Grappling with Graphite: A Machining Guide

Despite being a softer material, graphite is actually one of the most difficult materials to machine. There are many considerations machinists need to make in terms of tooling, coolant use, and personal safety when it comes to machining graphite parts. This “In The Loupe” post will examine graphite’s material properties, the key machining techniques to consider, and tips for properly selecting cutting tools to achieve success in this tricky material.

What is Graphite?

While graphite is an allotrope of carbon, the two terms are not simply interchangeable. Carbon is an element that can form into several different allotropes including graphite, diamond, and fullerite. Graphite happens to be the most stable form of carbon, and is the most common, as carbon naturally occurs as graphite under standard conditions.

Graphite is most recognized for its superior conductivity and resistance to high heat and corrosion. This makes it a common material in high heat, high-pressure situations in the aerospace, electrode, nuclear, energy, and military industries.

graphite cnc material

Even though graphite can handle intense high-pressure situations with ease, it is actually a very soft, abrasive, and brittle material. This can cause serious challenges when machining, as graphite can eat up cutting tools, and severely minimize a tool’s usable life. However, with the proper tooling and techniques, there are ways to optimize graphite machining to be more cost-effective than the competition.

Graphite Machining Techniques

Since graphite is such a soft and brittle material, special consideration needs to be made when machining to avoid chipping it. To get a good cut, it is recommended that you take light chip loads and use lower feed rates in graphite. If you were to take a heavy cut at a fast feed rate, you would start chipping the graphite and could cause it to fracture completely. To give a comparison point, chip loads for graphite are similar to those for Aluminum materials, but with less than half the feed rate.

To give you an idea of speeds and feeds for graphite, here is an example using a 1/4″ Harvey Tool CVD Diamond Coated, 4 flute Square End Mill. If that tool was running at a standard RPM of 12,000 at 780 SFM, the recommended chip load would be .00292 for a feed rate of 140 IPM.

graphite electrode machining

In terms of machine setup, the one major tip to remember is to always avoid using coolant. Graphite is a fairly porous material, and so it can absorb coolant and act as a “coolant sponge,” which will cause problems with finished parts. Inside the machine and on the tooling, the coolant can actually react with the graphite dust and create an abrasive slurry, which will cause problems while machining. A vacuum system is recommended for clearing material while machining graphite. Otherwise, coated tools should be able to run dry.

Another thing to note when machining graphite is that because graphite does not produce chips, but rather a cloud of very abrasive dust, it can be harmful to operators and machines without proper care. Operators should be wearing a protective mask to avoid inhaling the graphite dust. Proper ventilation and maintaining air quality in the shop is also key for the protection of machinists when working in graphite.

Since the graphite dust is also extremely conductive, it can easily damage non-protective circuits inside your CNC machine, which can cause major electrical issues. While coolant is not recommended, a vacuum system can help to remove the dust, keeping it from accumulating too much inside the machine and preventing serious problems.

Cutting Tools for Graphite Machining

As previously mentioned, graphite is a notorious cutting tool-killer due to its extremely abrasive nature. Even the highest quality carbide end mills, if left uncoated, will wear quickly on most graphite jobs. This extreme wear may force a tool change during an operation, which could lead to an imperfection in the part when trying to restart the operation where the worn tool left off.

graphite cutting tools

When selecting a cutting tool for graphite machining, the coating and cutting edge is the most important consideration. Flute count, helix angles, and other key features of the tool geometry ultimately come second to the coating when purchasing tooling for graphite.

For graphite machining, a CVD (Chemical Vapor Deposition) diamond coating is recommended whenever possible to maximize tool life and tool performance. These coatings are grown directly into the carbide end mill, improving the hardness and leaving the tool with a coating layer that is 5 times thicker than a PVD Diamond Coating. While not the sharpest edge, the CVD diamond coating provides much longer tool life than other diamond coatings due to the thicker diamond layer.

