Posts

The Geometries and Purposes of a Slitting Saw

When a machinist needs to cut material significantly deeper than wide, a Slitting Saw is an ideal choice to get the job done. A Slitting Saw is unique due to its composition and rigidity, which allows it to hold up in a variety of both straightforward and tricky to machine materials.

What is a Slitting Saw?

A Slitting Saw is a flat (with or without a dish), circular-shaped saw that has a hole in the middle and teeth on the outer diameter. Used in conjunction with an arbor, a Slitting Saw is intended for machining purposes that require a large amount of material to be removed within a small diameter, such as slotting or cutoff applications.

Other names for Slitting Saws include (but are not limited to) Slitting Cutters, Slotting Cutters, Jewelers Saws, and Slitting Knives. Both Jewelers Saws and Slitting Knives are particular types of Slitting Saws. Jewelers Saws have a high tooth count enabling them to cut tiny, precise features, and Slitting Knives are Slitting Saws with no teeth at all. On Jewelers Saws, the tooth counts are generally much higher than other types of saws in order to make the cuts as accurate as possible.

Key Terminology

Why Use a Slitting Saw?

These saws are designed for cutting into both ferrous and non-ferrous materials, and by utilizing their unique shape and geometries, they can cut thin slot type features on parts more efficiently than any other machining tool.

Common Applications:

  1. Separating Two Pieces of Material
    1. If an application calls for cutting a piece of material, such as a rod, in half, then a slitting saw will work well to cut the pieces apart while increasing efficiency.
  2. Undercutting Applications
    1. Saws can perform undercutting applications if mounted correctly, which can eliminate the need to remount the workpiece completely.
  3. Slotting into Material
    1. Capable of creating thin slots with a significant depth of cut, Slitting Saws can be just the right tool for the job!

When Not to Use a Slitting Saw

While it may look similar to a stainless steel circular saw blade from a hardware store, a Slitting Saw should never be used with construction tools such as a table or circular saw.  Brittle saw blades such as slitting saws will shatter when used on manual machines, and can cause injury when not used on the proper set up.

In Conclusion

Slitting Saws can be beneficial to a wide variety of machining processes, and it is vital to understand their geometries and purpose before attempting to utilize them in the shop. They are a great tool to have in the shop and can assist with getting jobs done as quickly and efficiently as possible.

How to Extend the Life of Your End Mill

Breaking and damaging an end mill is oftentimes an avoidable mistake that can be extremely costly for a machine shop. To save time, money, and your end mill it is important to learn some simple tips and tricks to extend your tool’s life.

Properly Prepare Before the Tool Selection Process

The first step of any machining job is selecting the correct end mill for your material and application. However, this doesn’t mean that there should not be an adequate amount of legwork done beforehand to ensure the right decision on a tool is being made. Harvey Tool and Helical Solutions have thousands of different tools for different operations – a vast selection which, if unprepared – can easily result in selecting a tool that’s not the best for your job. To start your preparation, answer the 5 Questions to Ask Before Selecting an End Mill to help you quickly narrow down your selection and better understand the perfect tool you require.

Understand Your Tooling Requirements

It’s important to understand not only what your tool needs, but also general best practices to avoid common machining mishaps. For instance, it is important to use a tool with a length of cut only as long as needed, as the longer a tools length of cut is, the greater the chance of deflection or tool bending, which can decrease its effective life.

tool life

Another factor to consider is the coating composition on a tool. Harvey Tool and Helical Solutions offer many varieties of coatings for different materials. Some coatings increase lubricity, slowing tool wear, while others increase the hardness and abrasion resistance of the tool. Not all coatings increase your tool’s life in every material, however. Be wary of coatings that don’t perform well in your part’s material – such as the use of AlTiN coating in Aluminum (Both coating and material are aluminum-based and have a high affinity for each other, which can cause built-up edge and result in chip evacuation problems).

Consider Variable Helix & Pitch Geometry

A feature on many of our high performance end mills is variable helix or variable pitch geometry, which have differently-spaced flutes. As the tool cuts, there are different time intervals between the cutting edges contacting the workpiece, rather than simultaneously on each rotation. The varying time intervals minimizes chatter by reducing harmonics, increasing tool life and producing better results.

Ensure an Effective Tool Holding Strategy

Another factor in prolonging tool life is proper tool holding. A poor tool holding strategy can cause runout, pullout, and scrapped parts. Generally, the most secure connection has more points of contact between the tool holder and tool shank. Hydraulic and Shrink Fit Tool Holders provide increased performance over other tightening methods.

tool life

Helical also offers shank modifications to all stocked standards and special quotes, such as the ToughGRIP Shank, which provides added friction between the holder and the shank of the tool for a more secure grip; and the Haimer Safe-Lock™, which has grooves on the shank of the tool to help lock it into place in a tool holder.

tool life

Trust Your Running Parameters, and their Source

After selecting the correct end mill for your job, the next step is to run the tool at the proper speeds and feeds.

Run at the Correct Speed

Understanding the ideal speed to run your machine is key to prolonging tool life. If you run your tool too fast, it can cause suboptimal chip size, ineffective chip evacuation, or even total tool failure. Adversely, running your tool too slowly can result in deflection, bad finish, or decreased metal removal rates.

