By Jack Kerlin, BIG DAISHOWA—Americas

Even among experienced machinists, choosing the right insert for boring a hole remains a difficult process fraught with myth and misconception.

However, it is no myth that insert selection can completely save or kill the performance on an application. We can spend all day talking about the best insert substrate/coating (or lack thereof), shape, chip breaker geometry, etc. for a job, but I feel it's important to address one of the most common problems that I come across: use of improper insert nose radius.

I've spoken to machinists who are loyal to one nose radius size or leaving a certain amount of stock on a hole simply because it worked on a job years ago and seems to work well on most other jobs. They are then dumbfounded when working on a new job and suddenly there is heavy chattering or poor surface finish.  

​The truth is, proper nose radius selection depends on the unique specifications of each job, mainly:

• How much material stock remains
• Desired feed rate or surface finish
  
  

In general, you want to minimize radial forces and maximize axial forces acting on the cutting edge. The dreaded chattering phenomenon is caused by excess radial force deflecting the tool, causing it to "bounce" rapidly on and off the wall of the bore. The typical rule of thumb is to have a radial depth of cut one-half to two-thirds of the nose radius.

For example, when using a 16 thou nose radius insert, leave a stock of 16-20 thou on diameter for your finishing pass (be careful not to confuse radial depth of cut with depth of cut on diameter). Maintaining these proper cutting forces encourages good chip formation.

Try to use a smaller nose radius as your boring jobs get longer, as this will combat the overwhelming radial forces that cause chattering. But above all, make sure you're leaving the right amount of stock for your particular inserts.

Sometimes, jobs will require a certain surface finish. Surface finish, insert nose radius and feed rate go hand-in-hand. Without getting too technical, surface finish improves as you decrease the feed rate (keeping speed the same) and increase the size of the nose radius.

These are the first two options you will want to consider. For this reason, don't forget to increase the amount of stock if you switch to a larger nose radius. Also, decreasing the feed rate too much in an attempt to get a better surface finish runs the risk of chattering because the axial depth of cut is less than the hone on the insert tip.

If all else fails, you can "cheat" by changing the shape of the nose radius itself to a wiper geometry. This makes the radial cutting edge effectively flat, which produces a surface finish 2x better than a standard insert nose radius at the same feed rate.
​
Yet another factor to keep in mind is the fact that a smaller nose radius corner will be more prone to breakage than an identical-sized insert with a larger nose radius.

So, as you can see, many different factors are at play and it's easy for your head to start spinning. Hopefully, some of these tips point you in the right direction. If stubborn applications don't seem to respond to anything you do, or if you need assistance in selecting the right insert, BIG DAISHOWA's technical department is here to assist you. Please contact us 

For all BIG KAISER fine boring heads type AW, EW, EWN, EWD, EWE, EWB and EWB-UP, the frequency for lubrication depends on use.

If used daily, the recommendation is to oil the boring head every two to three months.

​The best procedure is to range the cartridge to the maximum diameter. Using a lubrication gun, pump oil in the unit until it stops accepting oil and then range cartridge to minimum setting. Excess oil will come out around the dial face (this is normal). If oil is excessively dirty, repeat the process.  

Recommended oils are Mobil Vactra No. 2, BP Energol HLP-D32, Kluber Isoflex PDP 94, or a similar light machine oil. 

By John Zaya, Product Specialist, BIG DAISHOWA—Americas

As the title implies adjusting screws, also known as back-up screws, stop screws and preset screws, are not just a simple set screw. They are a screw with a purpose--three actually.

The first is to provide a fixed stop for a cutting tool to rest against during tool changes. This allows an operator to save time as they do not have to pull out a ruler, setting jig, etc. to reassemble the cutter into a holder.

A secondary purpose of the adjusting screw is to assist the tool holder in keeping the cutter from being pushed up into the holder if the cutting loads increase to the point where the tool may slip up into the holder.

​The third is to offer sealing for coolant-through tools. 

When an old cutter is swapped out and a new one put in its place, the repeatability of this process will vary based on a few parameters such as cleanliness and the OEM cutting tool overall length tolerances.

Cleaning the clamping bore or collet of a holder provides better runout repeatability which should be old news to everyone, but if old coolant and contaminants are not removed, they would get jammed between the end face of the shank and the adjusting screw, affecting the length setting. 

Cutting tool overall length tolerances may also vary from one OEM to another. We have seen them range from ±.3mm to ±.5mm (±.012” to ±.019”). Others may be tighter or looser.