Even though initial tooling costs may be higher with CVD coated tools versus uncoated tools, since CVD coated tools see considerably longer tool life than uncoated tools, this makes the cost per part shrink significantly. In difficult, abrasive materials like graphite, the uncoated carbide tool will last a short time before the abrasiveness of the graphite completely wears down the cutting edge. Having a CVD coated tool will give you a leg up over the competition, keep your machine running with less downtime for tool changes, and ultimately deliver substantial cost savings.

end mills for graphite
CVD Diamond Coated End Mill from Harvey Tool

Overall, graphite can be a difficult material to machine, but with the right cutting tools and proper speeds and feeds you will be making quality parts in no time. Harvey Tool offers a wide selection of CVD coated end mills in various diameters, reaches, and lengths of cut to ensure you have what you need for any job that comes your way.

5 Things to Know About Helical’s High Feed End Mills

Helical Solutions‘ High Feed End Mills provide many opportunities for machinists, and feature a special end profile to increase machining efficiencies. A High Feed End Mill is a High Efficiency Milling (HEM) style tool with specialized end geometry that utilizes chip thinning, allowing for drastically increased feed rates in certain applications. While standard end mills have square, corner radius, or ball profiles, this Helical tool has a specialized, very specific design that takes advantage of chip thinning, resulting in a tool that can be pushed harder than a traditional end mill.

Below are 5 things that all machinists should know about this exciting Helical Solutions product offering.

1. They excel in applications with light axial depths of cut

A High Feed End Mill is designed to take a large radial depth of cut (65% to 100% of the cutter diameter) with a small axial depth of cut (2.5% to 5% diameter) depending on the application. This makes High Feed End Mills perfect for face milling, roughing, slotting, deep pocketing, and 3D milling. Where HEM toolpaths involve light radial depths of cut and heavy axial depths of cut, High Feed End Mills utilize high radial depths of cut and smaller axial depths of cut.

2. This tool reduces radial cutting forces

The end profile of a High Feed End Mill is designed to direct cutting forces upward along the axis of the tool and into the spindle. This reduces radial cutting forces which cause deflection, allowing for longer reach tools while reducing chatter and other issues that may otherwise lead to tool failure. The reduction of radial cutting forces makes this tool excellent for use in machines with lower horsepower, and in thin wall machining applications.

3. High Feed End Mills are rigid tools

The design and short length of cut of High Feed End Mills work in tandem with the end geometry to produce a tool with a strong core, further limiting deflection and allowing for tools with greater reach lengths.

4. They can reduce cycle times

In high RDOC, low ADOC applications, High Feed End Mills can be pushed significantly faster than traditional end mills, saving time and money over the life of the tool.

5. High Feed End Mills are well suited for hard materials

The rigidity and strength of High Feed End Mills make them excellent in challenging to machine materials. Helical’s High Feed End Mills come coated with Tplus coating, which offers high hardness and extended tool life in high temp alloys and ferrous materials up to 45Rc.

In summary, High Feed End Mill tools with specialized end geometry that utilizes chip thinning and light axial depths of cut to allow for significantly increased feed rates in face milling, slotting, roughing, deep pocket milling, and 3D milling applications. The end profile of a High Feed End Mill applies cutting forces back up into the spindle, reducing radial forces that lead to deflection in long reach applications. Combining this end geometry with a stubby length of cut results in a tool that is incredibly rigid and well suited for harder, difficult to machine materials.

High Efficiency Milling for Titanium Made Easy With Helical’s New HVTI Cutter

Titanium is a notoriously difficult material to machine, especially in aggressive toolpaths, such as those associated with High Efficiency Milling (HEM). Helical Solutions’ new line of tooling, the HVTI-6 series of end mills, is optimized specifically for this purpose, and proven to provide 20% more tool life than a competitor’s similar tool.

