Machinists ask me all the time, “When do I go fast and when should I go slow with a single flute end mill?” Well, as you can imagine, there are a lot of variables at play regarding feed rates for single flute end mill, but let’s try to break it down.
Slow (60″/min) – Finishing – If you need an exceptional quality in the finish of a floor or wall, it helps to slow the machine down to take a fine chip and decrease cutter load/cutter deflection.
Medium Feed Rates for Single Flute End Mill
Medium (120″/min) – Slotting – Something a single flute does particularly well is slotting, which is a tool path that has 100% of the tool diameter engaged in the material. Using a proper depth cut (25% of tool diameter), you can cruise along at a decent pace without worrying about clogging up on chips.
Fast Feed Rates for Single Flute End Mill
Fast (180″/min) – Traditional Roughing – When you are using a normal milling strategy, in the range of 33-50% depth of cut (2-3mm) with a 50-70% stepover, you can be fairly safe kicking the speed up, just keep an eye on your spindle load.
Very Fast Feed Rates for Single Flute End Mill
Very Fast (240″/min) – Trochoidal Roughing – If you are using Mastercam (Dynamic milling) or Fusion 360 (Adaptive clearing) you may have heard of this strategy before. Instead of going about the traditional method, this method utilizes more of the flute to boost efficiency. For instance, we could use 100-200% depth of cut (6-12mm) with this strategy because our stepover would be decreased to 10-20%. In many cases, this prolongs the life of the tool and puts less strain on the spindle, so you can safely bump the feed rate up.
Extremely Fast Feed Rates for Single Flute End Mill
Extremely Fast (300″/min) – Shallow roughing – If you are taking off less than 10% depth of cut (0.60mm), then you should be safe cranking the feed way up. With such a shallow cut, you won’t have to worry about overloading the tool or spindle.
Question: “Should I use a drill vs. end mill?” DATRON Application Technician, Dann Demazure answers, “It depends on what you’re trying to achieve.
When to Use a Drill vs. End Mill
If you’re making a very small hole, say, less than 1.5mm in diameter, go with a drill. End mills under 1.5mm become increasingly fragile, and subsequently cannot be run as aggressively, as a drill can be.
If you need to make a very deep hole – in excess of 4x your hole diameter, choose the drill. Past this point, chip evacuation can become very difficult with an end mill, which will quickly wreck your tool and your part.
Are you making a lot of holes? Drilling is probably the way to go. In most instances, a drill will best the fastest time you can achieve with an end mill.
Need to make an extremely precise hole? While milling is typically perfectly acceptable, sometimes the tolerances require a drill and a reamer for the perfect finish.
When to Use an End Mill vs. Drill
However, there’s a lot to be said for using an end mill instead.
Need to make a big hole? Big holes need big drills and lots of horsepower, this is where helical milling shines. Use an end mill that’s 60-80% the diameter of the hole you’re making to quickly clear out while leaving plenty of room for chips to escape.
Print calls for a flat bottomed hole? Normal drills can’t do that, so you might be better off milling the feature.
Making lots of different size holes? Try to use the end mill, you’ll save time on tool changes and room in your tool changer.
Rapid prototyping? End mills will be appealing for their flexibility. Being adaptable to take on some features that may normally be drilled means you can spend less time CAMing a part and more time making chips.
With either one, there are two simple rules to remember:
Break your chip – don’t try to be a hero and blast through your hole in one go, program a quick retract to get the chip out and let the coolant in.
Turn up the coolant – unless you have through tool coolant, you’re going to want to be sure to turn up the coolant flow and decrease your air pressure. The coolant needs to be able to flow into the hole during your retract.
Since the equipment our company offers is ideal for sign engraving and processing flat sheet material, we’ve seen the inside of a good number of sign companies over the years. But, walking into Ellis & Ellis Sign Systems in Sacramento, CA becomes a different experience as soon as you pass through the lobby and corporate office of this family-owned business. That’s because the overall size of the place is impressive. Well, it has to be really, considering the work they do – this includes billboards, architectural signage, landmark signs, amusement park signs and even those dazzling neon jobs enticing patrons at the many casinos in Reno. They even made a 16-foot tall Tyrannosaurus Rex, a gigantic Frankenstein and a not so menacing (but still sizable) Curious George for Universal Studios.
But not everything they do at Ellis & Ellis is so big. Take for example the Braille required for way-finding signs and architectural signage. This is intricate work often done on smaller signs that must be ADA compliant for elements like position and tactile height. Braille can be produced using a variety of different processes. For example, Photopolymer Braille uses UV light and a chemical process to remove negative space material. In contrast, Route-in-Place with Raster Braille is a process where small acrylic beads are mechanically pressed into predrilled holes.
