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.
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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 

By Jack Kerlin, BIG DAISHOWA—Americas

There’s more than one way to skin a cat, just as there’s more than one way to finish a hole. The most effective option will depend on the number of parts, acceptable cycle time and tolerance callouts. One of the most effective options is boring.

Boring, in its most basic sense, is internal turning. The first and foremost goal, like any other finishing process, is to enlarge a drilled hole to final diameter, which will usually have a precise tolerance.

​A capable boring tool will also clean up after the drill and produce a nice surface finish. Finish boring can be a delicate operation. After all, it takes only one oversized hole to scrap an entire part. So, oftentimes the drilled hole needs to be further prepped in order to improve the odds of success of the final cut-to-size. This is where the use of “rough” boring tool becomes a necessity.

The question is, when is it appropriate to use a rough boring tool versus a finish boring tool? Or should you use both?

Casting processes dominate the metalworking process in many industries and will continue to dominate for the foreseeable future, despite advancements in additive manufacturing. They make possible the fabrication of otherwise difficult-to-machine parts, at relatively low cost and production time. But one thing casting is not known for is tight geometric tolerances.

Fresh out of the mold, a hole diameter can potentially be tens of thou away from a nominal value, which is why they’re typically cast well undersize. But equally as concerning (when it comes to boring) is the fact that the hole will also almost always be slightly curved or ovular to some degree. A rough boring tool is required to correct these issues before a finish boring tool can be used.

Another common cause of crooked holes is a wandering drill. This occurs when a drill “walks” off center very slightly when creating the initial hole, which mostly happens if the drill is slender, fed too hard or has a damaged tip. While the drilled hole might certainly appear straight to the naked eye, oftentimes using precise measuring equipment will reveal quite the opposite.

Why is a finish boring tool so sensitive to curved/out-of-round holes? Mainly because it’s one-insert effective, so it will only really experience radial force acting from one side. A finish boring tool is more likely to bend from radial cutting forces because it isn’t supported by an insert on both sides (as with a rough boring head) and taking off very little stock.

What this means is that feeding one of these tools into a crooked hole will encourage it to follow whatever path is set before it. The longer the hole, the easier it is for a boring tool to bend when cutting.

This is also a problem encountered with reaming. So, it’s good practice to be extra cautious and make sure a long hole is already “true” before doing your finish pass. In contrast to a finisher, a rough boring tool does not really care about how straight the initial hole is, it will pretty much bore true regardless because most of the forces are axial.
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Though it probably goes without saying, it also comes down to surface finish. Typically, a rough boring pass surface finish isn’t terrible, but some applications will specify a finish that isn’t practically attainable by a rough boring head.

Obviously, a rough boring head isn’t as precise as a fine boring head, so this will show up in the surface finish, among other places. Surface finish only depends on feed and nose radius (by definition), but if it’s specifically called out in a bore, this is usually a good sign that you will want to use a single-insert finisher regardless of how you’re cutting.

by Bernard Martin

Workholding Solutions
Recently, Jack Burley, the President and COO of BIG DAISHOWA, discussed innovative workholding solutions that are effective in combating vibration, with particular emphasis on the ROC® mineral cast solutions. These advanced solutions play a crucial role in increasing capacity and throughput by reducing burden and transport weights.

Much like a skyscraper, ROC® constructs a steel substructure for stability, precision machined and filled with ground positioning components and fasteners. The assembly is then encapsulated with a composite structure of mineral particles and epoxy resin, creating a working platform that is lightweight, yet stable and superbly dampened.

Mineral particles constitute about 90% of the added weight in these solutions, with the remainder being resin and curing agents. This composition results in an excellent density-to-weight ratio of 2.3 kg/dm^3.

The entire composite structure is produced without the application of heat, which preserves the integrity of the precision machined surfaces and clamping components. Furthermore, the low thermal conductivity and excellent resistance to corrosion of ROC® mineral cast enhance the durability and performance of the workholding solutions.

