Xometry’s Greg Paulsen offers insights on what engineers should bring to the table when talking to a contract manufacturer.
Xometry has sponsored this post.

As computer-aided design (CAD) becomes democratized, more companies are creating 3D models for outsourcing parts and assemblies to contract manufacturing networks. Legacy businesses are also updating their documentation and processes with the help of on-demand manufacturers. The following questions often arise: How can engineers come to the table prepared? What design factors do they need to think about before kicking off the manufacturing cycle? How are immediate versus long-term requirements distilled?
Xometry is one on-demand manufacturer that helps companies source custom parts through an integrated network of more than 5,000 suppliers across 46 U.S. states and 22 countries. It offers capabilities ranging from a 3D printing service and a CNC machining service to injection molding, sheet metal fabrication and urethane casting.
Regularly tasked with hitting tight tolerances and supporting unique features, Xometry has a deep understanding of what is required when manufacturers approach with part specifications. The on-demand manufacturer works on a wide variety of projects, offering expert tips for navigating the manufacturing process. With applications extending from prototyping to production, Xometry serves various industries including aerospace, automotive, medical, robotics, industrial and consumer electronics.

“Customers in industries like aerospace and automotive have typically engineered and gone through design verification test (DVT), and their released drawings are built to spec,” said Greg Paulsen, director of applications engineering at Xometry. “Their user specification list is long enough that our capabilities match well, whereas it may be very hard to source by going shop to shop.”
On the other side of the coin, Xometry works with companies that are early in new product development cycles or are working with materials such as plastics that involve a considerable number of unknowns in comparison to metals. Alloys are well-characterized and widely understood, while plastics may require an understanding of the differences between HDPE, ultra-high molecular weight and polypropylene.
“Those things are nuanced and require more of a conversation understanding the customer’s goals, and the environment of the work,” said Paulsen. “We have experts in-house to help guide through that process.”
Gaps in specifications can often prove to be a challenge. As Paulsen stated, “When you are specifying your quote on Xometry, you are making a love letter to your manufacturer. It’s the customer communicating what they think they are going to receive. It’s us reading what we think we are going to make—and in Xometry’s case, because we work with suppliers of the marketplace too, it’s our suppliers understanding what they’re making. If they are all the same, the specifications are good and we are all on the same page. When specifications aren’t there for certain things, assumptions get made—and they may be industry-standard assumptions, but they may deviate from the customer’s expectations.”
One common example is tapped holes, which are frequently only partially specified. While the hole size may be established, details such as depth or thread type may not be fleshed out—leading to potential delays.

“Customers need to look to best practices for how to specify a certain thing,” advised Paulsen. “Don’t just say anodize, but specify which type—I, II, III, etc.? Finishing that sentence will go a long way.”
Companies each have a different drawing template and their own way of specifying things. Xometry works as a universal translator, using global industry standards to create a baseline. Certain dimensional tolerances, such as those for surface roughness and flatness, can be esoteric—leading to an incomplete notation on the box or rendering. For quality assurance, Xometry provides tolerances and manufacturing standards typical to different processes. The on-demand manufacturer is often faced with “perfect” designs that lack manufacturability based on unforgiving tolerances.
“We work to value add—for example, with design for manufacturability (DFM) feedback to make things function better—because we want everybody to win in the end,” said Paulsen. “Xometry can do highly specified tolerances, but there are costs behind that. For example, my measuring tool usually has to be 10 times more precise than the feature I’m measuring. We have seen a trend of overall surface profile tolerances in drawings or title blocks. This means I’m going to require a CMM inspection—which is going to add hundreds of dollars to the inspection process, when it turns out that feature was not critical.”
“I was asked a question recently: based on your experience with 3D printing, what processes and material will be best for prototyping a part that will be eventually made out of aluminum?” related Paulsen. “In my design phase, I have a part that will eventually become CNC machined at end-of-life. I’m not there yet, though. I’m going through iterative stages. Maybe I need to fit check. Maybe I need to get design buyoff from my stakeholders.
“A very quick conversation with the customer tells me they want something rigid. Something in that mechanical shape, but in a timely manner. Our general-purpose SLS nylon options make strong, rigid parts, and ship in a couple of days. But what if they said it has to be metal? Then we may move to a metal 3D printing option, which is more expensive and takes a bit longer.
“This is one of my favorite sayings that goes down to the specifications: is it a requirement, or a desirement? Is it something that would be nice to have, but I could go without it for this iteration? That’s really important, especially if you’re trying to figure out that fast and cheap option versus the expensive and fast option, or whatever your tradeoff is going to be.”

