The Problem with Unnecessarily Tight Tolerances (And How We Can Help)
When part designs include unnecessarily tight tolerances, customers can expect extended quoting times, longer lead times, and increased overall prices.
Keep reading to dig deeper into:
Understanding over-tolerancing
How Summit CNC approaches tight tolerances
Avoiding over-tolerancing
Understanding Over-Tolerancing in Precision Machining
There are a number of reasons you might find yourself over-tolerancing a part design. Here are two common ones:
You’re simply trying to design the “perfect” part and don’t realize how much maximally tight tolerances will cost you.
You’ve had bad experiences with CNC machine shops that didn’t achieve your precise specifications, so you overcompensate by making your tolerances unnecessarily tight.
If you do need precision tolerances, we can machine them. If you don’t need precision tolerances, we can save you money!
Let’s start with the good news: Summit CNC regularly machines both standard (+/- 0.005”) and precision (down to +/- 0.0002”) tolerances—and we reliably meet all specifications. So you can go ahead and cross number two off your list of concerns!
Not every customer knows this right off the bat, however. We quoted one recent customer's part with tight tolerances (down to +/- 0.001”) according to the specifications on their drawing. Later, we learned that the customer had ordered the part from an on-demand industrial parts marketplace instead. Why? Because they didn’t actually need the tight tolerances, and the online marketplace was ostensibly “cheaper.”
The thing is. . . our precision machine shop could have quoted lower pricing had we known that the tolerances could be loosened.
The moral of this story? Talk to us! Let us know if there are opportunities to relax your tolerances, and we’ll help you get a fair price for high-quality parts you won’t always get from an online marketplace.
Now, let’s move on to the other big reason you might over-tolerance your part design: you want the perfect part. Contrary to popular belief. . .
Unnecessarily tight tolerances do not = a “perfect” part
There are certainly some parts that require exceptionally tight tolerances to function properly. However, many parts can function just as well when the tolerances of some or even all features are relaxed. And relaxing tolerances to a permissible degree for a part’s application can significantly improve quoting times, lead times, and overall costs.
How Standard vs. Precision Tolerances Affect Quoting Times, Lead Times, and Overall Costs
Before submitting your quote request for precision machining services, consider how standard vs. precision tolerances can impact cost and lead time.
Here’s an example of our process for quoting and machining parts with standard vs. precision tolerances:
Step 1: Quote Request Received
Standard tolerances (down to +/- 0.005”):
Estimator receives and reviews your quote request, verifies that your part’s features are machinable
Consults with machinist if necessary
Precision tolerances (down to +/- 0.0002”):
Estimator receives and reviews your quote request, verifies that your part’s features are machinable
Verifies that the part’s tolerance specifications are achievable
Consults with machinist if necessary
Step 2: Quote Created and Delivered
Standard tolerances:
Estimator draws up quote, calculates lead times, and sends you the quote
Precision tolerances:
Estimator accounts for additional raw materials that may be required to dial in the tolerances for the first article
Estimator calculates additional programming and machining time required to achieve precision tolerance features
Estimator adds any additional time to the standard lead time to accommodate for the longer times it may take to program and machine the part
Step 3: Customer Places Order and Machining Begins
Standard tolerances:
Machinist programs and machines your part without needing to set tool wear offsets or use brand new tools
Machinist verifies standard tolerances on the machine per the engineering drawing and/or 3D design file
Precision tolerances:
Machinist sets tool wear offsets during set up
If necessary, machinist sources new tooling for precision tolerances
Machinist slows the machining time for precision tolerance features
Machinist verifies the part’s precision tolerances both on and off the machine—any features that are out of specification are remachined, or the stock is scrapped and the part is machined from the beginning until precision tolerances are achieved
For some precision tolerance parts, it can take up to a few days to dial in just one feature!
Step 4: Parts Shipped to Customer
Save Time and Money: Avoid Over-Tolerancing Your Parts
As you can see, precision tolerances demand careful attention to detail that may require additional quoting and setup hours, along with costly tooling solutions and extra material for scrap. Even tightening a tolerance from +/- 0.002” to +/- 0.001” can significantly impact cost and lead time.
We love the challenge of achieving precision tolerances, and we machine tight tolerances every day! But we also want you to get the best value for your parts, and over-toleranced parts don’t benefit anyone—least of all our customers.
If you’re uncertain about any aspect of your part design, reach out and talk with us. We’ll help you ensure that you haven’t designated unnecessarily tight tolerances—and that the tolerances you do receive are precisely what you ask for.