Absolute vs. Incremental Movement – What’s the Difference?

Absolute vs incremental movement is discussed in this machinist's blog detailing the use of each method.

Absolute vs. Incremental Movement? These are two terms that you will hear or use in the machine shop, and there are many people who don’t really understand the difference.  When I am in a customer’s shop training them on their new machine, it’s a little surprising to me how many people don’t know what the distinction is. Don’t get me wrong, there is nothing wrong with not knowing – after all, if you already knew then you wouldn’t be reading this right now and then my existence would be meaningless.

Absolute vs. Incremental Movement

In my experience there are a couple ways to convey the difference between absolute movement and incremental movement. When it comes to machine movement, simply put:

An ABSOLUTE movement moves TO A COORDINATE based on your ZERO POINT.

An INCREMENTAL movement moves A DISTANCE based on your CURRENT POSITION.  An incremental movement does not take your part zero point into consideration.

Absolute movement tells the CNC machine to move to a coordinate based on your zero point.
Absolute Movement – used to move the machine from a random location at the back of the work area to the zero point (in this case, top of the left front corner on the workpiece).

Let’s run through an example.  We will work on the assumption that you have a fixture and work piece set up on your machine, and your zero point is the front left corner, with top of stock being Z zero.  You just finished setting up your tools so you are located near the back of your table at some random coordinate.  We will pretend that your program starts from X0 Y0 Z0.5.  So here is your dilemma – you are currently at X6.753 Y14.265 Z2.37 and you need to get to X0 Y0 Z0.5. How will you do it?

Absolute vs. Incremental?

Well, technically you can use either absolute movement or incremental movement. To make this incremental movement you would enter X -6.753 Y-14.265 and then you do some math. You are currently at Z 2.37 and need to reach Z 0.5.  2.37 – 0.5 = 1.87.  So for your Z input you would enter Z -1.87.  This would get you to X0 Y0 Z0.5.  On the flip side, if you make an absolute movement your input will be X0 Y0 Z0.5.  You are telling the machine “I want to move the X axis to 0, I want to move the Y axis to 0, and I want to move the Z axis to 0.5.”  This is where the real benefit of an absolute movement comes in.  When you are moving TO A POINT absolute is the much simpler way to go.

Incremental movement is telling your CNC machine to move a distance away from your current position
Incremental Movement – used after milling a hole in a part and needing to mill another feature 6″ away.

On the other side of this argument, is the situation where you have drilled a hole or pocket in your part, and you know that you need another feature six inches away.  Now, if your first feature is at X0 Y0 then it’s really not a concern, since both absolute movement and incremental movement would be the same. However, if you are not at zero, then suddenly your absolute movement becomes more difficult as you need to determine a point in relation to your zero point, rather than a distance from your current position.  Let’s use the same numbers as before. You drilled a hole at X6.753 Y14.265.  You need a second hole six inches away in the X axis.  In order to use an absolute movement your XY input would be X12.735 (6.753 + 6.000) Y14.265.  Not too complicated, but certainly there’s a possibility for error.  On the other hand, if you choose to do an incremental movement your XY input is X6 Y0.  You are telling the machine “I want to move the X axis 6 inches in the positive direction, and I want to move the Y 0 inches.” With incremental movement you are telling the machine A DISTANCE.

It is altogether possible that I just made this more confusing for you. This is not an easy thing to understand at first, and as I have found in my training of others, it is not always an easy thing to teach.  Hopefully what I said makes sense – if not feel free to comment and ask any questions you may have.  Understanding the difference between absolute and incremental can make your job a whole lot easier and more efficient.

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AUTODESK Fusion 360 CAM Challenge – DATRON’s Adrian Montero Wins Best Surface Finish

Fusion 360 CAM Challenge won by DATRON's Adrian Montero using a DATRON neo high speed milling machine.

When an Autodesk Fusion 360 Product Manager put out a “key chain challenge” to see who could produce the best quality sample part, many CNC machinists on social media took note and got right to work.

Fusion 360 part being programmed with Autodesk Fusion 360 CAM software by Datron's Adrian Montero.
Fusion 360 Part being programmed by DATRON Application Technician, Adrian Montero.

Appropriately named the AUTODESK Fusion 360 CAM Challenge, participants were asked to produce a Fusion logo made into a key chain.  Autodesk supplied all participants with the same file in their software. There were only 3 requirements to the Autodesk Fusion 360 CAM Challenge:

  • Use Autodesk Fusion 360 to program
  • Take a photo of yourself programming the part
  • Supply a photo of the final end product
Fusion 360 CNC milling performed on DATRON neo high speed machining center.
Fusion 360 CNC milling challenge on DATRON neo, compact high-speed mill.

All participants of the Autodesk Fusion 360 CAM Challenge were given 1 week to complete their sample parts and submit their photos. In that week 56 people participated and tagged 152 photos that were viewed by 129,000 people.

Fusion 360 CNC machining challenge won by Adrian Montero who used a DATRON neo high speed milling machine.
Original Fusion 360 key chain next to the one milled in acrylic on a DATRON neo by Adrian Montero.