A key advantage of ROC® mineral cast is its exceptional attenuation rates, which are 6 to 10 times better than those of traditional grey cast iron, thus potentially increasing cell output significantly. ROC® mineral cast components are designed to resist impacts without disturbing the steel positioning and clamping components, due to their low tensile and impact strength.

Customizable to client specifications, ROC® also offers standard columns for horizontal machining center applications with options like integrated Unilock zero-point chucks or grid patterns.

Burley highlighted the ergonomic benefits and how ROC® mineral cast solutions facilitate machine capacity management in manufacturing settings.

Many of these solutions are about 50% lighter than their alternatives, making them highly advantageous for companies looking to standardize operator interfaces and streamline production processes.

By adopting ROC® mineral cast workholding solutions, manufacturers can significantly enhance their machining quality and operational efficiency.

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).  
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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.  

By Matt Tegelman, Senior Product Specialist, BIG DAISHOWA—Americas
​Edited by Bernard Martin

 A common question asked for boring operations is when would I use a ground chip-breaker vs. a molded chip-breaker?

A ground chip-breaker is recommended for chip control issues. The high-positive rake angle will help to make shorter chips, and the chip groove orientation forces the chips forward to more easily evacuate them from the bore, especially when used with high-pressure coolant through the tool.

Ground chip-breaker inserts also provide lower cutting forces, so they are better suited for deep-boring or long-reach applications, and other situations where part or tool stability may not be optimal.

Ground chip-breakers are also recommended for tight-tolerance applications where stock allowance is typically light for the final size pass.
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​A molded chip breaker is recommended for stable applications in short-chipping materials. Because these situations don’t require a super-sharp edge for cutting the material, these inserts hold their edge longer for better tool life, and in most cases are less expensive.

Hoffman Estates, IL - The BIG KAISER EWA Automatic Fine Boring System from BIG DAISHOWA performs closed-loop boring operations without a human operator. This breakthrough eliminates the need to stop the spindle to manually adjust the boring tool, which results in considerable time savings. Also, eliminating human interaction reduces cost, improves accuracy, and minimizes scrap. The adjustment range of this fine boring head allows for the handling of multiple bore sizes with the same tool and ensures a repeatable boring process. 

The EWA fine boring head is available in two sizes, one with a boring range of Ø2.677"-5.276" (Ø68-134mm) and the other with a range of Ø.394"-2.126" (Ø10-54mm). EWA kits are also available for each of these head sizes. These can include inserts, insert holders, a controller, antenna and protective case. 

The EWA can be used on machines with BT/BBT30-40-50, CV/BCV(SK)40-50, BIG CAPTO 5-6-8 and HSK-A63-80-100-125 spindles. The Automatic Fine Boring System can be integrated in three primary configurations: fully integrated, PC control, or tablet control. 

​Fully Integrated
A fully integrated system has the EWA control software running directly on the machine tool control via an app or technology cycle, requiring no external control device. The fully integrated system can only be integrated on new machine tools. 

​PC Control 
For legacy machines, a PC interface between the machine tool and the EWA can provide a fully automated, closed-loop control cycle. Commands are sent from the machine tool to the EWA, automatically adjusting the tool in synchronization with the machining process. 

The PC acts as a synchronization interface between the machine tool and the EWA. It stops the machining cycle after the touch probe makes a measurement, reads the result and sends the corresponding adjustment value to the EWA. After the EWA has been adjusted, the PC notifies the machine tool to continue the process. 

​Tablet Control
​The EWA can also be operated as a standalone tool, controlled manually with the BIG KAISER app on a tablet or smartphone. This enables the option to measure bores using an in-machine probe or manually, and to make fast adjustments in the app. Adjustments also can be done semi-automatically, where the head will move to pre-entered diameter values after a stoppage. 
To see the EWA Automatic Fine Boring System and other innovations from BIG DAISHOWA, visit booth #431610 at IMTS.