Here at CNCMachinistTraining.com, we want to educate you on everything CNC manufacturing related, and that’s why I’m taking the time to explain what a 3D printer is, and why they are making people thousands of dollars while doing it right in their home.
First of all, what exactly is a 3D printer, and what does it do? Another name for these printers is a rapid-prototype machine, because it can make you a one-off part without having to ‘cut’ or machine any materials.
That’s right, it actually ‘prints’ out a a real part that you can hold and use, as opposed to my typical 2D printer that prints out flat pieces of paper… Want to make action figures, model cars, tools, or a special replacement part that you can’t buy in any stores?! These machines really are amazing, and everyone that finds out about them are in awe of what they can do.
Depending on how sophisticated the printer is, you can take and scan a P-51 Mustang scale model airplane, transfer it to the computer program, pick your colors, and then click print. It will come out just like your existing plane, with moving parts and all!
If you’ve ever seen those older movies where they punch in their request onto a microwave-like machine, and out comes their order in seconds, a 3D printer is very similar, albeit the cycle time is a little longer.
While pretty much all of the personal or hobby printers are restricted to mostly plastics or composites, there are machines out there that can print out real metals, also known as additive manufacturing, but that’s for another article…
Drilling, boring, then reaming is the proper order of operation when machining a hole. This is just one of the fundamentals you will learn in Machining 101. Whether you’re on a manual mill or a cnc milling center, this process will get you the most accurate hole size.
Why can’t I just drill? That is a very good question, if you’re just starting out as a machinist or are in training, you probably won’t know how every kind of tool is going to perform. While a drill, even when spot drilled, can make a nice looking hole, it can’t always hole a tight diameter or circularity tolerance. A standard drill can walk, and that can change the location if it’s a thru-hole. Drills are not always ground perfect, resulting in one lip bigger than the other. This causes the hole to be more egg-shaped and often over-sized.
Want a perfectly circular hole? The boring bar comes next because, unlike a drill, it is sturdy and will follow the same path all the way down the hole. A drill is floating in its holder that causes run-out, but a boring bar is sturdy and will make a circular hole, whether the existing hole is already or not.
The reamer comes last if you want an accurate hole. You should only leave several thousandths left after boring, depending on what material you’re cutting. A reamer is much more precise than a drill, but it will follow the path of the existing hole. This is why you should bore the hole prior to reaming, otherwise the ream will follow the path of the drilled hole, which may not be straight. A bore is accurate, but you can get a better finish with a reamer, and it can still hold tenths for a tolerance if you have a good reamer.
Reading a blueprint accurately is extremely important in the machining industry. If you can’t decipher a print or flip your views (more on that later), you’ll have a hard time meeting the part requirements.
The first thing to look at is the job description box. It has all of the material, part number, revision, date, and other information about the part. If you’re just an operator or a set-up guy, the most important things are the material and part number, as well as the tolerances if given. Always check to see if there are revisions, however, in case the program needs to be modified to meet the new dimensions/tolerances.
If you’re on a milling, look at the overall length of the part. If it’s square or rectangular, how wide is it, and what is the height? What are the tolerances? If there’s no specified, there’s generally a set tolerance in the description box that depends on how many decimal places the dimension is. So, if the part is 4.75″ long, and the tolerance for .xx decimal numbers is .01, then the tolerance is 4.750″ + or – .010″.
If there’s any milling features involved, you’ll need to check the length, depth, width, and possibly angles of them too. Calipers, micrometers, and depth mics are good tools to check dimensions quickly, but if you need to check something that has a very tight tolerance, more expensive tools or machines are required.
Holes are pretty straight forward. They can be drilled, bored, reamed, and even circulated-interpolated by an end mill. Look at the blueprint to see if the specified hole is a through or blind hole with a called out depth. If it has a given depth, does it need to be a flat bottom, or can it be left with a drill bottom? If a hole has a tolerance of .002″ or less, ground gauge pins should be used. Large holes can be checked with more expensive tools, depending on what your machine shop has.