At face level, these new Helical end mills feature corner radius geometry, 6 flutes, and are Aplus coated for optimal tool life and increased cutting performance. But there is much more to these end mills than the typical geometry of standard 6 flute tools. The HVTI-6 was designed with a combination of a unique rake, core, and edge design that give it a leg up over standard 6 flute tools for Titanium while cutting HEM toolpaths. Click here to watch the HVTI-6 in action!

End Mills for Titanium

The design of the HVTI-6 was the result of significant testing by the Harvey Performance Company Innovation and New Product Development teams. These teams spent many months testing tools, doing in-depth analysis on materials and tool geometry, and pushing these tools through dozens of hours in the cut at testing sites across the country.

The new HVTI-6 cutter experienced higher metal removal rates (MRR) and 20% longer tool life while performing HEM in Titanium when compared to a standard 6 flute tool offered by a Helical Solutions competitor. This type of tool life improvement will produce huge cost savings on tooling, as well as shortened cycle times and lower cost per part.

Helical HVTI Titanium

The Harvey Performance Innovation team targeted Titanium grade Ti6Al4V for their testing, which accounts for the vast majority of the Titanium being machined in North America. The test part was designed and programmed to allow for a more defined agility test of the tool, taking the tool into key geometry cutting exercises like tight corners, long straight line cuts, and rapid movement.

Many hours were spent with Lyndex-Nikken, manufacturers of high-quality rotary tables, tool holders, and machining accessories, at their Chicago headquarters. By working with the team at Lyndex-Nikken, the Harvey Performance Company team was able to test under optimal conditions with top-of-the-line tool holders, work holding, and machining centers. Lyndex was also available to provide their expert support on tool holding techniques and were an integral part of the testing process for these tools. Video of the impressive test cuts taken at the Lyndex facility can be seen below.

WATCH THE HVTI IN ACTION

In these tests, the HVTI was able to run HEM toolpaths at 400 SFM and 120 IPM in Ti6Al4V, which served as the baseline for most of the testing.

While the standard 6 flute tools offered by Helical will still perform to high standards in Titanium and other hard materials (steels, exotic metals, cast iron), the HVTI-6 is a specialized, material-specific tool designed specifically for HEM toolpaths in Titanium. Advanced speeds and feeds for these new tools are already available in Machining Advisor Pro, and the complete offering is now available in the Helical CAM tool libraries for easy programming.

To learn more about the HVTI 6 Flute End Mills for Titanium, please visit the Helical Solutions website. To learn more about HEM techniques, download the HEM Guidebook for a complete guide on this advanced toolpath.

Simplify Your Cutting Tool Orders

With the launch of the new Helical Solutions website, Harvey Performance Company is proud to introduce a new way to order Helical cutting tools. Now, users of our new website are able to send a “shopping cart” of Helical tools they’re interested in directly to their distributor to place an order, or share it with a colleague. Let’s dive into the details about this functionality and learn how you can take advantage of the time savings associated with sending a “shopping cart” to your distributor for simplified ordering.

Get Started with a HelicalTool.com Account

First, you must create an account on HelicalTool.com. Having an account on the Helical website allows you to save and edit “shopping carts,” which can be sent to a distributor to place an order; choose a preferred distributor; auto-fill your information in any important forms; and to manage your shipping information.

Create Helical Account

 

Now that you have an account, it is time to start creating your first “shopping cart.”

Creating a “Shopping Cart”

To begin creating a new shopping cart, simply click on the “My Carts” text in the top right menu. This will take you to the management portal, where you can add a new “shopping cart” by selecting “Create New Shopping Cart.”

Helical Solutions Order

Once complete, you can name your “shopping cart” anything you would like. One example might be creating a collection of tools for each of your jobs, or for different machines in the shop. In this case, we will name it “Aluminum Roughing Job.” You can create as many different “shopping carts” as you would like; they’ll never be removed from your account unless you choose to delete them, allowing you to go back to past tooling orders whenever you’d like.

Helical Solutions Website

Now that you have a “shopping cart” created, it is time to start adding tools to it!

