End Mill Holder and Runout

As a general rule most cutting tool & end mill manufacturers prefer to use single angle (ER/DR style) collet chucks for most cutting tool holding applications under 1/2". Why? Runout and uneven chip load. This is because of two reasons:

• The error accumulation on ID tolerance of the end mill holder and the OD shank tolerance of the end mill or drill. The smaller the diameter the more potential for problems...
• The imbalance created in the toolholder by the setscrew used to clamp the tool. When you tighten down the setscrew you not only offset the tool but also create an imbalance condition that is not repeatable due to the ANSI shank tolerance on all end mills.

Depending on the application, end mill holders can be used for holding larger insert style end mills, spade drills, etc.  But somewhere between 1/2” and 3/4” there is a line that only you can determine when you need to move from a collet chuck to end mill holder. Generally we recommend using end mill holders only for very specific applications

Using small diameter end mills (1/4" and below) in end mill holders with set screws will have a adverse affect of both surface finish and tool life.  

"The most important thing to say about toolholders in high speed milling of aluminum,” said Dr. Sinan Badrawy, formerly of Cincinnati Machine in a 2001 article “is not to use a set-screw holder.” Because the set screw moves the end mill off center to hold it against the wall opposite the set screw, it creates run-out.  “At high speeds, at set-screw holder will chatter no matter what,” he said.  The better choice are collet holders and shrink fit holders. Both do clamp the tool from all directions around the shank.”

AT3 Taper Tolerances

As the CNC manufacturing industry continues to grow we're meeting more and more new people coming into our industry.  Although many experienced machinists have lots of knowledge, we're finding that the new people are asking questions about some things that may be common knowledge to the old hands. One of the questions relates to "Why the heck is the cone on the toolholder the angle that it is?" We're here to help answer that....

By now, many have undoubtedly heard that most steep taper (CAT, BT) Toolholders hold an AT3 taper tolerance or better. So what exactly is AT3?

Steep Taper, Fast Tapers & Locking Tapers

Before we get into the tolerance and specs it's important to understand that there are basically two classes of tapers: 

• Locking tapers - These can be at any angle less than 7° per side (14° included). The shallower the angle the better the holding. 

• Self Releasing or "Steep Tapers" - These tapers are typically made with short shanks and with an included taper angle of 16° or 3.5" (88.9 mm) per foot.   These are also sometimes called "Fast Tapers"

• Toolholders are 'case hardened"

• Taper fit to spindle is critical

Most of the taper standards originated in the early days of the aircraft industry with rotors and propellers. There's quite a bit of thought that went into why the two types of tapers exists: It has a lot to do with "Van der Waals Forces" if you want to know about it in more detail.  

What's important to know is that CNC spindles are made with Steep Tapers. Why? Well, just as the two names state the first is "locking" taper and the second is "free-releasing"  Since Toolholders have to be automatically changed in the CNC machine you want them to be as close to a locking taper as possible (8°/side) without, well, 'locking' in place (7°/side)!  This is also the reason the ER/DR style collets also are made to an 8°/side angle as well by-the-way.

What is AT3?

That brings us to the "AT" standard for steep tapers. "AT" is an ANSI/ASME (ASME B5.50-1994) and ISO Standard (ISO 1947 ) that runs from AT1 to AT11. Since the AT tolerance is essentially logarithmic, the lower the number the tighter the tolerance (and harder it is to 'hit' in manufacturing). In other words the difference between AT 3 and AT4 is NOT the same increase in tolerance as between AT3 and AT2. AT3 is harder to attain than AT4 and AT 2 is substantially harder to reach than the jump from AT 4 to AT3. Again, the lower the number, the tighter the 'self releasing' tolerance.

Most CNC Machines steep taper spindles are made to an AT2 Specification. In order to stay competitive most all toolholder manufacturers are holding an AT3 tolerance (or better). Because there are much fewer spindles made than rotary toolholders this makes manufacturing sense.  The key words here to pay attention to is "or better"  Just like when you make parts in your shop to a tolerance, that doesn't mean that every part is exactly the same. The parts are within a tolerance band. That's what the "AT" defines!  So when a toolholder manufacturer says "AT3 or better" that can mean that some of the holders are actually holding an AT2 tolerance... and this is sometimes the cause of the tolholders 'sticking' in the spindle:Not because they are out of tolerance, but because they are actually holding a closer tolerance! (...nearer a locking taper)

By-the-way, most all steep taper toolholders are made from some derivative of 8620 steel and then case hardened.