DATRON Dynamics Application Technician, Adrian Montero won the Autodesk Fusion 360 CAM Challenge in the Category of Best Surface Finish. His part was machined on the DATRON neo, compact high-speed milling machine.

Learn more DATRON neo download the brochure:

Nameplate Manufacturer Calls DATRON Source of Efficiency

Nameplate milling and engraving at Willington Nameplate is performed with DATRON high speed milling machines

Willington Nameplate in Stafford Springs, CT manufactures metal engraved nameplates and Identification tags for a wide range of customers from aerospace and defense to Gillette Stadium – they actually produced all of the seat tags for “Casa de Brady”. Their metal nameplates and ID tags are made from a range of materials including aluminum, brass and stainless steel.

Willington Nameplate was founded over 50 years ago by Marcel Goepfert and day-to-day operations have been run by his son, Mike Goepfert, since 1990. Since that time, there have been many changes and a lot of growth. This includes a critical decision in 1999 to purchase their first DATRON high-speed milling machine.

Nameplate milling including control panels, data plates and dials is performed at Willington Nameplate on their DATRON high speed machining centers.
Nameplate milling at Willington Nameplate includes control panels, data plates and dials.

Willington Nameplate’s Fabrication Group Leader, Jamie Vale Da Serra, recounts this story saying that, “Prior to installing the DATRON machine we used a manual kick process.” He goes on to say, “We needed to get away from that process because we needed a tolerance higher than .005”. Vale Da Serra refers to the DATRON milling machine as a “set it and forget it” piece of equipment that runs unattended freeing up staff to attend to other tasks.

Nameplate engraving and milling at Willington Nameplate is performed on DATRON high speed milling machines that can run unattended.
Nameplate machining by Willington Nameplate is optimized by DATRON features like vacuum chuck workholding, probing and automatic tool change – resulting in their ability to run this machine unattended.

Quick job setup and the ability of the DATRON machine to run unattended are the result of a number of integrated features – all operating in concert. This starts with integrated vacuum table or vacuum chuck technology that allows the operator to quickly setup the workpiece – for nameplates this is generally sheet material such as aluminum, stainless steel or Metalphoto®.  An integrated probe for part location and measurement also speeds up job setup and enables uniformity by automatically compensating for material irregularities like surface variance. An automatic tool changer with an integrated tool-length sensor provides a full stable (and wide variety) of necessary tooling that can automatically be changed at given intervals and/or when a tool is broken.

Nameplate machining by Willington Nameplate is done with their DATRON CNC mills and produces labels, tags and UID marked nameplates.
Willington’s nameplate machining yields labels, ID tags and UID marked tags.

Vale Da Serra says, “Consistency is there with the DATRONs from the first to the last they all measure the same, whereas with the manual process human error is possible that could give you a deviation.”

The growth at Willington Nameplate is not limited to adding DATRON machines, the company has recently purchased three other companies in New England, thereby expanding sales by 35% in five years. With a staff of more than 80 people, Willington Nameplate has now set their sights on additional acquisitions elsewhere in the United States.

Learn more about Nameplate Production download the White Paper:

Shop Safety for CNC Machinists

Shop safety includes the use of personal protective equipment (PPE) as well as lockout tagout policies.

Shop Safety? Go ahead. Roll your eyes. Get it out of the way now. We have all seen the cheesy safety movies with terrible acting and fake blood. Don’t worry though, this isn’t like that – I’m a terrific actor. Seriously though, I took classes.

All joking aside, I know how easy it is to laugh it off and ignore the safety rules. Let’s be honest, a lot of those safety rules make all of our lives in the shop more difficult. I had one safety officer (any of you working for a large corporation will know exactly the type I am talking about) who required us to make Plexiglas covers for every moving part on all of our machines. Try setting a gear hobbing machine through three levels of six year old plexi. You get the point. However, one thing I learned very fast was that those safety rules were not created to make you less productive. They were created and enforced to – get this – KEEP US SAFE! One close call is usually all it takes (that’s all it took me) to start taking those rules a little more seriously and my goal today is to prevent the close call and maybe just speak some sense into you. If I manage to save a finger or two, or even a pint of blood, then I have achieved my goal!

Shop Safety PPE or personal protective equipment can include a wide range of items, but should always start with proper eye and ear protection.
Shop Safety PPE – Personal Protective Equipment starts with eye and ear protection.

Why don’t we start with my favorite basic rule – If you don’t do it while you’re driving, don’t do it while you’re machining. Don’t sleep, eat, consume alcoholic beverages, use drugs, call Grandma, text your buddies, or make unsafe lane changes while running your machine. Whether it is a high end CNC or an engine lathe it requires your full and undivided attention at all times. All of these machines are incredibly powerful tools that don’t have brains – don’t argue, even your half million dollar five-axis VMC doesn’t think for you. Machines do what you tell them to do, make sure you are aware of what you’re telling them. Common sense is not a part of the final sale, you have to bring that with you. Respect the equipment, it deserves it.