Sign Engraving with ADA Compliant Braille
Having tried both of these processes, Ellis & Ellis experienced significant obstacles as follows:
Photopolymer Braille: First and foremost, the Braille was not completely round and was, therefore, subject to ADA liability. They also found the necessary raw materials to be expensive. Ellis & Ellis Director of Manufacturing, Bill Rogers, explained, “The excessive costs of the materials were compounded by costs associated with the human labor required for processing and finishing.”
Route-in-Place with Raster Braille: Similar to Photopolymer Braille, Ellis & Ellis found that additional human labor was required for finishing in the Raster Braille process because of the excessive glue that remains after tactile copy is placed and engraved. Bill Rogers said, “Additionally, the alcohol, solvents and cleaning products would cause crazing to occur on the acrylic beads which often shattered them.” Plus, they found this process to be limited in terms of surface finish possibilities.
Eventually, Ellis & Ellis decided to research other processes and equipment to produce the intricate ADA compliant Braille they needed to manufacture these way-finding signs. Ultimately, they decided on a DATRON M8 high-speed machining center after demonstrations proved that the machine was not only capable of producing spot-on Braille, but could also perform many other functions – thereby adding flexibility to their shop floor. (See aluminum and acrylic letters at bottom of Blog).
Plus, there were other factors involved in their decision. Rogers said, “Well clearly floor space in California has a premium cost associated with it and the DATRON’s footprint fit nicely into the small enclosed space that we designated for this process.” He added, “With the small footprint, it’s amazing that this machine provides such a large work envelope.”
Sign Engraving CNC Machine for Batch Machining
In fact, the DATRON M8 (as well as the newer M8Cube) has a 40” x 32” machining table made of solid polymer concrete that provides exceptional rigidity delivering the accuracy that Ellis & Ellis needs. The large work envelope is not diminished by the 15-station automatic tool changer located at the back of the table. This covered pneumatic unit includes a tool-length sensor which allows Ellis & Ellis to monitor tool life as a means of maintaining a high level of quality. In many cases, the signs that they manufacture are produced in batches and the tool length sensor helps in allowing them to run these parts unattended. Here’s how it works. Within the machine’s control software is a macro program that can be set up to run a tool check after executing a number of lines of code. For instance, a tool check macro can initiate a check after every 500 lines of code. This is known as an “if/then” statement, in other words, “Measure this tool; if the length is shorter than the listed parameter, then change the tool.” As a result, if a tool becomes dull in the middle of running a batch of signs, it is replaced automatically even if the machine operator is not present. This helps to maintain quality and minimize waste.
However, running batches of signs, whether unattended or with the operator present, requires the ability to accommodate and fixture sheet material from which the individual signs are milled. So, Ellis & Ellis was pleased to find that DATRON manufactures their own vacuum table workholding. In the case of their M8 machine, the vacuum chuck is affectionately known as a QuadraMate due to its four independently activated 12” x 18” segments – which can also be simultaneously activated providing a full 24” x 36” of workholding.
Bill Rogers said, “The vacuum table combined with the machine’s integrated probe makes it so easy to set up a job – it’s faster and takes out the element of human error.”
That’s because once the operator sets the material on the table, even if it is not situated perfectly straight, the probe takes measurements that compensate for that. In fact, even if there are irregularities in the material such as surface variance, the measurements are fed into the control software and the program is adjusted accordingly. Since Ellis & Ellis performs so much alphanumeric engraving and milling to produce their signs, this guarantees an even depth of those characters even if the material topography is not consistent. According to Rogers, “All of this equates to more efficiency, higher quality, less waste and ultimately cost reduction.”
The machining center itself is not the only area where DATRON has helped Ellis & Ellis add efficiency to their operation — and Bill Rogers says that they have become quite a proponent of DATRON solid carbide cutting tools. “We saw the exceptional performance of DATRON tools being used with the DATRON machine in terms of cut quality and tool life, so we decided that we’d give them a try on some of our larger machines.” Those larger machines include MultiCam CNC Routers, and as they anticipated, the DATRON tools did, in fact, improve the performance of those larger machines. Bill said, “In terms of tool life, we’re looking at an improvement of about 3 to 1 which is a big cost saving over time.”
In addition to using DATRON tooling with the MultiCams, they also decided to try DATRON’s coolant with these routers and that too helped to impact cutting quality.