Food for thought

So although most people think that the drive dogs on the spindle are doing the 'driving' of the rotation of the toolholder, it's actually the taper connection that is driving the rotation of the tool. If that wasn't the case, then you would see the drive dog notches in the toolholder start to show signs of wear when the spindle impacted them all the time. Afterall, the 8620 is only case hardened.

There are a couple of last things to make note of and think about:

So if you over tighten your retention knob (pull stud) it can expand the smaller part of the taper.

The sPINner Deburrs Small, Precision Parts

The sPINner magnetic deburring units use magnets to to 'spin' tiny 304 stainless steel 'pins' to deburr and polish parts. The pins resemble small roller bearings and are slightly magnetic themselves. When using the sPINner with non magnetic parts there is obviously little concern for any residual magnetism to be imparted to the material being deburred.  However, we are often asked about what happens when we deburr magnetic components.  It's actually very very simple!

Demagnetizing after a cycle
After magnetic parts have been processed, it is important to demagnetize them so the media and other parts will no longer be attracted to them. One simple procedure is to remove the container from the sPINner while the magnetic field is in motion. At the end of a cycle, simply start the machine again waiting for the magnetic field to fully accelerate. Once this is done, simply pull the container from the machine. Please note, that due to the weight of the contents in the container and the magnetic attraction of the parts and media to the magnetic field in the machine, substantial force may be required to remove the container. Containers are easier to remove when the magnetic field is in motion. Also, if it is critical that the parts be fully demagnetized, Earth Chain USA recommends a separate de-gauss operation.

Removing Burrs From Media
After magnetic parts have been run in the sPINner some burrs may remain in the media. Separation of the media from the magnetic burrs is accomplished using a strainer. Place a wire strainer inside the separation container that ships with the machine. Pour in the rinsed and dried media. The strainer should be chosen so that it will not allow the media to pass through, but will allow the burrs to pass through. Place the lid of the separation container and start the machine. The magnetic field will pull the burrs through the strainer. The media in the strainer may need stirred or mixed to help remove all the burrs.

sPINner stories: Deburring Small Slots

Here is an example of an application where the sPINner is being used to deburr small slots (.027”) in the part that were being hand deburred. The sPINner has automated this process. Where the customer was spending several hours deburring these parts, the sPINner runs the entire batch of the parts in 20 minutes.

Frequently Asked Questions An In-Depth Look: Magnetic Parts

The sPINner deburring system uses a magnetic field, so there are several factors to bear in mind when processing parts with a magnetic property. This document will help explain the variables to factor in when processing or evaluating magnetic parts.

The parts will “stick” to the bottom of the container:

When magnetic parts are introduced in the sPINner, they will be attracted to the magnetic field. As the magnetic field is concentrated to the bottom of the container, the parts will tend to “stick” to the bottom and the media will move around the part. Non-magnetic parts will tend to tumble with the media in a circular motion. Magnetic parts (depending on size and material) will tend to move slowly along the bottom of the container during machine operation in the opposite direction of the flow of media. This is caused by the parts trying to keep up with a very fast moving magnetic field. Heavy part or parts with very sharp edges that are pulled along the bottom of the container by the magnets may score the container and may wear through the container over time. If this happens the container will need replaced. Also fixturing the parts can limit their movement and decrease the wear on the container. See below the Fixturing section for more details.

The parts will stay in the magnetic field:

Parts with a magnetic property will be attracted to the magnetic field at the bottom of the container. The parts will stay in the strongest parts of the field during operation. The parts will tend to “line-up” with each other during processing. As the parts are responding to the magnetic field, they will attract other magnetic items in the container. This includes the magnetic media and other magnetic parts. The result is the parts developing a layer of media around them during processing and parts sticking to each other during processing.

Picture of fixture used with magnetic parts. Shown here with a few parts, each part is placed on an arm. The angle of the arms allows the parts to sit in the flow of the media while preventing the parts for damaging each other. Parts are free to rotate insuring that all areas are exposed to the action of the media.

Single layer of parts:

As parts with a magnetic property will tend to attract other magnetic items in the container including other parts, only a single layer of parts should be added to the container at a time. If parts are allowed to stack on top of each other, they will “stick” to each other and may prevent areas from being exposed to the media. 

Again, a fixture may be required to insure the parts do not damage each other during processing.

Fixturing:

Sometimes it helps to fixture the parts in the processing container. This can provide some benefits and eliminate some issues that can arise when processing magnetic parts. Fixturing parts can keep them in the flow of the media to insure the parts are being subjected to the action of the media. Also, fixturing the parts will help keep them separated preventing any damage from other parts and eliminating any void areas (areas where the media cannot get to) from parts ”sticking” to each other.