Push at the Best Feed Rate

Another critical parameter of speeds and feeds is finding the best possible feed rate for your job, for sake of both tool life and achieving maximum shop efficiency. Pushing your tool too aggressively can result in breakage, but being too conservative can lead to recutting chips and excess heat generation, accelerating tool wear.

Use Parameters from Your Tooling Manufacturer

A manufacturer’s speeds and feeds calculations take into account every tool dimension, even those not called out in a catalog and readily available to machinists. Because of this, it’s best to rely on running parameters from tooling manufacturers. Harvey Tool offers speeds and feeds charts for every one of its more than 21,000 tools featured in its catalog, helping machinists to confidently run their tool the first time.

Harvey Performance Company offers the Machining Advisor Pro application, a free, cutting-edge resource that generates custom running parameters for optimized machining with all of Helical’s products.

tool life

Opt for the Right Milling Strategy: Climb vs Conventional

There are two ways to cut material when milling: Climb Milling and Conventional Milling. In conventional milling, the cutter rotates against the feed. In this method, chips will start at theoretical zero and increase in size. Conventional milling is usually recommended for tools with higher toughness, or for breaking through case hardened materials.

In Climb Milling, the cutter rotates with the feed. Here, the chips start at maximum width and decrease, causing the heat generated to transfer into the chip instead of being left in the tool or work piece. Climb milling also produces a cleaner shear plane, causing less rubbing, decreasing heat, and improving tool life. When climb milling, chips will be removed behind the cutter, reducing your chances of recutting.

Utilize High Efficiency Milling

High Efficiency Milling (HEM), is a roughing technique that uses the theory of chip thinning by applying a smaller radial depth of cut (RDOC) and a larger axial depth of cut (ADOC). The parameters for HEM are similar to that of finishing, but with increased speeds and feeds, allowing for higher material removal rates (MRR). HEM utilizes the full length of cut instead of just a portion of the cutter, allowing heat to be distributed across the cutting edge, maximizing tool life and productivity. This reduces the possibility of accelerated tool wear and breakage.

Decide On Coolant Usage & Delivery

Coolant can be an extremely effective way to protect your tool from premature wear and possible tool breakage. There are many different types of coolant and methods of delivery to your tool. Coolant can come in the form of compressed air, water-based, straight oil-based, soluble oil-based, synthetic or semi-synthetic. It can be delivered as mist, flood, high pressure or minimum quantity lubricant.

Appropriate coolant type and delivery vary depending on your application and tool. For example, using a high pressure coolant with miniature tooling can lead to tool breakage due to the fragile nature of extremely small tools. In applications of materials that are soft and gummy, flood coolant washes away the long stringy chips to help avoid recutting and built-up edge, preventing extra tool wear.

Extend Your Tool’s Life

The ability to maximize tool life saves you time, money and headaches. To get the best possible outcome from your tool, you first need to be sure you’re using the best tool for your job. Once you find your tool, ensure that your speeds and feeds are accurate and are from your tooling manufacturer. Nobody knows the tools better than they do. Finally, think about how to run your tool: the rotation of your cutter, whether utilizing an HEM approach is best, and how to introduce coolant to your job.

 

Main Differences Between Engravers & Marking Cutters

While similar on the surface, Half-round Engraving Cutters and Marking Cutters are actually very different. Both tools are unique in the geometries they possess, the benefits they offer, and the specific purposes they’re used for. Below are the key differences between Engraving Cutters and Marking Cutters that all machinists must know, as the engraving on a part is often a critical step in the machining process.

Engravers & Marking Cutters Serve Different Purposes

All Marking Cutters are Engraving Cutters, but not all Engraving Cutters are Marking Cutters. This is because Marking Cutters are a “type” of engraving tool. By virtue of their sturdier geometry, Marking Cutters are suited for applications requiring repetition such as the engraving of serial numbers onto parts. Harvey Tool has been able to customize specific tool geometries for ferrous and non-ferrous applications, offering Marking Cutters for material specific purposes.

engraver

Engraving Cutters, on the other hand, are meant for finer detailed applications that require intricate designs such as engraving a wedding band or a complex brand design.

engraver

These Tools Have Unique Geometry Features

Historically, Engraving Cutters have been made as a half round style tool. This tool allows for a true point, which is better for fine detail, but can easily break if not run correctly. Because of this, Engraving Cutters have performed well in softer materials such as aluminum and wood, especially for jobs that require an artistic engraving with fine detail.

Marking cutters are not as widely seen throughout the industry, however. These tools hold up in harder-to-machine materials exceedingly well. Marking Cutters are a form of Engraving Cutter that contain 2 flutes and a web at the tip, meaning that the tool has a stronger tip and is less susceptible to breakage.

engraver

While these tools do not contain a true point (due to their web), they do feature shear flutes for better cutting action and the ability to evacuate chips easier when compared to a half-round engraver.

