Below are excerpts from a Cutting Tool Engineering article by the same title. To read the entire article please click HERE.
Author Kip Hanson, Contributing Editor, Cutting Tool Engineering
Kip Hanson is a contributing editor for Cutting Tool Engineering magazine. Originally Published: September 12, 2017 - 3:00pm
Shopping for a machining center was simpler when buyers had only two basic spindle choices: CAT or BT. Both of these “steep tapers” have an angle of 3.5 in./ft., or 7" in 24" (7/24), and are based on the 1927 patent by Kearney & Trecker Corp., Brown & Sharpe Manufacturing Co. and Cincinnati Milling Machine Co.
With the development of automatic toolchangers in the late 1960s, machine tool builders in Japan modified the patented design and invented the BT standard. In the 1970s, tractor manufacturer Caterpillar Inc., Peoria, Ill., changed things again with a flange design now known as CAT, or V-flange.
During the late ’80s, machine tool builders began offering vertical and horizontal CNC mills with spindle speeds higher than the 6,000 to 8,000 rpm common at the time. As rpm increased, so did problems with steep-taper toolholders.
Chief among them is the tendency for the mating spindle and toolholder tapers to stick together. This is caused by the expansion of the spindle housing at high speeds, which allows the toolholder to be pulled upward into the spindle taper, jamming it in place.
HSK spindles, like the one shown in the illustration below, offer advantages steep-taper styles can't.
One way to eliminate this problem is by extending the toolholder flange upward, thus creating a hard stop against the spindle face and preventing further Z-axis movement.
This is the approach taken by BIG KAISER Precision Tooling Inc., Hoffman Estates, Ill. Jack Burley, vice president of sales and engineering, said the BIG-PLUS system—developed in 1992 by BIG Daishowa Seiki Co. Ltd., Osaka, Japan—relies on a bit of elastic deformation in the spindle to provide dual points of toolholder contact at its face and taper, eliminating upward holder movement as the spindle expands.
He said it’s also more rigid, with tests showing that the deflection on a CV40 BIG-PLUS toolholder measured at 70mm (2.755") from the spindle face is only 60µm (0.002") when subjected to 500kg (1,102 lbs.) of radial force, roughly half that of a traditional V-flange toolholder.
“There are now roughly 150 machine builders that either offer BIG-PLUS or have it as a standard,” Burley said. “The beauty of the system is that it can use either standard toolholders or BIG-PLUS interchangeably. So for drilling and reaming work, you can use a conventional collet chuck, but for heavy milling cuts or profiling operations at higher spindle speeds, BIG-PLUS improves accuracy and tool life.”
Burley does not recommend BIG-PLUS for older machines that have never seen these toolholders, because CAT and BT taper-only contact holders tend to bellmouth the spindle over time, leading to undesirable results.
BIG-PLUS, like any dual-contact toolholder, requires particular attention to cleanliness, as chips caught between the spindle face and the toolholder can cause serious problems.
He also recommends staying below 30,000 rpm when using 40-taper holders, noting that higher speeds are better handled by HSK spindles and holders.
Keep It Clean
Bill Popoli, president of IBAG North America, North Haven, Conn., said the company started building steep-taper spindles in the late ’80s, but 95 percent of its work has since transitioned to HSK spindles. As mentioned earlier, the extreme accuracy needed to guarantee near-simultaneous contact between the spindle face and taper is challenging, requiring micron-level tolerances in toolholder and spindle alike.
These requirements were impossible to meet when steep taper was first developed, Popoli said, resulting in looser standards overall for CAT and BT spindles than the ones applied to HSK spindles and toolholders. Because of this, purchasing an HSK or equivalent toolholder automatically makes one “part of the club” when it comes to balance, accuracy, repeatability and tool life.
That’s not to say, however, that shops firmly married to steep tapers should settle for less. Popoli recommends purchasing the highest-quality tooling possible and paying close attention to the stated tolerance.
Always stay below 20,000 rpm with 40-taper holders, and reach no more than 30,000 rpm with 30-taper ones. Use balanced holders and high-quality retention knobs that have been properly torqued—otherwise distortion at the small end of the taper may occur. And whatever the taper type, keep the spindle and toolholder clean at all times.
Bob Freitag agreed. The manager of application engineering at Minneapolis-based metalworking products and services provider Productivity Inc. said the lines are evenly split between traditional 40- and 50-taper CAT or BT tooling (much of which is BIG-PLUS) and HSK.
