Craig Powers is the Customer Support Manager at DATRON Dynamics and has been with the company for 7 years. Prior to coming to DATRON Craig was a machinist and managed a job shop in New Hampshire. Craig is in charge of all "after sales" support including the implementation of operator training programs, maintenance programs, machine rebuilds, as well as the sales of accessories and tooling.
In the world of manufacturing, specifically machining of material, there is an art to proper CNC workholding.
You may have the concept and design of a valuable product or part, the program skillfully complete with the optimum machine and material. But if you do not have a means to hold the material during your process, rigid throughout all surfaces and vibration free, the race is lost. “A horse, a horse! My kingdom for a horse!” This quote is fully understood by every machinist, tool and die maker, Production Cell Supervisor, Project and Plant Manager. Nothing will stop a successful process in it’s tracks like material poorly held causing tool breakage, material slip, high scrap rates, possible machine damage and worse, potential operator injury. A fixture, a fixture my process needs a fixture!
At DATRON we have heard this cry many years ago and sought solutions to be used with our machines for the many varied process requirements that the DATRON machine is used for. These had to be versatile, minimal labor requirement for use, repeated usage, allow accuracies to match the DATRON machine and like the DATRON machine provide thousands of hours of reliable use.
Another great benefit of using tested CNC workholding with your DATRON machine is the savings of time and material loss. Once you have optimized your product, program, material and machine process the last element to review and add profit margin points to your product is time. Operator time lost while loading and unloading the machine. Increased scraping of product due to slippage. The loss tool rate or shortened tool life requiring operators to change tools prematurely. These are all examples of time cost/time loss occurrences that translate to dollars lost. The end loss could be in cents or dollars per part but multiplied by the number of parts could very well be a significant amount of money making or breaking the production project. The reduction or elimination of these occurrences will reduce the loss or add profit margin points to your end result.
I would like to introduce the CNC workholding royalty to augment the DATRON machines:
Wedge Clamping Elements
Compact Centric Clamps
Pneumatic Clamps: Short stroke, positional
Pneumatic Vertical Clamps
Vacuum Chuck, Vacuum Table
Precision Rotary Axis
Precision Rotary Axis with Tailstock
Rotary Swivel Table (Trunnion 5 Axis)
Pick n Place System (Automation)
In the coming weeks I will discuss each of these products, description and use. Each of the above products have the DATRON “Test of Time” for versatility and longevity of use. When used properly they can achieve perfect holding with production labor time/material loss savings adding profit margin points to your process.
For more information on these Workholding Options, download our Accessories Catalog.
There are as many opinions of high speed milling with small milling tools and their proper use in the manufacturing industry as there are nuts and bolts. The benefit of high speed milling is that it allows for lower cutting loads and chip rates producing better surface finishes. In our world of high speed, high tolerance, high production machining there is a marrying of many points to create a perfect part. At DATRON we promote a strategy of the proper DATRON Machine configuration, material holding and cutting tools with optimized speed and feeds to define this strategy.
This discussion will concern the fourth item, tooling.
So your shop has made the investment of a high speed milling machine and you have been presented with a program to run. Might be one test piece, or several, or a production run of hundreds. There isn’t a question if the milling machine will perform, that process was confirmed prior to purchasing it. So, work holding and tooling will make or break the success of this piece.
For discussion we will assume the other four points above have been met (vibration free speed/frequency spindle, vibration free X Y and Z axis, rigid full support vibration free work holding, optimized program) so let’s discuss High Speed Milling Tool Strategies.
Composition of High Speed Milling Tools
High speed steel or carbide? We can all agree that vibration is a killer and more so in high speed milling. The operation at higher speeds and feeds to meet production, cost perimeters and to achieve the best finish dictates the most rigid and vibration-free tooling. There is the potential of flex with high speed steel tooling and vibration at high speed rates. So, the need for rigid tooling leans toward carbide … high-quality, solid, micro-grain carbide tooling.
Design of High Speed Milling Tools
The geometric design of high speed carbide tools, and specifically DATRON Tools, allow for the most proficient and clean cut of material at high speed and feed rates. This would allow for heavy roughing passes creating a full-shaped chip without curl putting the full cutting energy of the spindle into material removal.
Holding of High Speed Milling Tools
Next comes the proper holding of the tool. Vibration in tooling is usually a result of tooling not made for high speed milling, improperly balanced tools or tools chucked improperly. With both direct shank spindles or balanced tool holders for HSK spindles vibration free cutting can be achieved. Loading the tool properly (direct shank tools with brass stop ring or HSK tool holders) requires a space of 20% or 4-6mm between the top or fade out of the flute to the stop ring or HSK tool holder. This allows for the chips to move freely away from the tool when milling. However, there should only be approximately 80% of the shaft filling the direct clamp collet or HSK tool holder. The top of the tool should not come into contact with the top of the collet or HSK tool holder. This could cause damage to your spindle.
