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Micromachining: What to Know About Toolholders, Drills, End Mills, and CNC Machines.

9/21/2021

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About the author: Jack Burley, Vice President of Sales and Engineering and Big Kaiser Precision Tooling Inc.
Micromachining, cutting where the volume of chips produced with each tool path is very small, is not a high-speed operation in relation to chip load per tooth. Rather, it involves a high spindle speed relative to cutter diameter. The part may be physically larger, but details of the part require ultra-small profiles achieved only by micromachining. In other words, micromachining is not limited in scope to only miniature parts.
Big Kaiser considers tools with <3mm to be micro tools with unique geometric considerations.
Big Kaiser considers tools with <3mm to be micro tools with unique geometric considerations.
TOOLHOLDING
In medical work, where tight tolerances are standard, dynamic runout; the measurement of the spindle at high speeds, performed using laser or capacitance resistance technology, and balance must be controlled to deliver and maintain viable tool life.
Much of this burden falls on the holder. Balance doesn’t change as spindle speed increases, however the forces it creates increase exponentially alongside speed. The impacting results appear quickly in micromachining.

When runout occurs, the edge most affected takes over the bulk of the cutting. Uneven wear causes the tool to fail more quickly than if the tool rotates about the centerline as intended. In one customer application, we found that drilling into a steel workpiece 0.590" deep with a 0.118" diameter carbide drill in a holder with 0.00008" runout accuracy produced 2,300 holes.
BIG KAISER HSK-E32, E25, or E20
Micro milling machines, ideally suited for small tools and small workpieces, are characterized by spindle speeds of more than 50,000rpm using small HSK tool holders such as HSK-E32, E25, or E20.
A holder with 0.00060" runout accuracy produced nearly two-thirds fewer holes, only 800. In this scenario, the shop could save hundreds of dollars a month in carbide costs – as well as labor costs due to less tool changing – by making one smart tool holder choice.

Holder attributes that can boost production include symmetrical design, a perfectly concentric collapse of the collet around the cutter, and a ball-bearing raceway nut with precision-ground threads.

CHALLENGES
While these characteristics are good rules of thumb, things change fast in this field and, like our customers, we must adapt as trends emerge.

Batch sizes are getting smaller. Bone screws, for example, were typically run on multi-axis, Swiss-type lathes where the same tools and programs ran for days at a time. Traditionally, prototyping in this arrangement was not an option because of the complexity and time involved in programming and setup. Today’s need for customized sizes demands flexibility and quick changeover to remain productive.

We are investing a large portion of our research and development (R&D) in tackling this challenge. We are working on hydro-clamping tool holder systems that could make the decades-long approach of using ER collets obsolete. It would make it possible, for example, to perform a simple drill change on a gang slide in seconds.

COOLANTS
Another trend in medical manufacturing being driven by the U.S. Food and Drug Administration (FDA) is clean machining without the use of water-soluble coolants.
Super-chilled CO2 or cryogenic machining with liquid nitrogen are considered possible replacements. Protecting small holder parts at the nose from coolant has always been a concern, but using gas requires more attention for holders to be effective.
Mega Micro Coolant Nut for Mega Micro Chuck 6S
The Mega Micro Coolant Nut for Mega Micro Chuck 6S provides a more efficient coolant supply for micro cutting tools and is designed for high-speed micro machining up to 6mm.
We are focusing on two features:
  • Holders that remain completely sealed to outside atmosphere
  • Very small delivery holes in collet faces or clamping nuts that properly restrict gas flow
Big Kaiser hydro- clamping tool holder system for Swiss-type lathes
Matching medical components to each patient demands flexibility. This hydro- clamping tool holder system for Swiss-type lathes would make the decades-long approach of using ER collets obsolete by making it possible to perform a simple drill change on a gang slide in seconds.
TOOLING
Tool considerations also must be taken into account to keep up with the demanding medical field. Better results often cannot be achieved by simply increasing spindle speeds or using smaller tools; a deeper understanding of cutters is necessary.

We consider tools with diameters <3mm to be micro tools. These aren’t simply smaller versions of their macro counterparts. They have geometric considerations all their own. For example, the 1mm Sphinx drill can run at 80xD. But this is only possible because the cylindrical shaping extends further down the tool, closer to the tip, to facilitate pecking and maintain strength.

Tool carbide should be ultra-fine grain (nano or submicron grain size) to ensure high abrasion resistance and good toughness. Coatings are valuable too, but it’s important to understand how coatings can negatively impact micro tool performance. Micro tools have extremely fine surface finishes and sharp cutting edges. Coatings can fill in valuable space – a flute on a drill, for example – needed for proper chip evacuation, which is critical in these applications.

Coatings must be ultra-thin (<1µm) and smooth; our experience shows that misapplied coatings result in poor tool life due to breakage; the coating reduces cutting edge sharpness, increasing torque force on the drill. When coating is necessary, consult with the cutting tool manufacturer to provide this directly.

Chips and small tooling naturally do not get along well. Compensating for low spindle speeds with tools that have more flutes support an ideal feed rate, but chip evacuation may suffer. Determining the appropriate chip load – as close to the cutting edge as possible – allows operations at the highest possible spindle speed, accelerating the cycle and improving surface finish.
Optimal conditions exist when the chip load is relatively equal to the cutting edge radius.

