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Alternatives to steep tapers

12/13/2017

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Below are excerpts from a Cutting Tool Engineering article by the same title. To read the entire article please click HERE.
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Author Kip Hanson, Contributing Editor, Cutting Tool Engineering
(520) 548-7328
khanson@jwr.com
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. 
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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.

“Sticking” Together

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. ​
HSK Ibag Spindle Cutaway
HSK spindles, like the one shown in the illustration above, offer advantages steep-taper styles can't. Image courtesy of IBAG North America.
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.
For people who think they can’t take advantage of this technology because they don’t plan to buy a new machine, they might want to check with their distributor, as their machine may already be equipped for BIG-PLUS.
Big Plus vs Standard Steep Taper contact
​“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.”

Revving Up

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

clamping mechanism for HSK toolholders
The clamping mechanism for HSK toolholders is distinctly different from that of steep-taper holders. Image courtesy of BIG KAISER Precision Tooling.
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.
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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.”
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Remember to Replace Your Spindle Cleaners Regularly

8/9/2017

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Guest Blog: Douglas Sumner
Product Manager TMS
​BIG

douglas.sumner@us.bigkaiser.com
Tel: 224.770.2915

Remember to replace your spindle cleaners on a regular basis so that you aren't using worn out cleaners. What you think is helping to preserve your valuable Machine Tool/Presetter might actually be hurting it.

​When replaced regularly, spindle cleaners can prolong the life of your machine, tools & holders, and tool cleaners enhance the repeatability to the machine spindle. This is a perfect example of how a small investment can make a big impact.
CAT BT Toolholder taper cleaners
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Next Generation Tooling Now Offers Technical Training!

6/14/2017

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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.
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Training Classes Available:
Machining 101
  • Basic Boring
  • Basic Chamfering
  • Basic Drill Training
  • Basic End Mill
  • Basic Indexable
  • Basic Tap Training
  • Basic Tool Holders
  • Basic Work Holding / Fixturing​

Advanced Part Manufacturing:
  • Programming Tool Path – Climb versus Conventional
  • Material Machinability – Cubic Inches of Stock Removal
  • Part Set Up / Work Holding / Fixture 
  • Tool Holder Selection, Collet, Solid, Hydraulic, Shrink Fit
  • Cutting Tool Selection – Substrate, Geometry, Coating, Speed and Feeds 
  • Estimating Part Cycle Time
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Rotary Toolholder Maintenance Best Practices

8/12/2015

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To get the maximize life our of your Steep taper rotary toolholders in your CNC milling machines here are some of the best practices you can implement in your shop.  Perhaps not all of them can be implemented every day or every time but it's well worth being aware of how to best protect your investment.
  • Take the toolholder form the Spindle after each usage
  • Clean the taper and the holder with a an air blast to remove any fine chips or dirt that may be adhering to the holder
  • Wipe the holder with a clean shop rag
  • Spray the holder down with anti-rust lublcricant
  • Put the holder in an antitrust bag 
  • Place the holder in the proper storage rack for that type of holder. 
  • If you are not going to be original shipping container using it again for some time, store it in the original shipping container
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AT3 Taper Tolerances

8/20/2014

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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: 
  • Locking tapers - These can be at any angle less than 7° per side (14° included). The shallower the angle the better the holding. 
  • Self Releasing or "Steep Tapers" - These tapers are typically made with short shanks and with an included taper angle of 16° or 3.5" (88.9 mm) per foot.   These are also sometimes called "Fast Tapers"
  • Toolholders are 'case hardened"
  • Taper fit to spindle is critical
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Most of the taper standards originated in the early days of the aircraft industry with rotors and propellers. There's quite a bit of thought that went into why the two types of tapers exists: It has a lot to do with "Van der Waals Forces" if you want to know about it in more detail.  
What's important to know is that CNC spindles are made with Steep Tapers. Why? Well, just as the two names state the first is "locking" taper and the second is "free-releasing"  
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.
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Advantages of the ER Collet System

7/17/2013

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ER, IT’S IN THE DETAILS

The ER collet system has several advantages when using today's CNC computerized milling machines. The most significant advantage is flexibility to hold any type of round shank tool. An ER collet can be used in drilling, reaming, and tapping as well as milling applications just by exchanging the collet. Its accuracy also provides greater tool life than older style collet systems like TG or DA.

Another advantage is the flexibility of the collet for clamping a wide range of tool shanks with a small number of collets. ER 16 through ER 40 provide a collapse range of ~.039" flexibility for clamping cutting tools. This is a benefit for you because you will not have to carry as many collets in inventory for the different jobs you need to do each day.

