Stop Comparing Unit Prices: What Xometry, a Boring Bar, and a Monport K40 CO2 Laser Taught Me About Custom Part Costs

Stop comparing unit prices. I know it sounds kind of counterintuitive, but the lowest number on a quote is rarely the lowest cost. After 200+ rush orders in the last four years, I'm convinced that buyers who use total cost of ownership (TCO) thinking make better decisions. Everyone else saves $100 on paper and then pays for it in expediting, rework, and stress.

I'm a production coordinator at a contract manufacturing services company. My job is getting parts made under impossible deadlines—aerospace, medical, the occasional event that cannot move. I do not have the luxury of assuming a quote is accurate until I see the numbers behind it.

I learned this 36 hours before a deadline

In March 2024, an aerospace client called at 9 a.m. with a critical part problem. A bracket had failed inspection, and their line was going to stop in two days. Missing that deadline meant a $50,000 penalty. I needed a replacement part fast, and I needed it right.

I logged into Xometry, uploaded a step file, and had an instant quote with a firm lead time. Around the same time, I asked a local shop that does CNC turning and milling in Saint Paul MN for a quote. Their number came back lower. I almost went with them, because local felt safer. Then the shop said "we'll get you a ship date by tomorrow." That's the exact moment I realized I was about to make a mistake.

Looking back, I should have gone straight to Xometry and skipped the local quote entirely. At the time, I told myself local support was worth more than a dashboard. It wasn't. I ordered the part from Xometry anyway, and I also approved an expedite fee on the local shop's part. The local part arrived late. The Xometry part arrived on time, but I still paid for the rush on the other one. The cheaper quote ended up costing me an extra $360 in expediting, not to mention two sleepless nights.

Even after I hit "approve" on the Xometry order, I kept second-guessing. What if the finish was wrong? What if the tolerance wasn't held? The 36 hours between order and delivery were brutal. But the part was right, and the client made their deadline.

What total cost actually looks like

Let me be direct: when I compare two quotes, I compare more than the base price. I use a simple TCO list:

• Base part price
• Setup and tooling fees
• Shipping, handling, and any rush charges
• Potential rework or replacement if quality misses print
• Engineering time spent on clarifications and troubleshooting
• Cost of the line being down while I wait

Once you see all six lines, a quote that is 15% cheaper on the first line can easily become 30% more expensive by the time it hits my desk. That's not a hypothetical. That's what happened with the Saint Paul shop.

I'd argue time is the most ignored line item. When I'm triaging a rush order, I don't ask "what's the least expensive?" I ask "what has the shortest reliable path to a good part?" That's why the Xometry aerospace 3D printer service is on my list for low-volume parts. A bracket that would take a week to fixture for CNC can be printed overnight, and the instant quote tells me exactly what I'll pay for that speed. As of January 2025, Xometry's website states their additive line includes aerospace-grade materials and works for many structural brackets. I don't have to call three vendors and wait for callbacks.

What is a boring bar used for? (And why it matters)

The first time I saw "tooling: $200" on a quote, I nearly fell out of my chair. I called the salesperson to argue. Then an older machinist explained the boring bar to me. The short answer to "what is a boring bar used for?" is: it's used to enlarge an existing hole to an exact diameter with a smooth, controlled internal finish. A drill makes a rough hole; a boring bar finishes it to spec. If the print calls for a bored hole, the tooling, setup, and machine time have to appear in the quote somewhere.

Per Machinery's Handbook, the rigidity of the boring bar and its cutter geometry are the biggest factors in hole accuracy and surface finish. That's exactly the kind of hidden cost that a cheap quote leaves out. The vendor who quotes below market isn't smarter—he's probably using a longer bar, a less stable insert, or more forgiving tolerances. You don't find out until a bearing doesn't seat or a pin won't slide through.

The laser trap: a cheap machine is still a TCO problem

The same logic applies to capital equipment. I learned this the expensive way, after three failed rush orders with discount vendors. Now I apply TCO to tools and machines too.

Take the Monport K40 CO2 laser. At first glance, the price looks great. It's an entry-level CO2 laser that fits on a bench and can cut and engrave wood, acrylic, and some other materials. But before you use it for serious work, you'll likely need a chiller or better airflow, an air assist system to reduce burning, a honeycomb bed for sheet materials, and a real enclosure for exhaust. The base unit cost can go up by a meaningful percentage. Then add the hours spent aligning mirrors and testing settings.

I'm not telling you to avoid a Monport K40 CO2 laser. For hobby and light prototyping, it has a place. But if you're buying one to produce customer parts, yes, that "cheap" machine is part of your total cost. It consumes time, floor space, and patience. Count those hours before you compare it to a more expensive, more rigid machine.

(Note to self: I really should design a better air assist mount for our K40 instead of printing another test piece. It's been on my list for a year.)

But won't the cheapest quote ever win?

Sometimes. If a part is non-critical, the tolerance is generous, and the deadline has slack, then the lowest quote might be the right quote. I make that call myself at least once a month. TCO thinking does not mean refusing to save money. It means knowing when you can afford to take the risk.

The trouble starts when people treat every quote as if the only difference is unit price. One recent example: a client needed 12 machined parts for a product launch. Their usual shop quoted $800 and said "about three weeks." A discount vendor quoted $500 and two weeks. The client chose the discount vendor. The parts showed up on time but out of tolerance, the client paid $250 to a local shop to rework them, and the launch moved a week later. The "cheap" parts cost more than the original quote. I still kick myself for not pushing harder against that decision—I had the data on the table, but I let the client chase the lower number.

That's also why I use the Xometry login more than I used to. Once I'm in, I can see past orders, reorder with one click, and compare processes side by side. It's not just a convenience. It's a way to keep the total cost data visible. If I reorder a part that worked before, I don't have to gamble on a new source. The platform's history becomes part of my TCO memory.

Bottom line: price is what you pay, cost is what you live with

I'll say it again: stop comparing unit prices. Compare everything.

Total cost of ownership is not a buzzword. It's how an emergency part from the Xometry aerospace 3D printer line wins over a cheaper quote from a shop that can't commit to a date. It's how a $200 boring bar tooling charge becomes obviously worth it. And it's how you decide whether a Monport K40 CO2 laser is actually a deal or just a low-priced entry into a higher total cost.

I don't care if you use Xometry or a shop down the street. I care that you ask for a complete quote, count the time cost, and assume nothing is a bargain until the part is in your hand and working. In my world, the worst cost is the one you don't see until it's too late.