< Expansion Link >
I made expansion links from mild steel flat bars. The drawings show front and side view of the expansion link. It is made of three parts, those are a center body and two side covers. There are two gaps between the three parts. Forked end of 'radius rod' will go through the gaps. The center body has a groove in which a die block slides. Radius of the groove is 180 mm, while radius of the front edge is 240 mm and that of back edge is 140 mm.
My rotary table's radius is only 75 mm, so I extended the table with piled base plate. Each part of the expansion link is aligned on the base plate with 2.5 mm pins.
Before machining, the three blanks are roughly cut out with band-saw, filed and drilled.
I started cutting with the front edge, that is the largest radius. The blank is aligned with pins and fixed with bolts. Note aluminum sheet is packed between the blank and base plate, so as to clear tip of end mill. Also a suitable block is packed between base plate and milling machine stage.
Next, back edge is cut. That is the minimum radius. Note difference of the blank position on the base plate.
Cutting a straight part. The blank is set at the center of the rotary table.
Groove of the center body is cut. It was done at last in order to cancel distortion.
All of rounded edges are cut in the rotary table.
Die blocks are made from phosphor bronze rod. It is cut to the same radius as the groove. Note two blocks are cut in a piece and separated off.
Cutting the section of the side covers. First I cut inside middle recess, then reversed and cut outside shoulders.
Rounded shoulders are finished in the rotary table.
Trunnions are made from steel bar. They are silver soldered to the side covers.
Temporary assembled expansion link. Note dummy oil pots are screwed into the top and the bottom of the body.
The photos show how to put the expansion link into the motion plate. At first the side plates are inserted to the bush, after that the center body is fixed between them. The bushes are made from phosphor bronze bar and glued into the motion plate with Loctite 648.