Bill Rogers said, “Staying competitive means trying new things, new technology, and always looking for ways be more efficient.” To that end, Bill and his team are frequent visitors at the DATRON Technology Center in Livermore, CA. According to Rogers, “DATRON has informal events like TechDay at their facility where we can go see advancements in the technology. I can always count on their guys to get us the answers we need. It’s a great partnership.”
In the world of computer-controlled milling equipment, there’s always been something of an understanding when it comes to work envelope and precision: as the ability of a machine to achieve ever smaller numbers when it comes to positional accuracy and repeatability goes up, the size of the work envelope (and therefore the largest part you can physically fit in the machine) must go down. Now, like any rule of thumb, there are exceptions to this out there – but these exceptions generally carry with them one significant caveat: they’re expensive as all get-out. Enter DATRON MLCube LS Large Format Milling Machine with linear scales.
There are many legitimate reasons that this convention has become the norm. In ball-screw-driven machine tools, using a ball screw with a very tight pitch to achieve stellar accuracy and repeatability usually results in a decrease in the maximum rapid rate – which is a real bummer if you need the machine to move large distances. Technologies such as linear motors are capable of moving very fast over long distances, but sacrifices often need to be made when it comes to resolution and accuracy of the encoders that feedback the motors motion to the machine’s control system. Even linear scale technologies, while being readily able to increase a numerically controlled machining system’s ability when it comes to accuracy and repeatability, must by default be an additional piece of hardware which accompanies the linear motor or ball screw/linear guide system. Any additional hardware, as any engineer will tell you, is subject to damage, misalignment, or in the case of milling equipment -contamination from the chips, dust and coolant that are part of the milling process. It would seem that the combination of large, capable, precise, and economical has been an elusive one in machine tool industry.
Fortunately, this very problem that the DATRON MLCube LS has been created to solve.
Linear Scales for Precision in Large Format Milling
The ML Cube LS represents the latest in a long lineage of ever improving portal/gantry designed CNC milling equipment from DATRON. Building on the success of the DATRON MLCube, which provides 3 m/s2 acceleration, advanced dynamics and jerk control, 0.1 micron resolution, and the ability to exercise up to 60,000 RPM across its 60“ by 40” work envelope, the MLCube LS makes the significant addition of an integrated linear scale system on X and Y axes.
To avoid the hurdles common to achieving tight accuracy across a large area, DATRON engineers have employed a unique combination of technologies that together present a robust and highly precise positioning system: the integrated measurement system. This integrated system marries the accuracy and repeatability advantages of the external linear scale, with the well-established and optimized mechanics of the ball screw-driven / linear guide axis. In the same way that unifying a servo motor with the associated ball screw by eliminating the drive belt, the ball screw/linear guide/linear scale system benefits in its operation and longevity overall by combining components and optimizing the system.
Benefits of Large Format Milling Machine MLCube:
Benefits if this unification are numerous, but in the case of the MLCube LS the most significant benefits show themselves where they matter most:
System is free of wear or maintenance
Highly resistant to contamination
Exact positional measurement is achievable even under dynamic load changes
Effects of thermal expansion are essentially eliminated
Scale system is completely free of external influence by magnetic fields or electromagnetic vibration
Positional accuracy is improved by 50% compared to the same machine without linear scales
But at the end of the day, the real question is: Why should I care about this machine? Well, fortunately, that’s the simple part:
With a starting price of just under $250,000 including typical options and a positional accuracy of ±25µ across nearly 17 square feet of workspace, the MLCube LS arguably offers the most capability, across the largest work envelope, with the highest degree of positional accuracy, for the least amount of money.
So whether you need to produce a few very large and precise parts, or you need to batch machine hundreds of small precise parts in one long unattended machining session – the MLCube LS offers advantages that are not easily matched.
Download DATRON MLCube LS Large Format Milling Machine Brochure
With additive manufacturing and 3D printers being such a hot topic these days, it’s important to remember why subtractive processes like milling are still incredibly important to rapid prototyping. But first, let’s examine some of the benefits and limitations of additive rapid prototyping (or direct digital manufacturing).
Benefits of Additive Rapid Prototyping
The process of additive rapid prototyping joins and fuses materials like liquid resins together, layer upon layer to produce a 3D object from model data. Additive rapid prototyping is generally simple, relatively inexpensive and fast. Additive rapid prototyping also allows for a substantial amount of complexity within cavities or internal areas of a part that would require undercuts and may even be impossible with subtractive processes like milling.
Limitations of Additive Rapid Prototyping
The primary drawback of additive rapid prototyping is that the resulting part usually is not made of an end-use material like metal … and even if it is, it lacks structural integrity. That’s because the point where one layer is joined to another lacks the physical strength exhibited by a solid block of the same material (with no layers or joints).
