with my lowers.

I did this for two main reasons. I wanted to refresh my skills on the mill as it has been many years since I last used one, and secondly, just to see if I could.

I made my first trunion out of 6061 aluminum just to test my measurements out and I have found that a few needed to be adjusted.

I learned a lot from this project and I find things like this much more rewarding than the usual beginners projects.

I will continue to tweak this until I am happy with it then I will start a new one using the first as a template. I think I will make the trunion out of 4140 unless y’all have any advice.

Some pictures that show what I have been up to for the last two days.

BAA27431-FC29-4C64-A01D-7BA5B691A574_zpsupjjv6pk A8E5D090-0D64-4122-9EF5-4E1F0425FE7B_zpswfvpyqae DA7C5E48-16C7-4747-8461-3EB436C12881_zpsxjaqzspa 109826B5-10FE-4A0E-81BB-1D1F8AF25A9E_zpsa4ffx1zk C2674BD1-29E5-4544-9617-A70BA6015107_zpsfmhx7zun

Some things to note if you attempt one of these yourself. The interior of the tubing is not perfectly square so some hand fitting will be necessary. The tubing spreads open once the bottom is cut. Some method of squeezing it back before welding would have to be considered. Lastly, all of this will be rendered moot once Chuck makes new uppers and flats available. Until then I will use this as a way to improve my machine skills and better learn my tools.