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. 

Here are some simple quick tips when you are machining machining hard materials. 

• As material hardness goes up the SFM goes down.
• Use the strongest possible insert shape to maximize insert strength.
• Ceramic is a hard material therefore, the insert needs some edge preparation in order to withstand cutting forces and optimize performance.
• Utilize positive geometries for close tolerances or thin-walled parts.
• If multiple passes are required with one edge, vary the DOC to move the wear on the insert edge and improve tool life.
• If you encounter chatter, increase your feed rate. Heavy chatter is often a sign of the tooling being above centerline or there is too much toolholder overhang. The machine, part and tooling set-up must be rigid.

When you're considering inserts from NTK Cutting Tools for hard turning, take a look at the grades and styles.

1.  Light edge preps T styles ( T-land:  T0425  & T0525)
2.  Heavy edge preps:  Z and S style ( T-land and honed edge: Z0820, Z0825, S0820, S0825) or  J, P, and Q style (Double Chamfered and Honed edge: P4815,  P8015, Q8015)

Alpha Granite & Tile in Austin, TX, has grown steadily since its opening in 2003, adding and diversifying machinery, materials and service offerings along the way, eventually earning the title “Accredited Natural Stone Company” from the Natural Stone Institute. They’ve expanded to deliver a range of custom residential and commercial stone surfaces, from wall cladding to kitchen countertops, in more than 150 colors of granite, marble, onyx, quartz, quartzite and ultra-compact sintered surfaces.

To keep up, Alpha Granite has invested in several advanced CNC machines, diminishing or altogether eliminating many of the laborious and time-consuming processes. Despite the technological advances, there was still a bottleneck that frustrated owners Denis and Sonia Phocas.

“Measuring tools in the stone industry was always a very laborious process,” explained Denis Phocas. “It’s archaic. You get wet, dirty and it takes a really long time. In reality, the process destroys tools because employees know the time and effort involved, so they tend to skip the necessary measuring intervals [ultimately cutting tool life roughly in half].

Dressing of the tools is also skipped, as this process needs to be done after a set amount of linear feet of work. In essence, the tools need to be measured and sharpened at set intervals to increase life.”

The traditional measuring process is manual. Measuring height and diameter to set up and inspect tools requires handheld instruments like calipers. Phocas explains how important accurate and sharp tools are to cutting stone profiles.

Since each profile requires several passes by six or seven different tools, each dependent on the accuracy, and more delicate than the one before. In other words, if the first tool isn’t dialed in right, the profile shape will be deformed, tools wear faster and the hours spent preparing them are wasted.

“Finding the center of one tool is hard enough,” he said. “Finding the center in relation to six others is very difficult.”

Phocas had heard about tool presetters, essentially a powerful microscope with a high-resolution monitor and basic computing power. It allows for precise inspection and measurement of tool edges. The process is relatively new to the stone industry and mostly limited to larger fabricators. As he explored further, Phocas began to understand why — only the big guys could afford them.

​The presetters he saw from his distributers were big, expensive and, frankly, had more bells and whistles than a family-owned independent shop like Alpha Granite would need. Phocas recalled thinking, “It was such a major expense. Who needs to spend $60,000 on something you don’t need fully automated? There had to be a smaller solution.”

Phocas approached suppliers about entry-level options, but they continued pushing more expensive options. He got creative and found a metalworking supplier, Big Kaiser Precision Tooling in Hoffman Estates, IL, that might be able to help. The Speroni STP Essentia they offered featured a compact bench-top design, could work with any brand of router tools and handle the more complex tool profiles in stone cutting with ease. Most importantly, it was much less expensive than the other options he had found.

After working closely with a representative from Big Kaiser, even trying out an Essentia in his shop, Phocas was convinced and decided to purchase one. While there are significantly fewer types of tools used for profile cutting, this new capability and process would be an adjustment at first, starting with installation.

“I had never worked with one of these,” said Phocas. “It’s a precision tool. I wouldn’t call it daunting, but the process was interesting. We installed it in the workshop manager’s office because we wanted to keep it in a clean environment and because it’s got a computer hooked up to it. In the end, the installation process was pretty straightforward.”

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.

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.

The Dyna Force measurement tool provides a precise digital reading that reveals reduction in retention force in increments of 0.1kN.

If you would like a demonstration for any of these tools contact us or set up an appointment for one of our Next Generation Tooling engineers to visit you!

As more applications require the use of super-hard alloys, manufacturers are demanding tooling that can deliver precision threads and high production in less time.

To meet these challenges, Carmex Precision Tools Ltd. has engineered carbide grade HBA — an extra-fine, submicron grade with high toughness for optimized performance on hardened steel Titanium and super alloys including Hastelloy, Inconel and Nickel base alloys up to 62 HRc.

Available for internal and external threading in both 60° and 55° partial profile, as well as ISO metric and UN, HBA delivers high wear and heat resistance and excellent edge stability. The unique combination of carbide substrate, coating type and edge conditions provide superior performance over extended tool life.

In a recent test involving an external right-hand thread:

• Thread: M32x1.5 and a length of 65mm (2.56")
• Material: D2 hardened steel @ 53-56 HRc,
• Insert: 16 ER 1.5 ISO grade HBA
• Results: Operated at 1772 IPM (45 m/min) at 28 passes produced 36 threads per corner.

Hard machining is increasingly becoming the rule rather than the exception in complex part production. Carmex HBA was engineered to meet the challenges inherent in threading hard materials while delivering high production and longer tool life. 

Bring us your most challenging hard threading applications and lets try  the new Carmex HBA engineered performance carbide .

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.

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.

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!