DEPTH OF CUT COLUMN
by Jack Burley, President and COO at BIG KAISER Precision Tooling Inc.
It’s time for machine tool builders and machining companies to shelf the long-standing ISO 1940-1 standard in favor of ISO 16084:2017. Not only is balancing tools rarely necessary, it can also be risky.
A lot of conflicting information has circulated over the years about balancing tools. As an author of the new standard for calculating permissible static and dynamic residual unbalances of rotating single tools and tool systems – ISO 16084:2017 – allow me to clear some things up and, hopefully, make life a little easier for you.
Since its institution in 1940, the G2.5 balance specification has been widely accepted across the industry; i.e., “it’s how things have always been done.”
However, machines were much slower 80 years ago. Back then, the most advanced machines would have spun larger, heavier tools at a maximum speed of about 4,000 RPM. If you applied the math from those days to today, you’d get unachievable values.
For example, the tolerances defined by G2.5 for tools with a mass of less than 1 pound rated for 40,000 RPM calculates to 0.2 gram millimeters (gm.mm.) of permissible unbalance and eccentricity of 0.6 micron. This isn’t within the repeatable range for any balance machine on the market.
Similarly, application-specific assemblies, for operations like back boring and small, lightweight, high-speed toolholders, can’t be accurately balanced for G2.5.
Machine tool builders rely on an outdated number, too, often basing spindle warranty coverage on using balanced tools at very specific close tolerances. While it’s true that poorly balanced tools run at high speeds wear a spindle faster, decently balanced tools performing common operations won’t wear spindles or tools drastically and deliver the results you’re looking for.
While it’s true that poorly balanced tools run at high speeds wear a spindle faster, decently balanced tools performing common operations won’t wear spindles or tools drastically and deliver the results you’re looking for.
A Little Lesson About Forces
This all begs the question: When do you need to take the time to balance holders? I would argue that tools require balancing only if they’re notably asymmetrical or being used for high-speed fine finishing. Here’s a rule I’ve long followed: If cutting forces exceed centrifugal forces due to unbalance, high-precision balancing isn’t needed because the force required to balance the tool will most likely be less than cutting forces.
At that point, aggressive cutting – not unbalance – is going to damage the spindle.
Unbalanced tools are also blamed for issues that turn out to be misunderstandings about a machine’s spindle. I’ve visited shops with new high-speed spindles that had trouble running micro tools over 15,000 RPM. They rebalanced all the tools on the advice of their machine tool supplier, but to no avail. It turned out the machine was tuned for higher torque and higher cutting forces. Before going to the effort of balancing toolholders, work with your machine builder to understand where a spindle is tuned.
Not only is balancing tools rarely necessary, it can also be risky. Our inherently asymmetrical fine-boring heads are a good example. Because we balance them at the center, a neutral position of the work range, you lose that balance if you adjust out or in.
To adjust, you’d typically add weight to the light side, which can be a problem for chip evacuation and an obstructor. Or you can remove weight from the heavy side, but that means you have to put some big cuts on the same axis of the insert and insert holder, ultimately weakening the tool.
In longer tool assemblies, common corrections made for static unbalance can also cause issues. It happens when a toolholder is corrected for static unbalance in the wrong plane; i.e., adding or removing weight somewhere on the assembly that’s not 180 degrees across from the area where there’s a surplus or deficit.
Once the tool is spun at full speed, those weights pull in opposite directions and create a couple unbalance that often worsens the situation.
A Cautionary Tale
If you do go down the balancing road, you’d better know where you can modify tools, what’s inside, how deep you can go, and at what angles. Whether you’re adding or removing material on a holder, I highly recommend consulting the tool manufacturer for guidance first.
As a cautionary tale, consider a customer who was attempting to balance a batch of our coolant-fed holders. Based on the balancing machine, the operator drilled ¼-inch holes at the prescribed angle into the body of the holders. Not realizing what was inside, he drilled into cross holes connecting coolant flow and ruined several holders.
Tooling manufacturers are doing their part to avert disasters like this. For most, simple tools like collet chucks or hydraulic chucks are fairly easy to balance during manufacturing. We account for any asymmetrical features while machining and grinding holders and pilot each moving part, ensuring they’ll locate concentrically during assembly. These measures ensure the residual unbalance of the assemblies is very, very low and eliminate the need for balancing.
Decades of the same standards have conditioned us to think a certain way about balancing tools. While it seems logical that every tool must be balanced, it’s just not the case: Many issues attributed to unbalance aren’t caused by unbalance, and the risks of balancing every single tool often aren’t worth the reward.
Save your balancing time and resources for high-speed fine finishing. If you do have work where balance is crucial, consider how the tools you buy are balanced and piloted out of the box and/or consult your partners before making any modifications.
A machine’s spindle is one of the key links in the machining chain. In other words, if there are irregularities inside or at the face, they can show up on your part.
It makes regular inspection and spindle maintenance critical to getting the most out of your equipment and maintain process efficiency. These three accessories, the Dyna Contact Taper Gage, the Dyna Test Bar and the Dyna Force Measurement Tool, can help you perform this maintenance easily without eating into valuable spindle time.