Adding Tools to Your “Shopping Cart”

There are multiple ways to add tooling to your “shopping cart,” but the easiest method is by heading to a product table. In this example, we will be adding tooling from our 3 Flute, Corner Radius – 35° Helix product line. We want to add a quantity of 5 of EDP #59033 to our “shopping cart.” To do this, simply click on the “Add To Cart” icon located in the table row next to pricing and tool descriptions. This will open up a small window where we can manage our selection. The first step will be to choose which “shopping cart” we want to add this tool to, so we will select our “Aluminum Roughing Job” collection.

Helical Online Ordering

Since this tool is offered uncoated and Zplus coated, we need to select which option we would like from the drop down menu. For this example, we will select the Zplus coated tool. Now, we simply need to update our quantity to “5”, and click “Add To Cart.” That tool will now appear in your “shopping cart” in the quantity selected.

If you need more information on a tool, you can click on an EDP number to be brought to the tool details page, where you can also add that EDP to your collection.

If you know the EDP number you need and want to check stock levels, use our Check Stock feature to check quantities on hand, and then add the tools to your “shopping cart” right from the Check Stock page.

check stock

Now, it is time to send the “shopping cart” to place an order with your distributor!

Placing An Order With Your Distributor

Once you have completed adding tools to your “shopping cart,” navigate back to the My Carts page to review it. From here, you can update quantities, see list pricing, and access valuable resources.

On the right side of the My Cart screen, you will see an option to “Send to Distributor.” Click on the text to expand the drop down. If you have previously added a preferred distributor from your account page and they are participating in our Shopping Cart Program, you will see their information in this area.

If you have not yet selected a preferred distributor, select “Update My Distributor.” This will bring you to a new page where you can select your state and see all participating distributors in your area. Select one distributor as your preferred distributor, and then head back to the My Cart page.

Now that you have a distributor selected, you can do a final review of the “shopping cart,” and then simply click “Send Cart.” This will send an email order directly to your distributor with all of your shipping information, your list of tools and requested quantities, and your contact information. You will also receive a copy of this email for your records.

Helical Distributor

Within 1 business day, the distributor will follow up with you to confirm the order, process payment, and get the tools shipped out and on the way to your shop. No more phone calls or emails – just a single click, and your order is in the hands of our distributor partners.

To get started with this exciting new way to shop for Helical cutting tools, click here to begin creating an account on HelicalTool.com!

Show Us What You #MadeWithMicro100

Are you proud of the parts you #MadeWithMicro100? Show us with a video of the parts you are making, the Micro 100 Tool used, and the story behind how that part came to be, for a chance to win a $1,000 Amazon gift card grand prize!

With the recent addition of the Micro 100 brand to the Harvey Performance Company family, we want to know how you have been utilizing its expansive tooling offering. Has Micro 100’s Micro-Quik™ system helped you save time and money? Do you have a favorite tool that gets the job done for you every time? Has Micro 100 tooling saved you from a jam? We want to know! Send us a video on Instagram and show us what you #MadeWithMicro100!

How to Participate

Using #MadeWithMicro100 and @micro_100, tag your video of the Micro 100 tools machining your parts on Instagram or Facebook. Remember, don’t share anything that could get you in trouble! Proprietary parts and trade secrets should not be on display.

Official Contest Rules

Contest Dates:

  • The contest will run between December 5, 2019 to January 17, 2020. Submit as many entries as you’d like! Entries that are submitted before or after the contest period will not be considered for the top prizes (But we’d still like to see them!)

The Important Stuff:

  1. Take a video of your Micro 100 tool in action, clear and visible.
  2. Share your video on social media using #MadeWithMicro100 and tagging @Micro_100.
  3. Detail the story behind the project (tool number(s), operation, running parameters, etc.)

