A day at my job, part 2

　
A DAY AT MY JOB
PART 2

As you may recall I’m in the process of machining a rough part into a finished Gear. The next step is to put it in the chuck on the AXLESON lathe that I’ve been working on. I clamp on the hub, the hub is that 3.5 diameter part that was welded to the flange. To cut the metal we use carbide inserts, these inserts are very hard. They range in size from smaller than a dime to about quarter size, with most being in between that size. Each insert has from 2 to 6 cutting edges. You clamp this insert into a tool holder that you then clamp to the tool post on the lathe. As I told you I’ve 33 years in this trade and I’m still amazed watching those inserts just peal away at that metal. We also use inserts with diamond edges for extremely hard material. I will post some photos of inserts and other things.

Ok, I have delayed starting the lathe and getting to work. The first thing I do is turn the 10.5 diameter to size. To explain this, its back to the cookie, say your cookie is too big so you bite away at the outside edge till you get it to the size you like, so I turn the flange to size, Next I face the front of the part. Another thing, in all machining work the machines use the Cartesian coordinate system, Xyz. On my lathe I use X and Z: Z- is towards the chuck, Z+ is towards the tailstock. This moves the carriage back and forth. X- is towards the part. I move the cross side in and out. All this movement slides on the "ways" of the machine. Back on that tree limb, You cut the down the length of it by moving the carriage in the Z- direction. X- would cut deeper in the part. Now I have the nicely turned the outside diameter to 10.437.

Next I need to faced it to size. These Rough faces may be wobbling quite a bit so with the machine running, I move the tool tip towards the wobbling face until it hits the face, and you know it when it hits the face. Next you move towards yourself using the cross side in the X+ axis to get away from the part. I use a dial indicator that is attached to a magnetic holder. I put it on the way closest to me and zero it out against the carriage. I move Z-, .03 of an inch. Many people’s hair measures .002-. 006 thousands of an inch. So if I move .03 in the Z- direction its like moving the distance of 5-15 hairs. I set the rpm of the machine to 450. I double check things. I engage the automatic feed with a feed rate of around .01; it moves .01 thousands per revolution. That is the low end of the feed rate for roughing.

To finish a part use feed rates of .001-. 004 /for each revolution of the chuck. I have already engaged the feed and the tool tip is now facing off .03. I need to repeat this until I face it to the needed size. I do this operation to four other parts needed for the order. Next with a shinny Face and OD (outside diameter), I change the jaws on the chuck so I can clamp the side I just did in the chuck. The machined area is now running "true" clamped in the chuck. This is very important. To make the 2nd side run true with the first, there can’t be any "run out". When complete the part must be "concentric". Now I face the flange to the finished thickness, I can only face it down to the 3.5 hub. Next I face the hub to the finished length. I turn the OD of the hub to around 3.985 so it "cleans up". Cleans up means the whole face needs to have been cut, or the OD turned till it is completely round.

This entire metal cutting produces a lot of metal chips, they are recycled. So when that cutting tip is cutting the metal, chips are flying. On this job I have been producing a spiral chip that is maybe 2-3 inches long that turns blue as it leaves the surface. Blue because it is extremely hot. The chips vary greatly in size. I had one the other day bounce off my safety glasses. Its real nice when one sticks on you lip, or goes down you shirt. It is good though, that they are turning blue as they are taking the heat of the cut away from the part. You try and keep the part from getting to hot. Remember this is an old manual lathe, on the "CNC" machines that I also program and run, the machining area is enclosed so the coolant is keeping the part cool. On a CNC machine you can make a part with much higher speeds and feeds. One other note, you want chips and not "stringers". If the feed rate is two slow the chips don’t break and stingers can be a big hazard, they can grow to be incredibly long. I’ve witnessed several bad cuts and worse because of them. One thing they can do is create a "rats nest". That’s when the stringer gets caught on the chuck. The chuck is spinning fast. This stringer is one long piece that has been building up in the chip pan. The chuck can yank all that mess up and wrap it around the chuck spinning as fast as the chuck is turning. When that happens, pieces of the stringer are flying all over the place. Try to imagine what that would look like.

I next put in a boring bar, if you recall I rgh. drilled a hole before it was even welded up. So I move the boring bar up close to the face of the part. Make sure my X-axis is set so I don’t cut too much on the first pass. Now I’m using the z-axis automatic feed. I bore the part out to 1.376-1.378. A 1.375 shaft will have to slide through it. That range of 3 thousands of an inch is the "tolerance" I have worked with tolerances of .0004/. 0000. Many machined parts have tolerances of much smaller, I just haven’t run parts with that close of tolerances. I do the other 4 pieces. I am now done with the lathe work.

This is the end of part