Feeds and Speeds for High Speed Milling Tools (Plus Chip Removal)
Now, comes the fun part. What is the best speed and feed rate? And for what type of chip removal should you have for your program?
Generally stated the milling strategy with high speed mills will not follow the same path as a conventional, commodity (non-high-speed) milling machines. The ability to use smaller tools faster, cleaner, and at high feed rates, allows for multiple passes with a shorter cycle time than standard commodity machining practices. The high finish removes the need for added second and third step processes normally needed in commodity machine milling.
With this in mind your strategy will include a selection of tools that will meet your most common milling practices. It also enables you to “dial in” the feed and speed rate of the tools selected and to look for the best speed and feed rate for each tool and milling operation. This can be done in a variety of ways: Tap Testing, Vibration Testing, Octave (harmonic pitch) Testing or the old fashioned Trail and Test method. The end goal is to find the best feed and speed rates for the best results. The majority of successful DATRON operators will use the Trial and Test method.
Published Speed (rpm) and Feed (cutting travel) are good starting points but are only starting points at best. You must consider the machine, spindle, material and tool? Remember it is a marrying of several factors to maximize your strategy: high speed/frequency spindle, rigidity and tolerances of X Y and Z axis, rigid work holding. Type of tool (geometric design, diameter, flute, length and tool holding) and depth of pass will all affect the feed and speed rate.
There are also a few anomalies in high speed milling. In high speed milling chatter and vibration are a killer and usually tell the operator to dial down the speed and or feed rate. However in the high speed milling community there are many times where dialing it up, increasing speed rate allowing for a better feed rate, better chip load will actually solve the issue.
Checking the Chip Load.
Chip load is the actual thickness of chip that is produced in the machining process. It is a reflection of the combination of the cutter feed rate (moving in the material) and speed rate (how fast it is turning; RPM). Too high of a chip load will cause an unsatisfactory edge finish and/or part movement from increased cutting pressure. It will place higher stress on the spindle and tool (risking breakage) and certainly cause higher wear on the tool … ultimately shortening is useful life. The need for a good chip load helps reduce the major cause for tool loss: Heat. The heat is created from the friction of the cutting action of the tool, cutting edge to material. With the proper evacuation of the chip comes the release of heat generated from the cutting action reducing possible damage to the tool.
Chip load is measured in thousandths of an inch (i.e. 0.010) and is influenced by the spindle speed and the feed rate of a CNC machine. Number of flutes, length of flute, shank diameter and depth of cut will also have an effect on the chip load. The number of cutting edges on a tool determines how the chip load is divided. A single edge tool provides all the chip load during a revolution, while a double edge tool divides the load over two edges and so on.
Formula for Determining Chip Load:
chip load= feed rate/(rpm x #cutting edges)
Manipulating the Chip Load:
To Increase Chip Load:
Increase the feed rate
Decrease the RPM
Use less flutes
To Decrease Chip Load:
Decrease the feed rate
Increase the RPM
Use more flute
For your reference the chip range for DATRON End Mills will be:
1mm Dia = .01mm (.000394)
20mm dia = .15mm (.7874)
This will depend greatly on shank diameter and flute length. Always use the shortest flute length for the milling depth requirement. Slowing down production to avoid the additional cost of a tool is rarely justified.
Chip load ability is also affected by the manufacturer’s geometrical design. Therefore it is always required to be familiar with the manufacturer’s specifications for the tool.
Lastly, dial in the best speed and feed in real world application. Watch and Listen. The finish of the material and the pitch the spindle makes with the tool during operation will give a good indication if you are going in the right or wrong direction. Having tested the tools prior to specifying them in production will give you the “cutting edge” for your application. Knowing when the vibration of the tool is introduced (at what speed) will allow you to bring the tool operation as close to this without introducing the devastating results. This will give you the ability to maximize the use of the tool, machine, spindle and program to mill the best part and finish.
Learn More: Download the DATRON High Speed Milling Tool Catalog:
Recently a customer visited DATRON Dynamics to take a first-hand look at DATRON’s broad line of solid carbide micro tooling, watch a demonstration to better understand the benefits … and oh, by the way, maybe even purchase one of our high speed milling machines. I showed them the appropriate tooling for their applications for the medical implant industry, as well as the superior cutting tools that we offer for milling titanium and plastic. As almost an afterthought, I brought out some new tools that DATRON has developed for milling polyurethane (PU) foam. Being so close to the development of these tools, I guess I took them for granted and was taken aback by the customer’s reaction of complete surprise and excitement. They simply didn’t know that they could use their milling machine for cutting foam. They conveyed to me a particular annoyance of theirs in that they often take nicely machined parts and leave them in the hands of “the powers that be” during the process of shipping them to a customer or another production location. Up until now, their shipping method for these pristine parts has been to wrap them in bubble wrap, kiss them up to God, throw some salt over their shoulder and hope for the best. But the samples I displayed of perfectly cut, custom shapes in foam changed all of that for them in an instant.