Harvey Tool Product Offering

Harvey Tool offers a wide variety of both Engraving Cutters and Marking Cutters. Choose from a selection of pointed, double-ended, tip radius, and tipped-off Engraving Cutter styles in 15 included angles ranging from 10° to 120°.

engraver

Marking Cutters are fully stocked in tip radius or tipped-off options, and are designed specifically for either ferrous or non-ferrous materials. Marking Cutters are offered in included angles from 20° to 120°.

While Engraving Cutters are offered uncoated or in AlTiN, AlTiN Nano, or Amorphous Diamond coatings, Marking Cutters are fully stocked in uncoated, AlTiN, or TiB2 coated styles.

Marking Cutters & Engravers Summarized

While both Engraving Cutters and Marking Cutters can accomplish similar tasks, each tool has its own advantages and purpose. Selecting the correct tool is based largely on preference and applicability to the job at hand. Factors that could impact your selection would be final Depth of Cut, Width of Cut, the angle needing to be achieved, and the desired detail of the engraving.

Liberty Machine – Featured Customer

Liberty Machine, Inc. is a small Aerospace and Defense-focused machine shop located out of owner Seth Madore’s garage in Gray, Maine. In just a few years, Liberty Machine has transformed from a side hustle into a full-fledged machine shop with customers all over the world.

We were given the chance to visit Seth at his shop in Maine and interview him for this post. We picked Seth’s mind about entrepreneurship, the online manufacturing community, some interesting home construction choices made to accommodate a machine shop, and more.

Thanks for having us come out and visit the shop for this Featured Customer post. To get started, tell us a little bit about Liberty Machine’s history, and what sort of products you typically manufacture.

I founded Liberty Machine, Inc. out of my garage about 6 years ago while I was still working full-time at one of Maine’s largest (and best) Aerospace and Defense shops. I was working close to around 80-100 hours a week, maintaining my full-time job as well as coming home and making chips in the evenings and weekends. At first, I was doing a lot of smaller pieces and one-off parts, such as fixtures and prototype work to help build up a customer base and make enough money to eventually upgrade my machine.

In the early years, I was using an old 1982 Matsuura MC-500 Mill that I picked up for around $6,000. I used that machine to generate enough cash flow and eventually pull the trigger on a 2015 DMG Mori Duravertical 5100 with a 4th axis, probing and high-pressure coolant which really allowed me to take on the type of aerospace and defense work I had been doing at my day job and make the leap into full time entrepreneurship in my own shop. Now, we have the capabilities to focus on aerospace and defense work for major clients all over the country.

We are still working out of my garage, with myself and one other employee, but there are hopes for further expansion in the future as we acquire more work and expand our customer base. If you want to keep up with our shop, follow us on Instagram @liberty_machine!

Liberty Machine

You have a great shop here and are definitely maximizing the space. How much square footage are you working with?

Currently, we are working out of a 940 sq/ft shop. We “technically” have room for one more CNC mill if we really squeezed things together. I don’t think that is in the cards though; it is more likely that we will move to a larger space if and when the time comes for expansion. Heat management and air quality are real issues when working in small spaces with low ceilings, which is something we deal with currently.

What sort of machines and software do you have here in the shop?

For now, we have two VMC’s and a decent amount of inspection equipment. We have the DMG Mori machine I previously mentioned, as well as a 2016 Kitamura-3XD. Both machines have 12k spindles, Renishaw probes, and feature coolant through spindles.

For inspection equipment, we have a 2014 Mitutoyo QM-Height 350 Digital Height Gage, a 2003 Brown & Sharpe Gage 2000 CMM with Renishaw MIP Articulating Probe Head, and a 2003 Mitutoyo PH-A14 Optical Comparator. We also recently acquired a Scienscope Stereo/Digital microscope. This allows us to perform visual inspection of our parts at an extreme amount of detail.

Liberty Machine

There are still holes in our inspection lineup, so we are always looking at adding onto what we do to provide our customers with quality machined products.

For CAD/CAM software, we use Autodesk’s Fusion 360 as well as Inventor HSM.

You mentioned using Fusion 360 for CAD/CAM. Some of our readers may know you from the Autodesk CAM forums as an “Autodesk Expert Elite.” How did that come together?

About 4-5 years ago, I knew I needed a legal, supported, capable CAM solution. After several “30-day trials” of the more affordable packages, I stumbled upon Fusion 360. Having a fair amount of experience with Esprit and MasterCAM, I taught myself Fusion 360 in between running my shop and trying to spend what little time I had with my wife and children. Even though I had prior experience in other CAM packages, I still had lots of questions. I turned to the Fusion CAM Forums for assistance. The employees and other users were excellent to work with and got me sorted out quickly.

Liberty Machine

After I became more comfortable with the Fusion 360 software, I decided to spend some of my free time helping others by answering their questions on the forums. I wanted to give back to the community that had helped me learn. Autodesk eventually took notice of my constant presence on the forums and granted me the title of “Autodesk Expert Elite,” an honor given to some of their most prolific community members and advocates. Now I work with them to help test new features, provide insight from a user’s point of view, and participate in events like Autodesk University.

How did you first get involved in manufacturing?