Types of Fixtures: There are as many different types of fixtures as there are different parts.  Below are some common fixture types that can either provide a station for each part or simply “cage” of “harness” the parts.

These fixtures are placed in the processing container. Since the parts can no longer contact each other during processing, the potential to damage each other is eliminated. The associated batch size is limited to the number of stations on the fixture. Please note, many different designs of fixtures are possible and the design is dependent on the specific application. Precision Finishing can help design and build a fixture for any application. Call us for details.

Machine Speed: In order to minimize the cushioning effect of a layer of media around the part, the spin rate of the magnetic field may need to be slowed to about 30-40 Hz.

ID burrs are difficult with magnetic parts:

Because the sPINner uses a magnetic field to impart energy to the media as opposed to gravity or vibration, one advantage of the system is the ability to deburr ID areas. This benefit is primarily limited to non-magnetic parts. For a 

Heat build-up:

During processing the friction of the media and the parts will produce heat. For non-magnetic parts the amount of heat is less than that of magnetic parts. The reason is that the magnetic parts create vibration that generates heat. Processing times of 30 minutes and longer in the sPINner on magnetic parts will generate heat and the contents of the container should be allowed to cool prior to handling.

Compounds:

There are several materials that magnetic parts may be made of that will need a compound other than the soap and water solution typically used in the sPINner. When rust of other corrosion is a concern, a compound should be chosen that has an inhibitor. The results from using various compounds may vary greatly and should be carefully tested prior to mass usage. When using a compound other than the compounds provided by Precision Finishing, make sure to use a compound that has a flash point above 180° F. Also, make sure to try the compound in a little media first to help determine the effects on the media.

Please contact us at 317-842-8934 to discuss any specific application or if we can help provide any additional information on processing magnetic parts.

Our Power Coated ER Collet Nuts really ARE special

We view CNC tool holders for routers and milling machines to be a critical component of the entire machining process.
Each component of our toolholder systems has been looked at in great detail to determine who we can improve tool life and reduce cycle time for our customers. 

One of the most important elements of the toolholding 'system' is the collet nut. Each toolholder "system" consists of a precision ER tool holder that comes with a special "Power Coated" high power nut that holds tighter than any other nuts. John Stagge, President of Techniks, says: "The 'Power Coat' nut is the secret to our high holding power. Because it holds so tight, the 'Power Coat' nut improves T.I.R., extends carbide tool life, and even permits light milling operations". Techniks recommends that for best results always tighten the nut to the proper torque using a torque wrench with a tightening stand, and never over-tighten the nut because this can damage both the collet and the collet pocket.

What makes the difference?

As anyone knows who has changed a flat tire on their car, tightening down a nut on a 60 degree thread involves some friction as the mating metal surfaces interact.  That's why nuts can be a bit 'hot' to the touch when you take them off. Our objective with our "Power Coated" nuts was multifold: 
First we needed to reduce the coefficient of friction on the thread angle to enable more lubricity for the nut to tighten down farther. As we all know 'heat' causes metal to "grow" so what may at first appear to be tight, in fact, loosens, as soon as you stop tightening it.
Second we needed to make sure that the front surface of the collet that engages the shorter 30 degree taper on the front of an ER collet did not 'twist' as the night tightened down.
Both problems really involved reducing friction and through a combination of engineering tolerances and unique coating process we believe that we've found the most economical solution to eliminate the use of cheater bars and collet over torque. Here's what we've found  our in testing our "Power Coated" Nuts:

• Up to a 75% increase in holding power
• Can extend tool life by 20% by reducing TIR
• "Engineered" balance for high speed machining

“Power Coat” is an innovative, permanent coating that increases clamping pressure of the nut up to 75% compared to standard ER nuts. More holding power reduces the chance of spinning the shank of the tool inside the collet, which can cause premature failure of the collet.

You know our toolholders...

...but did you know with Techniks you also get:

• Live phone support - 8:00 am to 6:00 pm by our experienced team of customer support representatives
• Fast, friendly response to your quote requests(phone or email)
• Each order checked 4 times - 99.9% shipping accuracy
• Same day shipping on orders in by 2:00 pm EST (standard ground orders - expedited orders ship same day until 5:00 pm)
• In-house applications support – toolholding and workholding – call us with your questions
• Field support provided as needed by our customer support team
• All products backed by our 100% satisfaction warranty! 

Stocking over $6,000,000 toolholder inventory for CNC machines and CNC routers in our 42,000 sq/ft central warehouse. We also provide turn-key solutions for magnetic workholding and magnetic deburring machines as well as out complete line up of CNC modular boring tools.