Personal Protective Equipment (PPE) for Shop Safety

Personal Protective Equipment (PPE) is a very important aspect of shop safety. This includes everything from safety glasses to gloves, earplugs and aprons. I have worked in shops that required hard hats because of a 20 ton overhead crane, as well as shops that would send you home if your sleeves were loose or long, or long hair wasn’t pulled back. On the opposite end of that spectrum I have worked in shops where sneakers and flip flops were more common than steel toe boots and safety glasses. Just because your company may not enforce the rules does not mean you shouldn’t follow them. If you ever need the safety glasses you will be glad you have them on. Always be your own advocate when it comes to safety, because even if you have that annoying safety guy always sneaking around to write you up for not putting your earplugs in he can’t be there all the time, and all it takes is a split second for things to go wrong.

Shop Safety Gloves can protect your hands when moving sharp material but could harm them if caught in moving parts of a CNC machine so know when to wear them and when not to.
Shop Safety Gloves – know when to wear them and when not to.

Shop Safety – Gloves … when to wear them and when NOT to!

Gloves are a tricky piece of PPE, because depending on what you are doing and which machine you are running they can be either helpful or harmful. Very harmful. If you are going over to the stock rack to grab a plate of steel a thick pair of leather work gloves will protect you from any sharp edges while you carry that stock. However if you are running ANY machine with a running spindle DO NOT wear gloves. Whether it is a CNC machine, a lathe, a knee mill, or a drill press wearing gloves near a rotating spindle and spell disaster. A lot of folks think they can get a better grip on their part while running the drill press if they were a heavy pair of gloves and the sharp edges won’t cut them. I can tell you first-hand how disastrous this can be – it is very easy for the drill or material to grab right onto that drill, and I will let your imagination take you from there. Assuming safety features haven’t been disabled (again, the common sense thing) then most CNC machines will not allow you to put your hand near the spindle while it is running. However, on the off chance you have both the chance and opportunity – DON’T! The only times that I ever suggest wearing gloves when running a CNC are either when fingerprints need to be avoided or when the coolant tank is full of month old flood coolant and your company hasn’t invested in anti-microbial/anti-bacterial additives. I have seen some pretty nasty skin infections from old coolant, so make sure you keep that in mind. In these cases wear latex nitrile gloves – tight fitting non leather gloves that will break with minimal force if necessary.

Avoid “Danglers” for Shop Safety

When running manual machines especially it is very important to keep any “danglers” in mind. Long sleeves, pony tails, baggy shirts, jewelry, etc. Anything that hangs off of your body – keep it to a minimum. Again, all of the above could spell disaster. I know you want to be the best dressed guy in the shop, but I would rather be the guy with all his limbs and digits. Just my personal preference.

Shop Safety Lockout Tagout is extremely important in the machine shop and when working around CNC milling machines.
Shop Safety Lockout Tagout is often overlooked but is critical when working around CNC machining centers.

Lockout/Tagout – take it seriously!

Finally I want to discuss Lockout/Tagout. The number of people whom I witness not following this procedure enough (myself included at times) is alarming. Lockout/Tagout for anybody who is not familiar is the process of powering down the machine and locking the power switch with a lock that only the service technician has the key for. The purpose here is to prevent anybody but the service tech from doing ANYTHING with the machine. Every time you service that machine without powering down and locking it out you are inviting accidents. Especially when dealing with CNC machines the consequences of this mistake could be fatal- it’s not worth the extra thirty seconds.

Safety is absolutely no joke. PPE can be uncomfortable, inconvenient and cumbersome. Safety procedures can be time consuming. Plain and simple, you never want to be in a position where you finally understand why they enact all these rules – just trust in them and follow your common sense. It is the most useful tool you will have with you in the machine shop. Stay safe friends.

Micro drilling: An incredible (and Incredibly Frustrating) Adventure

Micro drilling using drills far smaller than a human hair requires experience, research and the right milling machine.

So micro drilling has never been my forte.  I have done a lot of drilling but never anything much smaller than 1/64th or so.  Well friends, if you were a part of that club too then there is a whole other world of drilling that you have never experienced, and there are some pretty amazing things going on.  Some of the more recent research I have done on micro drilling has been very eye opening, and the project I am currently working on has been one of the most challenging in my career – all to drill holes slightly larger than a human hair.  We will discuss many of the things to watch out for and some basic parameters to start some of your own research projects.

Much like anything else in the machining world, the numbers don’t lie.  Many of the same formulae apply.  However, there is MUCH less room for error.  Everything from the length of your flute to the geometry on the tip of your drill needs to be scrutinized, and with micro drilling there is no easy answer for anything.  Tooling manufacturers will be your best resource for parameters to start with, since they are the experts on their own tools.  I am not a tool salesman, so I am not going to promote one brand over the other.  That, friends, needs to be part of your research.

Step 1 in Micro Drilling – Research the Material

Micro drilling stainless is shown in these impressive Xrays of a 0.004" hole drilled 0.040" deep in stainless steel rods.
Micro drilling stainless: Xrays of a 0.004″ hole drilled 0.040″ deep in stainless rods.

