When it comes to broad capability, there are a few clear machine tool choices that production units and shops consider most – Five-axis, Vertical and Horizontal Machining Centers. The criterion for choosing looks different depending on what seat you sit in – from ownership to management to purchasing and finance – but from the shop floor perspective it’s all about making chips.

Getting the most out of these highly sophisticated machines involves a combination of processes, programming, tooling, workholding and human creativity. Set up between them is very different, too. Workholding on a 5-axis and Vertical Machining Centers is very straight forward – literally – since the spindle points directly to the table.

Setting up a Horizontal Machining Center (HMC) requires quite a bit more thought because the spindle points to . . . well nothing, just into the open space within the machining envelope. So, what’s the call for it?

Over the years, HMCs have evolved from single station to double, with the use of pallet changers, to pool pallets for multiple setups, and now to even include hydraulics within the pallet to load and clamp on the machine. And the evolution continues.

Today’s HMCs have great productivity characteristics including the ability to continue machining in one location while part change can take place in another. Many feature automatic tool changers and automatic pallet changers making them well-suited for uninterrupted, unmanned and continuous machining.

Configurations with multi-axis spindles also permit true five axis machining. And thanks to gravity, the chips naturally fall away from the parts.

​To meet this great potential, requires a review of several workholding issues at the outset.

1.  Angle Plate or Tombstone
First, let’s get back to the open-air orientation. All machining on an HMC starts with a workholding solution. That’s either going to be an angle plate or tombstone (column) that mounts to the HMC indexing table to provide the position and orientation of the workpiece to the spindle. The choice of this fundamental base is dependent upon the answers to remaining things to consider.

2. The Four Basics
As with all machining, all fundamental requirements must be met. Workpieces must be held securely. They must be positioned to allow access to machine all sides (ideally without having to change). Operations have to be repeatable (within tolerance). And the setup has to be designed to be easy for the operator. That includes the ability to clear chips, load, move and other ergonomic factors with the safety of that individual always being priority one.

3. What is your current need?
If you’re gearing up for the next run of parts, it’s best to begin with an SOW (Scope Of Work) including everything from what you’re looking to accomplish now, to opportunities for greater productivity, and how to best support operator skill level.

4. What is down the road?
On the heels of that, savvy engineers are mindful of future needs. Plan for it now and be ready when the demand arises. This past-the-horizon approach saves time for further utilizing technology such as incorporating robotics and other automation.

5. Opportunities for increased productivity
There are two additional productivity boosters available depending on the application. The first is the move from an angle plate to a tooling column for the ability to load a greater number of workpieces for any given setup. This is just a matter of math – a two-sided column essentially doubles that number, three-sided triples, and four-sided quadruples.

For every incremental increase, there is a corresponding decrease in overall setup time (or downtime), and conversely an increase in productivity (or uptime).

​Connections are standard T-slots or grid patterns. The second opportunity is the addition of a quick-change system that allows the entire column to be removed, changed and the next one connected, fully loaded and all in a matter of minutes or even seconds. This quick on and off works when repeatability is high and avoids having to again find zero for every changeover.

Finding the sweet spot for your shop’s productivity is very much a human effort, and a matter of choosing the best combination of man and machine. In the case of high producers like HMCs, the goal continues to be loading and changing parts faster than the machine can make them.

It is critical to properly assemble the collet and collet nut to avoid damage to the collet and make the most accurate and rigid assembly possible.

The extraction groove of the collet must be properly seated to the extraction ring of the collet nut.

If the collet extraction groove is not properly seated to the collet nut extraction ring, the collet will appear seated below the face of the nut.

This typically occurs when the collet is placed in the collet pocket of the tool holder and then the nut is threaded on the tool holder. In a correct assembly, the collet will seat at the face of the collet nut.

The image below shows a correct assembly on the left and an incorrect assembly on the right.

DO NOT tighten the collet nut if the collet appears seated below the face of the nut as this will create galling on the 30° face of the collet. Galling appear as grooves or lines in the lead face of the collet.

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. 

compiled & edited by ​Bernard Martin

RMS and Ra are based on different methods of calculating the roughness. Both are done with a profilometer, but the profilometer calculates the roughness differently for Ra and RMS.  

Ra is the arithmetic average of surface heights measured across a surface. Simply average the height across the microscopic peaks and valleys.

Ra and RMS are both representations of surface roughness, but each is calculated differently. 

Ra is calculated as the Roughness Average of a surfaces measured microscopic peaks and valleys. 

RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys. Each value uses the same individual height measurements of the surfaces peaks and valleys, but uses the measurements in a different formula. 

