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.”
Guest Blog: John Zaya
Clamp confirmation for any system, UNILOCK or otherwise, is a sound design criterion when building any workholding system.
It is very common to see clamp/un-clamp confirmation in many automated loading systems as safety interlocking of the CNC machine, robot, robot EOA (end-of-arm) tooling, and workholding can all be integrated to a single master control.
Un-clamp confirmation does have a place in manual situations as well, mostly in large part processing, where cranes are used to lift parts off.
When a clamping system is not directly visible underneath a large part, then this requires an external indicator confirming that the system has successfully un-clamped and that it is safe to lift.
The indicators and sensors can be pneumatic switches which are offered by BIG KAISER or electrical proximity switches as offered by many other companies.
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.
Guest Blog: Douglas Sumner
Product Manager TMS
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.
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:
Engineering Manager & Product Manager
Proper clamping techniques will ensure the proper operation of all mechanical milling chucks.
With MEGA Double Power and Hi-Power Slim type chucks it is very important to stop when the nut contacts the main body.
If the operator over tightens or “jerks” the wrench after contact is made, the two faces will wring together making it much more difficult to loosen the tool.
After the tool is released it is also very important to rotate the nut two additional rotations after the tool can be removed. This makes sure the chuck is fully released and is ready to be clamped again.
If the chuck is retightened without fully releasing the nut the gripping strength will be reduced.
Since the introduction of the XT Series 4 flute, 5 flute and the new 279 series 4 flute ball nose end mills they have proven to be a huge success in the machining of Titanium and stainless steels. These tools have already made their impact in the machining of many other areas such as all steels and super alloys.
MA Ford's spotlight focus is on some other materials that are widely used in the market. 17-4 PH stainless many feel is somewhat difficult to machine and performance may vary depending on the material hardness. That is not the case with the new XT series end mills. These tools do not seem to care what hardness is presented to them! 28-42 RC is primary range for this series of stainless steel.
Example: A customer had a very difficult 17-4 PH medical component with lots of contouring both roughing and finishing. A 1/2" 279 Series was used for roughing the profile at 600 SFM with a depth of .015 and .025 step over at 80 IPM. The customer had to double the speeds and feeds as well as increase the step over to get the desired finish required!
The 277 Series 4 flute can full slot up to 1X dia. depth at speeds as high as 260 to 340 SFM. The chip loads will be lighter than profile milling dependent on the tool diameter and fixture set up. The slotting depth can be increased even beyond 1X depth (which generally requires a reduction in speeds and feeds).
The 278 Series 5 flute can slot up to 1X depth effectively but slotting is more suited for the 4 flute 277 Series if a lot of slotting is to be done. The speeds and feeds are the same as the 277, but calculations must be made for the additional cutting edge. It is not recommended to slot over 1X the tool diameter with this 5 flute tools as it is best suited for profile milling both conventional and high speed machining.
The new 279 Series 4 flute ball nose end mill is an excellent choice for both conventional and high speed machining of stainless steels. With the added radial relief and a thicker cross section in the center of the tools it can withstand extreme speeds and feeds both roughing and contouring.
Complex part shapes have time consuming part loads to assure the part is properly nested before machining. Blue Photon makes a hard to load part easy and reduces the number of loads.
Traditional workholding does not usually utilize a machine’s full capabilities because of limited machining access therefore multiple workholding fixtures and process steps are required.
*Labor cost per part was calculated @ $50.00 per hour, based on 21 hours run time per (3) 8 hour shifts/5 day work weeks. 6,240 total hrs. per year
How the blue photon system realized reduce labor cost
With Blue Photon workholding technology, once the part is bonded to the transfer tool it can be loaded into all machines using the same machine mounted workholding fixture system such as Erowa, System 3R etc. The workpiece loads in seconds.
The ability of Blue Photon workholding technology to hold the workpiece on one side providing 5 and in some cases 6 side machining access is unheard of when machining castings and other near-net shape parts.
There is also reduced foot print for this cell and reduced capital investment to create the cell because multiple operations can be done in one workholding.
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.