I will be honest – I never meant to end up working in manufacturing. When I was a teen, I had glamorous ideas about law enforcement, federal work and so forth. But, life doesn’t always work out that way (I met a wonderful girl and goals shifted, so I started looking for alternate career paths).

My friend (future brother-in-law) was a machinist, so I started asking about his work and what it involved. He was working in a “job shop” using all sorts of cool machines and technology I had never really heard about. I was very excited about this career shift and I pursued it with fervor. 19 years later and I still LOVE this trade. The thing that intrigued me most about manufacturing, and the real reason I became so fixated on the trade, was the integral role the machinist plays in every aspect of manufactured society. I believe it is the most fundamental profession there is, and I take great pride in it. The evolution of the trade from manual machining to skilled programmers running CNC machines has always fascinated me as well and has kept pushing me to learn more and continue growing as a machinist.

Liberty Machine

Is it true that you built an addition to your garage specifically for the DMG Mori machine?

That is true! Before I bought the machine, I knew it was going to be too tall for my existing space, and was also going to need a solid foundation to sit on (it weighs 7 tons). Before the machine arrived, I had a concrete slab poured right against the side wall of the existing garage, and placed the DMG Mori on that slab.

After a couple days of unfortunate rain and multiple layers of tarps covering the machine, I had several family members (carpenters by trade) help me build the addition. Ok…I helped them. They were able to get it all framed and covered in just one day, breaking down the side wall of the garage and literally building the new space around the dimensions of the machine. Like they say, if there is a will, there is a way!

Running a shop out of your garage must have been a challenge to startup. What were some of the growing pains you experienced as this shop was built out?

On a professional level, the struggle was real. Two jobs, huge payments on the horizon, wondering where all the work (and money) is going to come from… As I mentioned, at that point, I was working 100 hours a week between the two jobs, and really feeling wiped out at the end of each week. However, the hard work did eventually pay off. Once I was able to get the DMG Mori and prove to customers that I had the capabilities to go full-time on my own, it was all worth it.

Liberty Machine

Outside of that, there were the literal growing pains, like cutting holes in my garage ceiling to fit the column on the Kitamura machine, and of course, building an addition to house the DMG. But like I said, it was all worth it in the end to own my own shop.

What is the best thing about working for yourself?

I’d say the best thing about working out of my shop (and for myself) is seeing my family on a daily basis. Yes, I still work 60-70 hours a week, but to have breakfast with them each morning before our day starts and have the flexibility to shift schedules around for doctor visits and other “life stuff” is worth its weight in gold. We are all so busy in life and I think we suffer as a society because of it. I want my children to know what it’s like to have a parent that is around. Busy, yes. But still present.

You mentioned that you had used a lot of Harvey and Helical tools at your last job. However, once you were on your own, you could choose any tooling you wanted to use. What made you stick with the Harvey Performance Company brands as your go-to tools?

The thing with Harvey Tool and Helical products that keep me coming back is the consistency of quality. I know that when I buy one of these tools, I am going to get a high-performing tool that has gone through multiple levels of inspection and is consistently ground within the tight tolerances that were promised. I honestly cannot remember a single time I have had to send any Harvey or Helical tools back for quality issues.

Liberty Machine

I tell friends and others in the manufacturing community about the tools, and the hurdle is always getting them to look past the slightly higher cost. That additional cost is always worth the payoff in the end knowing that you have a tool that will produce quality parts and shave valuable minutes off your cycle times. The slightly higher cost of the Harvey/Helical product is small change compared to the long term cost savings associated with their performance.

Can you remember a key moment where Harvey Tool/Helical products really saved the day?

Truthfully, Harvey and Helical are my first thought when I’m looking at a challenging feature on a new part. If they offer something that looks like it will work, I don’t even look for an alternative. Order it, get it in house. I’d say where Harvey helps the most is their awesome selection of long reach/stub flute end mills for stainless steel. I cut so much of that, so it’s great to have a vendor stock what is truly needed.

Liberty Machine

Would you recommend entrepreneurship to other young machinists hoping to open their own shop some day?

Yes! But like all things in life, “It depends.” Entrepreneurship is certainly not for everyone. The amount of work required to get a shop rolling and out of “crisis-mode” is insane. There is no other term for it. If you have a significant other in your life, MAKE SURE they are on the same page as you. I am blessed to have a wife by my side who sees the end goal and is understanding of the sacrifice needed in the short-term for the long-term benefit of our family.

What advice might you want to give to someone starting in this trade?

Don’t stop learning. Keep your ears open and your mouth shut. That old guy in the shop has likely forgotten more than you will ever learn. The amount of tools in your Kennedy box doesn’t mean you’re a good machinist. Some of the best toolmakers I knew had small boxes with only the common tools. Learn how to excel with limited resources. Ask questions, and own up to your mistakes.

Workholding Styles & Considerations

Machinists have a number of variables to consider when setting up workholding devices for a machining operation. When it comes to workholding, there are some major differences between holding a loosely toleranced duplicate part with a 10-minute cycle time and holding a tightly toleranced specialized part with a 10-hour cycle time. Determining which method works best for your machining job is essential to maintaining an efficient operation.