Prizes

All submissions will be considered for the $1,000 Amazon gift card grand prize. Of these entries, the most impressive (10) will be put up to popular vote. All entries put up to vote will be featured on our new customer testimonial page on our website with their name, social media account, and video displayed for everybody to see.

We’ll pick our favorites, but the final say is up to you. Public voting will begin on January 21, 2020, and a winner will be announced on January 28, 2020.

The top five entries will be sent Micro 100’s Micro-Quik™ tool change system with a few of our quick change tools. The top three entries will be offered a spot as a “Featured Customer” on our “In The Loupe” blog!

The Fine Print:

  • Please ensure that you have permission from both your employer and customer to post a video.
  • All entries must be the original work of the person identified in the entry.
  • No purchase necessary to enter or win. A purchase will not increase your chances of winning.
  • On January 28, 2020, the top 5 winners will be announced to the public. The Top 5 selected winners will receive a prize. The odds of being selected depend on the number of entries received. If a potential winner cannot be contacted within five (5) days after the date of first attempt, an alternative winner may be selected.
  • The potential winners will be notified via social media. Each potential winner must complete a release form granting Micro 100 full permission to publish the winner’s submitted video. If a potential winner cannot be contacted, or fails to submit the release form, the potential winner forfeits prize. Potential winners must continue to comply with all terms and conditions of these official contest rules, and winning is contingent upon fulfilling all requirements.
  • Participation in the contest constitutes entrants’ full and unconditional agreement to and acceptance of these official rules and decisions. Winning a prize is contingent upon being compliant with these official rules and fulfilling all other requirements.
  • The Micro 100 Video Contest is open to residents in US and Canada who are at least 18 years old at the time of entry.

Selecting the Right Chamfer Cutter Tip Geometry

A chamfer cutter, or a chamfer mill, can be found at any machine shop, assembly floor, or hobbyist’s garage. These cutters are simple tools that are used for chamfering or beveling any part in a wide variety of materials. There are many reasons to chamfer a part, ranging from fluid flow and safety, to part aesthetics.

Due to the diversity of needs, tooling manufacturers offer many different angles and sizes of chamfer cutters, and as well as different types of chamfer cutter tip geometries. Harvey Tool, for instance, offers 21 different angles per side, ranging from 15° to 80°, flute counts of 2 to 6, and shank diameters starting at 1/8” up to 1 inch.

After finding a tool with the exact angle they’re looking for, a customer may have to choose a certain chamfer cutter tip that would best suit their operation. Common types of chamfer cutter tips include pointed, flat end, and end cutting. The following three types of chamfer cutter tip styles, offered by Harvey Tool, each serve a unique purpose.

Three Types of Harvey Tool Chamfer Cutters

Type I: Pointed

This style of chamfer cutter is the only Harvey Tool option that comes to a sharp point. The pointed tip allows the cutter to perform in smaller grooves, slots, and holes, relative to the other two types. This style also allows for easier programming and touch-offs, since the point can be easily located. It’s due to its tip that this version of the cutter has the longest length of cut (with the tool coming to a finished point), compared to the flat end of the other types of chamfer cutters. With only a 2 flute option, this is the most straightforward version of a chamfer cutter offered by Harvey Tool.

Type II: Flat End, Non-End Cutting

Type II chamfer cutters are very similar to the type I style, but feature an end that’s ground down to a flat, non-cutting tip. This flat “tip” removes the pointed part of the chamfer, which is the weakest part of the tool. Due to this change in tool geometry, this tool is given an additional measurement for how much longer the tool would be if it came to a point. This measurement is known as “distance to theoretical sharp corner,” which helps with the programming of the tool. The advantage of the flat end of the cutter now allows for multiple flutes to exist on the tapered profile of the chamfer cutter. With more flutes, this chamfer has improved tool life and finish. The flat, non-end cutting tip flat does limit its use in narrow slots, but another advantage is a lower profile angle with better angular velocity at the tip.

