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.

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.

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.

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
  

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.

The four critical requirements for tool holders are clamping force, concentricity, rigidity, and balance for high-spindle speeds. When these factors are dialed in just right, there’s nearly no chance of holder error and considerable cost reduction is achieved thanks to longer tool life and reduction of down-time due to tool changes. 

Easier said than done, our experts shared some of their best, quick-hitting advice for top tool holder performance in different situations. 

Long-reach milling has some unique demands; when setting up this type of job, always balance tool holders as a complete assembly. While many tooling providers pre-balance their holders at the factory, it’s often inadequate, especially for long-reach applications.

 Wear and tear on holders can be costly in the end, but there are ways to protect against it. Inspect and care for your holders. Trauma on a holder or spindle—dings, scratches, gouges, etc.—can magnify quickly. One bad holder can spread its problems like an illness. If you’re seeing disruptions like these on your holders, get them out of the rotation. 

Looking for affordable ways to avoid vibration? Start by opting for a holder with a combination of the largest diameter and shortest length possible.

What many don’t realize about tapping operations is that a perceived strength of collet chucks—their rigidity—can actually be detrimental. Rigidity does very little to counteract the dramatic thrust loads imposed on the tap and part, exacerbating the already difficult challenge of weathering the stop/reverse and maintaining synchronization.

Five-axis machining introduces a whole new set of tooling challenges. While important in any type of machine, balance may be of most importance in full five-axis work. A well-balanced holder helps ensure the cutting edge of the end mill must be consistently engaged with the material in order to prevent chatter and poor surface finish quality. 

If you have to choose between shrink-fit and hydraulic holders in a long-reach application, consider the spindle speed required. If a hydraulic chuck exceeds its rated RPM, fluid is pulled away from the holder’s internal gripping gland, causing loss of clamping force. But when used within its recommended operating range, a hydraulic tool holder offers superior runout and repeatability. On average, a good shrink-fit holder has about 0.0003-inch runout, while a hydraulic chuck offers 0.0001 inch or better.

The cutting tool affects holding ability more than most machinists and engineers realize:

1. Polished shanks reduce friction, as does the cleanliness.
   
2. Oil and coolants reduce gripping power.
3. Cutter shank roundness is often assumed to be close enough to perfect to ignore, but in reality, a 25 millionths tolerance is necessary for high-speed performance.

Anyone in the market for BIG-PLUS dual-contact tooling should consider this simple statement: Only a licensed supplier of BIG-PLUS has master gages that are traceable to the BIG grand master gages and have the dimensions and tolerances provided to make holders right. Everyone else is guessing and using a sample BIG-PLUS tool holder as their own master gage—a practice that any quality expert will advise against.

Look for the marking: “BIG-PLUS Spindle System-License BIG DAISHOWA SEIKI.”

You’d be surprised how often we hear from our certified regrinders or engineers in the field about folks that didn’t realize their machine had a BIG-PLUS spindle—the message can get lost in the supply chain or during the sales process. 

The easiest way to know if an interface is BIG-PLUS is to place a standard tool into the spindle and see how much of a gap there is between the tool holder flange face and spindle face. Without BIG-PLUS, the standard gap should be visible, or about 0.12 in. If it is BIG-PLUS, the gap is half of this amount, or only 0.06 in. These values change depending on 30 taper, 40 taper or 50 taper sizes, but the gap is visibly less than usual.

It may be how it’s traditionally been done but touching off holder assemblies in each machine to establish negative tool offsets based on the zero-point surface—the vise, machine table, workpiece, etc.—is not the most efficient process. We think the choice is pretty clear: adapting machines to a single presetter so they can receive positive gage lengths is superior to using all types of machine-specific negative offsets. 

This is a change to “the way things have always been done” that can be met with some resistance, but in the grand scheme of things, it’s a relatively small and simple step that makes life much easier. It’s a relatively low-cost opportunity to introduce more standardization of holder setup to the shop floor.

Holders are the bridge between the machine and the part. That’s a lot of pressure—literally and figuratively. It’s important to select, care for and use holders carefully from the day they are purchased until they’re tossed into the recycling bin. 

From collet chucks to coolant inducers, BIG KAISER is North America’s source for standard-bearing tool holders that guarantees high performance. Explore the full lineup. 

Here is a very helpful video on 'how-to' setup a subplate with SpeedLoc by mPower.

1. Install the Locators though the subplate into the receivers finger tight
2. Use a Precision Straight edge to span the locator shanks
3. Use an indicator to to "tap in" the subplate to align with machine table
4. Complete the X -Axis and then do the same for the Y-Axis
5. Recheck the X-Axis

by Bernard Martin
There have been some who claim that drawbar gripper fingers and/or ball marks that appear on retention knob head after several tool changes is normal.