Counter-bores and counter-sinks are usually machined in relation to holes. A counter-bore will have dimensions for the diameter and depth of the bore. A counter-sink will have diameter dimension, as well as a given angle. Not all counter-sinks called out are 90 degrees, so always pay close attention.
Another common feature to look for is threaded holes. They can be tapped or cut with a thread mill. Nothing too special about threads either, just check the minor diameter with go and no-go gauge pins, as well as the major diameter of the thread with thread gauges. Your shop should have a collection of thread gauges of all common thread sizes and pitches, as well as any specialty thread required by a customer.
Are there any radius features on the part blueprint? A radius can with be milled by and end mill, or cut with a radius tool cutter. If you are running a part that has been made in the past, then you shouldn’t have to adjust the tool or radius offset much, if at all. The radius should make a perfect blend with the flats. Check it with a radius gauge or optical comparator.
A chamfer is often used on the edges of a part as a part of deburring and to make the part look much cleaner and more professional. It is a simple call-out on the print, as you only need to check the size and angle of the chamfer. If you have a large amount of tolerance, you can check it with a depth micrometer.
Also, hole or feature dimensions are very critical. They will usually come from the origin or the edge of the part. Dimensions often come from part features as well. Such as if there’s a line of several holes, the first hole dimension will come from the part edge. then the second hole dimension will come from the location of the first hole, and so on and so forth.
In reality, reading a blueprint isn’t all that difficult, it’s basically just a lot of common sense, and memorizing certain manufacturing symbols. Don’t be intimidated by a print with lots of numbers and detail, just take your time and read everything carefully. In fact, I would rather have a part blueprint with too much information than too little, although having the print cluttered with extra numbers is not efficient.
So you’ve decided that you want to be a full-time Machinist for a career, but you’re not sure if you can find a job without going to school… If you haven’t already, check out my article on CNC machinist training.
While many career’s start right after or during college these days, there are a lot of jobs that don’t necessarily require schooling. Years ago you could start out as a shop helper during weeknights while going to high school, but now it seems like you need take at least two years of post-secondary education to get any ‘real job’.
To answer the question plainly, no, you don’t NEED to go to school to be a full-time cnc machinist. There’s plenty of machinists that didn’t go to school and are doing well. In fact, there’s some guys that never took anything past high and ended up owning their own machine shop.
With that said, it may be hard to find a job in the manufacturing industry with little to no experience. In this case, the old saying, “It pays to know” couldn’t be more true. If you have a friend or a friend of a parent works in a local machine shop, ask them if there are any openings at that shop. If they don’t, that friend will usually suggest another shop or be on the lookout if they know you well enough.
Going to your local Tech school for Machining classes will definitely give you a head start, or an accelerated start if you just graduated from high school and already work in a manufacturing shop. You will be able learn all of your basic machining 101 knowledge, and then work your way up from there until you can program and make your own parts.
There’s shops out there that will start from scratch if they find a young and motivated worker, but the learning process will usually be more gradual over a longer period of time. Unfortunately, those can be hard to come by, and the wages probably won’t be enough to live off of.
One of the biggest problems is that most companies want someone with several years of machining experience, and don’t want to spend their time trying to train someone in, hoping that they will weed out the ill-performing machinists. While they may work some of the time, there’s no real way to tell how good of a machinist someone is until you give them work to do. You can take someone with 1-2 years of schooling and a year of on the job experience, and they might do better than another machinist that has been in the industry for 10+ years.
In the end, it’s up to YOU to decide what to do. The smartest route would be starting right off the bat when you graduate high school and going to a Tech school for machining, and possibly finding a small shop to work for at the same time. However, not everyone is young enough to do that. For those that are older and need a steady full-time job, there are people that take machining classes during the day, and go do to work at night. It can be gruesome, but if you work hard at it and really think that you want to pursue this great career, I encourage you to put the hammer down and quit slacking off!