Machinists’ Tips for Achieving Precision Small Metal Parts
At Metal Cutting, we like to say we can machine any part. And it is absolutely true that we have a team of experienced machinists who are highly skilled in using an array of equipment for CNC machining services to produce complex, small, precision components.
The question always is, can we machine a part efficiently — in a way makes the part cost-effective both for our customers and for us? Below are some common issues to keep in mind when considering metal CNC machining and its cost.
1. Avoiding “Back to the Drawing Board” in CNC Metal Machining Services
One of the challenges in CNC cutting is often not the process itself, but preparing to do the work — specifically, making sure machinist and design engineer are on the same page. When machinists receive a drawing, we look at it to determine:
- If the part can be made
- How it is going to be made
- What attributes are important for the type of machine that will be used
Realistically, not everything that is on paper can be made on a machine. So, before engineers do a drawing, it is helpful for them to do some research to make sure their vision is in harmony with the machining capabilities and the equipment that their CNC company (such as Metal Cutting) has available.
For example, a design engineer might provide a very thorough drawing, showing every step that needs to be done to produce a part. However, a closer look might reveal that not all of the steps can be accomplished using the same discipline.
For instance, it might be the case that we can do seven out of ten steps on a CNC lathe, but two other steps would need to be done using electrical discharge machining (EDM) and a final step would require an additional process from an outside vendor. These added steps and a secondary process from a third-party vendor would all have an impact on cost.
2. Needing More Steps in the Precise Machining Process
A common challenge in CNC machining small parts — one we handle every day here at Metal Cutting, where we specialize in very small precision components — is the deburring of parts that have extremely small attributes. A case in point is a part that appears to be the size of a pencil in a drawing but in actuality, when you look at the specifications and scale, turns out to be the size of a pinhead.
With a part having such small dimensions, it’s difficult to physically get into tiny spaces within the part, such as blind holes. That is where the addition of a secondary process such as electropolishing would be necessary to ensure that the part is burr-free.
Sometimes, stumbling blocks appear when you least expect them. A good example is a high-pressure coolant fitting that one of our customers needed. Our CNC Swiss lathe machine shop was perfectly suited to the part — however, we lacked an extra tool for the back spindle.
As a result, a secondary process was required to add the necessary threading. While it only added about 30 seconds (per part) to the entire operation, it would have been more efficient to complete the part in a single process, from solid bar stock to finished fitting.
3. Simple Features Requiring Complex Machining
Of course, sometimes the little issues in CNC machining services DO occur somewhere within the process itself.
A good example is when we produced a part for a cathode ray tube — a project that required a lot of demanding ID work. It involved taking a solid piece of metal and machining it into a part that looked like two separate tubes joined at the center by a solid plate.
The job required not only removing 98% of the mass of the part, but also drilling a burr-free center hole that would join the two asymmetrical ID cavities. This hole needed to have a 0.020” (0.5 mm) diameter with a concentricity that referenced the overall OD datum to 0.0002″ (0.005 mm).
While creating the hole — making sure it was dead center and the correct size — was challenging, once we figured out the best technique to use, it was not that difficult. Instead, the trickiest task was trying to bore out the major ID without breaking the tools or having the boring bars wear out.
Similarly, another project required us to take a solid and turn it into a very thin-walled tube with a scooped end. While tubes are so commonplace at Metal Cutting that we cut them every day, here we had to (and did) overcome three challenges:
- Holding the part while maintaining its roundness
- Not distorting the OD when the tube wall was only 0.0025” (0.0635 mm) thick
- Deburring the part inside and out
These challenges are great examples of where having the latest and greatest machine technology comes in handy. Citizen has developed a pulsating mode known as LFV, or low frequency vibration, which changes the cutting chips from the typical long, stringy ones — which are prone to entangling tools and remaining as burrs — to short discrete pieces that are much more like what the name “chips” implies. These tiny pieces of removed metal simply cannot wrap themselves around a tool, nor do they cling obstinately to the part as a burr.
4. How Choice of Material Affects the Process
In CNC high precision machining, the choice of material is another critical consideration. For instance, we might look at a drawing and initially think it is a great part to machine, but on closer examination we might discover the engineer wants to make the part out of tungsten — a material that not everyone can machine well.
Even for Metal Cutting, if the drawing specified using a CNC mill, CNC lathe, or Swiss-style CNC screw machine, it might be very challenging to finish the part exactly the way the customer wants it, making it more likely that the tungsten part should be ground rather than machined.
In another example, an engineer might specify making a small tube from a solid piece of 304 stainless steel — a very popular material known for its corrosion resistance, among other beneficial traits. However, SS304 is very tough and burrs don’t break off very easily, so it might not be the best choice for a very small tube that needs a burr-free finish.
5. The Value of Communication in Metal CNC Machining Services
As expert practitioners of CNC machining services, we were able to figure out how to resolve all of the issues above. In addition to (1) our own expertise, (2) the expertise of the design engineers, and (3) the accuracy of the drawings they provide to us, it is the partnership we have with design engineers that enables us to:
- Recommend the best CNC machining method
- Provide an accurate quote for the total cost
- If necessary, come up with a viable solution in the event of the unexpected
In the end, good communication between engineer and machinist is essential to making sure CNC machining services can achieve a particular part according to specifications, on budget, and on schedule.
For tips on how to create the best specs for your precision metal part needs, download our free guide How to Fine-Tune Your Quote Request to Your Maximum Advantage: Frequently Asked Questions in Small Parts Sourcing.