It is NOT.  
​THAT IS FALSE. ​

According to Haas CNC, ball or gripper marks on the edge of the pull stud indicate that the drawbar does not open completely.

​If you see these indication marks you should check your drawbar and replace these pull studs immediately.

compiled & edited by Bernard Martin

As more and more of our customers are using Martindale Gaylee Circular saws we put together this guide to the commonly asked questions such as "Is there a rule-of-thumb for the number of teeth?" or "How much side clearance should I have?" Here we cover a lot of the fundamentals of selecting the right circular saw blade configuration, some tips, tricks, and troubleshooting for when things go wrong. 

These are general cutting speed recommendations for circular saws used in metalcutting from Martindale/Gaylee. The may vary from application to application but are basically some general suggestions starting parameters when using high speed or carbide saws. 

• HSS Saws: .002”-.006”  (IPT-inch. per tooth / CLPT-chip load per tooth)
• Carbide Saws: .0002”-.0015”  (IPT -inch. per tooth / CLPT - chip load per tooth)

This is a conservative recommendation as a starting point for feed rates, and may vary depending on material being cut and cutting speed (SFPM).

Generally speaking, deep cuts and soft material require fewer teeth for chip clearance and stronger teeth (landed).

Thin material requires more teeth, but keep-in-mind that at least 2 teeth on the blade need to be engaged in cut. Hard materials and narrow slots (under .025”) likewise require more teeth.

Hard Materials require more teeth, and  give a smoother cut,  but at a much lower production rate.  ​

Alternately beveled teeth keep chips from sticking in the cut and in the tooth gullets.

And Remember that there should be at least 2 teeth engaged in the cut at all times.

RAKE ANGLES
​Just as in an end mill or a band saw blade, a rake angle is the term used to describe the direction of the blade’s teeth, as referenced from the rotation and central axis of a saw blade. If you imagine a line going from the exact center of the blade to each tooth, having the front of the tooth directly on that line would be a zero degree rake angle. The rake angle of the blade is described in comparison to that imaginary line.

A positive rake angle meana that the teeth are angled more towards the angle of rotation, while a negative rake angle would mean that they are angled backwards, away from the direction of rotation. Generally speaking, the preferred rake angle is:

• 5° to 10° positive for other soft materials.
• 5° negative for yellow brass
• On center for steel.

SIDE CLEARANCE (Tangential Clearance Angle)
This is also known as dish or hollow grind.  You measure down the side of the tip and the difference it is the difference between front and back.  As you cut, material it gets compressed and springs back after the cutting edge passes.

​A steep side clearance angle gives plenty of room for the material to expand and prevents thermal expansion of the base material.  Keep in mint that a very flat side clearance angle can provide a smoother cut in some materials.  For stainless steel and tenacious metals such as copper, zinc, tin or lead an increase in the side clearance is desirable as these materials tend to "spring back" (thermal expansion) on the blade. 

It's commonly known that when saw thickness is less than 0.125″, keyways can cause stress risers and cracks.  That is why washers are often used.  However, Breakage, Wobble and Rubbing problems are often caused by how the washers are mounted on either side of saw. 

Remember, washers drive the saw in the absence of a drive key. They must always be clean, flat and bur-free. A speck of dirt will let saws wobble and cut oversize. 

If a saw breaks, it may score the washers. Always check for scoring marks around saw hole for dirt, chips or grit.  Shiny spots, as small as a pinpoint, indicate that chips where imbedded under washers.

Circular skid marks indicate the nut was not tight.

Generally speaking:

• Thin saws should especially be supported by washers as large as possible.
• Washers must be of equal diameter or they will flex out saw dish and cause one side of saw to rub.
• The nut must be wrench-tight.

Saw Blade Teeth most often break as a result of:

• Too high a feed rate.
• Spindle bearings are worn.
• Drive belts  are loose or sheaves worn.
• Improper tightening: If saw blade pauses momentarily in its rotation while feed advances, it WILL break.
• Workpiece indexed before the saw has cleared the slot.
• Improper workholding - The workpiece not tight or not well supported.
• Saw is dull, even the best tools do eventually wear out.

NOTE: HSS saws will turn colors as they heat during cutting. A straw color is the limit. The saw will lose its temper when it starts turning blue.

DEPTH OF CUT COLUMN
by Jack Burley, President and COO at BIG KAISER Precision Tooling Inc.

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.

​by Bernard Martin
Retention Knobs are the critical connection between your machine tool and the tool holder and they are the only thing holding a steep taper tool holder in the machine’s spindle.