When it comes to the design of injection-molded parts, a small tweak could make an order of magnitude difference to the manufacturing cost.
“It depends on where the customer is in their product development stage,” said Paulsen. “For example, I can get away with machining a thin wall, or even printing a thin feature, on a one-off because we can usually assume that risk or slow down the machine toolpath. A lot of that upfront cost may just be those operations that are encompassed in the parts—i.e., setups and ops versus that actual machine step. As you add quantities, small DFM characteristics and improvements become more of the conversation piece because what is driving costs is what that tool is doing.”
Making changes is no easy feat when in production with a tooled option such as injection molding. It is important to review DFM before tool construction to avoid costly downstream changes. This is part of Xometry’s molding kickoff, which covers both design and tool aspects to assure the success of the project. In many cases this can include design revisions such as adding draft angles and minimizing thick features.
“You cannot argue with plastic,” declared Paulsen. “If your part is going to have sink or warp or deflection based on a thick-to-thin geometry, it’s one of those things that we want to prevent upfront in the conversation. We do not want to cut metal until we build those expectations and update the design to give the best outcomes.”
While machining involves direct control where toolsets or patterns can be changed to create a smoother surface, processes such as additive manufacturing demonstrate inherently rougher surfaces that cannot be altered—since they are based on the resolution of the 3D printer. It becomes a different language where molding is concerned; it is not the part itself exhibiting the roughness, but the surface of the tool.
“We have different classifications for what that surface is going to be, including SPI standards,” said Paulsen. “For example, SPI-A level would be glossy, whereas SPI-C or -D is going to have more of that stone matte finish. So, it is different than the measurement of the ups and downs you would have in CNC machining—i.e., the RA value which is the measurement of that surface roughness.”
Paulsen was also handy with tips for manufacturers. For example, roughness can be used as a technique for hiding sink—an issue demonstrated by some plastics more than others.
“Polypropylene is really forgiving,” asserted Paulsen. “HDPE, or polyethylene, will show every sink mark you ever wanted or didn’t want on that part. Adding texture reduces glare and is remarkable at mitigating some of the cosmetic defects that are inherent in the design features of a part.”
According to Paulsen, Xometry differentiates itself from other contract manufacturers by actively working with customers to optimize their molding processes.
“We’ll teach you from our experience, the tricks of the trade that will help you make your design better,” said Paulsen. “You need to add draft here. If you change those ribs to about 60 percent of the outer wall thickness, you will mitigate these features. When you order from Xometry, we’re not just cutting that tool right away. We actually spend the first couple days after order on the kickoff, to make sure we’re signed off on the specifications. Molding is a marriage. You really want to make sure you have everything in those vows.” (From love letters to marriage, it’s clear that Paulsen loves his job.)
Apart from design outcomes, Xometry’s engineers discuss parting, ejection and gating (PEG) strategies. Here, the customer can define things such as keep-away zones where ejection pins should not be placed.
One standard notation from the old days is “break sharp edges” which refers to ensuring that edges are not so sharp that operators could get cut. A newer call-out is “machine break,” of which Paulsen is a big fan.
“CAM programming has just made it a checkbox now, and I am so happy for that,” Paulsen said. “We see it more and more on notations, and it is becoming a natural step with the programmers across our supplier network. Once they click it in their CAM program, the toolpath runs a pass-through and cleans up all the edges automatically.”
Xometry casts a wide net across industries, and is happy to work on special-purpose applications. On Xometry’s drag-and-drop menus, even hard-to-source finishes such as PTFE hard coatings are available, with specs behind them including different types of plating.
“One of the exciting things I’ve seen in additive manufacturing recently is that we’ve been adding post-processes to typically rough surfaces, commoditizing surface finishes that are more applicable to molding,” revealed Paulsen. “Chemical vapor smoothing is one of the newest additions to our finishing options for 3D-printed thermoplastics. The smoothing is not just an abrasive smoothing that will remove the peaks but leave the valleys on the surface roughness of the part; it will actually liquefy the material on the surface level and reseal it. In comparison to flame polishing, this is a much more controlled process that gives very consistent, repeatable results part to part.”

“I’ve found that—especially with legacy defense components—some of the parts may originally have been created before regular CNC machining was a thing, or before certain finishes were available,” said Paulsen. “Why was this a cast part? It could be machined. You find out the drawing is from 1959 and casting was the most economical and viable option at the time. Sometimes you do have to ask and converse, and sometimes they absolutely need it that way, or there can be deviations made to reach up to a more modern technology.
“I’ve seen a lot of new private aerospace companies using the latest and greatest materials in different alloys and specifications. And sometimes these new alloys are perfect for these legacy applications. Trying to introduce the new to the legacy, and bringing some of these other industries into the realm, is really interesting to help transfer learning there.”
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