Many micro end mills are designed so the cutting edge radius has a positive rake angle to create a shearing action. A chip load less than the cutting edge radius often results in a negative rake angle where the tool rubs rather than cuts. This increases the force required and generates more heat which can result in built-up edges and poor tool life. A chip load significantly bigger than the cutting edge radius often leads to premature failure because the tool is not robust enough to withstand such forces.

MACHINE TOOLS
Micromachining requires machine tools with very high sensitivity, fine resolution in the feed axis, and very precise spindles capable of high speed with low dynamic runout. For micro-drilling operations, specialized micro machines are best.

Micro milling machines are suited for small tools and small workpieces. They are characterized by spindle speeds faster than 50,000rpm using small HSK tool holders such as HSK-E32, E25, or E20. With the right holder, tool runout can be controlled to less than 1µm (0.000040") at the cutting edge, ensuring sub-micron accuracy.

In medical micromachining, understanding each piece of the equipment puzzle is critical. It’s also important not to make assumptions based on other tools or parts you may have worked with, especially in more standard sizes. Invest the right time and energy in gearing up for the next medical job and you’ll get more parts done right faster.

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To Balance, Or Not To Balance? Toolholders, That Is

3/16/2021

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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.
An argument can be made for balancing almost every tool put in a machine. In the world of rotating tools, small changes to an assembly, like a new cutting tool, collet, nut or retention knob, can put an assembly out of tolerance.

​Therefore, it stands to reason that any unbalance could translate to the part, tooling and/or machine spindle in harmful ways. You’ll hear the case for balancing every single tool based on the 
long-standing ISO 1940-1 standard.
over-balanced-tool-holder
Balancing a toolholder several times causes the toolholder to become excessively modified. It's OVERBALANCED
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.
In other words, if you’re rough milling with a heavy radial cut, the different forces will start bending the tool. When that happens, the cutting forces and all the feed forces will be substantially higher than whatever the unbalance forces might be. If that’s the case, it’s not that you take the unbalance force and add it to the cutting force and find your adjustment. 
Big Kiaser New Baby Chuck and Mega New Baby Chuck are balanced for High speed machining
Big Kiaser New Baby Chuck and Mega New Baby Chuck are balanced for High speed machining. The Precision collet is guaranteed to produce a maximum runout of only 1 micron at the collet nose.
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.
BIG KIASER Mega ER Balanced holders
All the components of Big Kaiser's Mega ER Grip Series - Body, Collet and Collet nut - Are all balanced for high speed machining

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.
Auto-balancing boring heads are designed specifically for the high-speed finishing I mentioned earlier, where unbalance force can be greater than cutting force. Our EWB boring heads, for instance, have a small internal counterweight that moves in direct proportion with each adjustment. Because the weight is carbide, it’s three times more dense than the steel in the tool carrier and is maintained inside the head’s symmetrical body.
Picture
Autobalance boring heads, Series 310 EWB, maintain perfect balance throughout the work range due to the integrated counter-balance mechanism. Even at maximum speeds, balanced tools guarantee vibration-free boring, resulting in increased productivity and high precision.
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.
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OSG Releases ADO-MICRO Small Diameter Coolant-Through Carbide Drill Series

10/7/2020

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Small Diameter Coolant-Through Carbide Drills 2D · 5D · 12D · 20D · 30D
OSG Corporation has announced the release of the ADO-MICRO small diameter coolant-through carbide drill series for stable and high efficiency drilling in small diameter deep-hole applications.
ADO-MICRO-Drill Double margin IchAda Coating
The ADO-MICRO features a unique double margin geometry with an extended flute and shortened end margin to enhance chip evacuation capability
Poor chip evacuation is a common complication in small diameter deep-hole drilling. Micro sludges can be easily accumulated around the outer periphery of the cutting tool, which is a key cause of abrupt tool breakage.

The ADO-MICRO features a unique double margin geometry with an extended flute and shortened end margin to enhance chip evacuation capability.

In addition to the outstanding chip ejection performance, the double margin configuration supports the straightness stability of the tool and reduces rifle marks on the inner surface of holes.

Furthermore, the ADO-MICRO features a pair of large oil holes and employs a hollow shank design to allow large coolant flow volume for trouble-free chip evacuation.

The ADO-MICRO is coated with OSG’s original IchAda coating that provides excellent surface smoothness in conjunction with high abrasion resistance and heat resistance to enable small diameter tools to achieve long tool life.

​With the ADO-MICRO’s unique tool geometry and IchAda coating, non-step drilling is made possible even for deep-hole applications, enabling high processing efficiency.
Picture
The ADO-MICRO’s large coolant holes increase the coolant flow volume resulting in stable drilling
The ADO-MICRO is suitable for carbon steel, alloy steel, stainless steel, cast iron, ductile cast iron, aluminum alloy, titanium alloy and heat resistant alloy. The ADO-MICRO is available from diameter 0.7 mm up to 2 mm for drill lengths 2xD and 5xD, and diameter 1 mm to 2 mm for drill lengths 12xD, 20xD and 30xD.

Got an application you want to try this on? Give us a call! 
Contact NGT

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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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    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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