Workholding Devices

Ideal workholding devices have easily repeatable setups. For this reason, some machines have standard workholding devices. Vises are generally used with milling machines while chucks or collets are used when running a lathe machine. Sometimes, a part may need a customized workholding setup in order to secure the piece properly during machining. Fixtures and jigs are examples of customized workholding devices.

Fixtures and Jigs

A jig is a work holding device that holds, supports and locates a workpiece and guides the cutting tool into a specific operation (usually through the use of one or more bushings). A fixture is essentially the same type of device, but the main difference is that it does not guide the cutting tool into a specified operation. Fixtures are typically used in milling operations while jigs are generally used in drilling, reaming, tapping and boring. Jigs and fixtures are more precise relative to standard workholding devices, which leads to tighter tolerances. They can also be indexable, allowing them to control the cutting tool movement as well as workpiece movement. Both jigs and fixtures are made up of the same basic components: fixture bodies, locators, supports, and clamps.

The 4 Fixture Bodies

There are 4 basic types of fixture bodies: faceplates, baseplates, angle plates, and tombstones.

Faceplates: Typically used in lathe operations, where components are secured to the faceplate and then mounted onto the spindle.

Baseplates: Common in milling and drilling operations and are mounted to the worktable.

Angle plates: Two plates perpendicular to each other but some are adjustable or customized to change the angle of the workpiece.

Tombstones: Large vertically oriented rectangular fixtures that orients a workpiece perpendicular to the worktable. Tombstones also have two sides to accommodate multiple parts.

workholding

Locators

Locators are characterized by four criteria: assembled, integral, fixed, and adjustable. Assembled locators, can be attached and removed from the fixture, which is contrary to integral locators that are built into the fixture. Fixed locators allow for no moving components, while adjustable locators permit movement through the use of threads and/or springs, and can adjust to a workpiece’s size. These can be combined to provide the appropriate rigidity-assembly convenience ratio. For example, a V-locator fixture is the combination of assembled and fixed locators. It can be secured to a fixture but has no moving components.

workholding

Supports

Supports do exactly what their name suggests, they support the workpiece during the machining process to avoid workpiece deformation. These components can double as locators and also come fixed, adjustable and integral, or assembled. Generally, supports are placed under the workpiece during manufacturing but this also depends on the geometry of the workpiece, the machine being operated and where the cutting tool will make contact. Supports can come in different shapes and sizes. For example, rest buttons are smaller support components used in series either from underneath the workpiece or from the sides. Concurrently, parallel supports are placed on either side of the part to provide general support.

workholding

Clamps

Clamps are devices used for strengthening or holding things together, and come in different shapes, sizes and strengths. Vises and chucks have movable jaws and are considered standard clamps. One atypical example is the toggle clamp, which has a pivot pin that acts as a fulcrum for a lever system. One of the more convenient types is a power clamping system. There are two type of power clamping methods: hydraulic and pneumatic.

workholding

Example of a standard fixture setup.

Hydraulic Systems

Hydraulic Systems create a gripping force by attaining power from compressing a liquid. This type of power clamp is generally used with larger workpieces as it usually takes up less space relative to pneumatic clamps.

Pneumatic clamps

Pneumatic clamps attain their gripping force from the power created by a compressed gas (usually air). These systems are generally bulkier and are used for smaller workpieces that require less room on the worktable. Power clamping offers a few advantages over conventional clamping. First, these systems can be activated and deactivated quickly to save on changeover time. Second, they place uniform pressure on the part, which help prevent errors and deformation. A significant disadvantage they pose is the cost of a system but this can be quickly offset by production time saved.

Key Guidelines to Follow

Lastly, there are a few guidelines to follow when choosing the appropriate fixture or jig setup.

Ensure Proper Tolerancing

The tolerances of the workholding device being used should be 20%-50% tighter than those of the workpiece.

Utilize Acceptable Locating & Supporting Pieces

Locating and supporting pieces should be made of a hardened material to prevent wear and allow for several uses without the workpieces they support falling out of tolerance. Supports and locators should also be standardized so that they can be easily replaced.

Place Clamps in Correct Locations

Clamps should be placed above the locations of supports to allow the force of the clamp to pass into the support without deforming the workpiece. Clamps, locators and supports should also be placed to distribute cutting forces as evenly as possible throughout the part. The setup should allow for easy clamping and not require much change over time

Maximize Machining Flexibility

The design of the fixture or jigs should maximize the amount of operations that can be performed in one orientation. During the machining operation, the setup should be rigid and stable.

Bottom Line

Workholding can be accomplished in a number of different ways and accomplish the same task of successfully gripping a part during a machining operation with the end result being in tolerance. The quality of this workholding may differ greatly as some setups will be more efficient than others. For example, there is no reason to create an elaborate jig for creating a small slot down the center of a rectangular brick of aluminum; a vise grip would work just fine. Maximizing the efficiency and effectiveness of an operators’ workholding setup will boost productivity by saving on changeover, time as well as cost of scrapped, out of tolerance parts.