The ER collet also provides more holding power by using two principles.
  1. The first is the 8 degrees (16 degrees included) back taper which is based on the engineering principle that 7.5 degrees is a mechanical lock for tapers. You notice that steep taper toolholders (CAT & BT) have the same taper for the same reason.
  2. Secondly, the ER collet has a larger front nose taper than many other collets. It's 30 degrees and provides more surface area for the nut to contact the collet. This translates into higher clamping pressure against the shank of the tool. Most manufacturers can also provide a bearing nut, which enables the clamping power to increase by 100%. Coated Nuts can increase this clamping power even more.
ER Collet diagram
In addition to mechanical differences, the ER collet is also user friendly. It is a self-extracting collet, which eliminates the need for collet squeezers to extract the collet by any other means than screwing the nut off. This enables the operator to spend time running the machine, not extracting collets.
These basic principles allow the ER collet system to be the most widely accepted collet system in the world for holding round shank cutting tools.

ER style collet chucks should be used for the bulk of your needs. They are the most dependable, with the least runout, both in and out of the cut, are readily available (so the prices continue to drop) and will give you the best tool life out of the lot of them
ER Collet Range Inch Metric
Advantages of the ER Collet System
  • Flexibility - Drill, tap and ream with same collet holder.
  • Accuracy - all collets are 100% examined for accuracy.
  • Longer Tool Life - Less runout, greater tool life for carbide tools.
  • Wide Clamping Range ~.030"
  • Less Inventory of Collets - Larger clamping
  • range reduces inventory.
  • Easy to Use - Self-extracting collet from holder .
  • Can effectively eliminate the need to dedicated tap holders.
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Rotary Toolholders: Understanding the problems to watch

12/12/2012

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Modern CNC machines feature high-capacity tool changers that automatically swap toolholders in and out of the spindle as needed, by means of a high speed swing arm or a rotary carousel. Periodically, toolholders should be examined for wear and if necessary replaced to maintain cutting performance.

New operators should be taught how to properly evaluate toolholders so they can recognize when toolholders need to be replaced to prevent premature cutting tool failure, or even expensive damage to the spindle. Many operators do not know why it is necessary to replace their tooling, or have the experience to tell when it is time to do so.
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Determining if toolholder components need to be replaced is not a difficult task, but does require that the operator knows what to look for. Here's a few things you should be aware of when checking your rotary toolholders.
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ATC Alignment Issues

It’s crucial to maintain proper ATC swingarm alignment. If the ATC does not insert the toolholder perfectly, damage to the spindle and toolholder may result. Also poor cutting tool performance and reduced tool life will be evident. A trained professional will be required to check and repair ATC issues.

Evaluating Toolholders for Wear

A worn out toolholder will not provide good accuracy and will quickly wear out your cutting tools. Worn tooling can also cause poor surface finish, and may even damage your spindle. Keep and eye out for these issues and your tool life, surface finish and cycle time will all improve to help you make more money on every job in your machine shop.

Special thanks to TechniksUSA for providing this detailed information!

Checking For Spindle Mouth Wear

A worn spindle can cause runout issues that affect toolholder accuracy and reduce cutting quality and productivity. This is a condition known as bell mouthing. If toolholder issues can be eliminated by bench checking T.I.R., then the source of the problem is often a worn out spindle mouth. A trained professional will be required to check and repair bell mouthing.

T.I.R. (total indicator runout) is the measurement of axial deflection of the cutting tool in the toolholder assembly. Techniks toolholders are manufactured to minimize runout and extend cutting tool life. You lose 10% of cutting tool life for every “tenth” (0.0001”) of runout. That's what the chart above depicts.

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Evaluating your CNC Rotary Toolholders for Wear & Fretting

11/16/2011

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A worn out toolholder will not provide good accuracy and will quickly wear out your cutting tools. Worn tooling can also cause poor surface finish, and may even damage your spindle.
Taper Wear / Fretting
Check the taper for signs of wear or damage where it contacts the spindle mouth. Any problems with the taper will have a direct effect on machining accuracy. If there are any imperfections on the taper, the toolholder should not be used. 

If noticeable marking is evident on the taper (see photo next page) a condition called fretting may be occurring. Fretting happens when two steel parts (holder and spindle mouth) are rubbing against one another. Fretting is caused by imperfect mating between tooholder taper and spindle, creating vibration and heat which develops the fretting. It is visible as small copper colored pits or marks on the taper. This is evidence that the toolholder is becoming worn. Fretting is easily mistaken for rust, but it is not. 
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Once noticeable fretting develops the toolholder should be replaced. New toolholders that quickly develop fretting, or toolholders that stick in the spindle, may indicate a spindle that needs to be reground.

A worn taper causes an out-of-round condition when the holder is inserted into the spindle. This is called “runout”. Runout causes premature tool wear and excessive vibration during operation.

This vibration can cause poor surface finish which may require additional operations to correct. Vibration can also cause heat build-up in the spindle and damage spindle bearings.

​See our video below to learn how to check toolholder T.I.R. “How to check Runout”.
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    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
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    Authorship

    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.

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