That brings me to step one of your micro drilling adventure.  Research.  You need to know your machine, you need to know your material, you need to know your coolant and coolant system, and you need to know your tools.  When I say you need to “know” I don’t mean a basic knowledge.  Research it, become as much of an expert as you can on everything you are doing before you even consider cutting metal.  When it comes to micro drilling in general there is a lot of research out there, and much of it provides conflicting or confusing information.  Arm yourself with the knowledge to fight through it and you will be OK. Research different coolants, research different drills.  Drill suppliers and coolant suppliers should both have people that you can talk to over the phone for more information – most importantly specific information about your material.

Micro drilling plastic like these tiny holes drilled in small cavities on a Delrin part.
Micro drilling plastic – this shows small holes drilled through circular cups (or cavities) in a Delrin part.

Currently I am drilling .008” holes into 15-5 PH stainless.  The first thing I did was learn as much as possible about 15-5 stainless.  It’s an interesting material because it is considered a stainless steel, but it acts like a die steel.  Because I knew that before doing my research I was able to navigate my way through the tooling manufacturers’ charts, skip right by stainless steel and take the parameters from the die steel section.  I avoided many headaches, because the parameters were very different – much slower spindle speed for the stainless.  My point is, material knowledge is key.  Know that first.

Step 2 in Micro Drilling – Understand the Coolant

Micro drilling of rounded surfaces like the one shown in this photo requires a 4th axis solution.
Micro drilling requires research to understand the material being drilled and the available coolants.

The second step, after you do your homework and figure out the specifics on the material you are running, the coolant you are going to use and narrow it down to two or three drill manufacturers is to look at your program.  First and foremost, when you are programming a micro drilling operation is the drill cycle itself.  There is varying information available on the most successful strategy, but one thing everyone agrees on is that it has to be a pecking cycle.  A chip break cycle (where the drill does not retract fully out of the hole, only enough to break the chip) is generally ineffective because it leaves chips in the hole. On a standard drill the flute is carrying those chips up and out of the hole. Technically, micro drills will do the same, except you really don’t want them to.  Drills that small (.008” in my case) DO NOT like re-cutting chips and will eventually break because of it.  A full retract on every peck is the strategy I choose, and while it may take a little more time it is the best way to ensure the longest life of your drill. There are machinists (and tooling manufacturers) who will suggest a “chip break, chip break, full peck” strategy, which will be faster but I would only apply this at the upper end of the “micro drilling” scale.  This scale by the way is another point of contention.  A micro-drilled hole is generally considered any hole smaller than .1”, but you will always have people who disagree.  Call it what you will, it’s small.  Anyway, back on track.  Strategy is very important.  You want to make sure that the tool clears the hole with enough distance and time to clear the chip and receive some coolant.

Optimal Coolant for Micro Drilling

Micro drilling coolant shown cooling a micro drill (in comparison to a pencil tip).
In micro drilling coolant is a key consideration. Here a spray mist (minimum quantity coolant) sprays on a micro drill (shown in comparison with a pencil tip). Yes, we drilled the pencil tip … because we can!

Coolant.  It’s an interesting term – true to life, since it is actually cooling the tool, or at least acting as a vehicle for heat transfer.  However, in micro drilling the more important aspect is the lubrication.  Water-soluble coolants do a very funny thing that most people don’t realize when you’re drilling.  When the bottom of your hole fills with coolant and the tool enters the hole, it actually becomes pressurized.  Under normal circumstances this is not a concern, but with micro drills being so fragile it can easily be enough to overpower the tool.  I am using a misting system for my operation, along with a thin oil that flows well.  What happens is the oil pools on top of the part, so no matter what the drill passes through the coolant and lubrication before contacting the part. The only problem this presents is chips.  As you machine holes you notice chips building around the completed holes.  Due to the fact that the oil is not flowing like a flood coolant, it doesn’t carry the chips away.  This is currently a problem I am trying to remedy, but again it’s a very time consuming process that involves much patience … and frustration.  You will be OK.  Plan to break a few drills, and plan to try different things.  Just don’t plan on drilling a hundred holes in ten minutes.  Micro drilling is not, and should not be considered a high-speed machining operation.  It takes care and precision.

Optimal Tools for Micro Drilling

Micro Drilling Tools can be as small as this 0.0015" drill shown in comparison to a penny.
Micro drilling tools like this 0.0015″ drill (in comparison to a penny) require research, experience and the right CNC machine to use effectively.

Finally, I’m going to discuss a little about the actual tools.  There are many tooling companies that provide micro drills.  In your research you will find that many of them have very specific information on the geometry they use for their cutters and the coatings and every other bell and whistle you can imagine.  Do yourself a favor and pay attention.  Some of it may seem like fluff, which it may be, but some of it is very important.  If you have read any of my other blogs then you know that sometimes seemingly small things make all the difference.  Such is the case here.  These tools need to be precision ground and incredibly sharp.  As is the case with most aspects of micro drilling, there are differing opinions on the tooling material – carbide or high-speed steel.  While carbide offers better rigidity and longer sustainability of the cutting edge, high-speed steel offers more flexibility. Carbide is brittle and will break as soon as it’s dull – high-speed steel is more forgiving and lower cost.  It all comes down to the workpiece material.  This is another situation where I hand it off to the true experts – the ones who make the tools.  One last bit of advice on the tooling – don’t go cheap.  If you do your research and you find that you can achieve your goals with a $15 drill that’s fantastic. Just don’t shy away from a drill just because it costs $75.  The name of the game is value, and be sure to explain to your finance department that the best value doesn’t mean the cheapest drill.  If “Drill A” costs $15 and drills 100 holes, and “Drill B” costs $75 but drills 1,000 holes then the better value is Drill B, even at five times the cost.