Dyna Contact Taper Gage
Dyna Test Bar
With the help of a dial indicator, you can uncover any runout while safely spinning the spindle at a very low RPM and verify the parallelism of Z-axis motion.
Dyna Force Measurement Tool
The Dyna Force measurement tool provides a precise digital reading that reveals reduction in retention force in increments of 0.1kN.
NTK CeramiX HX5 replaces CBN
NTK developed this latest game changing ceramic material NTK CeramiX HX5 to replace CBN. As a ceramic cutting tool specialist, NTK has been researching new advancements for ceramics in the industry for decades.
They recently introduced a new grade that matches CBN on performance.
The new CeramiX "HX5" grade provides a cost saving solution for hard turning applications. It's designed for Hard Turning with continuous cut in the Hardness range of 55 to 66HRc
With this innovative centering tool from Big Kaiser, spindles and tools can be centered quickly and easily. It's ideal for limited spaces within small lathes. The Centering Tool is a static dial gauge for easy centering.
Accu is the message that is displayed when the battery needs to be changed.
This message does not mean there is an error or accuracy malfunction with the boring head. The head should still continue to function for a few more adjustments. If this message appears on the EWE heads, the wireless connectivity to the App and history functions are deactivated until the battery is replaced.
NTK offers an extensive line of high precision boring tooling designed for Swiss machines. One of these produce lines is called “Mogul Bar”. The Mogul Bar system provides the user outstanding chip control and higher rigidity than most conventional tooling on the market.
Outstanding chip evacuationThe most notable characteristics of the Mogul Bar is excellent chip evacuation and chip control. Mogul Bars outfitted with NTK’s “F” or “FG” chipbreaker inserts will evacuate chips backwards.
This means that when a Mogul Bar machines an I.D. bore, chips comes out towards the bore entrance. The major-ity of boring processes on Swiss machines are done on the main spindle side and thus the bore itself is a blind hole. This machining process creates many issues if you use conventional boring bars designed for CnC lathes.
Typical difficulties incurred during a boring process on Swiss machines are either chips remaining in the bore and rough surfaces caused by inconsistent chip control. However, Mogul Bars equipped with nTK uniquely designed chipbreakers, evacuate chips straight backwards and solves both of these problems at once.
Another important feature of the Mogul Bar series is high rigidity. Mogul Bars increased rigidity is a result of a newly designed bar head configuration and a minimal flat width on the bar.
Steel shank Mogul Bars can machine as deep as L/D=5, a depth which nor-mally requires expensive carbide shank boring bars.
NTK carbide shank Mogul Bars can machine up to L/D=7 depth and this gives users flexibility of machin-ing deeper bores in a single process. rigidly and mini-mal flat widths reduce vibration.
Variety of Insert Grades
NTK offers both coated carbide grades and cermet insert grades for Mogul Bars. As most tooling engineers know, cermet grades can machine at faster speeds with higher productivity, provide better sur-face finishes and can achieve more accurate dimen-sion control, than carbide grades. These benefits come from the fact that the primary substrate of cermet grades, Tin /TiC, are chemically stable compared with WC of carbide grades and have better adhesion resistance.
Mogul Bars are available from a minimum machining diameter of 5mm. With the combination of NTK unique chipbreakers, you can enjoy better chip control and highly rigid boring bars. In comparison with solid carbide boring tools, Mogul Bars has cost advantage as well.
If you are facing chip control or chattering issues, NTK believes that Mogul Bars can be the answer to your problems.
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:
The EWD Smart Damper damps vibrations and reduces chatter in deep-hole finish boring and extended-reach face milling applications – thus achieving better surface finishes and improved metal removal rates.
For precision machining of deep bores, it has previously been necessary to choose low cutting data in order to prevent vibrations, which massively increases processing time. The EWD Smart Damper overcomes this problem, and enables high cutting parameters to be used. This means that extremely short turnaround times can be achieved, which improves productivity by up to a factor of ten.
Smart Damper products are designed for deep-hole boring with BIG KAISER’s CKB modular boring system, and also for extended reach milling with both inch- and metric-pilot shell mills and face mills.
The original rollout of the Smart Damper for finish boring included an integral BCV50, BBT50 and HSK-A100 tool holder with a CKB modular connection at the business end. A BCV50 integral 1” shell mill holder was also available.
The next phase of the Smart Damper accounted for more flexibility towards assembling a more custom tool assembly.
A modular CKB Smart Damper Extension allowed customers to mount it to any combination of standard CKB shanks, extensions and reductions to create the exact tool configuration for their job.
At the same time, a modular thread-on face mill damper head extension was also developed to be used with matching basic holder with different interfaces and gauge lengths.
This new design for boring shortens the distance from the damping mechanism to the cutting edge, which is the source of vibration. This produces higher damping effects to the tool assembly to minimize the chatter or vibration – thus achieving better surface finishes and improved metal removal rates.
For more information on Smart Damper Models:
Visitors at the 2015 EMO tradeshow in Milan, Italy, were the first in the world to see our newest solution in the Smart Damper family – EWN and EWD BIG KAISER boring heads with an integral damping system.
If you're just learning about it now you should get in touch with us so we can show you lots of new application solutions!
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.
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