Every once and awhile, I pick up a good practical idea for remedying a machining problem. Some of these ideas come from other people, and some I've always known. In any event, here are a few I would like to pass along.
When having to turn 6-32 threads on pieces of 0.375-in.-diameter hex stock measuring 2-in. long, I found that the diameter was too small for a live center, my smallest center drill was too big for the tips of the parts, and the lathe tool would not clear the centers I had.
I didn't have any box tools, so I attempted to turn the parts unsupported, but with dismal results. The solution was a broken center drill ground down to where it would clear the lathe tool. I then ground a sharp point on the end of the center drill.
With the parts spinning and the modified center drill in the lathe tailstock, I fed the center drill into the part ends about 0.015 in. to 0.020-in. deep to support the work. You need to grease the center drill prior to this and keep coolant on it during operation.
This next idea is more of a process for accurately edge finding on a knee mill. For step one, you should set your machine table/knee at the height that will allow tools to clear your set up. Lock the knee and don't move it during the process. Also, make sure the machine's head is properly trammed in.
Next step, lock the axis that you are not edge finding – if you are setting the X axis, lock the Y axis. This helps eliminate errors in the machine ways. Next, snug the X-axis lock and turn on the machine spindle fitted with your edge finder in a collet. Run the edge finder at 15,000 rpm.
When the edge finder kicks out, meaning you've contacted the part edge, zero the machine's digital readout, back the edge finder off and repeat the process to see if the edge finder kicks out at the same number/position. Once you get two digital readings the same for the kick out, set zero there and move over the radius of the edge finder.
Here are a few more ideas:
• For a dull squealing reamer, rub a dowel pin along the inside cutting surfaces of each of its flutes. I have also used a piece of high-speed steel.
• For center drilling and drilling holes on a knee mill to within 0.0005 in. needed for dowel-pin hole locations,
I first drill the hole locations two drill sizes under finished diameter then "drill bore" with the largest drill available that will leave stock for
a reamer to take the hole to size. By drill bore, I mean drill with a slow enough feed so that the drill doesn't follow the existing hole but actually bores the hole true to the machine spindle axis. Stub the drill up as short as possible to reach the desired depth. An appropriate undersized end mill will also work.
• When turning a part requiring 0.001-in. concentricity using a lathe with a three-jaw chuck that won't run true, I mount a fourjaw chuck in the three-jaw one. The piece can then be indicated in as accurately as needed. Beats the trial-anderror shim solution.
• This idea is an alternative to wearing yourself out cranking a lathe handle to back a drill out of a deep hole to clear chips just to have to crank the drill all the way back in to resume drilling. Set your starting depth and lock the machine's tailstock in place. Move the machine saddle back until it bumps against the tailstock and lock it (the saddle) in place. Begin drilling, and when you get to the point where it takes longer to crank on the hand wheel than you care to, loosen the tailstock, pull it back to clear the chips, shove the tailstock forward until it bumps the saddle, lock the tailstock, and resume drilling. This is faster than doing all that cranking, and you won't loose track of how deep you have drilled.
• Instead of throwing away that metal strapping you just cut off a skid, use it to make thin parallels for when you have to drill holes that are too close to a part's edge for normal width parallels. No more drilling into your nice parallels.