The Forgotten Keyway Broach Dimension

Understanding the Depth Radial Keyway Dimension

The Forgotten Keyway Broach Dimension: A keyway, internal or external, has three dimensions. However, when going over applications with clients for Internal Keyways CNC Broach Tools needs clients to provide us with four dimensions. Not the drawing, just four dimensions. They are:

1) The Width of the keyway and the specific width tolerance needed
2) The Bore size that the tool and insert must fit into
3)  The Length of Stroke needed. Most refer to this as the Depth. Specifically it is the Axial Depth of the application.
4) and the forgotten keyway dimension, which is the Depth Radial Dimension
Historically, the standard for the Depth Radial keyway dimension is half the width of the keyway.

Example: a 3/16 width keyway typically should have a .090” – .100” Depth Radial Dimension

CNC Broach Tools coined a new machining vocabulary term calling the Depth Radial the Height of the Groove to differentiate it by terminology from the Depth Axially. Most of the clients that call give us the Length of Stroke Depth, or Axial Depth, instead of the Depth Radially when we ask for the Depth. Even when we ask for the Depth Radially they keep giving us the Depth Axially.  It gets very frustrating for both parties when there are two “depths”. We try to explain that it’s not possible for the Depth Radial to be 2” and that that’s the Depth Axially! or the Length of Stroke! We have had to educate thousands of clients on the meaning and importance of the Depth Radial Dimension.
Making the situation more frustrating is that I’ve never seen a drawing with the Depth Radially called out specifically. Sometimes, you’ll have a Bore size and then another bore dimension to the “top” of the keyway. Other times it’s from the centerline of the bore and you have to divide it by two. It’s odd to us that this is not a standardized dimension and procedure.
We call the Depth Radially the forgotten Keyway Broach dimension because very rarely do clients know what we are talking about when we ask for it. Engineers with decades of experience need the dimension explained to them. But more important than the engineer is that the machinists and operators know what the Depth Radial dimension is and that on a CNC Broach Tool the capability to cut it is a Finite Dimension!

Example: the depth radial capability of our 3/8 internal keyway insert is .200” meant for a standard internal keyway. I had a first time user call saying the insert had ripped out of the pocket of the tool. After reviewing everything I remembered to ask what his Depth Radial was and he said his application needed  .220”. He crashed because he did not think of this dimension and that how high our insert sticks up above the tool with clearance to cut is a Finite amount. 

Understanding why the Depth Radial is important is because some jobs are NOT standard and need a deeper Depth Radial than our standard insert will do. We can special grind the widths of larger inserts that have more Depth Radial Capability, but that larger tool and insert must fit your bore size.
I see a gap in education here both on the machining and engineering side. Many engineers do not seem to grasp as they design that the standard Depth Radial for a internal keyway is half the width. They’ll arbitrarily make the Depth Radial more than it needs to be not understanding the issue with tooling this creates for the manufactures of their parts. Most cutting tool companies make standard tooling product lines for standard dimensions. When an engineer does a random dimension not in line with standard procedure expensive special tooling, one-offs, must be made costing more money and increasing lead times. For the broaching process in particular this “goof-up” is hard because the higher or farther an insert sticks up above the tool to cut the slot the more tool bar meat you need to support it.

Meaning if you have more depth radially you need a bigger bore to fit into because you need a larger tool body. 

A broach insert for an internal keyway that sticks way high up above the broach tool and a large thick tool body and a small bore to fit, you just can’t make it all work. As they design engineers need to keep in mind that geometrically there are physical constraints on inserted broach tools, so we encourage them to make the Depth Radial standard.
Finally, you can use our broach tool and “step it over” to do wider keyways, but remember this possibility is limited by the Depth Radial capability.