I would give you an idea of some of the parameters I am running but that would essentially defeat the purpose of my post.  Do your research, find your numbers and run with it.  I have been very impressed with the success of the base parameters I have received from tooling companies, so always remember – trust in the numbers.

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CNC Milling Laminated Shims

Milling laminated shim with a high speed CNC machining center featuring vacuum workholding and a 40,000 - 60,000 RPM spindle.

Let’s face it, some materials are just no fun. Inconel, hardened steels, ceramics. Everybody likes a material that will cut like a butter, and a typical dread is associated with stuff that doesn’t. So recently, we were presented with a material in the latter category. Milling laminated shims from stainless steel sheet stock.

Everyone we asked had a similar reaction. “Stainless shim stock? That stuff sucks.” And there were many reasons. Delamination during machining, enormous burrs, difficult fixturing. General misery.

Milling laminated shims out of stock like this laminated stainless steel sheet material is best handled using a high speed CNC milling machine with vacuum table workholding.
Milling laminated shims from stock like this laminated stainless steel can present some challenges.

So when addressed with this difficult task, I cringed a bit, and got to work. Luckily for us, DATRON’s technology is a perfect fit for machining shims. But why?

Vacuum Workholding is Ideal for Milling Laminated Shims

Your typical shim machining fixture looks something like this; A base plate, a layer of adhesive, a layer of shim stock, another layer of adhesive, then a sacrificial layer of aluminum on top to prevent delamination. Needless to say, setup takes a long time, and break down takes even longer. With our vacuum table fixturing, the setup is bit more manageable; the vacuum table, a layer of vacuflow sheet, then shim stock. Done. Probe the material and go to town.

CNC milling laminated shims with a high speed machining center equipped with vacuum table workholding for quick setup.
CNC milling laminated shims can be an easier process by using vacuum table workholding. This photo shows how it works.

High RPM Spindles for Reduced Chip Load When Milling Laminated Shims

With a typical VMC, RPM does not get too high. Maybe 10,000 RPM. The issue with this is the cutting forces being applied. Let’s consider a 1.5mm double flute end mill, cutting a part at 10,000 RPM, at 60 inches a minute. That ends up being a 0.003” chip load. That is a problem, and it’s also the reason delamination is so prevalent in shim machining. Cutting forces are too high. Using the same tool at the same feed rate, but at 30,000 RPM, we just reduced our chip load to 0.001”, bringing the cutting force down by 2/3. This is what allows us to cut the shim stock without a sacrificial top layer, thus saving time and aggravation.

Milling laminated shims using a 40,000 - 60,000 RPM spindle helps to reduce chip load which prevents delamination.
Milling laminated shims with reduced chip load is achieved with a 40,000 – 60,000 RPM spindle.

Milling Laminated Shims – Clean and Accurate

There are other methods of cutting shim stock, obviously. Some work better than others. Laser cutting can have issues with welding layers of material together. Waterjet can manage it, but the tolerances aren’t really there, requiring machining after the fact. This is where a DATRON can shine. With high speed machining, edges come out clean and burr free, and tolerances come in within 0.001” (over the work envelope). The benefits here are significant; remachining, cleaning, deburring, can be cut down tremendously, allowing you to move on to the next job.

Now that doesn’t sound so bad, does it? Next time you’re dealing with a problem child like shim stock, give us a call, we can help.

Learn more about vacuum tables – download the data sheet:

Machine Shop Math – Common Formulas and Strategies

Machine shop math blog detailing feeds, speeds and formulas associated with CNC machining and milling machines.

One of the more common problems I have seen in my years in the machine shop is a general lack of readily available and handy information on machine shop math – specifically on feeds, speeds and related formulae.

Machine shop math for feeds, speeds and other important aspects of CNC machining and milling applications.
Machine shop math is an important consideration for CNC programmers and machinists.

Whether you are programming a 5-axis CNC machine or turning handles on a 60 year old knee mill the numbers don’t lie.  However, one very important lesson I have learned is to respect the variables.  Any common formula you are going to use in the machine shop will provide you with the information you need to approach the cut appropriately but remember to always treat that number as a starting point.  There are an immeasurable number of variables with any cut, all the way down to the atmospheric conditions in the shop.  Tooling manufacturers will provide you with suggested numbers whether it be surface feet per minute, chip load per tooth, revolutions per minute, inches per minute or any combination of those and more.  It can all get very confusing and overwhelming but don’t quit on me now.  I am hoping this post can serve as go-to information for you and your shop, and hopefully I can make some sense of it for you.

Machine shop math formula for RPM, SFPM, Feed Rate and Chip Load per Tooth to help machinists and operators of CNC milling machines.
Machine shop math formula for SFPM, RPM, Feed Rate and Chip Load per Tooth.