Type III: Flat End, End Cutting

Type III chamfer cutters are an improved and more advanced version of the type II style. The type III boasts a flat end tip with 2 flutes meeting at the center, creating a center cutting-capable version of the type II cutter. The center cutting geometry of this cutter makes it possible to cut with its flat tip. This cutting allows the chamfer cutter to lightly cut into the top of a part to the bottom of it, rather than leave material behind when cutting a chamfer. There are many situations where blending of a tapered wall and floor is needed, and this is where these chamfer cutters shine. The tip diameter is also held to a tight tolerance, which significantly helps with programing it.

In conclusion, there could be many suitable cutters for a single job, and there are many questions you must ask prior to picking your ideal tool. Choosing the right angle comes down to making sure that the angle on the chamfer cutter matches the angle on the part. One needs to be cautious of how the angles are called out, as well. Is the angle an “included angle” or “angle per side?” Is the angle called off of the vertical or horizontal? Next, the larger the shank diameter, the stronger the chamfer and the longer the length of cut, but now, interference with walls or fixtures need to be considered. Flute count comes down to material and finish. Softer materials tend to want less flutes for better chip evacuation, while more flutes will help with finish. After addressing each of these considerations, the correct style of chamfer for your job should be abundantly clear.

How Boring Bar Geometries Impact Cutting Operations

Boring is a turning operation that allows a machinist to make a pre-existing hole bigger through multiple iterations of internal boring. It has a number of advantages over traditional drilling methods:

  • The ability to cost-effectively produce a hole outside standard drill sizes
  • The creation of more precise holes, and therefore tighter tolerances
  • A greater finish quality
  • The opportunity to create multiple dimensions within the bore itself

 

Solid carbide boring bars, such as those offered by Micro 100,  have a few standard dimensions that give the tool basic functionality in removing material from an internal bore. These include:

Minimum Bore Diameter (D1): The minimum diameter of a hole for the cutting end of the tool to completely fit inside without making contact at opposing sides

Maximum Bore Depth (L2): Maximum depth that the tool can reach inside a hole without contact from the shank portion

Shank Diameter (D2): Diameter of the portion of the tool in contact with the tool holder

Overall Length (L1): Total length of the tool

Centerline Offset (F): The distance between a tool’s tip and the shank’s centerline axis

Tool Selection

In order to minimize tool deflection and therefore risk of tool failure, it is important to choose a tool with a max bore depth that is only slightly larger than the length it is intended to cut. It is also beneficial to maximize the boring bar and shank diameter as this will increase the rigidity of the tool. This must be balanced with leaving enough room for chips to evacuate. This balance ultimately comes down to the material being bored. A harder material with a lower feed rate and depths of cut may not need as much space for chips to evacuate, but may require a larger and more rigid tool. Conversely, a softer material with more aggressive running parameters will need more room for chip evacuation, but may not require as rigid of a tool.

Geometries

In addition, they have a number of different geometric features in order to adequately handle the three types of forces acting upon the tool during this machining process. During a standard boring operation, the greatest of these forces is tangential, followed by feed (sometimes called axial), and finally radial. Tangential force acts perpendicular to the rake surface and pushes the tool away from the centerline. Feed force does not cause deflection, but pushes back on the tool and acts parallel to the centerline. Radial force pushes the tool towards the center of the bore.

 

Defining the Geometric Features of Boring Bars:

Nose Radius: the roundness of a tool’s cutting point

Side Clearance (Radial Clearance): The angle measuring the tilt of the nose relative to the axis parallel to the centerline of the tool

End Clearance (Axial Clearance): The angle measuring the tilt of the end face relative to the axis running perpendicular to the centerline of the tool

Side Rake Angle: The angle measuring the sideways tilt of the side face of the tool

Back Rake Angle: The angle measuring the degree to which the back face is tilted in relation to the centerline of the workpiece

Side Relief Angle: The angle measuring how far the bottom face is tilted away from the workpiece

End Relief Angle: The angle measuring the tilt of the end face relative to the line running perpendicular to the center axis of the tool

Effects of Geometric Features on Cutting Operations:

Nose Radius: A large nose radius makes more contact with the workpiece, extending the life of the tool and the cutting edge as well as leaving a better finish. However, too large of a radius will lead to chatter as the tool is more exposed to tangential and radial cutting forces.