Keyway Broach Dimension

Keyway Broach Dimension

Keyway Broach Tools Size Chart

Lathe Broaching 4140 Internal Keyway

Broaching 4140 with Razorform CNC Broach Tools

To read a Modern Machine Shop article about CNC Broach Tools Lathe broaching 4140 internal keyway at 56Rc on Okuma Cadet Lathes at OEM electric motor manufacturer Baldor Electric Motors click here:
This article titled, “The Future of Broaching”, is from September 2007 when our broach tools were sold through a different company called Razorform Tools. Which indicates just how long this proprietary, inserted broaching system has been successful for our clients. We frequently get Razorform Broach Tool clients asking if the old broach tools and keyway inserts are interchangeable. The answer is Yes!
We also get calls from concerned 1st time users concerned about wear on their lathes from broaching. Hopefully this article eases fears as we would not be in business if the broaching process damaged our clients lathes. As you can see this broach tool system for lathes has been around for more than a decade!
Lathe Broaching 4140 Internal Keyway

Broaching with Razorform CNC Broach Tools

Okuma Lathe Broaching Programming Template


Blind Keyway Broaching Monel Interrupted Cut

Blind Broaching Monel

Thank you Karl for your testimonial on blind keyway broaching monel interrupted cut!

We recently ran up against a tough lot of Monel sockets requiring slotting six places through a helix. The material was far harder than usual, and our usual rotary broach couldn’t handle it. Because the run was short, we couldn’t spend a lot on tooling. The CNC Broach Tool Company tool cut the nasty stuff beautifully, even though the interrupts, and got the job done with less burring and deformation. Even managed to salvage the part that the old broach broke down on. Good job! Thanks for the help.

Karl Mech
Hydrasearch Co
Stevensville, MD
Blind Keyway Broaching Monel Interrupted Cut

Blind Keyway Broaching Monel Interrupted Cut

CNC Broach Tools Blog


Blind Keyway Broaching for CNC Lathe

Monty Twingstrom Testimonial

Thank you Monty Twingstrom for your testimonial on blind keyway broaching for your CNC Lathe!

We currently implemented a broach tool from CNC Broach Tool Company, it was a broach application that was not a through hole which required us to look into farming out this application. With implementing the CNC Broach Tool Company tool we were able to not only keep this operation in-house, we were able to combine it to the lathe operation and also because of that we were able to add the drill and tap cross holes to make it complete in one operation which is always a cost saving if you don’t have to handle the parts more than once. Centerline held really well because the bore and the broached keyway were done in the same operation.

Monty Twingstrom
CNC Manager
K-Manufacturing, Inc.
Osseo, MN
Blind Keyway Broaching

Blind Keyway Broaching on CNC Lathe

CNC Broach Tools Blog

Tormach Mill Broaching Program Template

Tormach Mill Broaching Program Template

CNC Broach Tools offers a free Tormach Mill Broaching Program template. If you want to broach your keyways or splines CNC Broach Tools can help!

Click to download PDF >> CNC BROACH TORMACH MILL

Click to download .NC >>  TORMACH MILL G CODE BROACH.NC

Tormach Mill Broaching Program

Mill Broaching Blind Keyway

  • Please do not ask CNC Broach to program your machine for the keyway slotting application.
  • We can never know the different CNC program options purchased with your lathe or mill. Please reach out to your Haas dealer and find out what CNC programming options you purchased with your lathe or mill.
  • CNC Lathe and Mill manufacturers come out with updated controls frequently. Things may have changed since this CNC Broach Template.
  • The CNC broach program templates are a guide or foundation for the user to tailor to their specific application.
  • There is more advanced CNC Keyway Slotting program information in our Keys to Programming CNC Broach Tools guide.

“The Only Inserted CNC Broaching System Manufactured in the USA”

Please feel free to leave a comment below to better help improve our templates to help you!

DISCLAIMER: This CNC Broach Tool Program Template is for informational and reference purposes only. It is provided without guarantees or warranty. CNC Broach Tool LLC makes no warranties of any kind, either express or implied, including but not limited to warranties of merchantability, fitness for a particular purpose, of title, or of non infringement of third party rights. Use of this programming template by a user is solely and completely at the user’s risk.

Programming the Broaching Process


The Keys to Programming CNC Broach Tools PDF contains valuable tips accumulated over 12 years of feedback from machine shops about programming the broaching process for CNC broaching systems and using your lathe or mill as a CNC Broaching Machine.
Back when this patented broach tool (US Patent # 8,622,669,B2) was sold through Razorform Tools, we failed to offer broach program process support for our CNC broaching system. CNC Broach Tools is now very excited to add this level of service for our lathe and mill broaching tools.
CNC Broaching Programs for specific machines are located here on our Broaching Blog:

                                                                            For Informational Purposes Only

Please feel free to leave a comment below to better help improve our templates to help you!