As you can see in the above formulae in order to calculate any of these you need to already know some of the other data to input.  This is where the tooling manufacturers come in.  They can provide information to you for their specific tools and applications.  However there is some basic information based on the material you are cutting that I will provide to you right now.  Keep in mind that these are starting points, the best judge will be your eyes and ears.  The following is a list of suggested SFPM for common materials:

Machine Shop Math – SFPM for Common Materials:

Surface feet per minute parameters associated with particular millable materials.
Surface Feet Per Minute (SFM) parameters based on material.

So let’s say we are using a .500” solid carbide end mill cutting aluminum.  Looking at our chart the suggested SFPM is 800.  In order to determine our suggested RPM we use the above formula SFPM x 3.82 / Tool Diameter:

Machine shop math formula for calculating revolutions per minute (RPM) can be used by CNC machine programmers and machining center operators.
Machine shop math to calculate RPM (revolutions per minute).

I will give you another example, this time with a significantly smaller tool.  We are going to use the same material but this time with a .125” solid carbide end mill.

In machine shop math SFPM or surface feet per minute can be calculated using this formula.
In machine shop math SFPM is surface feet per minute and can be calculated with this formula .

You can clearly see where the tool diameter drastically changes the suggested parameters, and where a high RPM spindle is a valuable factor.  This table can be used for these common materials however the manufacturer of the tools you choose will most likely have specific information on the tools you purchased which should always be used when available.

Are you still with me?  I know, you feel like you are in high school algebra again.  All of these numbers will make more sense when you start applying them to jobs in YOUR shop on YOUR machine, until then stick with me!  I promise it will be worth your time.  We are going to move on to Inches per Minute.  If you reference the formula above Feed Rate (inches per minute) = RPM x Chip Load per Tooth x Number of Flutes you see that in order to calculate this you need tool information.  Chip Load per Tooth is the amount of material a tooth, or flute, of the tool is removing in one revolution.  Most tooling manufacturers have suggested chip load information available, but you can also use your own knowledge and expertise to make a suggestion.

In this example we are going to be using a .500” solid carbide end mill with three flutes to cut aluminum.  Since we already know from the first example that the suggested RPM is 6,112 all we need is the chip load per tooth.  The manufacturer suggests .005” per tooth chip load on this tool, so we have all of the information we need to calculate our feed rate.

Machine shop math inches per minute formula used by CNC machine programmers and operators.
Machine shop math inches per minute formula.

See?  That is not as confusing as it looked.  However, here is where some of variables come into play.  Serious consideration needs to be made for the type of cut you are performing.  If you are milling a slot with full tool engagement then you need to be more conservative.  However, if you are utilizing a dynamic strategy (as discussed in another blog post) then you could potentially be more aggressive.  As I stated in the beginning, these numbers are starting points.

Finally, we will discuss how to calculate Chip Load per Tooth.  This is a useful formula for both preparing for a cut or programming and analyzing an existing cut.  You can easily look at your program while trying to optimize either surface finish, cycle time, or tool life and this will be a good indicator of proper tool utilization.  Let’s say we were running that last example at 4,000 RPM instead of the suggested 6,112.  We also ran it at 120 IPM rather than 91.68 IPM.  Our results weren’t great and Quality Control wants answers… NOW!  I know!  Let’s check the numbers!


This is double the manufacturers suggestion, therefore a very good place to start looking for problems.  Using the formula that you have now mastered, you know that you either need to bring your feed rate down or your RPM up to meet the requirements.

Now that you are armed with a basic understanding of these formulae and the knowledge that NONE of this is set in stone, you are ready to start applying it to your everyday work.  You will be amazed how quickly you won’t need to reference any charts or websites to be confident in your numbers and the job of programming a very expensive CNC machine will become a little less stressful.

If you want to put these formulas to work using the best cutting tools of the market, just download the DATRON Cutting Tools Catalog by filling out the following form.

Download Cutting Tool Catalog:

Halftone Engraving on a CNC Machine

Halftone engraving of a DATRON M8Cube high speed milling machine that is actually made on the M8Cube milling machine.

When you get to work with a DATRON every day, you get to see some pretty cool things. There are so many cool things to observe, or be involved in, that you can become a little numb to just how cool these things are. So, every once in a while, it’s good to stop and look back at what you’ve been doing and take a second to appreciate it. In this case, it’s halftone engraving.

I thought this might be a unique topic to share with you, the reader, so you too can enjoy the cool things you can do with your CNC machine (hopefully a DATRON!).

What is a Halftone?

First, a little background on our subject. A halftone image, according to Wikipedia, is “the reprographic technique that simulates continuous tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient like effect.”

Halftone engraving is the simulation of a continuous tone image using dots that vary in size or distance.
Halftone engraving is a reprographic technique simulating a continuous tone image.

Essentially, the trick behind a halftone image is to use varying size dots to create a grey scale image. It’s comparable to some comic book printing or pointillism, but is a bit unique.

Halftone engraving using different size dots milled into the surface of blue sheet material (with a silver surface finish) to create a grayscale.
Halftone engraving on blue sheet material with a silver surface finish requires milling varying size dots to create a grayscale image.