Another way this feature affects the cutting action is in determining how much of the cutting edge is struck by tangential force. The magnitude of this effect is largely dependent on the feed and depth of cut. Different combinations of depth of cuts and nose angles will result in either shorter or longer lengths of the cutting edge being exposed to the tangential force. The overall effect being the degree of edge wear. If only a small portion of the cutting edge is exposed to a large force it would be worn down faster than if a longer portion of the edge is succumb to the same force. This phenomenon also occurs with the increase and decrease of the end cutting edge angle.

End Cutting Edge Angle: The main purpose of the end cutting angle is for clearance when cutting in the positive Z direction (moving into the hole). This clearance allows the nose radius to be the main point of contact between the tool and the workpiece. Increasing the end cutting edge angle in the positive direction decreases the strength of the tip, but also decreases feed force. This is another situation where balance of tip strength and cutting force reduction must be found. It is also important to note that the angle may need to be changed depending on the type of boring one is performing.

Side Rake Angle: The nose angle is one geometric dimension that determines how much of the cutting edge is hit by tangential force but the side rake angle determines how much that force is redistributed into radial force. A positive rake angle means a lower tangential cutting force as allows for a greater amount of shearing action. However, this angle cannot be too great as it compromises cutting edge integrity by leaving less material for the nose angle and side relief angle.

Back Rake Angle: Sometimes called the top rake angle, the back rake angle for solid carbide boring bars is ground to help control the flow of chips cut on the end portion of the tool. This feature cannot have too sharp of a positive angle as it decreases the tools strength.

Side and End Relief Angles: Like the end cutting edge angle, the main purpose of the side and end relief angles are to provide clearance so that the tools non-cutting portion doesn’t rub against the workpiece. If the angles are too small then there is a risk of abrasion between the tool and the workpiece. This friction leads to increased tool wear, vibration and poor surface finish. The angle measurements will generally be between 0° and 20°.

Boring Bar Geometries Summarized

Boring bars have a few overall dimensions that allow for the boring of a hole without running the tool holder into the workpiece, or breaking the tool instantly upon contact. Solid carbide boring bars have a variety of angles that are combined differently to distribute the 3 types of cutting forces in order to take full advantage of the tool. Maximizing tool performance requires the combination of choosing the right tool along with the appropriate feed rate, depth of cut and RPM. These factors are dependent on the size of the hole, amount of material that needs to be removed, and mechanical properties of the workpiece.

 

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.

An Introduction to Reamers & CNC Reaming

Most machinists are familiar with CNC drilling, but did you know that the common practice for holemaking is to always use a reamer? When done correctly, reaming can be a fast and highly accurate operation that results in precision holes.

Critical Reamer Geometries

reamers

By examining a Harvey Tool Miniature Reamer and its critical dimensions, we can better understand the functionality of this useful tool. In the above image of a straight flute reamer, D1 references the reamer diameter, the specific size intended for your hole; and D2 points to the shank diameter. At Harvey Tool, reamer shanks are oversized to help maintain tool strength, stiffness, and accuracy. Shanks also have an h6 tolerance, which is crucial for high precision tool holders, such as heat shrink collets. Other critical dimensions of a reamer include its overall length (L1), margin length (L2), overall reach (L3), and chamfer length (L4).

Harvey Tool also offers Miniature Reamers – Right Hand Spiral. This tool is designed to leave a superior part finish and help with chip evacuation in blind hole applications.

