I’m going to use the door actuators pioneered by Peter and implemented many times by Allan and others. Allan has two videos (here and here) that describe what to purchase and how to do the installation. I made a couple of changes:
Pivots
The actuators are powerful and exert a lot of tension on the door when closed. The original design pivots on the threads of a 1/4”-20 flathead screw tapped into a 1/4” thick piece of angle aluminum. I replaced that screw with the largest flathead shoulder screw that would fit in the base plate. I then added a high-load oil-embedded bronze sleeve bearing. As can be seen below, the bearing projects 3/16” below the bracket which isn’t an issue because the self-lubricating plate is 1/4” thick.
Right-angle brackets, bottom plates and flathead shoulder screw
As can be seen below, the shoulder extends past the bearing so it’s important to use a 3/8” (shoulder diameter) rather than a 5/16” (thread diameter) washer to ensure that the nyloc binds on the bearing rather then the shoulder. Washers have one side which is nicer than the other and I usually face the nice side towards the nut because it looks better. However, since there may be some movement between the washer and the bearing I oriented the nice towards the bearing.
The shoulder screw and nyloc collided with the bracket so I machined a hole in the bottom of the bracket. Since I had the end mill chucked up I decided to machine 12 additional holes to lighten the bracket.
Bracket with 12 weight reduction holes (left). Bottom of bracket with slot to accommodate the shoulder screw and nyloc (right). Two weight reduction holes where subsequently added to the bottom.
The part numbers are as follows:
High-Load Oil-Embedded 863 Bronze Sleeve Bearing, Flanged, for 3/8" Shaft Diameter and 1/2" Housing ID, 1/2" Long (McMaster #2938T7)
18-8 Stainless Steel Shoulder Screw; 3/8" Shoulder Diameter, 5/8" Shoulder Length, 5/16"-18 Thread (McMaster #92944A132)
Material
Allan recommends a 12” long piece 6” x 6” x 1/4” right-angle aluminum and cutting 3” off of one of the legs to use as a base plate. Instead I purchased a 12” piece of 6” x 3” x 1/4” right angle aluminum and a 12” long piece of 3” x 1/4” flat aluminum. This reduces the amount of cutting and results in perfect edges. I also drilled a 2"-5/8” hole to lighten the bracket.
Rod End Mounting
Allan drills and taps the actuators’ rods to mount the 3/8”-24 rod ends. This is a bit tricky because the cross section is small (see picture below) and since the hole is going into the tip it’s hard to fixture in a mill or drill press. Instead, I welded a Grade 8 hex nut to the tip. I used a “high” (also know as a “tall”) nut because I wanted more thread engagement than what a standard nut provides (McMaster #90565A360). To accomplish this I removed the aluminum C-channel cover to provide access to the weld joint and to facilitate removal of the grease.
Tall 3/8”-24 nut welded to the tip of the rod (left) and 3/8”-24 rod end on top of rod (right)
Next Steps
Peter has designed an emergency release which I will test once the actuators are installed. I am also looking into a more sophisticated motor controller.