​Most modern machining centers come with tool length offset measurement systems which will provide the final precise gage length of a tool assembly. With the rough position provided by the adjusting screw, the machine operator can continue working and does not need to worry about tool clearances and stick outs. 

The clamping mechanism of the holder also affects the length repeatability. Both hydraulic chucks and milling chucks are radial clamping systems, whereas a tapered collet is drawn down into a taper by a threaded nut.

This draw down causes the cutter to be drawn down as well. For this we have two types of adjusting screws:

• HMA/HDA solid type - The solid type is a one-piece steel construction part
• NBA rubberized type - The rubberized type has a rubber padded conical pocket that absorbs the axial travel of the cutter shank as the collet is clamped. 

Milling chucks also have a second type of adjustment screw option that can be built into the back end of a reduction sleeve. As cutting tool diameters get smaller, the length of the shank also gets shorter.

​As such, the end face of the shank may not reach the HMA adjusting screw when installed it the body of the holder. The AC Type Collet adjuster screws into the back end of the reduction sleeve where the shank the tool can easily be reached. 

It is always recommended to consult the tool holder catalog or technical documentation to ensure that a holder can support an adjusting screw. Some holders are very short or have very deep internal features that may not allow for the use of any adjusting screw. In those cases, a depth setting ring or collar on the shank of the cutting tool may be an acceptable alternative. 

Caution should be used on shrink-fit holders. Thermal expansion/contraction occurs in all three axes, so as the body of a shrink-fit holder cools down it will draw the cutter down jamming onto the adjusting screw. This could lead to damage to the screw, the holder or the cutter. 

By John Zaya, Product Specialist, BIG DAISHOWA—Americas

T​he L:D ratio of a tool assembly is calculated by using the length of the bar (or body) of a tool assembly and the diameter of the tool, not the workpiece bore diameter and depth. 

To expand on this concept, we see in the first configuration below the Ø16mm bar is sticking out 160mm which is a 10:1 although the bore is only a 2.5:1.

In some applications this extra reach is needed to get around a fixture or a feature of the part. However, in those cases where it is not needed, decreasing the overhang by 55mm means the new L:D of 105:16 is 6.5:1. This alone would represent approximately 10x increase in cutting speed by increasing from 20mm/min vs. 200mm/min. 

The use of modular reductions has also been found to be a good strategy to improve tool performance.

Comparing the lower two assemblies below, the middle assembly uses the same connection size for the length of the tool, ignoring the larger access diameter, and results in a 6.4:1 ratio.

​When a shank with a larger connection size is used along with a modular reduction, the ratio is halved, and provides a 350% productivity improvement (14mm/min to 50mm/min).  
​
In all cases, reducing the L:D ratio provides an improvement in speed which then provides longer tool life, better surface finish and size control of the bore.  

Charlie Mitchell, machinist for Andretti Autosport, discusses how Unilock pallets reduced his setup time by as much as 80%.

By John Zaya, Product Specialist, BIG DAISHOWA—Americas

As the title implies adjusting screws, also known as back-up screws, stop screws and preset screws, are not just a simple set screw. They are a screw with a purpose--three actually.

The first is to provide a fixed stop for a cutting tool to rest against during tool changes. This allows an operator to save time as they do not have to pull out a ruler, setting jig, etc. to reassemble the cutter into a holder.

A secondary purpose of the adjusting screw is to assist the tool holder in keeping the cutter from being pushed up into the holder if the cutting loads increase to the point where the tool may slip up into the holder.

​The third is to offer sealing for coolant-through tools. ​

When an old cutter is swapped out and a new one put in its place, the repeatability of this process will vary based on a few parameters such as cleanliness and the OEM cutting tool overall length tolerances.

Cleaning the clamping bore or collet of a holder provides better runout repeatability which should be old news to everyone, but if old coolant and contaminants are not removed, they would get jammed between the end face of the shank and the adjusting screw, affecting the length setting. 

Cutting tool overall length tolerances may also vary from one OEM to another. We have seen them range from ±.3mm to ±.5mm (±.012” to ±.019”). Others may be tighter or looser.

​Most modern machining centers come with tool length offset measurement systems which will provide the final precise gage length of a tool assembly. With the rough position provided by the adjusting screw, the machine operator can continue working and does not need to worry about tool clearances and stick outs. 

The clamping mechanism of the holder also affects the length repeatability. Both hydraulic chucks and milling chucks are radial clamping systems, whereas a tapered collet is drawn down into a taper by a threaded nut. This draw down causes the cutter to be drawn down as well.