A single large peak or flaw within the microscopic surface texture will effect (raise) the RMS value more than the Ra value, which is why Ra is more commonly used today as a measurement.

• The RMS is sensitive to the BIG peaks and valleys.  Ra is not.
• Both numbers can be expressed in metric or inch.
• RMS was more popular 40 years ago when most US industry still worked in inches. Old inch drawings specify RMS.
• Ra is more commonly used today. (now most US industries work in metric) So they specify Ra in metric.
• Both Ra and RMS can be expressed in metric or inch.
• There is no reliable way to convert between Ra and RMS. This formula can be used to convert: RMS (Microinch) = (Ra/.0254) X 1.11 (Micrometer) However, that is only an estimate based on guessing what the shape of the microsurface looks like.

Ra roughness average is the main height as calculated over the entire measured length or area. It is quoted in micrometers or micro-inches. For 2 dimensional computation: Ra = 1/n * SUM(ABS[Zi-Zmean] from i = 1 to n

RMS is a Root Mean Squared calculation. That means you:

1. Measure height across the microscopic peaks and valleys.
2. Calculate the SQUARE of each measurement value.
3. Calculate the MEAN (or average) of those numbers (squared).
4. Find the square ROOT of that number.

The Root Mean Square (RMS) average is precisely that: the square root of the average height deviations from the mean line/surface squared. 
RMS = SQRT[ 1/n* SUM(Zi-Zmean)^2 ] from i=1 to n

Collets are a high-precision wear component of a tool holding system and require maintenance to ensure accuracy. First, it’s important to remember that collets are the softest component in a collet-based tool-holding system assembly and are designed to wear out.

Here is an overview of the wear pattern of a collet-based tool-holding system. The machine spindle is harder than the tool holder/collet chuck that fits into the spindle, so any wear between these two components will mostly occur to the collet chuck. That’s good.  It protects the spindle from expensive maintenance.

Collets are softer than both the collet chuck body and the cutting tool, so any wear forces between these items will mostly occur to the collet. Since collets are generally the least expensive component in a collet chuck tool holding system, it is preferred that the collets wear out before the other components.

Worn-out collets will not achieve the same level of accuracy and rigidity that newer collets can provide. The result is more chatter when cutting workpieces, less accuracy, and shorter cutting tool life.

Collets are designed to wear out as they lose accuracy and rigidity with use. High side-load forces during milling operations cause cutting tool deflection as illustrated below.

Over time, these side-load forces will bell-mouth the collet at its face.

As the collet experiences bell-mouthing, the cutting tool is allowed to deflect more and more during milling operations.

​Unfortunately, the collet may still indicate good accuracy on a presetter where there are no side-load forces. However, once the tool is put into service and begins experiencing side-load forces, the cutting tool is allowed more room to deflect, resulting in increased chatter and reduced tool life.

It is recommended to change collets out every 4-6 months, depending on usage, to ensure the most rigid and accurate collet chuck assembly.

If you see signs of fretting on the collet, it is advised to replace the collet. You should also ensure that collet nuts are tightened to the correct torque specifications during setup.

CLICK HERE to see all of our more in-depth articles on FRETTING to learn more.

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.  

by Frank Twomey | OSG USA

Recently, Ross Industries was tasked with reducing cycle times on all of its aluminum parts. OSG Territory Sales Manager Frank Twomey has been in touch with Ross Industries through a distributor for about two years ago. In need to optimize productivity, OSG was given with an opportunity to test cut the upper chamber 6061 aluminum alloy part used in Ross Industries’ tray sealers for food packaging.

Ross Industries has been producing these aluminum upper chambers for more than 25 years. Approximately 80 chambers are made annually along with thousands of other aluminum parts. The upper chambers are machined using a Doosan HM 1000 horizontal machining center with CAT-50 spindle taper.

Ross Industries was originally using a competitor 1.5-inch diameter indexable shoulder cutter for the application. The competitor tool was used at a speed of 6,000 rpm (2,358 sfm, 717.8 m/min), a feed rate of 120 ipm (3,048 mm/min), 0.005 ipt (0.127 mm/t), 0.3-inch (7.62 mm) radial depth of cut, 0.375-inch (9.525 mm) axial depth of cut, and at a metal removal rate of 13.5 inch3/min (221.2 cm3/min).

Upon a detail evaluation of the application, Twomey recommended OSG’s 3-flute 1-inch diameter AE-TL-N DLC coated square end mill (EDP# 86301809).

​The AE-TL-N DLC coated carbide end mill is extremely effective for non-ferrous materials such as aluminum alloys that require welding resistance and lubricity. With excellent cutting sharpness, it is able to suppress burrs to achieve superb surface finish.

