You are viewing mackys

Adventures in Engineering - Machining class update.
The wanderings of a modern ronin.

Ben Cantrick
  Date: 2008-07-16 17:41
  Subject:   Machining class update.
Public
  Music:Rush - Working Man

Some of you may know that this week (and next), I am "getting my industrial on." This week I'm taking a machining class. Next week is welding.

The class starts early. Very early, by my night-owl standards. I have to get up at 6:45 am to make it to Duane Physics on CU campus by 7:50. (Hint: Park for $1.75/hr in the Euclid parking structure, then walk one block downhill to Duane.) The class is only one week long, so at least I don't have to do this forever...

This class was also scheduled for another session later in the day, but I took the 8-10am class because A) getting into the class means hurdling a wait list that often grows to 40+ people (for a class with a max of 6 students) and B) at the time I applied for the class three months ago, I thought I would still have a full-time job, and the 8-10 time-slot interfered less than the later one. (Actually, we tend to leave by 9:30-9:45, so I usually end up getting to work by 10. This being pretty much my normal hours anyway, I don't think anyone at work has noticed.)

But enough with the boring stuff. Let's talk machinery!

The first day of the class was almost entirely safety and terminology. This is a center drill, you use it to start the hole so your drill bit doesn't skitter all over your nice shiny metal plate. This is a transfer punch, you use it to make a mark on the plate where you're going to put the pilot hole with the center drill. Here is where the safety glasses are - wear them at all times when you're in the lab. We also went over things like units ("I talk in thousandths in this class. If I say 5, that means 5 thousandths of an inch.") and some of the more bizzare quirks of the imperial measurement system ("[tap and die] sizes mean nothing. They're based on some strange formula based on multiples of 13 thousandths of an inch. Don't even bother trying to understand them."). And maybe a little bragging ("A couple of nobel prizes were made in this shop."). ;] I also learned that coconut oil is an excellent lubricant for machine tool work, and we would be using it for almost everything here. The prof learned this from reading about how the Japanese made their machines in WWII, when petroleum products were very scarce.

Unexpectedly, the class has a fairly strict dress code. Jeans and t-shirts are a must. Long sleeves are not allowed, because it's very easy to get them caught in a rapidly spinning machine and break your arm (or worse). Shorts aren't allowed because with metal chips flying everywhere, you need all the protection you can get. (You wear a thick machinist's apron to protect your upper body.) You're also required to wear a belt, so the instructor can yank your ass out of harm's way if you screw up and do something dangerous. Needless to say, safety is a very high priority. Do something stupid and you're kicked out for the whole day - which means you miss 20% of the class. Probably miss using a whole machine. I think on the balance this is a good thing. Most of these machines have 1 HP motors, which doesn't sound like a lot. But if you consider what would happen if a horse were to somehow use all its strength in an attempt to wrap your arm around a rapidly spinning metal shaft... the results wouldn't be pretty. Forming good safety habits at the beginning is not a bad thing.

The first half of day 2 was much like day 1. We sat around a table and did more traditional learning. We learned to use a horseshoe micrometer, and calipers. Then we got to go into the shop proper and see the various sheet metal tools. The press break for bending hard lines, a roller machine for bending in curves, a couple of different punching machines, and three different guillotine-esque cutters.

After that it was time to learn to use the band saw and cut some material for use later. The professor opened up the band saw and showed us how the wheels move the band around. Advised us about safety procedures ("Never get your fingers anywhere near the blade. See these scars around my finger? Nearly cut it off once.") and we each got to cut a 1" chunk off an aluminium rod and another off a brass bar. Also, we all drilled a hole with the drill press (some kind of silly bureaucratic requirement, evidently.) Then we got to look at the wood shop (much less impressive than it sounds) and the metal stock room (ditto). Then day 2 was over.

Today, we got to use the lathe for the first time. There are 6 lathes in the shop, and they range in manufacture date from 1950 to 2001. Other than the color of the paint on them, you'd never know the difference. ("Obviously the design is pretty much perfected.") We chucked our piece of 1" diameter aluminium into the lathe, and slowly (40 thousandths at a time) carved down half of it until we had (as close as possible to) a .501" diameter rod sticking up out of a 1" dia base. Mine came out real close to .501 on the calipers - I'll try and take the micrometer to it tomorrow and get an exact read. Anyway, not bad for my first part.

The Prof has a Jamie Hyneman like approach to cleaning up: Do it or die! As soon as you're done with your work for the day, you get out the air hose, broom and dustpan and clean up. Except when you're brushing metal chips directly off the lathe - there's a special paintbrush for that, because we don't want to get floor dust into the precision machined surfaces of the lathe. And that was the end of day 3.

Tomorrow, I believe we'll be using the 3 axis mills to work on our little brass blocks. And on Friday, who knows?


Even with what little I've learned so far, I've gotten a profound respect for the job of the machinist. It's precise, physical, painstaking work. It took me about an hour to take a 1" dia piece of aluminium and lathe it down to half diameter. Of course that was my first time, but assuming that machinists in the real world take off only .040" at a time as I did, precision machining anything much bigger than your fist must take ages. I can't believe it's taken us so long to embrace CNC technology.

It's also made me more determined than ever to really start building some of the stuff I have floating around in my head. Like that new CVT design I've been thinking about for more than a year now. And at least the first few pieces of the exoskeleton.