So why is milling PU foam a relatively new and emerging process? Well frankly, up until now, milling foam simply wasn’t an ideal solution and other processes like wire, waterjet and laser gave better results. But the combination of DATRON machine dynamics along tooling that is geometrically optimized and manufactured specifically for milling PU foam has been a game changer. What this means for DATRON milling machine users is that the same equipment they use to manufacture parts in other materials like aluminum, steel and composites can also be used to mill PU foam carriers and packaging that allows them to deliver their product to their customers not only in a safe manner, but in a highly professional presentation.
So, how easy is it? Well, all you have to do is program and cut a negative of the part or product that you just milled. Now you have an impeccable presentation for your customer that took virtually no time or effort, but that goes a long way in boosting your reputation as a quality manufacturer.
Finally, I’d like to mention that DATRON Foam Tools have an excellent wear resistance for cutting this soft material which translates to extremely long tool life and a huge return on investment.
I often hear machinists complain about the difficulties in milling acrylic. Their problems range from chipping, melting, “bird nesting” (the gathering of material around the cutting edge of the tool) and not being able to achieve clear, see-through surfaces and edges. Even seasoned manufacturers who have perfected the milling of acrylic, often through the use of diamond-coated tools, still complain about the cost of these expensive acrylic cutters. I’m always pleased to mention to these frustrated folks that DATRON has a solution that is amazingly efficient and surprisingly inexpensive. In fact, DATRON offers a complete line of solid carbide acrylic milling cutters – from single-flute end mills to form end mills in lots of different variations – all with polished flutes that make them superior to any other acrylic tools on the market.
The advantage of DATRON acrylic tools is two-fold. First, the tool geometry is designed with aggressively acute cutting angles that are much sharper than conventional cutting tools. Second, the flutes are polished. These two elements work synergistically to achieve virtually transparent acrylic milling results at a fraction of the cost of diamond-coated tools. But the cost savings is not solely based on the upfront purchase price. What our customers have found, is that they can eliminate secondary polishing applications because parts come off the machine with a glossy, transparent appearance.
Groove Milling in Acrylic
So at this point in my blog, some of you may be ready to simply download our Acrylic Cutting Tools Catalog. For others who are interested in learning about some acrylic milling strategies, I’d like to expound on this topic a bit more. While Groove milling in acrylic can be performed with any number of single-flute end mills and double-flute ball nose end mills, the strategies are perhaps too diverse for this blog. So, I’ll focus on more specialized milling processes.
How to Face Mill Acrylic or Plexiglas
In general, use tools with a high positive or high shear cutting geometry. Plastic material that is fixtured properly, either with pneumatic clamps or a vacuum chuck, can be face milled with high speeds and feeds. The DATRON double flute end mill with edge radius and polished flute is designed with an advanced face geometry and a polished flute for added transparency in machined acrylic parts. One face milling strategy that we have used employs a roughing pass with a 5mm single-flute end mill at 15,000 RPM and a 197 inch per minute feed rate (3.75mm XY infeed, 0.9 mm Z infeed) followed by a face milling/finishing pass with a 3mm double-flute ball nose (spherical) end mill at 40,000 RPM and a 118 inch per minute feed rate (0.08mm XY infeed, 0.02mm Z infeed). Of course, materials and applications vary so please call or email email@example.com for tool suggestions that address your specific application.
Edge Chamfering Acrylic
As I mentioned earlier, DATRON has a number of form end mills including tools for external radius milling, countersinking and chamfering. These come in a range of different cutting angles. Our countersinks for acrylics feature a large flutes for added chip room, as well as a 15° spiral to guarantee optimum chip evacuation. While the milling strategy would depend on your application and desired results, I can share the specifications for a recent sample that we machined. In this case we used a 3mm double-flute countersink tool, 90° at 15,000 RPM and a 20 inch per minute feed rate for edge chamfering in acrylic with 0.2mm XY infeed and 0.2mm Z infeed.
Drilling Threaded Holes in Acrylic (using helix drilling and thread milling)
One strategy that we’ve found to be effective for milling threaded holes in acrylic consists of a one-two punch – helix drilling first and thread milling second. As an example, we recently helix drilled an acrylic part with a 2mm single-flute end mill at 20,000 RPM and a feed rate of 10 inches per minute with 1.0mm Z infeed. Then we used a M2.5 – M4 thread mill at 25,000 RPM and a 31 inch per minute feed rate with 0.75mm Z infeed.
The acrylic milling strategies detailed above are associated with specific applications and the applications for milling acrylic are diverse. So, please feel free to contact us with your tooling questions at firstname.lastname@example.org or 603.672.8423.