Just because a part can be designed a certain way doesn’t mean it’s ideal for machining.
When we talk about non-machinable features, we’re not implying that they can’t be done. As a solutions provider, Reata Engineering can figure out how to machine just about anything.
We like to tell customers, “We can make anything you want, but it may cost more than you like, so instead let us make what you need.”
Our goal is always to make your life easier—and one of the ways we do that is by providing useful advice to help you create a machineable design before you request a quote.
We’re happy to work with you to optimize your design for the shop floor, but if you want to streamline that process as much as possible, avoid these common design obstacles.
Avoid These Common Machined Part Design Obstacles
Obstacle #1: Designing internal square corners
Believe it or not, 95% of the back and forth we have with customers regarding design obstacles can be traced back to engineers designing internal square corners into a part. This issue is a prime example of the gaps that can occur between design and machinability.
Just because CAD software allows you to draw internal square corners doesn’t mean it’s conducive to the shop floor. In most cases, we’re machining with round tools that require internal radii and corners to fit the shape of the tool. It’s no big deal for us to machine one internal square corner, but when there’s more than one in your drawing, that’s when it becomes challenging.
This is an example of a boss and a pocket with square corners. The boss is no problem; the pocket would require EDM work due to the sharp internal radius.
For parts that require more than one square corner, there are certainly ways for us to add those features, whether through wire EDM or broaching, but it might not be the most economical solution for your part. If square corners aren’t vital to the functionality of the part, we’ll recommend adding a radius.
Typically we’ll present a couple of different options for the size and location of the radius and work with you to determine the ideal solution. If we have visibility into the final assembly of the parts, we can make more precise recommendations. Otherwise, we’ll provide a few suggestions (beginning with the easiest one) so that we have backup options in case anything changes during assembly.
Obstacle #2: Features that require long tooling
When features have a small diameter and a long reach, special tooling is required to machine the part. A standard size drill, for example, costs only $1-$2 per piece. But a long drill with a diameter measuring 25 times that of a standard drill costs $200 or more. That’s a big difference in the cost of tooling just to make a part more difficult to machine!
Long tools aren’t just expensive; they also have performance issues. The longer the tool, the higher the risk of it snapping and breaking. Long tools are also prone to causing chatter, a strong vibration that can affect the accuracy of the part, as well as producing holes that aren’t normal to the surfaces they’re going through.
There are perfectly good reasons to design features for long tooling—one of our customers recently had a part that they wanted to make solid before turning it into a die casting. We’re happy to accommodate these features when necessary, but we want our customers to know that there are often alternative solutions that can significantly reduce machining time and cost.
An example of a slot that took several hours and several staggered tool lengths to accomplish is pictured above. It required a custom-ordered tool, and there were no recommended speed and feeds from the manufacturer because the tool itself was not recommended! This part was a 1/4 ” diameter endmill with 4.90 hang out equal to almost 20:1. The tooling was to machine the colored radius that is modeled in the pocket directly adjacent to the wall.
One of the simplest solutions is to make the part into two separate components—and the team at Reata Engineering can work with you to do that. Another option is to simply avoid length to diameter ratios greater than 8:1.
Obstacle #3: Edge radii that change from one feature to the next
This final issue is another example of something that may look nice in CAD software but is difficult to transition quickly and easily into an actual part. If you’re going on a straight edge and you have a 1/32” radius curving along that edge, then you have an edge going up that has been randomly changed to 1/16″, it may seem fine in the design, but when we go to make that part it won’t look nearly as good.
We always try to tell it like it is, so we’re going to be honest with you here: there’s rarely if ever, a functional reason to design edge radii that change from feature to feature! It’s easy enough to stick with a uniform edge break radius. If you need that kind of radius transition for aesthetic reasons, we can make the part using our 5-axis machining capabilities instead, but it will increase the cost of your parts.
Now that we’ve shared our best tips to avoid designing problems into your part, please don’t feel like you’re on your own! The team at Reata Engineering is happy to help with Design for Manufacturability considerations before you even submit a quote.