Shank Tolerances, Collet Fits, & h6 Benefits

A cutting tool’s shank is one of the more vital parts of a tool, as it’s critical to the collet-tool connection. There are several types of shanks, each with their own tolerances and suitable tool holder methods. One of the most popular and effective tool holding styles is a shrink fit tool holder, which works with h6 shanks, but what does this mean and what are the benefits of it? How is this type of shank different from a shank with standard shank tolerances? To answer these questions, we must first explore the principals of tolerances.

The Principals of Tolerances

Defining Industry Standard Tolerances

There are two categories of shank tolerances that machinists and engineers operating a CNC machine should be familiar with: hole basis and shank (or shaft) basis. The hole basis system is where the minimum hole size is the starting point of the tolerance. If the hole tolerance starts with a capital “H,” then the hole has a positive tolerance with no negative tolerance. The shank basis system is where the maximum shank size is the starting point. This system is relatively the same idea as the hole basis system but instead, if the tolerance starts with a lowercase “h,” the shank has a negative tolerance and no positive tolerance.

Letter Designations

The limits of tolerance for a shank or hole are designated by the appropriate letter indicating the deviation. For instance, the letter “k” has the opposite minimum and maximum designations as “h”. Tolerances beginning with “k” are exclusively positive, while tolerances beginning with “h” are exclusively negative. The number following the given letter denotes the International Tolerance (IT) grade. For example, a tolerance with the number 6 will have a smaller tolerance range than the number 7, but larger than the number 5. This range is based on the size of the shank. A hole that has a 0.030” diameter will have an h6 tolerance of (+0.0000,-0.0002), while a 1.00” hole with have an h6 tolerance band of (+0.0000,-0.0005).

It is important to note that most sources list IT tolerances in millimeters, while the graph below has been translated to inches. Operations that require more precise manufacturing, such as reaming, will have lower IT grades. Operations that do not require manufacturing to be as precise will have higher IT grades.

shank tolerances

Preferred Collet Fits

Different types of combinations of hole basis and shank basis tolerances lead to different types of collet fits. The following table offers insight into a few different types of preferred fits and the shank tolerances that are required for each.

collet fits

Image: Machinery’s Handbook 29th Edition.

Shrink Fit Tool Holders

The shrink fit holder is one of the more popular styles of tool holders because of its ability to be more customizable, as evident in the chart above. In this method, a collet is heated to expand, then cooled to contract around the shank of a tool. At room temperature, a cutting tool should not be able to be inserted into a shrink fit holder – only when the holder has undergone thermal expansion due to the introduction of a significant amount of heat should the tool fit. As the holder cools, the tool is held tighter and tighter in place. Typically, a holder is heated through a ring of coils by an induction heater. It is important to heat the holder uniformly, paying mind to not overheat it. Doing so could cause the shank that is being held to expand within the holder and remain stuck.

 

Benefits of Shrink Fit Tool Holders

  1. Gripping power. The shank is held flush and uniform against the holder, resulting in a tighter connection.
  2. Low runout. A more secure connection will result in extended tool life, and a higher quality surface finish.
  3. Better balance for high RPM. With a tighter tool-to-holder connection, the opportunity exists for more aggressive running parameters.

Shank Tolerances Summarized

Understanding shank tolerances is an intricate part of the machining process as it impacts which tool holder is appropriate for your job. A secure holder connection is vital to the performance of the tool in your application. With an h6 shrink fit holder, the result is a secure connection with stronger gripping power. However, only certain shanks are able to be used with this type of holder. From the letter designation assigned to a shank, to whether that letter is upper or lowercase, each detail is vital to ensuring a proper fit between your tools shank and its corresponding shrink fit holder.

Best Practices of Tolerance Stacking

Tolerance stacking, also known as tolerance stack-up, refers to the combination of various part dimension tolerances. After a tolerance is identified on the dimension of a part, it is important to test whether that tolerance would work with the tool’s tolerances: either the upper end or lower end. A part or assembly can be subject to inaccuracies when its tolerances are stacked up incorrectly.

The Importance of Tolerances

Tolerances directly influence the cost and performance of a product. Tighter tolerances make a machined part more difficult to manufacture and therefore often more expensive. With this in mind, it is important to find a balance between manufacturability of the part, its functionality, and its cost.

Tips for Successful Tolerance Stacking

Avoid Using Tolerances that are Unnecessarily Small

As stated above, tighter tolerances lead to a higher manufacturing cost as the part is more difficult to make. This higher cost is often due to the increased amount of scrapped parts that can occur when dimensions are found to be out of tolerance. The cost of high quality tool holders and tooling with tighter tolerances can also be an added expense.

Additionally, unnecessarily small tolerances will lead to longer manufacturing times, as more work goes in to ensure that the part meets strict criteria during machining, and after machining in the inspection process.