​For this we have two types of adjusting screws: HMA/HDA solid type and NBA rubberized type. The solid type is a one-piece steel construction part, whereas the rubberized type has a rubber padded conical pocket that absorbs the axial travel of the cutter shank as the collet is clamped. 

Milling chucks also have a second type of adjustment screw option that can be built into the back end of a reduction sleeve. As cutting tool diameters get smaller, the length of the shank also gets shorter.

​As such, the end face of the shank may not reach the HMA adjusting screw when installed it the body of the holder. The AC Type Collet adjuster screws into the back end of the reduction sleeve where the shank the tool can easily be reached. 

It is always recommended to consult the tool holder catalog or technical documentation to ensure that a holder can support an adjusting screw. Some holders are very short or have very deep internal features that may not allow for the use of any adjusting screw. In those cases, a depth setting ring or collar on the shank of the cutting tool may be an acceptable alternative. 

Caution should be used on shrink-fit holders. Thermal expansion/contraction occurs in all three axes, so as the body of a shrink-fit holder cools down it will draw the cutter down jamming onto the adjusting screw. This could lead to damage to the screw, the holder or the cutter. 

John Zaya, Product Specialist, explains the concepts behind the UNILOCK Zero-Point workholding system.

He also discusses base pallets and options for 5-axis machines.
Chapters:
0:00 Introduction
0:13 Basic Concepts
0:52 Features of the UNILOCK Clamping Knob
1:50 UNILOCK 5-Axis Program

Put simply, the manufacturing process of boring is enlarging a hole in a piece of metal. There are quite a few different pieces of machinery or approaches that can be used to make holes from lathes and mills to line boring or interpolation. We wanted to do a quick break down of the different kinds of boring tools available to bore holes and/or secondary boring operations.

Boring deep holes can involve extreme length-to-diameter ratios, or overhang, when it comes to tooling assemblies. Since it can be difficult to maintain accuracy and stability in these scenarios, we need boring bars to extend tooling assemblies and while maintaining the rigidity to make perfect circles with on-spec finishes.

Solid boring bars
Typically made of carbide for finishing or heavy metal for roughing, solid boring bars have dense structures that make for a more stable cut as axial force is applied.

Damping bars
When cutting speeds are compromised, or surface finishes show chatter in a long-reach boring operation, damping bars are an option. They have integrated damping systems. Our version, the Smart Damper, works as both a counter damper and friction damper so that chatter is essentially absorbed.

Boring heads are specifically designed to enlarge an existing hole. They hold cutters in position so they can rotate and gradually remove material until the hole is at the desired diameter.

Rough boring heads
Once a bore is started with a drill or by another method, rough boring heads are the choice for removing larger amounts of material. They are built more rigid, to handle the increased depths of cut, torque and axial forces needed to efficiently and consistently make the passes to remove materials.

Fine boring heads
Fine boring heads are best used for more delicate and precise removal of material that finishes the work the rough boring head started. They are often balanced for high-speed cutting since that’s the best approach for reaching exact specifications.

Twin cutter boring heads
Most boring heads feature one cutter that cuts as its feed diameter is adjusted by the machine. There are twin cutter boring heads that can speed up cutting and add versatility. For example, the Series 319 and other BIG KAISER twin cutter boring heads include two cutters that can perform balanced or stepped cutting without additional accessories or adjustments by switching the mounting locations of the insert holders that have varied heights.

Digital boring heads
Traditionally, adjusting boring heads has been painstaking and time-consuming, especially when it’s done in the machine. It’s easy to make mistakes when maneuvering to read the diameter dial and adjusting it to the right diameter. Digital boring heads have a LED that makes precise adjustments much easier.

Since cutters are on diameter of boring heads and not their face, they are not able to initiate a hole on a flat surface or raw material. Especially in smaller bores, fluted drills called starter drills can be used to get the hole started before rough boring.

Specialty boring heads
Back boring and face grooving heads, as well as chamfering insert holders, are available for some of the most common secondary operations, after a hole is bored. We produce specific heads with cutters at the appropriate angles so each of these operations can be done without manually moving the part, changing the tool or adjusting the cutter angle.

Modular boring tools
Since limiting length-to-diameter ratios is so crucial to boring success, it’s extremely valuable to be able to make your tooling assembly as short as possible. Our modular components are based on a cylindrical connection with radial locking screw that allows for the ideal combination of different kinds of shanks, reductions and extensions, bars, ER collet adapters and coolant inducers.

Looking for some help finding the right boring equipment for your next job or new machine? Our engineers are here to help. Get in touch with us here.