Most of all though, what I love about the class is that I'm gaining knowledge that I never had before, and if my life had followed a more typical course I probably never would have gained. Programmers are supposed to sit around in their abstract world of bits, never actually doing anything physical. But I like physical, as evidenced by my motorcycling and other outdoor hobbies. Pushing my boundaries and expanding my skills is the one thing that I've never, ever regretted doing. I refuse to be put into a neat little pidgeonhole - to limit myself to only the skills that some narrow-minded hiring manager might expect.

"I have taken all knowledge to be my province." -Francis Bacon

Edit: Day 4: For the first half hour or so, we used the big jaws on the lathe to drill a hole in the top of the post in our aluminium part. Then we threaded the hole with a plug tap, and finished the last few threads with a bottom tap. Then it was grab your brass block, go to the mill. We learned how to insert and remove the spinning tool that does the actual cutting (in this case, a fly cutter) as well as the collet that holds it. Also how to use parallels (two identically dimensioned pieces of steel) to align a part squarely in the mill's holding vice. How to zero in on a surface on the part ("touch off") and then use the automatic feed to take 40 thousandths off. And using our calipers to measure the part as we went. After several passes along four surfaces, we had milled our blocks down to .750" tall by .375" thick. We haven't machined the length dimension yet - those are the very bumpy bandsaw-cut surfaces. Perhaps tomorrow? Come to think of it, we haven't machined one of the bandsaw cut surfaces of the aluminium piece yet either. I wonder if our "final project" will be to finish off either the brass or aluminium part? (Or both?)

I made one stupid mistake today - when I was making my ten-thou finishing pass on the last surface of my brass block, I stopped the machine a bit too early. Although the cutting point of the fly cutter had finished machining the surface, when it stopped spinning, the point ended up landing on the surface of the block. And when I moved the part out of the machine with the Y axis, it left a gouge in the nice finished surface of the part. It's about 5 thousands off if you measure on the scratch. But everywhere else it's perfect. Pro Tip: Use the knee to bring the part downward after you make your last cut on a surface, instead of using the X or Y to drag it out sideways.

On a side note, it's amazing how long days are when you get up at 6:45 and do two hours of machining, and then eight hours of work. I'm falling into bed like a rock at 11pm most nights now - at least a couple hours earlier than usual. Monday feels like it was three weeks ago.

Edit: Day 5: Back to the mill. We got rid of the fly cutter and used a standard endmill to machine off the rough bandsaw cut ends of our brass block. Then they said "you can cut by 100 thousandths today!" Good thing too, because then we had to dig a trench exactly .756" wide in our brass block. Even going 100 thou at a time that takes a while. Then we used the digital readouts on the mill (previously untouched) and an edge finder to precisely locate a hole 94 thou up from the bottom and 375 thou in from the outer edge of the (now u-shaped) part, and use the center drill to make a pilot hole. Then we drilled all the way through the part and tapped the hole to make it suitable for a 4-40 machine screw. (I'll put up some pics of the finished pieces I made in the class when I get home.)





I'm too lazy to take more pictures. If you'd like to see these in person, just let me know and I'll bring them along the next time I see you.
Post A Comment | 7 Comments | Share | Link






Alex Belits
  User: abelits
  Date: 2008-07-17 01:26 (UTC)
  Subject:   (no subject)
Congratulations!

I had to do similar things when building Trogdor parts, though I intentionally avoided anything that requires a mill or a lathe from getting into the final product -- it drives up the cost way too much compared to things made with a CNC punch press, laset cutter, brake or some custom-made press forms.
Reply | Thread | Link



Jack the Turbowuff!
  User: kai_darkwolf
  Date: 2008-07-17 02:46 (UTC)
  Subject:   (no subject)
As a machinist, I can assure you that yes, it does take a long time to machine part manually. CNC technology is a fantastic addition to any shop, but the only way to make it work effectively is to understand the processes behind the cutting operations.

It's great that your beginning the learning process with hands-on experience, but don't stop with just the one class if this is something that interests you. Explore the adult education courses at your local vocational school. I learned the trade in high school, taking precision machining 4 hours a day, 5 days a week, for 2 years. From there I worked in industry making everything from transmission gears to turbochargers. 5 years later I still consider myself a novice.

Also, I recommend checking out Lindsay Books (http://www.lindsaybks.com/) as a source for books about the forgotten and unusual. If you have an interest in hands-on learning, they can provide you with brain food for years to come.

later,
-Jack
Reply | Thread | Link



Ben Cantrick
  User: mackys
  Date: 2008-07-17 05:19 (UTC)
  Subject:   (no subject)
Very cool info, thanks!
Reply | Parent | Thread | Link



  User: (Anonymous)
  Date: 2008-07-17 03:21 (UTC)
  Subject:   (no subject)
As a masochist, I can assure you that, yes, I do enjoy being ball-gagged and... wait, wut??

-J
Reply | Thread | Link



  User: nickhalfasleep
  Date: 2008-07-17 04:52 (UTC)
  Subject:   (no subject)
Hot damn I am jealous.
Reply | Thread | Link



Ben Cantrick
  User: mackys
  Date: 2008-07-17 05:19 (UTC)
  Subject:   (no subject)
You're a CU Alum, you can take the classes too. But sign up a semester in advance... it's the only way you'll get in.
Reply | Parent | Thread | Link



Ashfae
  User: ashfae
  Date: 2008-07-17 12:19 (UTC)
  Subject:   (no subject)
Wow.
Reply | Thread | Link



browse
September 2014