DtD Update: Extraction tool

WARNING: MACHINING CONTENT

I have two parts that get pressed together for a semi-permanent assembly: the head and the copper sleeve that holds the LED driver circuit board. The press fit provides good electrical and thermal contact between the two parts. It's great once it's assembled...but how do you get it apart?

A "press fit" is when two parts are pressed together that have dimensions
that overlap very slightly. This can also be called an "interference fit." 

Funny, I asked myself the same question when it came time to remove a driver from a prototype. I knew in theory that I could pull it out, but how?I got the idea from Skip Adrian at Laser Center/Edge Finder. I just happened to have an appropriate pair of vise grips on hand that I could sacrifice to make a special tool.

Read on for more gruesome details...

I had to machine one part, TIG weld it to my vise grips, then split it on the band saw. That will make sense shortly. Just stick with it :)

A "roughing" end mill has small serrated edges. It requires less cutting force
and also makes small chips instead of tiny needles when machining steel

So my first task was to take a solid steel round and drill a 1/2" hole all the way through the center, on the lathe. Here I've put the part in a 5C collet holder and clamped it in my mill vise. The square collet block lets me flip the part exactly 180 degrees because I need to mill two flats for the vise grip jaws to rest on.

This is a close up after the machining. You can see how the jaws of the vise grips sit nicely in the little cut-outs I made. I set the locking tension to clamp firmly on the part.

Just a little further back. You like gratuitous photos right? Let's move on to the next step.

The chrome coating can be toxic if vaporized so I was careful to grind all of it
off the areas I would be welding and the small heat affected zone beyond the weld. 

A couple minutes with the TIG welder and I've got one solid (and really hot) pair of vice grips. They welded quite nicely. I wasn't sure how that would go :)

The last step was to split these back open on the band saw. There was nothing to it really. I just marked the center line roughly and shoved it in there. Then I deburred the edges with a pneumatic sanding disc. Will it work?

Like a charm! There is just enough room for the lip of the tool to fit between the internal threads and the wall of the copper sleeve. Since I only removed a tiny bit of material from between the jaws, they clamp perfectly at the desired diameter. It's basically the same principle as a set of soft jaws for the CNC mill. Cheers!