[chipsnpan]

for my classes final we were given a 1.500" diameter 4.300" long piece of 12L14 and had to do some machining on it. The back side was just a step shaft with a hole drilled in the end and the opposite side had a 3/4" 16 thread, 30 degree shoulder, steps and thread relief groove. both sides had various minor chamfer's. one step had a tolerance of .002" nearly all other dimensions had a tolerance of .010" with a few of the chamfers having a larger tolerance. We were only allowed to use HSS tooling, and used a 4 jaw chuck. We were given a time limit of one and a half hours to complete. no one in my class got further than about half way through it, but my instructor said that he was able to finish the same project in half an hour. Are we all sub par machinist's? I feel like I could finish it in about two and a half hours, I think I spent around 15- 20 minutes just re-chucking the part trying to keep everything coaxial with in a thousandth. How long should an operation like that take a professional machinist? I feel like I just fell flat on my face, looking for some perspective.

[The Blight]

With the machine we had on our school, I would not be able to do it in less than 1 hour. With the schaublin that I spent years working on, I would be able to do it in ½ an hour or so. It all depends a lot on how comfortable you are with the machine you are working on. With the schaublin I know exactly how it behaves under certain conditions. The tolerances aren't bad at all, and it's not a big piece you are machining. My final project had tolerances as tight as +/- 0.001. Aligning the 4 chuck takes quite a bit of practice to get used to, but it's not impossible.

I'm assuming that you have all the tools at hand when you start machining, and that you don't have to start out with grinding.

This has made me wonder if I could do it with the machine I have access to now. Perhaps I will give it a shot one day just to see if I'm talking bull**** or not. :-P

[underthetire]

Sounds similar to the part I had to make in what was called the VICA skill Olympics. Had a bunch of different operations for each machine type and 1 hour to complete as much as you could. I thought I bombed, didn't completely finish 1 part all day. Ended up with a silver.

[basalt]

Asking an apprentice to machine this part in 1 1/2 hrs I think is unreasonable. I could do it in 1/2 hr. as a machinist with 30 years experience with all my tools ground and at the ready. If the part fit into the chuck bore I would grab the 1.5"" dia. rough and finish the threaded end, flip it and drill the hole then rough and finish the steps. I wouldn't fuss too much with the chamfers--in fact I would use both the long and cross handles at the same time to get an approximate 45 degree chamfer then possibly file them or even just file them. When I was in school we didn't have digital readouts, we used indicators, stops etc. Also, all tooling was hand ground HSS. I would have given you 4 hours to make this part. How did the other guys do? As an aside, a quick way to dial in a 4 jaw chuck is to zero your indicator at say #1 jaw then rotate to the opposite jaw. If the indicator reads say 0.030" set it to 0.015" (1/2 the reading) then adjust all the jaws to zero.

[underthetire]

A lot of these tests are just too see how much of it and how well you do, not necessarily a finished part. We too had to grind our own tools, with the cheapest HSS bits known to man. No DRO's, not even travel dials, on machines surplussed from the military from WWII, and a lot of "learning" done too them.

[uperez]

These exams are designed to make you fail. What it does though is to test how you perform on a job with time pressure. Most new guys will jump the gun and start working aggressively overlooking safety. An experienced machinist will never trade safety practices over quantity of parts produced. Even companies do these kind of exams before hiring someone. You don't get skill from school, you get it through experience. What's expected of you is to use the equipments in a safe manner.

[SofiSSH]

Yes, passing the exam always caused me big problems. Especially if it is a written exam, in the form of an article. I wanted to write it myself, but I realized that I couldn’t do it without the help of https://www.masterpapers.com/. It’s good that now there are so many services that help students so much.