Be Careful Not to Over Dimension a Part

When an upper and lower tolerance is labeled on every feature of a part, over-dimensioning can become a problem. For example, a corner radius end mill with a right and left corner radii might have a tolerance of +/- .001”, and the flat between them has a .002” tolerance. In this case, the tolerance window for the cutter diameter would be +/- .004”, but is oftentimes miscalculated during part dimensioning. Further, placing a tolerance on this callout would cause it to be over dimensioned, and thus the reference dimension “REF” must be left to take the tolerance’s place.

stacking tolerances

Figure 1: Shape of slot created by a corner radius end mill

Utilize Statistical Tolerance Analysis:

Statistical analysis looks at the likelihood that all three tolerances would be below or above the dimensioned slot width, based on a standard deviation. This probability is represented by a normal probability density function, which can be seen in figure 2 below. By combining all the probabilities of the different parts and dimensions in a design, we can determine the probability that a part will have a problem, or fail altogether, based on the dimensions and tolerance of the parts. Generally this method of analysis is only used for assemblies with four or more tolerances.

stacking tolerances

                                                               Figure 2: Tolerance Stacking: Normal distribution

Before starting a statistical tolerance analysis, you must calculate or choose a tolerance distribution factor. The standard distribution is 3 . This means that most of the data (or in this case tolerances) will be within 3 standard deviations of the mean. The standard deviations of all the tolerances must be divided by this tolerance distribution factor to normalize them from a distribution of 3  to a distribution of 1 . Once this has been done, the root sum squared can be taken to find the standard deviation of the assembly.

Think of it like a cup of coffee being made with 3 different sized beans. In order to make a delicious cup of joe, you must first grind down all of the beans to the same size so they can be added to the coffee filter. In this case, the beans are the standard deviations, the grinder is the tolerance distribution factor, and the coffee filter is the root sum squared equation. This is necessary because some tolerances may have different distribution factors based on the tightness of the tolerance range.

The statistical analysis method is used if there is a requirement that the slot must be .500” wide with a +/- .003” tolerance, but there is no need for the radii (.125”) and the flat (.250”) to be exact as long as they fit within the slot. In this example, we have 3 bilateral tolerances with their standard deviations already available. Since they are bilateral, the standard deviation from the mean would simply be whatever the + or – tolerance value is. For the outside radii, this would be .001” and for the middle flat region this would be .002”.

For this example, let’s find the standard deviation (σ) of each section using equation 1. In this equation represents the standard deviation.

standard deviation

The standard assumption is that a part tolerance represents a +/- 3  normal distribution. Therefore, the distribution factor will be 3. Using equation 1 on the left section of figure 1, we find that its corrected standard deviation equates to:

tolerance stacking

This is then repeated for the middle and right sections:

standard deviation

After arriving at these standard deviations, we input the results into equation 2 to find the standard deviation of the tolerance zone. Equation 2 is known as the root sum squared equation.

root sum

At this point, it means that 68% of the slots will be within a +/- .0008” tolerance. Multiplying this tolerance by 2 will result in a 95% confidence window, where multiplying it by 3 will result in a 99% confidence window.

68% of the slots will be within +/- .0008”

95% of the slots will be within +/- .0016”

99% of the slots will be within +/- .0024”

These confidence windows are standard for a normal distributed set of data points. A standard normal distribution can be seen in Figure 2 above.

Statistical tolerance analysis should only be used for assemblies with greater than 4 toleranced parts. A lot of factors were unaccounted for in this simple analysis. This example was for 3 bilateral dimensions whose tolerances were representative of their standard deviations from their means. In standard statistical tolerance analysis, other variables come into play such as angles, runout, and parallelism, which require correction factors.

Use Worst Case Analysis:

Worst case analysis is the practice of adding up all the tolerances of a part to find the total part tolerance. When performing this type of analysis, each tolerance is set to its largest or smallest limit in its respective range. This total tolerance can then be compared to the performance limits of the part to make sure the assembly is designed properly. This is typically used for only 1 dimension (Only 1 plane, therefore no angles involved) and for assemblies with a small number of parts.

Worst case analysis can also be used when choosing the appropriate cutting tool for your job, as the tool’s tolerance can be added to the parts tolerance for a worst case scenario. Once this scenario is identified, the machinist or engineer can make the appropriate adjustments to keep the part within the dimensions specified on the print. It should be noted that the worst case scenario rarely ever occurs in actual production. While these analyses can be expensive for manufacturing, it provides peace of mind to machinists by guaranteeing that all assemblies will function properly. Often this method requires tight tolerances because the total stack up at maximum conditions is the primary feature used in design. Tighter tolerances intensify manufacturing costs due to the increased amount of scraping, production time for inspection, and cost of tooling used on these parts.

Example of worst case scenario in context to Figure 1:

Find the lower specification limit.

For the left corner radius

.125” – .001” = .124”

For the flat section

.250” – .002” = .248”

For the right corner radius

.125” – .001” = .124”

Add all of these together to the lower specification limit:

.124” + .248” + .124” = .496”

Find the upper specification limit:

For the left corner radius

.125” + .001” = .126”

For the flat section

.250” + .002” = .252”

For the right corner radius

.125” + .001” = .126”

Add all of these together to the lower specification limit:

.126” + .252” + .126” = .504”

Subtract the two and divide this answer by two to get the worst case tolerance:

(Upper Limit – Lower Limit)/2 = .004”

Therefore the worst case scenario of this slot is .500” +/- .004”.