Subtractive Rapid Prototyping with End-Use Materials
Subtractive rapid prototyping provides the ability to prototype in end-use materials. Since milling or machining removes material from a larger piece of material, the finished part has a solid composition rather than a layered composition as seen in additive rapid prototyping with 3D printers. This yields a higher structural integrity which is critical if the prototype part is to be used in product testing. Product testing with a part made through subtractive prototyping allows for an accurate analysis of the part’s viability and even durability since it is made from the same material that will be used to manufacture production parts.
A Wider Range of Surface Finishes and Textures with Subtractive Prototyping
Subtractive rapid prototyping processes also offer a wider range of surface finishes for the completed prototype as opposed to the standard “stepped finish” often achieved in additive rapid prototyping with a 3D printer. This could range from a completely smooth surface with a mirror-like finish to ones with milled or engraved textures. In this way, subtractive rapid prototyping with a high speed CNC milling machine is capable of producing prototype parts with a repeatability suitable for end-use production. The smooth surface finish that can be achieved with high-speed machining can be functionally beneficial if the given part needs to slide and aesthetically beneficial if the prototype is going to be used in market testing.
Additive Rapid Prototyping vs. Subtractive Rapid Prototyping
To illustrate the points made above, we asked our applications engineers to quickly prototype a part using both additive and subtractive processes. Since our favorite after-hours (wink, wink) past time is foosball, they decided to make a “replacement” foosball man for testing. This decision was based on an actual real-life need – since we had recently broken one of the men that came with our vintage 1985 foosball table. Using additive rapid prototyping (3D printing), they were able to design a very rudimentary foosball man in about 90 minutes. From there, they began printing and in just over an hour the part seen below was complete.
Using subtractive rapid prototyping (high-speed milling) programming the part took substantially longer and clocked in at 3 hrs. 45 minutes. However, milling the part below was considerably faster than 3D printing and took 28 minutes.
Product Testing an Additive Rapid Prototype vs. a Subtractive Rapid Prototype
Well, you knew we had to “test” the part right? So, in a series of 4 rather heated games using each prototype, here’s what we found. In terms of functionality and durability, the subtractive prototype was the clear winner. Not only did it last through the 4 games, the solid composition of the part made for stronger shots with high velocity. Plus, it clearly would hold up for hundreds of more games. By comparison, the 3D printed part began to show signs of delamination on its right side half way through game 3 — and by the game 4 we had to mend it with a bit of scotch tape to get through the rest of our “product testing”. The damage to the part revealed the inside composition of the 3D printed part as seen below.
The rather hollow nature of this part shined a bit of light on why we couldn’t achieve strong shots using this foosball man. In analyzing the resulting surface finish on both parts, we felt that the subtractive prototype was … well, simply more attractive. Plus, the milling process provided more flexibility to achieve different surface finishes. For example, we were able to make the majority of the subtractive prototype very smooth while giving the foot section a more textured finish for added “grip” or ball control. By contrast, the inherent “stepped” surface finish on the additive prototype served well in terms of ball control … but wasn’t very attractive over the entire part.
The Ultimate Subtractive Rapid Prototyping CNC Machine:
Last year’s introduction of the DATRON neo compact high-speed milling machine makes subtractive rapid prototyping more affordable and viable than ever. Plus it’s compact size and touchscreen operation make it easy to use and easy to fit in the tightest “lab-type” environment. To learn more download the brochure by filling out the form below:
So here we are. You have read all of my eloquent, informative, and groundbreaking (perhaps a minor exaggeration) blogs. You are ready. You have a pencil behind your ear and a calculator on your desk and you’re going to trust in the numbers! Slow down there cowboy, because the most important thing to remember is the numbers, formulas, and suggestions are just that – suggestions. They give you a reasonable starting point. They get you in the neighborhood but some good old CNC machinist trial and error might be in order. I know, if you bought an expensive GPS unit for your car (who buys those anymore?) and it GUARANTEED to get you within ten blocks of your destination and left the rest up to you then you might wonder why you bothered. Well my friend, if that building you were driving to was constantly moving and changing based on the simplest of variables then ten blocks isn’t too shabby. Besides, you got my Shop Math formulae for free. Stop complaining.
