10 Things Beginning CNC Milling Machine Users Need to Succeed

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Let’s assume you have a working CNC machine that you’ve just acquired, but that you know very little about CNC.  Let’s further assume it is a mill and that you will be focused on cutting metal.  You’re ready to start milling custom chopper parts, build a tool changer, or scratch build a Colt 1911 handgun.  With CNC, you can build almost anything and you’re chomping at the bit to get started on your pet projects.

Not so fast!  Remember, you just got the machine and you’re a beginner.  You’re not ready for those projects yet.If you have some idea how to make your first CNC parts, charge ahead with these 10 suggestions. You’re ready for this article. It is about 10 things you should focus on to maximize your chances of becoming quickly successful:

1.  Buy Some Decent Cutters

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Don’t get the package of assorted sizes of cheezy imported cutters. You also don’t need the solid green unobtanium aerospace cutters from Men-In-Black-Cutter-Supply. Get some decent cutters from a reliable source that has reasonable prices.

Having a decent quality cutter eliminates a whole bunch of problems right up front. I would also go with HSS when you’re just starting out.  You’ll eventually want carbide for a lot of uses, but HSS is cheaper and more forgiving.   The exception is high speed spindles such as CNC Routers commonly have. They need carbide to stand up to the higher speeds.

Get yourself a few sizes:

–  1/2″

–  1/4″

– 3/16″

Nothing smaller at this stage until you’ve learned on less delicate cutters.  Buy 2 or 3 flutes for aluminum and some 4 flutes for everything else.  I’d get 3 of each in each size to start.  You are going to break some cutters, so get over it and accept the idea.  It’s a good thing at this stage to remind you to wear your safety glasses because you will break some cutters!

While you’re at it, buy a full twist drill assortment.  HSS from a decent brand on sale will work fine.  I like the idea of replacing the ones I break with cobalt over time.  That way my most-used sizes wind up higher quality.  And one more twist drill tip–buy screw machine length, not the usual jobber length bits.  

The screw machine length bits are more rigid and you will seldom drill super deep holes anyway.

2.  Get a Decent Vise, a Clamping Kit, and a set of Parallels

Yeah, I know, vises are expensive, but workholding is very important.  

Get a decent Kurt-style vise for your mill.  It’ll be money well spent on a valuable piece of tooling that will last for years.  In my shop I have used Kurts purchased from eBay and a couple of brand spankin’ new Glacern vises.  There is sneaky stuff that goes on when you clamp a workpiece into the vise.  If you don’t have a good one, the workpiece will shift and you’ll be wondering what happened.

You’ll need a way to mount your vise to the T-slots of your table, so you may as well get a clamping kit too.  Any old kit will do.  Buy the one that is on sale at your favorite supplier.

Lastly, you’ll need a set of parallels, at least until you get proficient at making step jaws.

CNC Routers are a different story.  You’ll mostly be clamping things to your spoilboard.  Do yourself a favor and go read up on how that’s done so you can get a lot of good ideas before it’s your turn to start clamping.

3.  Get yourself a misting setup for coolant and use it while being paranoid about chip buildup

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If your machine didn’t come with flood coolant, and isn’t set up for it (i.e. you don’t have an enclosure to keep the wet inside), get yourself a misting setup.  I got mine off eBay for about $100.  It’s a Noga.  There are a lot of different brands.  Get a jug of coolant to go with it.  I use KoolMist, but again, there are a lot of brands.

Now train yourself to be paranoid about chip buildup.  

Recutting chips is bad for cutters and in the worst case leads to breakage.  Being paranoid means you’re watching the cut like a hawk and you fiddle with your mister’s nozzle until you figure out how to position it right the first time and every time thereafter to blow away the chips from the cut.  

If you’re a CNC Router user, the story is different, unless you plan to cut a lot of aluminum.  If you’re cutting aluminum, you still need a misting system.  Otherwise, a ShopVac or even just blowing the chips out of the way with compressed air will serve as you cut wood or plastics.

4.  Learn how to use MDI

Your next step is to learn to run your CNC as though it was a manual mill with power feeds and DRO’s on every axis.  In the process you’ll learn some basic g-codes so that you have some idea what your program is doing the first time you run a real g-code program (that’s a little ways away yet!).  It’s very convenient to be able to do this trick.

Start out with the cutter way high and don’t try make any moves in the Z-axis so you won’t crash the cutter into anything.  Practice making moves in X and Y.  Until the cutter goes where you want it to and you’re not making mistakes.

One more trick: don’t use G00 in MDI–that makes the machine move in rapids mode which is as fast as it can go.  Use G01 and set a slow feedrate.  “G01 F20” will make the machine move at 20 inches per minute (or metric units if you’re in metric).  You’ll have a lot more time to react this way if it starts heading into trouble.  Visualize pressing the red E-Stop many times so it’ll be almost automatic when you need it.

5.  Get yourself a feeds and speeds calculator and use it

You’re getting close to making your first cuts.

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Do yourself a favor and get a feeds and speeds calculator.  Trying to figure out feeds and speeds as a beginner or asking people on forums is a recipe for frustration and faillure.  And it is such a false economy to try to save a few bucks by skipping the calculator or using a cheezy free online calculator.  Stuff will go wrong that you’re just not equipped to understand.  So, get a decent feeds and speeds calculator so your spindle speeds and feedrate are perfect for that first cut.

