OK, how do I clean a fitted steel part that refuses to tin. I'm using Brownells HI-TEMP Hi-Force 44 and copper bond flux. My first try ended in total disaster, after talking with a Tech at Brownells we decided that the flux was not working. I later checked and discovered the flux has a one year shelf life. Replaced the flux and the new bottle works much better, but I'm still having trouble with getting the parts to tin, very spotty coverage. I did some practice runs on scrap pieces with low temp Hi-Force 44, common soft solder and some silver just to check myself and had no problems. I tried the High Temp, Hi-Force 44 on my parts and later a test piece and still no go. I'm thinking it's a cleaning problem. I've scrubbed both parts with cleanser and water and then denatured alcohol. I've tried to think of what I've done that would have contaminated the surface of both parts and how to correct it. I need to clean the parts with changing the dimensions significantly.
Any thoughts would be appreciated.