“It really depends on the application,” Freitag said. “Most of our die and mold machines in the 20,000- to 30,000-rpm range will have an HSK63A or HSK63F. When you get up around 45,000 rpm, you’re probably looking at an HSK32. But in horizontal machining centers and lower-rpm, high-torque verticals, you’ll see mostly steep tapers, as this is generally preferred for deep depths of cut and lower feed rates, where you’re removing a lot of material at once.”
For shops that want to make the leap to an HSK machine but are leery of investing in new toolholders, Freitag advised:
“Anytime you buy a new machine, you should buy new toolholders to go with it. If not, the imperfections of the old toolholders will soon transfer themselves to the spindle on the new machine.”
Precision Cutting Tools already holds one of the highest tolerances on shank diameter in the industry for their end mills. All PCT End Mills Shanks hold an h6 tolerance! That means that
1/8" - 1/4": -0.0001"/-0.0003"
1/4" - 1/2": -0.0001"/-0.0003"
1/2' - 1": -0.0001"/-0.0004"
A tighter grind tolerance often times will mean a much shinier polished shank. A polished shank is more apt to have lower coefficient of friction which makes it more prone to slip particularly while being held in a collet type toolholder.
We are very excited to announce that we are now able to offer on-site technical training to YOUR machinists at YOUR location! This is offered at no charge to customers who use any of the manufacturer's whom we represent in California and Nevada.
However, just because you don't purchase things from us, don't feel left out! We also offer on-site topic specter training on any of the following topics for $150/hour.
Each presentation lasts about 2 hours. The presentations last approximately 45-60 minutes with the remaining time for Q&A and discussion about unique applications in your facility.
Training Classes Available:
Advanced Part Manufacturing:
NTK's industry leading line of ceramic cutting tools recently expanded with new solid CERAMIC end mills! You can see our product announcement here: NTK now offers SX9 Ceramic End Mills for Cutting Exotic Alloys which contains the various features. Below is the technical info on how to run the NTK Ceramic End mills and a troubleshooting guide.
NTK's SX9 cermaic end mill grade can run at speeds of 2000 SFM. The line-up includes 4 and 6 flutes in inch and metric versions. Again, you can learn more about on our Blog Post.
Solid ceramic end mills are made with SX9 SiAlON grade substrate which features a balance of toughness and wear resistance. It's suitable for even the most demanding applications.
Gernarel Recomendations for machining heat resistant alloys & PH stainless steel
As with any other techncial questions please get in touch with us on our CONTACTS page and we can provide both over-the-phone troubleshooting or schedule at time for on-site techncial training.
Next Generation Tooling is excited to offer some new services coming in 2015!
Below is a very fast video of our new training series on Tapping which we can present to your manufacturing team at your site.
It's a comprehensive overview of screw thread terminology, thread forms, fundamentals of threads, classes of fit, Tap basics, types of chamfers, the tapping process,tap types, screw thread inserts, helix angles, core diameters, re an hook angles, thread reliefs, pitch tolerances, H limits, Tap substrates, Surface treatment and coatings, tapping speeds, tap drill sizes.
As the CNC manufacturing industry continues to grow we're meeting more and more new people coming into our industry. Although many experienced machinists have lots of knowledge, we're finding that the new people are asking questions about some things that may be common knowledge to the old hands. One of the questions relates to "Why the heck is the cone on the toolholder the angle that it is?" We're here to help answer that....
By now, many have undoubtedly heard that most steep taper (CAT, BT) Toolholders hold an AT3 taper tolerance or better. So what exactly is AT3?
Steep Taper, Fast Tapers & Locking Tapers
Before we get into the tolerance and specs it's important to understand that there are basically two classes of tapers:
Since Toolholders have to be automatically changed in the CNC machine you want them to be as close to a locking taper as possible (8°/side) without, well, 'locking' in place (7°/side)! This is also the reason the ER/DR style collets also are made to an 8°/side angle as well by-the-way.
What is AT3?
That brings us to the "AT" standard for steep tapers. "AT" is an ANSI/ASME (ASME B5.50-1994) and ISO Standard (ISO 1947 ) that runs from AT1 to AT11. Since the AT tolerance is essentially logarithmic, the lower the number the tighter the tolerance (and harder it is to 'hit' in manufacturing). In other words the difference between AT 3 and AT4 is NOT the same increase in tolerance as between AT3 and AT2. AT3 is harder to attain than AT4 and AT 2 is substantially harder to reach than the jump from AT 4 to AT3. Again, the lower the number, the tighter the 'self releasing' tolerance.