6.  Get yourself a Z-height measuring gizmo and learn to use it to touch off your tool lengths.  While you’re at it, get an Edge Finder and use it to touch off your Part Zeros.

Your machine needs to know where the tip of the tool is or terrible things can happen.  

Learn how to use these to tell the machine what your tool length is.  This process tells your machine where the tip is in Z.  To establish the position of X and Y you’ll need and Edge Finder. The first thing you’ll do after sticking a piece of material in your vise and inserting a tool in the spindle is to set these zeros.

Use your newfound MDI skills from #4 to start using your Edge Finder and Z-Height Touch Setter.

7.  Learn to Tram your Mill and Visehttps://www.youtube.com/embed/cn05fX55pqc

How to square and tram your vise on your CNC mill…

Tramming is what machinists call getting things square by sweeping an indicator around.  It’s a basic skill everyone needs to learn.  

When you first start machining, get into the habit of checking your mill’s tram every time you walk out into the shop.  You’ll know later on whether you need to do it every time, but for now, you could use the practice.  While you’re at it, be sure you know how to tram your vise so the jaws are aligned properly with one axis or the other.  Let’s don’t try to square you mill just yet, but tramming the mill and vise are a good step at this stage.

8.  Start out with wood, aluminum, brass, and plastic.  Avoid stainless.

Okay, the very next step involves making some cuts.  Sorry if it seems like you had to do a lot before getting there, but I did say I wanted to tell you some things that will help you succeed and there’s quite a few things in that category!

One more is to avoid difficult materials for your first cuts.  Stick with aluminum, brass, or non-metals like plastics and wood.

BTW, nothing wrong with sticking a piece of 2×4 in the machine to learn on, even if the eventual part is going to be made of metal.  I often use wood to prototype what I’m doing until I get everything right.  It’s a lot cheaper than metal!

When you’re doing okay with softer materials, graduate to mild steel.  Only after you feel like you’ve pretty well mastered cuts in these materials can you try tougher materials.  Master means you’re not breaking or wearing cutters out too quickly, and your surface finishes no longer look like the material was attacked by a pack of rabies-infected beavers.

One more thing.  It’ll be tempting to try some “mystery metal.”  This is metal you think you know what is, that you got essentially for free, and that is therefore expendable.  Trouble is, a lot of mystery metal is hard to cut.  It’s nasty cheap stuff that will break cutters and generally confound you.  Not worth it!

9.  For your first project, learn how to square a block of material and make yourself a few sets of step jaws in aluminum

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Let’s quit procrastinating and make some chips!

For this step, you’re going to start by learning how to square a block of material. Get your saw and cut out some pieces of material that are slightly oversized to serve as vise jaws.  Google “Kurt Vise Jaw Dimensions” to find drawings of jaws if you need some.  As mentioned, cut the stock slightly oversized from aluminum.  Now you need to square those blocks.  Squaring means you will make a series of milling cuts until all sides are properly parallel or perpendicular to one another, at which point the workpiece is “square”.

One thing about the Turner’s Cube material squaring:  I use a Face Mill, but you should start out doing it with multiple passes and a 1/2″ endmill.   Why?  Because Face Mills generate a lot of force.  You can stall the spindle, yank the work out of the vise and throw it across the room, and other shenanigans a beginner could do without.  

Leave the face mill in a drawer if you have one already and do it with a 1/2″ endmill the first time until you know a little more what you’re doing.  Same goes for fly cutters, and for the CNC Router crowd, those big cutters you use to surface spoilboards.  You’re not ready for them yet.

Having squared the material, your next task is to cut it to size by continuing to mill it until it is a perfect fit for your vise jaws (you’ll need 2 square pieces, one for each jaw).  The last step is to drill and countersink the mounting holes.

Actually, I wasn’t completely truthful.  Once you have mounting holes, the last step is to mill a step along each jaw, maybe 1/8″ square.  Now you can use that step instead of parallels when you drop material into the vise.  Over time, you’ll learn a lot more tricks with aluminum jaws, but remember: it all started here with your first set.

10.  Graduate to CAD/CAM

Friend, you’re now able to do the basics.  Sure, there’s a lot more learning to do, but you’re in a position to have a leg up on the manual machinist down the street who has a Bridgeport and no CNC.  Your next step is to start pumping out the g-code.  To do that, you’ll need to be proficient with CAD/CAM.  This is going to be your biggest step yet.  Neither CAD nor CAM is very easy to learn.

I give myself 2 weeks to feel comfortable with a new program, and I’ve had the luxury of learning quite a few so far.  If this is your first time, get ready to drink from the firehose.

Congratulations, you’ve got some Basic CNC Skills!

Congratulations, you’ve learned enough to start doing some useful things with a little confidence.  If you can design and generate g-code for basic parts with CAD/CAM software, you’re particularly proficient.  

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One comment

  1. 11. get a calculator with trig functions, learn to write basic programs by learning the code and calculating the numbers.
    NGXYZIJKFSTM (and more)
    More useful than you might think,
    and forces you to to step thru program first time to debug.
    Learn to be careful. CAD/CAM programs can do the math right, but
    they are not infallible.

    Like

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