Halftone Engraving Software (Free)

Now, let me introduce you to Halftoner, a free application created by Jason Dorie. It allows you to easily import any image and not only convert to a halftone image, but also apply a tool path to it at the same time. The elegance of this software comes from its simplicity; first, import an image and choose your values for minimum and maximum dot size, dot spacing, dot offset, etc… Then determine your milling values; retract height, minimum depth, feed rate, RPM, and so on. One of the most important values for Halftoner is the tool angle, since it will take the included angle of your tool to determine the necessary depth to make a certain size of dot. It’s really quite intuitive.

Once that’s all done, click “Write GCode” and voila, you’ve got a program ready to go.

Engraving halftone images with a DATRON high speed machining center and a free application called Halftoner.
Engraving halftone images with a high speed CNC milling machine can be done easily with a free application called Halftoner.

I was fortunate enough to get to play with this for a while on a recent project, and the outcome you get for a minimal amount of effort can be very impressive.

Engraving halftone graphics on an engraving machine requires the engraving of different sized dots that reproduce a graphic by simulating a continuous tone image.
Engraving halftone images is quick and fun using a high speed milling and engraving machine like the DATRON M8Cube.

Want more info on engraving? – Download Engraving Brochure

Hard Milling on CNC Machine

Hard milling of 63 Rockwell steel on a DATROn high speed CNC milling machine

The mention of hard milling is usually enough to give the average machinist/programmer anxiety.  Well save your Xanax friends, because hard milling is not as scary as you think.

There are many factors involved with successful hard milling and I am going to touch on them today.  My hope is that you will take the information I give you today and go learn even more.  The best thing you can do in approaching any hardened steel is educate yourself before you cut a single chip.

Hard milling steel like this 63 Rockwell 6,000 RPM, 100 inches per minute at .012 per pass (ramping)
Hard milling steel – 63 Rockwell, 6,000 RPM, 100 inches per minute at .012 per pass (ramping).

The first and probably most important consideration in hard milling is the construction of your machine.  In order to achieve ideal results with hard milling you need an extremely rigid machine that has a high degree of dampening ability.

Hard milling CNC milling machines require rigidity that can be provided by a machining table made of granite or concrete polymer.
Hard milling CNC machines require rigidity provided by polymer concrete or granite machining beds and cast steel construction.

Generally, machines constructed with polymer concrete have many times the dampening ability as machines made with cast iron. It is also important to have a CNC control that will handle the dynamic requirements of the constant and rapid acceleration and deceleration.

Hard milling machine with a solid granite machining table provides the rigidity needed for milling hardened steel.
The thick solid granite machining table on the DATRON M10 Pro makes it a rigid hard milling machine.

Next on the list is the spindle and tool holding.  Two very different things, but if one is off the other won’t matter much. You need a rigid spindle capable of high RPM with very little runout.  If your spindle has runout then the most concentric and true tool holder in the world will only help you so much.  That being said, combining a great high speed spindle with the best tool holders will yield results you never thought possible.  HSK series tool holders are probably one of the most popular in terms of hard milling because the interface with the spindle promotes great rigidity and concentricity.

Hard milling spindle and HSK tool holders exhibit both rigidity and low runout for superior results in machining hardened steel.
Hard milling spindle and tool holders should be selected based on rigidity and low runout. We’ve found the HSK tool holding system to be extremely effective.

Of course we cannot forget tooling itself.  If you do a little research you will find there are many tooling manufacturers who make application specific tooling for hard milling.  I tell my kids all the time that I know everything, unfortunately I don’t think you are quite so gullible. The majority of these tooling manufacturers have experts who can assist you in selecting the tool for the material and specific cut you are making, and I suggest utilizing those services.  The cutting tools you choose for your hard milling applications will need to be coated to stand up to the high heat and extremely high abrasive forces involved with these materials, so take your time and learn something.

Also, the tools will most likely not be cheap, so don’t be caught off guard.  DO YOUR RESEARCH!  If you bring a purchase request to your boss and he chokes on his coffee because the end mills you are buying cost so much, you will be able to throw so many big words at him to justify the purchase that he will have no choice but to sign it.  Also, if you need two make sure you request four.  That way when he authorizes the purchase of only two he feels he saved the company money and he can puff out his chest while you get what you wanted in the first place.  Tried and true techniques, this isn’t my first rodeo.

Hard milling tools including the 8mm 4 flute end mill, 0.5mm edge radius with x.ceed coating from DATRON perform extremely well and last longer
Hard Milling Tools like this DATRON 8mm 4 flute end mill, 0.5mm edge radius with x.ceed coating exhibit superior performance and extended durability.

OK, back to business.  The final piece of the puzzle (not really, the puzzle never ends…) is the CAD/CAM software.  One of the most important considerations in hard milling is a programming software that can control the load placed on the tool.  You want a constant load on your cutting tool without spiking, which means trochoidal milling is in order, or as I usually call it, dynamic strategies.  The principle behind dynamic milling in relation to hard milling is the light, constant engagement of your tool into the material.  No sharp plunges, smooth constant force.  Most of the major CAD/CAM packages out there now have some form of dynamic milling.  For more specifics on dynamic strategies see my recent blog post on the subject.

