My though is that one of the six flute countersinks pressed solidly against the pin should have more "bite" to keep it from rotating than a two flute drill applied more gently on the top. You could also fixture it horizontally so you can see the backside.
Any thought to simply getting a 6m/m- pin and an arbor press and pushing the pins out with a block to support the linkage, possibly soaking the assembly in penetrating oil first and some heat?
I do like the suggestion of two stub drills in a lathe to weaken the swedge, perhaps drilling and then pressing.
Sounds like a good compact method to retain pins. Is this strictly a Russian technique, European, or?
Anyone know if the holes in the linkages are straight or have a slight taper for this technique. Center drilling both ends of a pin and a suitable punch for assembly sounds attractive for the right application.
Weaken one end of pin with dremel by hand using either rod-shaped grinding wheel (slow) or an engraving "end mill" cutter at dremel. Just remove as much material at center of pin as possible. It will work ok even though the pin rotates a little. After that, firm impact with a hammer and small punch to center to remove the pin - it will break the pin at the weakened end at interface between the pin round body and bigger diameter end, leaving the pin and a ring. Preferable dremel a hole that is bigger than punch diameter.
That's how I would try it. It has worked on similar cases as the pins are usually quite hard and break (fracture) easily with such impact..
No, I recall reading a 1970s or 1980s ad from a US maker of relays crowing that they used this method to assemble their relays. Don't know if they invented the method or not. As I recall, they left the ball in the pin, so drilling would be difficult.
Ball end mill cutters are generally side cutting, in that there is very little/none cutting at the tip of the ball, unless you can source cutters that are similar to split-point drills. The same goes for countersink cutters.. they're just not as effective without a properly sized hole to feed into.
After using the Dremel to center the divots at the ends of the pin, proceeding with 2 split-point drills from opposite sides would likely be the easiest approach.
Split-point drills begin to cut immediately upon contact with the workpiece, whereas conventionally ground drills require feed pressure to force the drill's web into the workpiece.
This is a trick for removing broken off bolts, etc. Take an appropriate nut and weld it to the swaged pin. You now have a "handle" that is fairly easy to grip in a vise of some type. You should now be able to drill out the opposite swaged end and, hopefully, remove enough parts to grasp the drilled end to work on the nutted end.
Split-point drills have several advantages over coventionally ground points.
The s-p is far less likely to wander or skate when starting a hole.. because there's no web preventing the cutting edges from cotacting the workpiece.
The s-p requires less feed pressure because there's no web, the chisel edge of the web of coventional points has to continuously be forced into the workpiece to displace material.. essentially "wallowing out" a path for the web.
Since the s-p is constantly cutting, faster feed rates can be attained.
Split points aren't difficult to grind. The don't require a special, precision gash cut into the center.. instead, they're ground by removing material from the back/trailing side of each land, then the usual crowned grind is added. The second/crowned grinds can also be flat, creating a 4-factet split-point.
"Wild_Bill" wrote in news:S_Pvu.6125$ email@example.com:
Because the geometry, which has a shallow hole in the center, the ball end mills actually cut just fine, and in fact, most ball end mills are center cutting anyway. The pins are just a little larger than 7/32", so I actually got one that size, and a 13/64" one as well. My theory was that the smaller one would cut preferentially, so the big one would be "fixed".
Well, it worked! I put the 7/32" ball-end cutter in the headstock of my lathe, and the ball-end 13/64" cutter in the tailstock, disengaged the gears, and rotated the spindle by hand. Contrary to plan, the smaller cutter stayed put, and the larger one did all the cutting, but such is life... The next time (if there is one) I will reverse the position of the cutters for a better view of things. The cutter chatters a bit, but by the time I got to the critical point, it had pretty well centered itself.
Because there was less margin for error in centering, I carefully placed the best centered swage end of each pin towards the larger cutter. I could easily control the depth with the tailstock handwheel, and snuck up on the cut. It actually took a lot more cutting than I expected to get the pins to the point where they would drive out with a good blow with a fairly heavy hammer. Tapping with a small hammer got me nowhere. From the point where it first started cutting, I had to advance 35 to 40 mils to get the pins to drive out.
Once they were out, I was amazed at how much the ends had been flared out by the original swaging. The nominal OD of the pins is just under
5mm. I measured across the ends that were unmolested, and one pin was mashed out to 5.6mm, and the second one was 5.4mm.
I've got a selection of different OD ball bearings to choose from to flare the new pins, but I'll need to make some plates with shallow holes to hang onto & align them. It will be interesting to see if my 3 ton arbor press will produce enough flare, or it I will need one of my wife's sledge hammers.
Thanks for all the suggestions! Once I had a good plan of attack, this all worked very nicely.