​Techniks has recently introduced their MegaFORCE retention knobs that have some rather unique features when compared to standard pull studs.  Before delving into the features of the MegaFORCE pull studs, let's review some things that you may not know, or think about, on a daily basis. 

​According to Haas, you should expect a service life of about 6000-8000 hours for a retention knob.  

​Most all rotary toolholder manufacturers state that you should be replacing your pull studs at least every three years.

However, if you're running multiple shifts, 24-7, making lots of tool changes, making very heavy cuts with long reach or heavy cutting tools, and/or have ball lock style grippers instead of collet type grippers used on the retention knob, you will probably need to replace your studs at least every six months.

Given the spindle speeds that we are running at to remain competitive, retention knobs are not an item that you want to take a chance on breaking.  I can tell you firsthand that 5 pound toolholder with a drill in it flying out of the spindle at 23,000 RPM is not something you want to experience. 

Pull studs encounter catastrophic failure as a result of metal fatigue. The metal fatigue can be caused by a number of reasons including poor choice of base material, engineering design, machining process, poor heat treatment, and, sometimes, they have just met or exceeded their service life. We're going to dig into each of these reasons below but first let's look at some threading fundamentals.

The load on each subsequent thread decreases from there, as show in the table. Any threads beyond the first six are purely cosmetic and provide no mechanical advantage. ​

Additional threads beyond the sixth thread will not further distribute the load and will not make the connection any stronger. 

That is why the length of engagement of the thread on a pull stud is generally limited to approximately one to one & a half nominal diameter. After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession.

Repetitive cycles of loading and unloading subject the retention knob to stress that can cause fatigue and cracking at weak areas of the pull stud.

What are the weak areas of a standard retention knob?  ​

The most common failure point for a retention knob is at the top of the first thread and the underside of the pull stud where the grippers or ball bearings of the drawbar engage and draw the toolholder into the spindle.

Remember, bigger Radii are stronger than sharp corners. ​More on that soon.

Not all retention knobs are made from the same material, however, material alone does not make for a superior retention knob. Careful attention to design and manufacturing methods must be followed to avoid introducing potential areas of failure.

Techniks MegaFORCE retention knobs are made from 8620H. AISI 8620 is a hardenable chromium, molybdenum, nickel low alloy steel often used for carburizing to develop a case-hardened part. This case-hardening will result in good wear characteristics.  8620 has high hardenability, no tempering brittleness, good weldability, little tendency to form a cold crack, good maintainability, and cold strain plasticity.

There are some companies making retention knobs from 9310. The main difference is the lower carbon content in the 9310. 9310 has a tad more Chromium, while 8620 has a tad more nickel.  Ultimate Tensile Strength (UTS) is the force at which a material will break. The UTS of 8620H is 650 Mpa (megapascals: a measure of force). The UTS of 9310H is 820 Mpa. So, 9310H does have a UTS that is 26% greater than 8620H.

​That said, Techniks chose 8620 as their material of choice because of the higher nickel content.  Nickel tends to work harden more readily and age harden over time which brings the core hardness higher as the pull stud gets older. The work hardening property of 8620 makes it ideally suited for cold forming of threads on the MegaFORCE retention knobs.

​It should be noted that some companies are using H13. H13 shares 93% of their average alloy composition in common with 9310. 

Rolled threads produce a radiused root and crest of the thread and exhibit between a 40% and 300% increase in tensile strength over a cut thread. The Techniks MegaFORCE retention knobs feature rolled threads that improve the strength of the knob by 40%.  

By comparison, cut threads interrupt the grain flow creating weak points.

Overall Length
There are some claims that a longer projection engages threads deeper in the tool holder preventing taper swelling. While a deeper thread engagement can help prevent taper swelling, applying proper torque to the retention knob is an effective way to reduce taper swelling.

An over-tightened retention knob may still cause taper swelling regardless of how deep it engages the threads of the tool holder. Additionally, the longer undercut section above the threads presents a weak point in the retention knob.

Ground Pilot
There is a ground pilot, underneath the flange, which provides greater stability. The pilot means the center line of the tool holder and pull stud are perfectly aligned.

Magnetic Particle Tested
Each Techniks MegaFORCE retention knob is magnetic particle tested to ensure material integrity and physical soundness. MegaFORCE retention knobs are tested at 2.5X the pulling forces of the drawbar.

In order to maximize the life of your retention knob and prevent catastrophic failure here are some technical tips to keep your shop productive and safe.

Special thanks for Greg Webb at Techniks and Mike Roden from Fette Tools/ Turning Concepts, for providing technical insights.