Hard milling program developed with the appropriate CAD/CAM software for the effective machining of hardened steel
Blog author, Kevin Mulhern, the qualities in CAD/CAM software required for an effective a hard milling program.


As with anything you do in the machine shop, or garage, or anywhere else you are using these tools and strategies, KNOWLEDGE IS POWER.  Research, study, ask the old guys, google it – whatever you have to do, the name of the game is learning. The more you know heading into a challenge the easier it will be to overcome it.  Good luck in your first steps into the world of hard milling- it will open your eyes.

Need Tools for Hard Milling? – Download Tool Catalog

6 Easy Ways to Optimize CNC Program

Optimize CNC Program with tips and directions provided by DATRON Applications Engineer Dann Demazure in this blog.

“Optimize CNC Program” – it’s the instruction you hear in your head when you’ve finished a machining program. And it can be an arduous process that, if you’re like me, you slave over. Typically a bit too much, wasting a lot of time on changes that don’t add up to a substantial improvement. As we all know, time is money, so, I’ll try to relieve you of some of the labor of revamping your program. Here’s a list of quick, easy, and effective tweaks for your DATRON programs.

Optimize CNC program tips and detailed instructions in this blog by Dann Demazure from DATRON Dynamics.
Blog Author and DATRON Applications Engineer, Dann Demazure, optimizing a CNC milling program.


Optimize CNC Program Tip 1 –  Leave the coolant on

It may not sound like much, but this gain can really add up. If you’re using coolant in your program, consider switching it from the Positioning/Cutting feed setting from Cutting <0>, to Travers<1>. You may not easily perceive it, but there is a very brief dwell programmed into the software so that the coolant has time to begin spraying. This change in the command will leave your coolant spraying between positioning movements, thus avoiding the initial dwell. Now, each dwell may only last 1/10th of a second, but if you have 200 retracts in your program, you just shaved 20 seconds of your program, and that’s not nothing.

Optimize CNC program by leaving the coolant running during positioning movements to avoid the initial dwell.
Optimize CNC program by leaving the coolant spraying during positioning movements.


Optimize CNC Program Tip 2 – Ramp

If you’re cutting along a contour, consider changing your method. If you are currently doing depth cuts, try a ramp instead. A ramp keeps the tool engaged in your desired amount of material throughout (except for the very beginning and the very end), and has no retracts. Let’s say again that your part has 200 retracts cutting contours on 20 different features (10 retracts per feature). By ramping, you’d bring that number down from 200 to 20 (final retract), and if each retract takes half a second, you just saved 90 seconds.

Optimize CNC Program Tip 3 – Be smooth

If the devil is in the details, then small contours are your devil. If you’re doing intricate engraving or 3D contouring, then you’ve probably noticed that the machine will slow down to follow all contours tightly. It’s just following orders, but if you have a little leniency in your adhesion to contours, Smoothing can make a huge difference.

Optimize CNC program with smoothing functions to clean up jagged geometry for a tighter milling path.
Optimize CNC programs using Smoothing functions like PerfectCut to smooth jagged geometry. See the results in red above.


Smoothing will take jagged geometry, like what is pictured above (purple), and apply arcs to the contour to create a smooth, more continuous motion (red). Not only does this have benefits for surface finish, but since the machine doesn’t need to slow down nearly as much in an arc as compared to a vector, time savings can be abundant. And utilizing it is as easy as writing the code in your macro, editing the preset values (which work well for most things), and pressing the “Go” button.

Optimize CNC Program Tip 4 – Be dynamic

I’ve talked about dynamics at length before and all the benefits from using them to fine tune a process for speed optimization and ideal surface finish, so why am I mentioning them again? Easy, besides the fact the dynamics settings are one of the easiest ways to reel in cycle time, adjusting them in conjunction with smoothing yields even better results. A high dynamics setting combined with a smoothing filter means that a very minimal amount of deceleration is needed to turn a corner quickly, thus cutting your cycle time even further.

Optimize CNC Program Tip 5 – Get low

This is usually a gimme, but it takes about 10 seconds of your time to change your retract heights from 0.5”, to 0.050” (or lower). Minimizing your retract height won’t save you much time per retract, but think of the big picture. Even if you only saved 5 seconds per part, if you’re making 20,000 parts per year, you just saved over a day of machine time. Every second counts.

Optimize CNC Program Tip 6 – Keep your tools in order

It seems obvious, but try to keep your operations organized so that when a particular tool is done, it never gets used again in the program. Sometimes this is unavoidable, but each tool change will cost you somewhere around 15 seconds of time. Consider using combination tools to cut down on tool changes. Most importantly, if you have parts nested, use tools sequentially rather than by part. If you have to cut 24 parts, and each part uses 4 tools, you’ll either spend 24 minutes changing tools again and again, or 1 minute changing all the tools once.

If you’d like more information on the PerfectCut Smoothing mentioned in Tip 3, Download the Data Sheet by filling out the form below:

Download Optimizing CNC Program Smoothing Tip #3 Data Sheet