Control the Variables
The point is, no matter how sophisticated your CNC machine, software, tooling, or ego is you will always have to make adjustments. Sometimes minor, sometimes major. It all depends on what you are doing and how you are doing it. There are an endless number of variables involved with machining so I won’t even attempt to touch on all of them. The name of the game is eliminating or at the very least CONTROLLING those variables to get consistent results every time. Let’s say you set up a new job on Monday morning. This job uses eight tools and takes approximately two hours. The tools do well all day Monday and when you come in Tuesday morning the second shift guy tells you he had to look busy so he swapped out all the tools. When you ask if they were worn out he replies “I dunno.” You would think they would be smart enough to put a competent human being on second shift since there is far less supervision, but trust me I know how that goes. Anyway, you have many issues now. Judging by Gomer’s attitude and general work ethic you can assume that none of the new tools were properly measured before he put them in. So it’s time to get to work – measure all your tools, check your zero points, make sure your speeds and feeds are good. Should be all set, you say? Guess again. Same program, same machine, right tools, everything looks good. That doesn’t mean it will cut the same as it did yesterday. Or even two parts ago. Depending on the tolerance you are working with something as simple as the ambient temperature and humidity can affect the final result. This is where some CNC machinist trial and error comes in.
Warm Up the Spindle
Before you decide a program is ready for production and release it to Gomer, you need to make some determinations. First off, make sure no matter what that you always warm up the spindle. If you warm up the spindle properly before running your first job of the day then you will ensure that thermal expansion in the spindle will not become one of your variables. That way the fifth part will come off just like the first. Also, any time your machine is going to sit more than a couple hours it is a good idea to do a warm up, especially if you are working with tight tolerances.
Know Your Tools & Standardize Your Tool Library
Another consideration when preparing a job for production is tool life, so you can avoid the problem mentioned above. By testing and running through some “CNC machinist trial and error” you will learn a lot about tool life and be able to compile some simple information and expectations. You will find that the more you do this, the faster and easier it will become. You will reach a point (especially if you followed my advice from my previous blogs and set up a standard tool library) that the information will just be there and suddenly your reference material will be right off the top of your head. Once you know your tool life you can be much more proactive in your approach to shift change and work flow.
Trial and Error with Feeds and Speeds
CNC machinist trial and error also comes into play when efficiency and productivity are the goals (when are they not?). So my suggested speeds and feeds get the part done in twenty minutes, but if I take a 10% lighter cut and increase my feed 20% then the part is off the machine faster, and my tool will last for eight parts rather than five. I have cut time, increased tool life and made the boss happy. What about QC? Are they still happy? OK, so my surface finish suffered a little, but it’s still within specifications so we are good. Success!
Don’t be Afraid to Push the Envelope … or Break a Tool
If there is one thing for you to remember it’s that ERROR is half of trial and error. The best machinists I ever worked with broke tools on a regular basis, just because they wanted to see what they could do. A little bit of CNC machinist trial and error, pushing the envelope, will get you farther than you may think. You will discover very quickly that the envelope is far more expansive than you imagined.
Learn More: Download the High Speed Machining White Paper:
Have you ever wondered why after milling a hole or pocket that it measures larger at the top of the cut than at the bottom? Or why your gauge pin fits nice and snug in the beginning of the hole but won’t quite make it all the way through? The simple answer is tool deflection. Everything bends. And I mean everything. Tool deflection is an omnipresent yet little understood problem. Worry not my fellow machinists, because it is not your fault! There is no eliminating tool deflection, only controlling and minimizing it. Knowledge is power, and hopefully by the end of this post you will have a working knowledge of the causes of tool deflection and potential solutions.
Simply put, tool deflection is the bending of the tool. When you cut a feature, for this example we’ll say a deep pocket. While cutting you are applying forces to the tool and the material. The material gives, which is why you get chips. However, it does not go down without a fight. When the material pushes back it forces the end of the tool in the opposite direction of the forces being applied to the material. The farther the tool sticks out, the farther the end of the tool will move.
It is possible to calculate tool deflection, but the math involved is quite complicated. If you spend any significant time in a machine shop then you know how often optimization is achieved with your eyes and ears – I consider those two things the most important tools a good machinist can have. However, if you would like to calculate some numbers for tool deflection there are multiple calculators available online. For the purposes of today’s post we will rely on our trusty eyes ears and little bit of that common sense.
Rigidity is the most important factor. As you increase the distance your tool sticks out of your tool holder the rigidity decreases exponentially. There are situations when you need the length, in which case, your best course of action is to use the largest diameter with the least number of flutes. As you decrease the diameter of your tool you also decrease the amount of force required to make it bend. Also, every flute on your cutter reduces the rigidity of your tool. If you are cutting a deep feature, you want to make sure that you are using the largest diameter the print will allow in order to optimize tool performance. Even if you need to rough with a larger diameter tool, and finish with a smaller tool in order to meet specification on your corner radii that’s OK. You also want a tool with the least number of flutes, and only stick the tool out as much as you truly need to. When researching tools, you will find that there are tools for which rigidity is a major concern and many “micro” tools come with a tapered shank to increase rigidity.