The Functions of Miniature Reamers

Reamers Provide Precision – As mentioned earlier, reamers are great for machining precision hole diameters. To use a reamer properly, you must first have a pre-drilled hole that’s between 90% and 94% of the final hole diameter. For example, if you need a finished a hole of .220″, your predrilled hole should be somewhere between .1980″ and .2068″. This allows the tool to take enough material off to leave a great finish, but does not overwork it, potentially causing damage. The tolerance for uncoated reamers is +.0000″/-.0002″, while the tolerance for AlTiN coating is +.0002″/-.0000″. These tolerances provide you the peace of mind of knowing that your hole will meet exact specifications.

Achieve a Quality CNC Finish – When a high surface finish is required of a hole, reamers should always be used to reach the desired tolerance. Both the pre-drilled hole and the tool’s margin help to keep the reamer centered while cutting, leading to a better finish.

Minimize Machining Production Runs – For machine shops, consistency is a priority. This is especially true in production runs. The last thing a machinist wants to see is an oversized hole on a part they have already preformed many operations on. Remember, reamers have the benefit of offering consistent hole size, preventing an out of tolerance finish. These consistent holes lead to valuable time savings and reduced scrap costs.

CNC Machining Exotic Alloys: When machining Inconel, titanium, and other high-cost materials, reaming your hole is important to ensure that the desired finish specification is met. With reamers, a machinists can better predict tool life, leading to a better finished product and less scrap ratios. It is important to note that Harvey Tool reamers are offered AlTiN coated and fully stocked in every .0005” increment from .0080” to .0640”.

When To and Not To Use Drop Hole Allowance

Dovetail Cutters are cutting tools that create a trapezoidal-type shape, or a dovetail groove, in a part. Due to the form of these tools, special considerations need to be made in order to achieve long tool life and superior results. This is particularly true when machining O-ring grooves, as this operation requires the tool to drop into the part to begin cutting. Using an appropriate tool entry method, specifically understanding when drop hole allowance is (and is not) needed, is important to keep common dovetail mishaps from occurring.

What is a Drop-Hole?

When designing parts featuring O-ring grooves, the consideration of drop-hole allowance is a pivotal first step. A drop-hole is an off-center hole milled during the roughing/slotting operation. This feature allows for a significantly larger, more rigid tool to be used. This is because the cutter no longer has to fit into the slot, but into a hole with a diameter larger than its cutter diameter.

drop hole allowance

Why consider adding a Drop-Hole?

When compared to tools without drop-hole allowance, tools with drop-hole allowance have a much larger neck diameter-to-cutter diameter ratio. This makes the drop-hole tools far stronger, permitting the tool to take heavy radial depths of cut and fewer step-overs. Using a drop-hole will allow the use of the stronger tool, which will increase production rate and improve tool life.

Machining Operation with Drop-Hole Allowance

drop hole allowance

A maximum of 4 radial passes per side are needed.

When Not to Drop Hole

Drop-holes are sometimes not permitted in a design due to the added stress concentration point it leaves. Common examples for where a drop-hole would not be allowed include:

  • In high pressure applications
  • In seals requiring a high reliability
  • Where dangerous or hazardous fluids are being used

The issue with drop-hole allowance is that the additional clearance used for tool entry can create a weak spot in the seal, which can then become compromised under certain conditions. Ultimately, drop-hole allowance requires approval from the customer to ensure the application allows for it.

Machining Operation Without Drop-Hole Allowance

drop hole allowance

A maximum of 20 radial passes per side are needed.

Drop-Hole Placement

When adding a drop-hole to your part, it is important to ensure that the feature is placed correctly to maximize seal integrity. Per the below figure, the drop-hole should be placed off center of the groove, ensuring that only one side of the groove is affected.

drop hole allowance

It is also necessary to ensure that drop-hole features are put on the correct side of the groove. Since O-rings are used as a seal between pressures, it is important to have the drop-hole bordering the high pressure zone. As pressure moves from high to low, the O-ring will be forced into the fully supported side, allowing for a proper seal (See image below).

drop hole allowance