The AE-TL-N features a unique flute form to enable trouble-free chip evacuation and a large core design for high rigidity to prevent chattering. Its center cutting edge configuration enables the tool to be used for plunging. Furthermore, with the addition of OSG’s DLC-SUPER HARD coating, long tool life can be achieved. This end mill series is available in square, sharp corner edge and radius types to accommodate a wide range of applications.

The AE-TL-N DLC coated carbide end mill was tested at a speed of 5,125 rpm (1,343 sfm, 408.7 m/min), a feed rate of 231 ipm (5,867 mm/min), 0.015 ipt (0.382 mm/t), 0.14-inch (3.556 mm) radial depth of cut, 1.62-inch (41.148 mm) axial depth of cut, and at a metal removal rate of 52.39 inch3/min (858.5 cm3/min). Cycle time on the upper chambers went from 34.5 hours to nine hours.
​
By switching to the AE-TL-N, Ross Industries has reduced about 75 percent of cycle time on the upper chambers and is now on average achieving a 150 percent cycle time reduction on other aluminum parts.

“This end mill creates chips so fast that our machines chip conveyors couldn’t keep up,” said Ross Industries Machine Shop Manager Greg Williams. “We had to speed up the conveyors.”
Taken in consideration of factors such as tool change time, machine cost, labor, etc., it is estimated that an annual cost savings of $183,000 can be gained. In addition to the upper chamber part, Ross Industries has also converted all of its aluminum end mills to OSG’s AE-TL-N series in various sizes.

“With the performance and consistent tool life of the AE-TL-N we are able to run these tools lights out,” said Williams. “In some cases, it is able to achieve as much as four times the metal removal rate versus the competitor tool.”
​
For more information on OSG’s AE-TL-N DLC coated end mill for non-ferrous materials and Ross Industries

The ER collet system has become very popular due to the flexibility of the system to hold a variety of cutting tool shank types including drills, end mills, and taps. Also, ER collets provide several solutions for increasingly popular coolant-through cutting tools.

Most standard ER collets have between a 0.020” and 0.040” holding range, making them a good choice when needing to hold odd-sized cutting tool shanks. This holding range also means fewer ER collets are required to hold a range of cutting tool shank diameters as opposed to other collet systems like TG.

The popularity of the ER collet system has led to several variations to hold a wide assortment of cutting tool shanks. Some ER collets have been modified with squares at the bottom to hold taps. Others have been modified to provide quick-change capabilities or compensation, also called “float”, for rigid tapping cycles as shown in the images below.

Other modifications include special slotting designs that seal around the cutting tool shank and force coolant through channels in coolant-through tooling, as well as modifications to include coolant ports in the collet that direct coolant to the cutting area.

TG collets have about the same accuracy as DA collets, but because there are more slots, and therefore more faces clamping on the cutting tool shank, they tend to deliver greater holding power.

TG can be a good solution for larger shank diameter cutting tools, but they generally limit how far down into a pocket you can reach due to interference with the collet nut, as TG collet nuts tend to be quite large.
TG collets are not as popular as ER collets for several reasons. Most notably, the larger diameter collet nuts can require the use of extended end mills to avoid interference from the collet nut when milling pockets.

Also, since TG collets have a very small collapse range, they are intended for use with one size cutting tool shank.

ER collets, by contrast, offer a large collapse range that can be helpful when clamping odd-shank diameter tools.
On the flip side, TG collets tend to have a bit more holding power than ER collets due to the collet base having a 4° taper as opposed to the 8° taper found in ER collets. This can make TG collets a good choice when machining with longer-length cutting tools.

Double-Angle (DA) collets have been around for a long time and continue to be used in the market. There are, however, many issues associated with DA collets of which users should be aware.

Let's just clear the air and say it: Don't use them. If you have them in your shop, replace them with ER Collets and ER Collet Chucks as soon as possible and you will recoup the cost of the new holders and collets in your tool life probably within a month or two.

One of the primary issues with DA collets is that they essentially clamp on the cutting tool shank with only two opposing faces in the I.D. bore.

DA collets have four slots in the front of the collet and four slots in the back of the collet creating four clamping faces.

However, when DA collets are tightened towards the lower end of their collapse range, two of the faces tend to be pushed out of the way so only two of the faces are clamping on the cutting tool shank. This may cause some runout at the nose when the tool is inspected in a presetter.

Additionally, when the tool begins cutting and side forces are applied to the cutting tool, the cutting tool tends to deflect into the area where the faces are not clamping on the tool shank.

This results in excessive chatter that dramatically reduces tool life and results in rough surface finishes. You will be hard-pressed to find a quality end mill holder manufacturer endorsing the performance of their tooling in DA collets.