Carbide Tools vs. High Speed Steel Tools to Reduce Tool Deflection
If you think tool deflection is an issue, or you are performing cuts aggressive enough that it is causing you problems, then one thing you should always consider is carbide tooling. Aside from the benefits like higher SFPM and better tool life, carbide is about three times more rigid than high speed steel. Keep in mind however, that carbide is extremely brittle – that is not a good combination when talking about tool deflection. It takes more to deflect it, but if you provide enough force the tool is not as forgiving and will break, so beware.
As discussed in my “Climb Milling vs. Conventional Milling” blog post, cutting strategy can affect tool deflection. Utilizing dynamic toolpath strategies (see my blog post “Dynamic Milling”) can assist in minimizing tool deflection due to the light radial cut. If you rough the feature using a dynamic toolpath and make sure you are climb milling then you should be happy with your results. As discussed in these other posts, for the finish you have a couple options – either climb mill the finish or conventional mill a spring pass, or conventional mill a light finish pass with lubrication and you will be very happy with your results.
Hey folks, today we are going to talk about threading in multiple forms. For the most part I am going to discuss my experiences with the different types of thread cutting/forming, so if you are looking for tons of technical information I apologize, but there are so many variables when it comes to the threading –perhaps I can write a more technical blog on each type of thread forming. For now, we are going to give a general overview of cutting threads based on my experiences and opinions. I know, opinions are like… well, you get it, just stay with me and hopefully I can provide some insight.
First and foremost we have cut taps. In my experience cut taps are the most widely used across most industries. Cut taps are reasonably cheap and very versatile. You have all seen the drill charts that give you the tap drill sizes required for different threads. Pretty straight forward – drill the hole to the right size and depth, countersink the hole, then tap it. Cut taps can be used by hand, on a drill press with a tapping head, on a knee mill, or rigid tapping on a CNC machine.
Creating Threads in Through Holes with a Cut Tap
When determining which tap you need you should pay attention to the type of hole you are tapping. When tapping a through hole you can use a standard cut tap which has a lead on it. The lead is the tapered portion on the end of the tap that essentially centers the tap in the hole when engaging.
When tapping a through hole you need to make sure you go deep enough to cut threads all the way through the hole – the length of the lead will depend on the size of the thread. The larger the thread the longer the lead.
Threading a Blind Hole with a Bottoming Tap
However, if you are tapping a blind hole you would be wise to consider a bottoming tap. A bottoming tap has the lead almost completely ground off. This allows you to engage the tap deeper into a blind hole. These are used when there is a tighter tolerance on the depth of the hole, in situations where a hole too deep will break through into a feature. This is due to the main problem with cut taps … CHIPS. When using cut taps in a blind hole, regardless of standard tap or bottoming tap, you need to make room for chips. As the tap engages the hole it is cutting the thread geometry out of the material, therefore creating chips. Since you are engaging from above the chips are forced down in the hole along with the tap. If you do not provide enough room at the bottom of your hole, then you will break your tap. Simple as that. That is why bottoming taps are so helpful in blind holes – with a very short lead you do not have to drill as deep to form full threads to a certain depth. Keep in mind, there are taps available with helical geometry with the goal of lifting chips up out of the hole. In my experience, I have gotten mixed results. The complex geometry ultimately weakens the tap, so if you are tapping a tough material be careful. Just make sure you do your homework.
The Strength of a Roll Form Tap
Next, we have roll form taps. When I first discovered roll form taps, I was in heaven. It was after a particularly frustrating week of broken taps and bad parts. Chances are if you are reading this then you have had some of those weeks. We all have. Roll form taps are much stronger than cut taps, and the geometry is completely different. The one drawback to roll form taps, and a major reason most shops I have worked for never adopted them completely is because the standard tap drill size no longer applies. Most standard drill charts (the large ones you put on the wall in the shop) now have standard tap, roll form tap, metric tap and STI tap drill sizes all listed separately. However, after years of using standard taps many of us don’t reference the chart as much as we should, and since the hole for a roll form tap is significantly larger than that for a cut tap, bad things can happen. A roll form tap does exactly as the name hints – it forms the threads rather than cutting them. When the tap engages the hole rather than cutting material away it changes the form of it, and shapes it into the thread geometry. If you have ever done any work for a defense contractor, this is why most prints will have a note that all threads must be formed by a cut tap. The military generally frowns upon operations that change the structure of the material, at least in my experience. They also frown upon castings as opposed to solid plates for complex parts – too much unknown in what you can’t see. Anyway, roll form taps are great. They are difficult to break (no, that’s not a challenge) but they also require a bit more torque. I have really only used roll form taps in aluminum and other soft materials, rarely in cold rolled steel. I am not sure how they perform in harder materials, but most shops don’t like the idea of two sets of drills for the same size thread, which is why they are not more widespread.
