Quote:
Originally Posted by Nailhead
I used to work in the oilfield-- I've drilled hundreds of holes in steel, using a slow speed & oil as a cutting fluid. You can tell where the sweet spot is speedwise by the feel of the bit biting, and the shavings produced. NONE of that happened in this instance, and doesn't seem likely to, because I varied drill speed all over the place, and got nothing. As I mentioned, this was an essentially new, sharp cobalt bit. Ten minutes, and 3/32" ruined it, oil & all. There aren't enough cobalt drill bits in town to support that rate of success.
As for a write up, I have no idea what you mean.
Thanks, Jeff. I'm going to sleep on it, and see if I have any further interest in this thing when morning comes around.
Chris
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Chris, You say "cobalt drill". Cobalt brand or as ingredient ? You need a high quality drill, not what they sell in the local hardware store. Precision Twist or Guhring would be my first choices.
For write up , as in how to do it.
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Turn the engine so the hole is in a location that is comfortable for you to both drill and to stay centered. You said you got one pair of set screws out already. Use a 1/4" or "F" ( .257 ) drill to see where the threads start. If there is room, use that drill to give a good centered area on the set screw to start drilling.
I would start with a 3/16" ( .1875 ) drill and run it SLOW. Plenty of lubricant and steady , even pressure. I would NOT go to the tap drill size until you have drilled thru all the stuck set screws. Get a puller and pull the PTO off. there will only be a little bit of the set screw major diameter left and that will deform enough to come over the bearing.
Once it's off, then drill will the proper tap drill size. That's how I did the one on my first 125. I used three drill bits on each hole. ( actually the equivalent of three drill bits as I sharpened them. As a machinist for over 35 years, I have a good eye for hand sharpening )
Clean the threads with a good quality tap. ( once again not the junk they sell at the hardware store )
The tap drill size for 1/4-20 NC is a #7 drill ( .201 ) but use a 13/64 ( .203 ) if you don't have numbered drills.
Good luck
Jeff