Helical Solutions: Behind the Scenes

We have shown our end users bits and pieces of our manufacturing process on our website and via social media, but for the first time we decided to open our own doors to the public and show you every step behind how we manufacture and fulfill the Helical Solutions product. We partnered with John Saunders from NYC CNC to create a “Factory Tour” video, covering topics like our CNC grinding machines and setups, tool manufacturing, and our warehouse organization and fulfillment procedures.

In the video below, we first toured our Gorham, Maine manufacturing plan with Plant Manager Adam Martin. Then, we ran a few tests with the Helical tools on our Haas machine, before heading back to our warehouse in Massachusetts to talk about fulfillment and new products with Fulfillment Manager Megan Townsley.

 

 

7 Facts Revealed in Our Factory Tour (Plus 3 More That Didn’t Make the Cut)

We know you’re busy making amazing parts, and might not have time for the entire video. To save you time, here are some of the most important facts you should know about Helical.

We Take Quality Control Seriously

Our high performance end mills go through an extensive inspection and quality assurance process before they end up in your machine, with multiple inspection points along the manufacturing journey. At the 17 minute mark of the video, you can learn more about how we monitor the quality of the tools in batches as they are manufactured. If you skip ahead to the 29 minute mark, you can see some of our more advanced inspection machines in action.

We Stand Behind Our Tools with Our Renewal Services

Our Tool Renewal service is a great way to maximize your cost-savings and avoid having to re-purchase new tools without sacrificing any aspects of the original design. At Helical, we do not re-sharpen tools. Rather, we restore your tools to their original geometry. We will review the condition of your used tools and return the cutting edge to its original sharpness and strength, allowing the tool to retain its outstanding performance. The renewed tools go through the same rigorous inspection, edge prep, and coating process that we follow for all our of our new tools. To learn more about our Tool Renewal services, head to the 23:30 mark in the video.

Our Tool Coating Is Done In-House

We have multiple tool coating machines in-house which allow us to take the ground tools right off the line and transfer them to our coating room to have Aplus, Zplus, or Tplus coatings added. These machines also have the capability to create roughly 20 different coatings, which are reserved for specials and custom orders. If you want a close-up look at the coating room and learn how the PVD coating process actually works, head to the 35 minute mark.

Our Standard Catalog Items Are Stocked and Ready for Your Machine

We don’t make our standard catalog tools to order. All of our standard tools are stocked and ready to make some chips in your machine. We also introduce hundreds of new tools to our annual catalog to keep providing our customers with the latest in high performance tooling technology. You can check out our new tools for 2018, including our new High Balance Tools and Metric Tooling, by heading to 52:20, or take quick look at our rows of stocked tools in our warehouse by jumping to 56:55.

Diamond Wheels Grind Carbide Tools

Diamond grinding wheels are the essential tool (outside of the machine) when it comes to grinding carbide. We have a unique management system for our diamond wheels, and a redressing process which can see these wheels last up to a year or more before they need replacement. Adam goes through our “frozen wheel” room with John at the 32:45 mark in the video above.

We Track Every Batch of Tools With Laser Etching

Our tools are all laser etched on-site with our logo, phone number, and tool description, but also with a specific batch number. These batch numbers allow us full track-ability of every tool so we can quickly asses any questions or concerns a customer may have about a tool. With these numbers, we are able to track the tool’s journey all the way back to which machine it was made on, which grinding wheel was used, and who ran the program. We have a couple of these laser etching machines in Maine, which you can see in action at the 42 minute mark.

If You Can Dream It, We Have Probably Made It

We have had some crazy tool drawings come in to our custom tool program over the years, including oddly shaped form tools, tools with a crazy long length of cut, “paper cutters”, and more. You can see some cool examples of custom tools we have manufactured by jumping to the 20 minute mark. If you are more interested in how we actually make them, head to the 27 minute mark to see one of our large custom tools being ground on our Walter machines.

Our Technical Resources Are Second To None

We don’t leave you hanging after your purchase of Helical tools. We have a multitude of technical resources and How-Tos available here on our blog, and we also offer the HEM Guidebook, a complete guide to High Efficiency Milling techniques.

If you are looking for information on speeds and feeds, we suggest you try our Machining Advisor Pro application. This application is designed to increase metal removal rates and shop productivity by generating customizable running parameters optimized for your Helical Solutions end mills. You can click here to get started with Machining Advisor Pro today.

You Will Always Get a Real Person When You Call Helical

If you have technical questions about an upcoming job, a special application, or tooling selection, you can contact Helical by phone at 866-543-5422. Our technical experts are available over the phone Monday-Friday from 8 AM to 5 PM EST, and you will always get a real person to talk to with no automated systems to navigate through. You can also reach our team by email at [email protected].

Questions about where to buy Helical tools? You can give our team a call, or you can find your local distributor by using the “Find a Distributor” tool on our website. Simply choose your state to see a complete list of authorized distributors in your area.

We’re Hiring!

We have a current list of our open opportunities on our website! Open jobs include CNC Machinist, Quality Control Inspector, and Customer Service Representative.