The Versatility of Making Threads with a Thread Mill
The final type of thread cutting is thread milling. Thread milling is a great operation that seems scary at first, but once you get it down it is truly amazing. There are many different types of thread mills, which I will get into in a different blog post. For now, I will discuss a single point thread mill. With a single point thread mill, you have great versatility, with most thread mills cutting a wide range of threads. You can create custom pitch threads, right hand or left hand, inside threads or outside threads all with one tool. Since I have recently started using helical boring for my holes rather than drilling, you can accomplish many different holes, with many different threads all with two tools. You bore a hole to the minor diameter of the thread, send the thread mill in to cut the threads, and you can use the thread mill itself to chamfer the top of the hole, as long as it doesn’t have to be a ninety-degree countersink, since most thread mills will be somewhere between thirty and sixty degrees. Due to the geometry of the tool, the only distance you need to make up for is from the outside edge (cutting edge, or point) of the tool to the flat tip, which is generally less than .02” on the smaller thread mills. The real benefit here is that once you mill the hole, you can send the thread mill to the bottom of the hole and mill from the bottom up, rather than top down. By doing this you are avoiding any concern of the tool running into chips at the bottom of the hole since you are moving away from the bottom of the hole. Looking at the thread mills you may not believe at first that it is going to do what it is supposed to. I know when I used one for the first time I was sure it was going to break – but it didn’t. Thread milling is the most versatile and efficient of thread forming strategies, and it is going to be my go-to from here on out unless there is a good reason I can’t do it.
Do your homework, know your tools and your materials and approach anything you do in the machine shop with a good understanding and clear head. This doesn’t change when you are threading holes. Trust the numbers, and in this case, don’t be afraid of trying new things. I always scoffed at thread milling – I only wish I had found it sooner. Stay safe folks.
If you have spent any considerable time in a machine shop I am sure you have heard the term “dynamic milling.” There are many other names out there depending on the CAM software you use – Edgecam calls it “Waveform” while Surfcam calls it “TrueMill.” Solidcam calls it “iMachining” while Mastercam calls it “Dynamic Milling.” You get the point. Every CAM package will claim theirs is the best, and while they may approach certain cuts differently, they are all based on a simple principle that in practice will give you amazing results. I have been a machinist and CNC programmer for ten years, and my first experience with dynamic toolpaths had me speechless. Today I hope to open that same door for you.
Dynamic toolpaths are not a new concept by any means. There is a very good reason many machinists have long used light depth (axial) cuts with heavy side (radial) cuts to achieve their machining goals. Any machinist who has been in the industry more than 25 years remembers a day when CNC was the minority. Current CAM software allows for significantly more complex and lengthy programs and precision. When you are turning handles on a Bridgeport maintaining a 10% step or a specific chip load would be impossible with dynamic motion involved. Can you imagine hand writing and punching tape for a 600,000-line G-code program? It’s been done, but it certainly can’t be called efficient. So it’s not for a lack of knowledge, simply a lack of technology that dynamic toolpaths are not standard practice … yet.
Maximize Tool and Spindle Life with Dynamic Toolpaths
Dynamic strategies have a very simple principle – maintain a constant chip load throughout the entire cut utilizing a full depth (axial) cut and very light side (radial) cut. The benefits you will see from this type of cut include longer tool life, longer spindle life, improved surface finish, greater efficiency and awesome rooster tails. No really though, I’m not joking. You are going to have people standing there watching the machine run just because of how the chips are flying.
First and foremost is tool life. I will also throw spindle life in with tool life because they really go hand in hand. You get multiple benefits for both your tool and spindle if you properly apply dynamic strategies. If you are cutting a pocket or any internal feature that doesn’t allow an approach from outside the material, then entry into the cut is not only the first consideration, but one of the more important. I always use a helical entry motion with a 1%-3% helix angle, or entry angle. You want to use an entry diameter that is somewhere between 120% and 150% of your tool diameter – be careful, sometimes the CAM software asks for a radius rather than a diameter and that information makes a huge difference. Once you are at depth the real fun begins. Due to the light radial cut you can really be aggressive with your feed rate. Depending on the limits of the spindle RPM, use the tooling manufacturers specifications on chip load and surface feet per minute (check my blog on shop math). In my first experience with a dynamic toolpath I was running a 3-flute .500” end mill with a 1.5” flute length. The cut was 1.375” deep, with a 10% (.05”) step over with a feed rate of 144 inches per minute. I used a high helix end mill to assist in chip evacuation which created a “rooster tail” of chips trailing the cut. It was a thing of beauty. Even though the cut was so fast and seemingly aggressively deep, the tool lasted through 32 parts and gave the same finish on part 32 that it had given on part 1. The full depth cut means that you are wearing the entire flute length evenly, therefore you are not going to get lines on your finish. The light radial cut reduces the cutting forces, thereby reducing overall wear on both the tool and the spindle.