Most CNC Machines steep taper spindles are made to an AT2 Specification. In order to stay competitive most all toolholder manufacturers are holding an AT3 tolerance (or better). Because there are much fewer spindles made than rotary toolholders this makes manufacturing sense. The key words here to pay attention to is "or better" Just like when you make parts in your shop to a tolerance, that doesn't mean that every part is exactly the same. The parts are within a tolerance band. That's what the "AT" defines! So when a toolholder manufacturer says "AT3 or better" that can mean that some of the holders are actually holding an AT2 tolerance... and this is sometimes the cause of the tolholders 'sticking' in the spindle:Not because they are out of tolerance, but because they are actually holding a closer tolerance! (...nearer a locking taper)
By-the-way, most all steep taper toolholders are made from some derivative of 8620 steel and then case hardened.
Food for thought
So although most people think that the drive dogs on the spindle are doing the 'driving' of the rotation of the toolholder, it's actually the taper connection that is driving the rotation of the tool. If that wasn't the case, then you would see the drive dog notches in the toolholder start to show signs of wear when the spindle impacted them all the time. Afterall, the 8620 is only case hardened.
There are a couple of last things to make note of and think about:
So if you over tighten your retention knob (pull stud) it can expand the smaller part of the taper.
Collet Chuck Size
We often get asked to spec out tooling packages for new CNC mills and one of the questions we encounter most, or should, is how do you select the right toolholder collet size for your companies applications? The real choice is in the size of the collet chuck itself. So several considerations should be reviewed...
What size are your tools?
Your first consideration should be the size of end mills or drills you will be using most often. If you are doing smaller work you would require smaller diameter range collets. Generally you may prefer the ER16 and ER32 sizes. If the bulk of your tool requirements are in the mid range you can also use the ER20. The following is a list of tool diameters that can be used with each size collet chuck. Essentially, the most popular, and again, readily available from a number of sources, are the ER 16, ER20, and ER32... in no particular order.
How far do you need to reach?
A second consideration is the actual reach of the tool. Not projection reach, also know as “gage length” "l1" but projection diameter “D”. Obviously, stubbier is better for projection reach "L1". But, you also need to review the families of parts that you intend to run on the machine. If you intend to use the holder to "reach" into a tight fit then the OD of the projection "D" of the toolholder needs to be considered. Many shops don't always consider this and end up using much longer carbide shanked end mills to get into deep pockets when getting a smaller diameter ER collet and collet chuck would be much less expensive over the life of the job.
Sometimes there is just no getting around having a custom tool made. Give us a call at 916.765.4227 or email us if you just can't seem to reach into the part with your toolholder.
We often run end mill "tests" to determine which one performs best. Obviously, our goal is to "win' the test and get more business for our manufacturer's. This is article is about one our "tricks" and it's also why represent both cutting tool manufacturers and rotary tool manufacturers. We want to insure that the products work together.
As a general rule most cutting tool & tolholder manufacturers prefer to use single angle (ER/DR style) collet chucks for general purpose cutting tool applications under 1/2" (12mm). The rules are a bit different in High Speed Machining, as there are many more things to consider, but the problems of TIR at high speeds, where you can hear and feel the chatter, are still there in general end mill cutting operations at lower RPM. It's all about runout and uneven chip load.
End Mill Holders are prone to runout problems for a couple of reasons:
Depending on the application, end mill holders can be used for holding larger insert style end mills, spade drills, etc. But somewhere between 1/2” and 3/4” there is a line that only you can determine when you need to move from a collet chuck to end mill holder. Generally we recommend using end mill holders only for very specific applications
Using small diameter end mills (1/4" and below) in end mill holders with set screws will have a adverse affect of both surface finish and tool life.
Technical Support Blog
At Next Generation Tool we often run into many of the same technical questions from different customers. This section should answer many of your most common questions.
We set up this special blog for the most commonly asked questions and machinist data tables for your easy reference.
If you've got a question that's not answered here, then just send us a quick note via email or reach one of us on our CONTACTS page here on the website
Our technical section is written by several different people. Sometimes, it's from our team here at Next Generation Tooling & at other times it's by one of the innovative manufacturer's we represent in California and Nevada.