“The Only Inserted CNC Broaching System Manufactured in the USA”

programming the broaching process

CNC Broach Tools

Keyway Slotting Tool Broach Length

Keyway Slotting Tool Broach Length

Frequently CNC Broach gets asked for a longer internal keyway length to broach than our standard slotting tool can reach. One-off special broach toolbars take much more time and money as opposed to modifying our off-the-shelf standard CNC Slotting Tool. Here are three solutions that have been tried and proven by many clients. The attached pictures were provided by clients that were happy with the result:

  1. Turn the “neck” of the tool back for a longer keyway stroke (see pic)
  2. Braise a couple of inches to the “butt” of the broach tool, turn both pieces so they are concentric, and then clamp on the longer length of the slotting tool
  3. Mount the broach tool in a home-made holder that extends it out, The attached pic shows a 13” long keyway being cut without the bar being modified
Internal Keyway Length

CNC Broach Tool LLC

Internal Keyway Length

CNC Broach Tool LLC

“The Only Inserted CNC Broaching System Manufactured in the USA”


ID Broach in 304 Stainless Testimonial

Derby Machine Client Testimonial

Thank you Derby Machine for your testimonial on how to ID broach 304 stainless!

Click here for YouTube video >> Derby Machine Testimonial

“We had a blind hole to id broach in 304 stainless and found it difficult to find a vendor who could broach our part to print. We were forced to ship our parts from Kansas to Chicago to get them broached. It cost us $15 per part with a $100 set-up fee plus shipping to and from Chicago. Our parts were continuously damaged in shipping so we began to ship them in ammo boxes for protection.

While searching the internet we found a broaching tool at We were very skeptical but had nothing to lose and decided to give them a shot. When we received the tool and started setting up the machine John was very helpful in instructing us on how to install the tool correctly and worked with us to get our program, feeds, and speeds correct.

This tool paid for itself several times over on the first run alone. We get well over 100 parts on a single insert point with a cycle time increase of only 2 minutes 14 seconds. We have ran over a thousand parts using very few inserts and never lost the tool itself we have never scrapped any parts because of the broach. It holds the broach depth and width thru the whole run. I am extremely happy with the results and cost saving of this tool and would recommend it to anyone who has an id broach issue or would like to machine their part complete.

Mike Turner
Operations Mgr.

Lathe Keyway Broaching Client Testimonial

Lathe Keyway Broaching Client Testimonial

ID Broach in 304 Stainless

ID Broach in 304 Stainless 


CNC Broach Tools Insert and Tool Life Testimonial

Accurate Gear & Machine, Inc.

Thank you Accurate Gear & Machine for your insert and tool life testimonial!

To Whom It May Concern:

Accurate Gear and Machine, Inc. purchased a 3/16” CNC Broach Tool for internal keyways for our Fellows CNC Shaping Machine to cut keyways into 200 pieces of 8620 material. The insert life is incredible. We were able to cut 130 pieces with one cutting edge and their inserts have two! This tool came with a standard 3/4” shank that we modified into a #2 Morse taper (medium) for rigidness.

200 IPM at .0008” DOC gave us cycle times of 1min 20 sec per part.

We were very satisfied with the longevity of the tool life and exceptional service and lead time was provided. We look forward to purchasing additional tooling in the near future.

Corey Smith
Accurate Gear & Machine, Inc.

Broach Tool and Insert Life

CNC Broach Tools LLC


Keyway Broaching on a Doosan Lathe

Tusk Manufacturing Inc. Testimonial

Thank you Tusk Manufacturing for your testimonial!

Hello John,
I just wanted to let you know that I was very impressed using your broaching tool for the first time this past week! The job was an aluminum casting that required a keyway width of .126+-.001 and a radial depth of .075 for a length of 1.500 machined on a Doosan Lynx 220 LSYC Lathe. Made 55 castings without any wear or change in size. The walls had little to no taper and the finish was beautiful. This was definitely one of our better tooling purchases this year and I look forward to see what doors this will open for us in the future. Thanks again.
Best regards,
Keith Zorn
Manufacturing Lead
Tusk Manufacturing Inc.
CNC Broach Tools Client Testimonial

CNC Broach Tools LLC