Efficiency is also a significant benefit. Pretend for a moment that you are cutting a 1.375” deep pocket with features at 4 different depths. Using a standard toolpath and a light depth with a heavy step over you will cut from the top of your part down. Depending on how aggressive you are with your step down you will cut many passes on each depth, with the deepest being the most time consuming. Utilizing a dynamic strategy you will cut from the bottom up, meaning each depth will consist of one pass, with all previous passes having already cleared out other material at that depth. Therefore, at each depth you are only cutting the remaining material, essentially creating a “rest rough” toolpath that minimizes total machining time.
With dynamic toolpath strategies you will not only improve tool life, spindle life and surface finish but also overall cycle time and cost efficiency. Not to mention you will impress the boss and anybody else who happens to walk by. Do me a favor, and give it a shot. You won’t be sorry you did.
This may seem like a strange topic for a blog post. Burrs, really? Snorefest, am I right? I understand, trust me. Let me ask you one question before you move on to the next post, what do you do to your parts after they come off the machine? Depending on your coolant you wash them, then are they ready to go to inspection? No sir, nine times out of ten they are not. When the part comes off the machine there is almost always some form of deburring operation. Unless of course the programmer includes small chamfers on your part as a deburring operation inside the program. Either way, when you spend as much time as you do performing a single omnipresent function, how could it be as trivial as everyone seems to think? I have worked from prints dating as far back as 1938, and even that print had a note on it requiring all sharp edges and burrs be removed. This post is intended to shed some light on the often ignored topic of burrs, and perhaps teach you a bit in search of strategies aimed at eliminating, or at the very least minimizing burring on your machined parts.
Burrs are a concern for multiple reasons. First and foremost, they can cause dimensional issues or fit issues. The dimension on your part may be right on, but if there is a burr on the edge then subsequent parts may not fit. Along those same lines, depending on the location of your burr you could have a part that is in fact within tolerance, but measures out of spec because of burring. Another major concern when dealing with burrs is cost. Deburring, like inspection, is not a productive operation – you are not producing parts, simply making the parts that you already produced meet requirements. Since the operation itself is not making money, it must be costing money. You know how it works – if it costs money, do less of it. It doesn’t matter how unreasonable the request may be, just do the same thing you’ve always done. Only, do it faster. And for less money. And with no overtime. I digress – deburring operations can be reduced, which will make you more efficient and your department more profitable. Many studies have been done on the causes of burring, and one of the reports I read was somewhat eye opening. On a part of medium complexity it is estimated that deburring accounts for 14% of the total manufacturing cost.
There is a lot of money to be made by optimizing strategies and tooling selection. One of the more common culprits is the tool you are using. Always make sure your tools are sharp, since a dull tool can cause serious burrs even with the optimal tool path. In fact, watching for burrs is one of the best ways to monitor tool life, at least until you have a good understanding of how your go-to tools are going to perform. Also, this is one reason it’s a good idea to use a different tool for finishing than you do for roughing – that way you ensure the best finish and also limit burring.
Minimize Burrs in CNC Drilling Applications
When it comes to drilling, many of the same rules apply. A dull drill is going to give you larger burrs on the bottom of your part when you drill through – fresh drills will help with that. One of the simpler causes of burrs when drilling is not drilling deep enough. When you are drilling through your part you need to make sure you make up for the angled tip – the larger your drill diameter the deeper you will need to go. Drilling too shallow will result in what almost looks like a cap on the bottom of your part, not to mention a taper at the bottom of your hole. If you drill deep enough with a good, sharp drill you should be good to go.
Burrs are a frustrating, time consuming problem that you will always deal with on some level. Just take care of your tools, mind your feeds and speeds and make sure you are drilling deep enough. It can be more efficient to utilize your CNC machine to deburr in process, just keep in mind there will always be geometry that you will need to deburr by hand. Get next to it folks, cause it’s never going away. Just keep it under control. Until next time, be safe and mind the numbers.