How One Machinist Started Big in CNC Metal Machining and Went Micro
When I got my start as a machinist 25 years ago, it was a very different world than what we see in CNC metal cutting services today, where the parts (and the tools) are getting ever smaller and the requirements, ever more demanding. Even 10 years ago, if someone had asked me if I’d be doing micro-machining, I would have said “Absolutely not! It’s TOO small, too finicky, too much of a headache.” But then I came to work at Metal Cutting Corporation, and my life — and my perspective on high precision machining services — changed substantially.
Here I am, having the time of my life and loving the challenges that come with micro-machining at a top CNC metal cutting company. So, what was so different when I transitioned from machining parts 6’ (182.88 cm) long to working at a shop that routinely makes small machined parts that are 6 mm (0.236”) or even shorter?
Machining Small Parts with Tighter Tolerances and More Challenging Deburring
At Metal Cutting, 99% of the parts we make are so small that we have to inspect them under a microscope or a loupe to be sure certain features are within the tolerance the customer asked for, look good, and are burr-free. As a rule, tolerances are much tighter when machining small parts, and deburring is more challenging due to the difficulty of accessing the very tiny features of the parts. How do you deburr a part with a diameter almost as small as a human hair?
In this micro-world, achieving tight tolerances and deburring might seem like the biggest challenges when transitioning from cutting large parts to cutting parts that are very small. However, here in the Metal Cutting shop, I quickly learned we had our own “secrets” that enable us to hold very tight tolerances and make deburring easier than I could have imagined, coming from a world of large parts.
In addition, I saw firsthand that when doing CNC metal cutting of small parts versus large, there are fundamental differences in the materials used; a dizzying choice of tools for completing very precise tasks; dramatic differences in the speeds and feeds used when producing very small parts; and even differences in how coolant is applied.
More Challenging Materials
When I began doing machining 25 years ago, I typically worked with basic materials such as 303 and 304 stainless steel, brass, and aluminum. Over time, CNC metal cutting shops developed specialties and niche markets, and this enabled me to learn about additional materials and work with more “exotic” metals.
Additionally, the CNC metal cutting process often uses very different materials for micro-machining. For instance, while nickel titanium may be used for making a small part such as a medical clip, this material is not made in larger sizes for making a big part such as a machine spindle. So, when I came to Metal Cutting in 2009, I had to learn about a whole new selection of metals, including superalloys and other materials that are extremely hard to machine. As I started working with tungsten and molybdenum, I thought I’d never be able to machine them to my satisfaction.
Fortunately, the Internet was — and still is today — a helpful resource that provided guidance as I explored new materials and different ways of doing things in the world of micro-machining. For instance, the site for Practical Machinist offers a comprehensive selection of forums and discussion threads where you can compare notes with and learn from other experienced machinists. Another good source is the CNCzone.com forums, from a site for professionals as well as hobbyists. The bulletin board system for the magazines Home Shop Machinist and Machinist’s Workshop is a clever DIY resource for simple projects; we even use it to supplement training for our shop apprentices.
Dazzling Tool Selection in CNC Metal Cutting
As I learned more about the more demanding materials used in CNC metal cutting services for very small parts, I came to also appreciate the selection of tools that can work with these materials and achieve the desired results without breaking. Likewise, when I came to Metal Cutting and started machining small parts with diameters as small as a human hair, I was in awe of the tools capable of such precise work, as well as the engineers who designed them. You would think something so small would break at the speeds and feeds at which we need to operate in order to handle the chip load from producing thousands of small parts.
Today, CNC metal cutting companies have the added advantage of tools that, if used properly, are stronger, longer lasting, and more precise; some don’t even require coolant, and many are available with different coatings. In fact, now there are almost endless possibilities in the availability of tools; if you can imagine a particular task, someone has probably made a tool that can do it.
Faster Speeds and Feeds in CNC Metal Machining
There is typically a big difference in the speeds and feeds when using CNC metal cutting to produce very small parts. When I first started doing machining, the highest speed I typically used was 2,000 RPM; 10,000 RPM was beyond my wildest dreams. When I came to Metal Cutting, the first job I did required 15,000 RPM to put a small hole in a part and, to my amazement, accomplished it perfectly. Today, when performing a task such as cutting a 0.013″ (0.3302 mm) diameter hole, I might routinely operate a machine at a speed of 24,000 RPM.
In general, speeds are based on the tool used and the tool manufacturer’s guidelines; the smaller the tools, the faster the RPMs generally are. Each manufacturer provides a formula for calculating the recommended speed and surface finish per minute (SFM). Feeds will vary depending on the tool and manufacturer, as well as the material being cut and any type of coating present.
Heeding the manufacturer’s guidelines for minimum and maximum speeds and feeds helps to both extend tool life and ensure you get good results. I’m sure that, like me, 99% of machinists would say they start slow and adjust as needed to achieve the desired results while striving to stay within the manufacturer’s parameters.
Coolant Delivery on the Cutting Edge in High Precision Machining
Back when I started in machining, the CNC metal cutting process almost uniformly used flood cooling, where both tool and part are flooded with coolant. Today, 99% of shops use through-spindle cooling, which allows coolant to be delivered directly to the cutting edge and blows the chips out of the area, to help prevent the tool from heating up and from building up material that can dull the edge or even cause the tool to break.
Whether you are using a turning tool, a drill, an end mill, or a boring bar, it is critical to make sure the chips are evacuated properly; this is especially true when you are making thousands and thousands of parts, as we do here at Metal Cutting. In addition, unlike with large parts, it can be more difficult to get behind the cut on a small part. However, our high-pressure coolant delivery helps to ensure we have no problems with chip buildup or tool breakage; in addition, it helps us achieve a beautiful surface finish on the parts we produce.
As with speeds and feeds, it is important to follow the tool manufacturer’s recommendations about what type of coolant to use in the CNC metal cutting process; doing so can help to avoid breakage, optimize tool life, and save on costs. Here at Metal Cutting, we typically use a water-soluble coolant or an oil, depending on the tool guidelines as well as the material that is being cut and the preference of the machinist.
Precise Machining: Where Learning Never Ends
Where once I was doing CNC metal cutting with parts having tolerances from 0.020″ (0.508 mm) down to 0.001″ (0.0254 mm), today at Metal Cutting I routinely machine parts with tolerances of 0.00020″ (0.00508 mm) or 0.00010″ (0.00254 mm), with 0.00050″ (0.0127 mm) TIR. Making that transition required developing new skills and exploring different ways of doing things.
I find this is still true today, when I continue to enhance my skills and work to further perfect the CNC metal cutting process with every project. Even with repeat jobs, I find I can always make improvements — for example, speeding up the feed or the spindle, using a different coolant, or adjusting other variables to increase productivity, speed up turnaround time, and enhance cost effectiveness.
For tips on how to create the best specs for your precision small metal part, download our free guide, How to Fine-Tune Your Quote Request to Your Maximum Advantage: Frequently Asked Questions in Small Parts Sourcing.